molecules
Review
Species Diversity and Secondary Metabolites of
Sarcophyton-Associated Marine Fungi
Yuanwei Liu 1 , Kishneth Palaniveloo 1, * , Siti Aisyah Alias 1 and Jaya Seelan Sathiya Seelan 2, *
1
2
*
Citation: Liu, Y.; Palaniveloo, K.;
Alias, S.A.; Sathiya Seelan, J.S. Species
Institute of Ocean and Earth Sciences, Institute for Advanced Studies Building, University of Malaya,
Kuala Lumpur 50603, Wilayah Persekutuan Kuala Lumpur, Malaysia; alec.liu2012@gmail.com (Y.L.);
saa@um.edu.my (S.A.A.)
Institute for Tropical Biology and Conservation, Universiti Malaysia Sabah,
Kota Kinabalu 88400, Sabah, Malaysia
Correspondence: kishneth@um.edu.my (K.P.); seelan80@ums.edu.my (J.S.S.S.); Tel.: +60-13-878-9630 (K.P.);
+60-13-555-6432 (J.S.S.S.)
Abstract: Soft corals are widely distributed across the globe, especially in the Indo-Pacific region, with
Sarcophyton being one of the most abundant genera. To date, there have been 50 species of identified
Sarcophyton. These soft corals host a diverse range of marine fungi, which produce chemically diverse,
bioactive secondary metabolites as part of their symbiotic nature with the soft coral hosts. The most
prolific groups of compounds are terpenoids and indole alkaloids. Annually, there are more bio-active
compounds being isolated and characterised. Thus, the importance of the metabolite compilation
is very much important for future reference. This paper compiles the diversity of Sarcophyton
species and metabolites produced by their associated marine fungi, as well as the bioactivity of these
identified compounds. A total of 88 metabolites of structural diversity are highlighted, indicating the
huge potential these symbiotic relationships hold for future research.
Keywords: octocoral; marine fungi; holobiont; secondary metabolites; diversity
Diversity and Secondary Metabolites
of Sarcophyton-Associated Marine
Fungi. Molecules 2021, 26, 3227.
https://doi.org/10.3390/
1. Soft Corals
molecules26113227
Soft corals, also known as octocorals, are Anthozoans (Ehrenberg, 1834) classified
under the subclass Octocorallia (Haeckel, 1866). They belong to the Phylum Cnidaria,
making them closely related to the sea anemones, hard corals and jellyfishes. Unlike
hard corals that are the building blocks of the coral reef, soft corals act as shelter for
juvenile fishes and food to some marine organisms. As the name octocoral is derived
from Latin “octo”, which means eight, soft coral species comprise of eight-tentacle polyps
and eight mesenteries, with minimal variance within the clade. The polyp in octocorals
is an individual zooid, and they together play important roles in the essential functions
of a colony, including growth, food capture, transport of nutrients, defence, irrigation
of seawater and reproduction [1]. As suspension feeders, soft coral food intake relies
on environmental conditions, especially water currents [2]. For small organic particles
(<20 mm), octocoral polyps can filter them from the water column, whereas larger particles
(such as zooplankton and larvae) could be captured or intercepted by the tentacles. Since
octocorals have simple stinging cells (nematocysts), their food is restricted to weaklyswimming, small plankton [3].
Octocorals are widely distributed, with their presence recorded from the intertidal
zone to depths up to 6400 m and from tropical to polar regions [4]. Their distribution
is heavily influenced by several environmental factors, for example, distance from the
coast, suspended organic matter and the presence of strong currents [5]. For instance, the
distribution of cold-water species is closely related to salinity, temperature, productivity,
oxygen, the broad scale of the highest diversity of soft corals in the world, of which
are mostly endemic [6,7]. However, the greatest diversity of octocorals is recorded in
Academic Editor: Rosa Durán Patron
Received: 30 March 2021
Accepted: 13 May 2021
Published: 27 May 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affiliations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Molecules 2021, 26, 3227. https://doi.org/10.3390/molecules26113227
https://www.mdpi.com/journal/molecules
Molecules 2021, 26, 3227
2 of 27
the Indo-Pacific oceans [8], part of the Coral Triangle Region, which has the highest
mega-biodiversity in the world. In fact, octocorals are particularly diverse in tropical,
subtropical shallow reefs and deep-sea waters, often being dominant occupiers of the
benthic community [9]. To date, up to 3500 octocoral species have been recorded and
classified in up to 400 genera.
The subclass Octocorallia comprises three orders: Alcyonacea, Helioporacea and
Pennatulacea. The order Alcyonacea (Lamouroux, 1816) has the most number of species
among octocorals [1]. Alcyonacea consists of stoloniferous forms, soft corals, and gorgonians [10]. This classification scheme is currently followed by most taxonomists, even though
Alcyonacea is still viewed as unstable together with many family-level classifications [9,11].
There are approximately 31 families of soft corals and sea fans under this order, despite
the lack of defining synapomorphies [9]. Although this order has been divided into six
sub-ordinal groups: Alcyoniina, Calcaxonia, Holaxonia, Protoalcyonaria, Scleraxonia and
Stolonifera, there is no molecular analysis to support this classification scheme, which
reflects morphological categories, not clades [1,9,11]. Most soft corals belong to the order
Alcyonacea, which includes the families Xeniidae, Nephtheidae, and Alcyoniidae. The
family Alcyoniidae consists of three genera Lobophytum (Marenzeller, 1886), Sinularia (May,
1898) and Sarcophyton (Lesson, 1834), and these genera are considered the most important
contributors to the total biomass of Indo-Pacific reefs, which cover up to 25% of the reef
surface [5].
Since the nineteenth century, soft corals have been the subjects of active biological
research [12]. Soft corals are prolific producers of terpenoids of the cembranoid skeleton.
However, due to the presence of symbiotic microorganisms in soft corals, there has been
plenty of debate on the origin of the secondary metabolites of the hosts. This has given rise
to investigations on the metabolites produced by coral symbiotic microorganisms. Since
the 1980s, plenty of reviews have been compiled, documenting the metabolites produced
by the coral-associated microorganisms. Based on the available compilation, we observed a
high number of metabolites reported between 2000–2010, and a reduction thereafter. Most
reviews report the metabolites produced by marine fungi and to date, there has been only
one specifically on octocoral-associated microbes with reports from the span of 2006 to
early 2016 with a focus on bioactivity [13]. This review reports metabolites produced by
marine fungi isolated from the soft coral genus Sarcophyton compiled over a duration of 10
years from 2010–2020.
2. Diversity of Sarcophyton
In 1982, Verseveldt revised the classification scheme of Sarcophyton based on a systematic examination of the morphology and microscopic images of Sarcophyton-like specimens [14]. According to his revision on Sarcophyton taxonomy, the genus Sarcophyton
contained 35 valid species, and since then, there have been reports on new species of
Sarcophyton. To date, there have been approximately 50 Sarcophyton species as shown in
Table 1. Most Sarcophyton species were identified in the Indo-Pacific regions.
Molecules 2021, 26, 3227
3 of 27
Table 1. Sarcophyton species diversity.
Species Name
Sarcophyton aalbersbergi Feussner and Waqa, 2013
Sarcophyton acutum Tixier-Durivault, 1970
Sarcophyton agaricum (Stimpson, 1855)
Sarcophyton aldersladei Feussner and Waqa, 2013
Sarcophyton alexanderi Feussner and Waqa, 2013
Sarcophyton auritum Verseveldt and Benayahu, 1978
Sarcophyton birkelandi Verseveldt, 1978
Sarcophyton boettgeri Schenk, 1896
Sarcophyton boletiforme Tixier-Durivault, 1958
Sarcophyton buitendijki Verseveldt, 1982
Sarcophyton cherbonnieri Tixier-Durivault, 1958
Sarcophyton cinereum Tixier-Durivault, 1946
Sarcophyton cornispiculatum Verseveldt, 1971
Sarcophyton crassocaule Moser, 1919
Sarcophyton crassum Tixier-Durivault, 1946
Sarcophyton digitatum Moser, 1919
Sarcophyton ehrenbergi von Marenzeller, 1886
Sarcophyton elegans Moser, 1919
Sarcophyton expandum Kolliker
Sarcophyton flexuosum Tixier-Durivault, 1966
Sarcophyton furcatum Li, 1984
Sarcophyton gemmatum Verseveldt and Benayahu, 1978
Sarcophyton glaucum (Quoy and Gaimard, 1833)
Sarcophyton globoverruccatum Benayahu and Verseveldt, 1983
Sarcophyton griffini Moser, 1919
Sarcophyton infundibuliforme Tixier-Durivault, 1958
Sarcophyton latum (Dana, 1846)
Sarcophyton mililatensis Verseveldt and Tursch, 1979
Sarcophyton minusculum Samimi Namin and van Ofwegen, 2009
Sarcophyton nanwanensis Benayahu and Perkol-Finkel, 2004
Sarcophyton nigrum May, 1899
Sarcophyton pauciplicatum Verseveldt and Benayahu, 1978
Sarcophyton portentosum Tixier-Durivault, 1970
Sarcophyton pulchellum (Tixier-Durivault, 1957)
Sarcophyton regulare Tixier-Durivault, 1946
Sarcophyton roseum Pratt, 1903
Region
Reference
Fiji Island
Western Central Pacific
Chinese, Japanese Sea
Fiji Islands
Fiji Islands
Red Sea
Micronesian Islands
Indonesia
China seas
Southern Taiwan
Madagascar
Madagascar, Vietnam, Japan
Madagascar, China Seas
Philippines, Madagascar, Vietnam, China seas
Madagascar, New Caledonia, South-West Indian Ocean
Philippines, Great Barrier Reef, West-Pacific islands, Madagascar, New Caledonia
Philippines, Madagascar, Vietnam, China seas
Philippines, Madagascar, New Caledonia, Hong Kong, Japan, China seas
Samoa Islands, South Pacific Ocean
Madagascar, South-West Indian Ocean
China Seas
Red Sea
Philippines, Madagascar, Red Sea, West-Pacific islands, China seas
Red Sea
Papua New Guinea
Madagascar, New Caledonia, South-West Indian ocean, China seas
Philippines, Malay Archipelago, Madagascar, China Seas
Bismarck Sea
Persian Gulf
southern Taiwan
Marshall Islands, North Pacific Ocean
Red Sea
New Caledonia
Indian Waters, Japan
Madagascar, New Caledonia
Maldives
[15]
[16]
[17]
[15]
[15]
[18]
[19]
[14]
[20]
[21]
[22]
[22–24]
[20,25]
[20,22,23,26]
[22,27,28]
[22,23,26,29,30]
[20,22,23]
[20,22–24,31,32]
[33]
[22,28]
[20]
[18]
[20,22,30,32,34]
[35]
[33]
[20,22,23,28]
[20,22,32,36]
[37]
[38]
[39]
[33]
[18]
[22]
[33]
[22,23]
[40]
Molecules 2021, 26, 3227
4 of 27
Table 1. Cont.
Species Name
Sarcophyton serenei Tixier-Durivault, 1958
Sarcophyton skeltoni Feussner and Waqa, 2013
Sarcophyton soapiae Feussner and Waqa, 2013
Sarcophyton solidum Tixier-Durivault, 1958
Sarcophyton spinospiculatum Alderslade and Shirwaiker, 1991
Sarcophyton spongiosum Thomson and Dean, 1931
Sarcophyton stellatum Kükenthal, 1911
Sarcophyton stolidotum Verseveldt, 1971
Sarcophyton subviride Tixier-Durivault, 1958
Sarcophyton tenuispiculatum Thomson and Dean, 1931
Sarcophyton tortuosum Tixier-Durivault, 1946
Sarcophyton trocheliophorum von Marenzeller, 1886
Sarcophyton tumulosum Benayahu and van Ofwegen, 2009
Sarcophyton turschi Verseveldt, 1976
Region
Vietnam
Fiji Islands
Fiji Islands
Madagascar
Laccadive Archipelago
Malay Archipelago, Madagascar
China Seas
Madagascar
Madagascar
West-Pacific islands, Malay Archipelago, New Caledonia
Philippines, West-Pacific islands, Malay Archipelago, Madagascar, New
Caledonia, Vietnam, Japan, China seas
Hong Kong
Red Sea
Reference
[23]
[15]
[15]
[22]
[41]
[22,36]
[20]
[25]
[22]
[23,30,36]
[33]
[20,22–24,30,32,36]
[42]
[35]
Molecules 2021, 26, 3227
5 of 27
3. Sarcophyton-Fungal Associations
Coral-associated microbes consist of endolithic algae, endosymbiotic dinoflagellates,
bacteria, fungi, alveolates, archaea, and viruses. The consortium of coral and its associated
internal and external microbes is often considered as the holobiont [43,44]. The associated
microorganisms provide extra carbon and nitrogen sources for their host, as well as play a
part in detoxification, nutrient cycling, genetic exchange, ultra violet (UV) protection, and
chemical defence [43,45]. In some populations of gorgonian, fungal diseases are common,
but relatively few investigations have been conducted on the causal marine fungi from
these octocorals [43]. In particular, the genera Aspergillus and Penicillium have often been
found in the Caribbean Gorgonia ventalina [46,47], Leptogorgia species distributed in the
Eastern Pacific regions [48], and many octocorals in the South China Sea [49] as well as
Singapore [50]. Other frequently identified octocoral-associated fungi include the genera
Cladosporium [46–48], Fusarium [48,50,51], Nigrospora [48,51], and Tritirachium [46–48,50]. As
for the soft coral genus Sarcophyton, Aspergillus terreus was obtained from the Sarcophyton
subviride, which was collected from the coast of Xisha Island in the South China Sea [52].
The marine fungus Penicillium bialowiezense was also isolated from the same soft coral
species [53]. Additionally, Chondrostereum sp. was isolated from Sarcophyton tortuosum of
the South China Sea as well [54].
The surrounding environment and host substrate have an impact on the composition
of fungal communities [51], with a varied abundance of the most common associated
fungal species. Knowledge of the fungal isolates is mainly obtained from culture-based
techniques, thus favouring species likely to be cultivated in the laboratory conditions [50,51].
Nonetheless, cultured marine fungi have been a promising reservoir of bioactive secondary
metabolites, usually with unique chemical structures, thus making octocoral-derived
fungi potential bio-prospecting sources [13]. Despite limited knowledge about the exact
ecological functions of these fungal species, some possess potential antifungal, antibacterial
properties and might have a role in maintaining holobiont health and regulating the
microbiome [13]. Table 2 summarises the soft coral Sarcophyton and its associated fungi.
Table 2. Soft coral genus Sarcophyton and its associated marine fungi.
Soft Coral Species
Fungi
Reference
Sarcophyton subviride
Aspergillus terreus
Penicillium bialowiezense
Chondrostereum sp.
Alternaria alternata
Aspergillus versicolor
Chaunopycnis sp.
Cladosporium cladosporioides
Cladosporium dominicanum
Cladosporium sphaerospermum
Didymella sp.
Hypocrea lixii
Microsphaeropsis sp.
Paraconiothyrium
cyclothyrioides
Penicillium citrinum
Tritirachium sp.
Penicillium janthinellum
Penicillium oxalicum
Phoma putaminum
Phoma sp.
Pseudocercospora sp.
Stagonosporopsis
cucurbitacearum
Talaromyces allahabadensis
Aspergillus elegans
Pseudallescheria boydii
[52]
[53]
[54,55]
Sarcophyton tortuosum
Sarcophyton sp.
[56]
[57,58]
[59]
Molecules 2021, 26, 3227
6 of 27
4. Metabolites of Marine Fungi Derived from Sarcophytons
Marine organisms are an important source of natural products with potential for drug
discovery. To date, more than 40,000 marine natural products (MNPs) have been identified
from the marine environment. Coral reefs are among the most productive ecosystems and
exhibit a large group of structurally unique biosynthetic products [60]. The coral reef is a
prolific source of metabolites synthesised by a wide range of organisms such as sponges,
cnidarians, tunicates, molluscs, echinoderms, bryozoans, macroalgae and microorganisms.
Interestingly, recent records have shown an upward trend in MNPs from marine microorganisms, with approximately 57% of the total metabolites reported in 2017 [60]. These
MNPs can be classified into terpenoids, alkaloids, steroids, lactones, polyketides, peptides, phenols, and lipids based on their biosynthesis pathways. Most of these metabolites
are of pharmaceutical interest due to the varying bioactivity exhibited, such as cytotoxic,
antimicrobial, anti-inflammatory, antimalarial, and antidiabetic activities [61].
Due to the lack of calcium carbonate skeletons for physical protection, soft corals
depend heavily on chemical defence mechanisms in order to resist predators and prevent
overgrowth and fouling by accumulating a variety of secondary metabolites in their bodies
and releasing them to the environment [62]. The soft coral genus Sarcophyton hosts a
wide diversity of marine fungi that interacts with the soft corals in multiple ways. The
microorganisms are expected to synthesise various secondary metabolites to adapt and
survive in their cohabitating environment either as a symbiont or as a parasite [62]. The
fungal genus Aspergillus, for instance, was once thought to be pathogenic; however, it was
not only found in diseased gorgonians but also healthy ones [46]. Therefore, it is now
considered as an opportunist rather than a pathogen. Soft coral-associated fungi have
an influence on the maintenance of holobiont health and regulation of the microbiome.
Previous studies have demonstrated that coral-associated bacteria communities regulate
the settlement of bacteria on the coral surface, thus controlling the resistance against coral
disease [63]. The protective mechanisms include competition for food and space, as well as
the production of antibiotics from the mucus or coral tissues [45]. Although corals naturally
produce a mucus microbiome as a defence system against pathogens [64], changes in the
microbiome could lead to the emergence of coral diseases. However, associated bacterial
communities produce antibiotic metabolites to inhibit the settlement and growth of many
pathogenic species, like Vibrio coralliilyticus, V. shiloi and Serratia marcescens [45]. Even
though there is no such study carried out on associated fungi, they could play a similar
role to coral-associated bacteria.
The conventional view of microbial symbionts has been that their biosynthesis of
natural products contributes greatly to the wide range of metabolites from sessile marine
invertebrates. In the case of sponges, there have been debates on the source of metabolites
from this organism. Eventually, it was determined that the microorganisms within are the
main contributors of secondary metabolites [65]. In the case of hard corals, the production of mycosporin amino acids (MAA) provides protection for the corals against solar
radiation [66]. Similarly to the relationship between fungi and soft corals, the metabolites
produced by the fungi are of interest. The bioactivity exhibited can be associated with the
protective role of the soft corals. Additionally, this work also confirms that the metabolites produced by the fungi are totally different from those reported from the soft corals,
ascertaining that the soft coral metabolites are synthesised by the coral itself. Even though
most octocoral-derived marine fungi are obtained through cultivation-dependent methods,
these fungi produce a variety of bioactive natural products, usually exhibiting an unusual
chemical structure [13]. Thus, octocoral-derived fungi provide a great candidate for bioprospecting. The following sections compile the soft coral-fungal associated metabolites
that have been reported over the years 2010–2020. Most of the secondary metabolites
belong to the chemical sgroup sesquiterpene and indole alkaloid. A list of compounds with
bio-activity is shown in Table 3.
Molecules 2021, 26, 3227
7 of 27
Table 3. Bioactivity of soft-coral associated marine fungi.
Soft Coral Species
Fungi
Bioactivities
Reference
cytotoxic activities against cancer lines A549, CNE2, and LoVo
potent cytotoxic activities against various cancer cell lines
potent cytotoxic activity against various cancer cell lines
potent cytotoxic activities against the cancer cell lines CNE-1
and CNE-2
[54]
[67]
[68]
chondrosterin K (15)
chondrosterins L (16)
chondrosterins M (17)
significant cytotoxicity against various cancer cell lines in vitro
[70]
3,3′ -cyclohexylidenebis(1H-indole) (33)
significant cytotoxic activity against various cancer cell lines
[59]
4′ -OMe-asperphenamate
Metabolites
chondrosterin A (5)
hirsutanol A (1)
incarnal (11)
Sarcophyton tortuosum
Chondrostereum sp.
Pseudallescheria boydii
antibacterial activity against Staphylococcus epidermidis
[57]
altersolanol B (50)
altersolanol C (51)
potent inhibitory activity against Gram-negative bacteria
[71]
Alternaria sp.
ampelanol (53)
mild toxicity against the L5178Y mouse lymphoma cells
[72]
versicolactone G (67)
potent α-glucosidase inhibitory activity
[52]
luteoride E (66)
(3E,7E)-4,8-dimethyl-undecane-3,7-diene-1,11-diol (68)
methyl 3,4,5-trimethoxy-2-(2
-(nicotinamido)benzamido)benzoate (70)
territrem A (72)
lovastatin (75)
significant anti-inflammatory activity against NO production
[52]
Aspergillus terreus
Penicillium bialowiezense
Sarcophyton subviride
[69]
Alternaria sp.
Aspergillus elegans
Sarcophyton sp.
chondrosterin J (14)
(61)
8-O-methyl mycophenolic acid (78)
3-hydroxy mycophenolic acid (79)
6-(5-carboxy-3-methylpent-2-enyl)-7-hydroxy-3,5dimethoxy-4-methylphthalan-1-one (80)
6-(5-methoxycarbonyl-3-methylpent-2-enyl)-3,7dihydroxy-5-methoxy-4-methylphthalan-1-one (81)
6-(3-carboxybutyl)-7-hydroxy-5-methoxy-4methylphthalan-1-one (82)
6-[5-(2,3-dihydroxy-L-carboxyglyceride)-3methylpent-2-enyl]-7-hydroxy-5-methoxy-4methylphthalan-1-one (83)
6-[5-(1-carboxy-4-N-carboxylate)-3-methylpent-2enyl]-7-hydroxy-5-methoxy-4-methylphthalan-1one (84)
N-mycophenoyl-L-valine (85)
N-mycophenoyl–L-phenyloalanine (86)
N-mycophenoyl–L-alanine (87)
mycophenolic acid (MPA) (88)
inhibitory activity against inosine-50-monophosphate
dehydrogenase (IMPDH2)
and
in vitro immunosuppressive activity against the proliferation
of T-lymphocytes
[53]
Molecules 2021, 26, 3227
8 of 27
4.1. Terpenoids
Sesquiterpene
Soft-coral associated fungi are reported to be an important source of sesquiterpenes.
The earliest reports on sesquiterpenes from soft-coral associated fungi are the isolation and
characterisation of the hirsutane sesquiterpenes hirsutanol A (1), E (2) and F (3) in 2011
from the marine fungus Chondrostereum sp., which was isolated from the soft coral Sarcophyton tortuosum [67]. The laboratory-cultured fungal isolate was extracted in over ethyl
acetate prior to fractionation using petroleum ether (Petr Eth), ethyl acetate (EtOAc) and
methanol (MeOH) as a mobile phase. A 60% gradient reverse phased high-performance
liquid chromatography (RP-HPLC) profiling led to the isolation of the hirsutanols A (1),
E (2) and F (3). Initial reports on hirsutanol A (1) were from the marine sponge Jaspis cf.
johnstoni fungal isolate in 1986, which was also isolated from an unidentified fungal strain
from the Haliclona sponge along with hirsutanol F (3) [73]. Hirsutanol E (2) (Cl5 H24 O3 ) comprises of three methyls, five methylenes, two methines, five quaternary carbons, and three
hydroxy groups. According to nuclear magnetic resonance (NMR) and single-crystal X-ray
diffraction data, the structure of hirsutanol F (3) was regarded the same as gloeosteretriol,
despite the opposite optical rotations [67]. Hirsutanol A was characterised as Cl5 H18 O3
with potential cytotoxicity against many types of human cancer cell lines and induction
of autophagical cell death through increased Reactive Oxygen Species (ROS) levels. An
investigation into the anticancer mechanism of hirsutanol A (1) towards MCF-7 breast
cancer cells exhibited the inhibition of cell proliferation, enhanced ROS production, apoptosis and autophagy. Hirsutanol A (1) could lead to apoptosis and autophagy through
accumulated ROS production, and MCF-7 cells could be sensitised if co-treated with an
autophagy inhibitor [74]. The bioactivity of hirsutanol A (1) was attributed to the presence
of an α-methylidene oxo group, which was absent in hirsutanols E (2) and F (3) [67].
In 2012, an additional hirsutane type sesquiterpene, hirsutanol C (4) was isolated
along with five triquinane-type sesquiterpenoids, chondrosterins A–E (5–9) from the fungus Chondrostereum sp. isolated from tissues of Sarcophyton tortuosum [54]. The isolated
fungi were laboratory-cultured in potato dextrose broth (PDB) medium that was eventually extracted over EtOAc. A two-stage column chromatography fractionation with Petr
Eth/EtOAc followed by EtOAc/MeOH and an RP-HPLC purification with a 60–100%
acetonitrile (MeCN) gradient system through a Shim-Pack Octadecylsilyl (ODS) column
(250 × 20 mm) yielded hirsutanol C (4). Subsequent Sephadex LH-20 gel column chromatography and RP-HPLC purification of the fungal fractions yielded chondrosterins A–E
(5–9) [54]. Hirsutanol C (4), C15 H20 O3 , isolated as powder, was previously characterised
by Wang et al. (1998) [73] from an unidentified fungus of the marine sponge Haliclona sp.
that yielded the hirsutanols A (1) and F (3) [54]. The relative configuration of hirsutanol C
(4) was determined via single-crystal X-ray diffraction. It was inactive against the human
lung cancer cell line (A549), human nasopharyngeal carcinoma cell line (CNE2), and human
colon cancer cell line (LoVo) at IC50 (half maximal inhibition concentration) concentrations
>200 μM [54]. Chondrosterins A (5) and B (6) were both isolated as yellowish oil. With the
presence of a α-methylene ketone group in its tricyclic system, chondrosterin A (5) showed
significant cytotoxic activities against various cancer lines A549 (IC50 = 2.45 μM), CNE2
(IC50 = 4.95 μM), and LoVo (IC50 = 5.47 μM) [54]. The metabolites from Chondrostereum sp.
cultured in PDB medium showed a difference from those in the glucose peptone yeast
(GPY) medium. This investigation also evaluated the difference in metabolite presence
through alteration of the fermentation conditions, such as the ratios of the carbon and
nitrogen source and inorganic salts, leading to the detection of the previously reported
hirsutanol E (2) in the GPY culture strain. This confirms that the Chondrostereum sp. is able
to produce diverse hirsutane derivatives under different conditions [54]
Chondrosterin C (7) is a compound with a hydroxyl, ketone carbonyl, α,β-unsaturated
carbonyl functionality, and its planar skeleton is determined entirely by 1 H-1 H correlated
spectroscopy (COSY) and Heteronuclear Multiple Bond Correlation (HMBC) analysis [54].
Chondrosterin D (8) was isolated as a colourless crystal. Similar to chondrosterin C (7), this
Molecules 2021, 26, 3227
9 of 27
compound also possesses three ketone carbonyl groups. Infrared absorptions at 1737, 1687
and 1610 cm−1 confirmed the presence of ketones and α,β-unsaturated carbonyls. X-ray
crystallography was used to confirm its relative configuration [54]. The fifth compound
from the cultured Chondrostereum sp. is chondrosterin E (9), which was reported as a white
solid. Compared to the other metabolites isolated from this study, chondrosterin E (9) is
the only compound where the carbonyl was positioned at C-5 instead of C-4 [54].
In a separate study, following the successful characterisation of chondrosterins A–E
(5–9), additional hirsutane sesquiterpenoids chondrosterin F (10), incarnal (11) and anthrosporone (12) were reported from the soft coral species Sarcophyton tortuosum-associated
marine fungus Chondrostereum sp. collected from South China Sea in 2013 [68]. Using the
similar culture and isolation protocol involving two stages of column chromatography
followed by RP-HPLC purification as the previously mentioned metabolites, chondrosterin
F (10) was isolated in the form of a colourless oil. This compound was determined to
have a rearranged hirsutane skeleton believed to be caused by the migration of a methyl
functionality from C-2 to C-3 as well as the formation of a lactone through the conversion
of a cyclic ketone [68].
The hirsutane incarnal (11), a compound previously first reported from fungus
Gloeostereum incarnatum, was isolated as red solids from the soft-coral-associated Chondrostereum sp. [68]. Compared to the reference data, the J value coupling constant of the
protons H-11α and H-11β reported in this study was calculated as 14.0 Hz instead of an
oddly lower value of 5.1 Hz that was previously reported. Incarnal (11) demonstrated
potent cytotoxic effects on various cancer cell lines, including LoVo (IC50 = 2.16 μg mL−1 ),
CNE2 (IC50 = 6.07 μg mL−1 ), A549 (IC50 = 12.37 μg mL−1 ), human nasopharyngeal carcinoma cell line (SUNE1) (IC50 = 3.99 μg mL−1 ), human breast cancer cell line (MCF-7) (IC50
= 4.57 μg mL−1 ), human nasopharyngeal carcinoma cell line (CNE1) (IC50 = 8.33 μg mL−1 ),
human hepatic cancer cell line (Bel7402) (IC50 = 23.36 μg mL−1 ), human epidermoid carcinoma cell line (KB) (IC50 = 28.55 μg mL−1 ) [68]. Based on these data, it is evident that the
α-methylene ketone functional group plays an important role in the cytotoxic activities of
hirsutane sesquiterpenoids. Arthrosporone (12) is another hirsutane sesquiterpenoid originally reported from an unidentified arthroconidial fungus and Macrocystidia cucumis [75].
In comparison with chemical data from the literature, it was confirmed that arthrosporone
(12) was also produced by the investigated soft-coral-associated fungi. Arthrosporone (12)
was not reactive in oxidation reactions, which is a common characteristic of the tertiary
hydroxyl groups present in the compound [68].
In 2014, two more hirsutane sesquiterpenoids, chondrosterins I and J (13 and 14),
were obtained from yet again the marine fungus Chondrostereum sp., which originated
from Sarcophyton tortuosum and cultured in a liquid medium with glycerol as the carbon source [69]. The compounds were isolated through repeated Petr Eth/EtOAc and
EtOAc/MeOH column chromatography on the EtOAc extract followed by RP-HPLC purification. Though cultured in a different medium, the fungal extract contained the previously
reported hirsutanol A (1), chondrosterins A (5) and incarnal (11). Compared to the previously mentioned hirsutane sesquiterpenoids, chondrosterins I (13) and J and (14) exhibited
a switch in methyl position from C-2 to C-6 and a presence of carboxylated methyl at
C-3 [69]. Chondrosterin I (13) was isolated as a colourless solid. The absolute configuration
of chondrosterin I (13) was determined as 1R, 6S, 8S and confirmed by X-ray single-crystal
diffraction. Chondrosterin J (14) was isolated as a white solid. The absolute configuration
for this compound was established as 1R, 6S, 7S, 8S. These compounds were screened for
cytotoxicity against the human nasopharyngeal cancer cell line CNE-1 and CNE-2, where
chondrosterin J (14) was cytotoxic against CNE-1 and CNE-2 cell lines with the IC50 values
of 1.32 and 0.56 μM [69].
The mycelia of Chondrostereum sp. of Sarcophyton tortuosum cultured in GPY liquid
medium was reported to contain four sesquiterpenoids, which included three triquinanetype sesquiterpenoids, chondrosterins K–M (15–17) and a previously identified metabolite,
anhydroarthrosporone (18) [70]. A similar fractionation and purification technique was
Molecules 2021, 26, 3227
10 of 27
applied in order to isolate and characterise the compounds 15–18. The use of GPY medium
often results in an altered metabolite profile compared to those cultured in PDB medium.
Chondrosterin K (15), C15 H22 O3 was obtained in the form of a colourless oil, with five
degrees of unsaturations. [70]. In contrast, chondrosterin L (16) lacks two methines and
possessed seven quaternary carbons compared to chondrosterin K (15) [70]. Chondrosterins
L (16) and M (17) from this fungal extract are hirsutanes with almost identical functional
groups. Both the chondrosterins were obtained in the form of yellowish oil. Structurally,
chondrosterin L (16) differed from chondrosterin M (17) due to the presence of an exomethylene at carbon position 3 instead of the secondary methyl, CH3 CH– functionality that
was found in chondrosterin M (17) [70]. The fourth compound reported from this study
was anhydroarthrosporone (18), a hirsutane sesquiterpene that was initially isolated from
the fungus Ceratocystis ulmi extract [76]. Huang et al. (2016) reported it for the first time
from soft-coral-derived fungi. Anhydroarthrosporone (18) is a metabolite that contained a
β-substituted α,β-unsaturated cyclopentenone. The anhydroarthrosporone (18) is a derivative of the previously reported arthrosporone (12) with the presence of a double bond
between carbons C-5 and C-6 [68]. Chondrosterins K-M (15-17) demonstrated significant
in vitro cytotoxicity against seven cancer cell lines; CNE1, CNE2, SUNE1, A549, epithelial
tumour cell line (HONE1), Gejiu Lung Carcinoma-82 (GLC-82) and normal human liver
cell (HL7702) [70].
Further investigation into the Sarcophyton tortuosum-derived fungi Chondrostereum
sp. cultivated in GPY medium continued to yield two more additional hirsutane-type
sesquiterpenoids, chondrosterins N (19) and O (20) [55]. These were isolated from its EtOAc
extract after repeated column chromatography followed by RP-HPLC over a 70% MeCN
mobile phase [55]. Both chondrosterins N (19) and O (20) were isolated as colourless oil.
Chondrosterin N (19) is comprised of an α, β-unsaturated carbonyl chromophore as indicated by UV absorption at 239 nm. On the other hand, chondrosterin O (20) was identified
as a stereoisomer to chondrosterin N (19). Both compounds were initially determined
as identical based on 1 H–1 H COSY and HMBC spectra; however, the differences in the
chemical shifts of H-4 and its coupling constants were able to distinguish these compounds
from each other [55]. They were screened against seven cancer cell lines: CNE1, CNE2,
HONE1, SUNE1, A549, GLC82 and HL7702, and were categorised as inactive with IC50
values exceeding 100 μM. Chemical structures of all the highlighted I-associated fungi
hirsutane sesquiterpenes are exhibited in Figure 1.
4.2. Alkaloids
Indole Type Alkaloid
Indoles are bicyclic molecules built by a six-membered benzene ring fused to a fivemembered pyrrole ring. These compounds are commonly produced by a wide variety
of microorganisms. As for the Sarcophyton associated fungi, in 2013, two cytochalasin
compounds, aspochalasin A1 (21) and cytochalasin Z24 (22), were reported from a Sarcophyton sp.-derived marine fungi Aspergillus elegans, originating from the South China
Sea [58]. The alkaloids reported in this study were isolated from the EtOAc extract that was
subjected to a petroleum ether/EtOAc followed by a chloroform (CHCl3 ) fractionation over
Sephadec LH-20 [58]. The reported compounds were purified over HPLC using an ODS
Kromasil C18 column with the mobile phase between 60 to 85% MeOH. Aspochalasins
are a subgroup of cytochalasans, consisting of a macrocyclic ring, isoindolone moiety
and a 2-methyl-propyl side chain. According to high-resolution electrospray ionisation
mass spectrometry (HRESIMS), aspochalasin A1 (21), isolated as a white powder, was
characterised as C24 H35 NO5 . The presence of a (2-methylpropyl) isoindolone moiety is an
indication of aspochalasin A1 (21) from a typical cytochalasin skeleton [58]. Cytochalasin
Z24 (22) was also isolated as a white powder and possesses a 10-phenyl-substituted 6,7epoxyperhydroisoindol-1-one type skeleton. Both compounds, aspochalasin A1 (21) and
cytochalasin Z24 (22), were determined to share identical macrocyclic properties similar to
Molecules 2021, 26, 3227
11 of 27
other known cytochalasins reported. The absolute configuration of cytochalasin Z24 (22)
was determined as 3S,4S,5S,6R,7S,8S,9S,13E,16S,18S,19E [58].
Figure 1. Hirsutanols from Sarcophyton-associated fungi.
Eight additional cytochalasin-derivatives (23–30) were also reported from the Aspergillus elegans [58]. All these cytochalsins were previously reported from various sources
of fungi from the genus Aspergillus. Aspochalasins B (23), a yellowish powder and D (24),
were previously reported from the Aspergillus niveus that was associated with a marine
crustacean [77], while aspochalasin H (25) was first identified from the aspochalasin Dproducing strain, Aspergillus sp. The common detection of a broad infra-red band at 1685
cm−1 shows the presence of lactone and ketone carbonyl in aspochalasins B (23) and D (24).
The carbon position C-18 of aspochalasin D (24) was attached to a hydroxyl moeity instead
of a carbonyl as in aspochalasin B (23). Aspochalasin H (25), C24 H35 NO5 was isolated as a
colourless powder [78] and was reported to have an identical stereochemistry to aspochalasin D (24). Additionally, the double bond between carbons C-19 and 20 was replaced
by an epoxy in aspochalasin H (25), which differed both these compounds structurally.
Aspochalasins I (26) and J (27) were obtained from Aspergillus flavipes associated with
the rhizosphere of Ericameria laricifolia, a turpentine bush [79]. Aspochalasin I (26) was
isolated as a white powder [79], while aspochalasin J (27) was isolated as a white solid. The
difference between aspochalasins (26) and J (27) was the presence of only one oxygenated
Molecules 2021, 26, 3227
12 of 27
methine bearing a hydroxyl with α-orientation in compound 27 [79]. The acetylation of
aspochalasin J (27) yields the monoacetyl derivative acetyl aspochalasin J confirming the
presence of hydroxyl (-OH) in the compound.
Aspergillin PZ (28) is a compound that was previously reported from the soil fungi
Aspergillus awamori as a colourless crystal [80]. Aspergillin PZ (28) shares an identical
skeleton to the compound aspochalasin C, which is also produced by fungi from the
genus Aspergillus. The addition of a hydroxyl followed by cyclisation of aspochalasin C
produced aspergillin PZ (28). Zygosporin D (29) was previously isolated from the fungus
Metarrhizium anisopliae [81], while rosellichalasin (30), a solid colourless needle, has been
reported from an Aspergillus strain from China [82]. Zygosporin D (29) is reported as
a deacetyl derivative of the compound cytochalasin D. These compounds are classified
as cytochalasins, a group of fungal alkaloids with diverse biological activities targeting
cytoskeletal processes. They can bind to actin filaments and block polymerisation and the
elongation of actin. The isolated compounds were screened for their bio-activity against
six terrestrial pathogenic bacteria (Staphylococcus epidermidis, S. aureus, Escherichia coli,
Bacillus subtilis, B. cereus and Micrococcus luteus) and two marine pathogenic bacteria (Vibrio
parahaemolyticus and Listonella anguillarum) [58].
Aspochalasin D (24) demonstrated a wide spectrum of antibacterial properties, especially towards four pathogenic bacteria, S. epidermidis, S. aureus, E. coli and B. cereus [58].
In contrast, aspochalasin I (26) displayed moderate minimum inhibition activity (MIC)
against the bacteria S. epidermidis (MIC = 20 μM) and S. aureus (MIC = 10 μM). In addition,
compounds aspochalasin D, H-J (24–27) also showed strong antifouling activity against
the larval settlement of the barnacle, Balanus amphitrite, with EC50 values of 6.2, 37, 34 and
14, respectively [58]. Despite the small differences in their structures, aspochalasin D (24),
which possessed an α,β-unsaturated lactone moiety, demonstrated that the electrophilic
α,β-unsaturated carbonyl moiety plays an important role in the antifouling activity of
these cytochalasins [58]. Since aspochalasin D (24) had higher antifouling activity than
aspochalasin H (25), the presence of a double-bond at C-19 and C-20 was deduced to be
the possible active site for cytochalasin antifouling activities [58]. The chemical structures
of these compounds are shown in Figure 2.
A total of 13 additional indole alkaloids were also isolated from the Saracophyton sp.
associated marine fungus Pseudallescheria boydii from the South China Sea [59]. These compounds comprised the two bisindoles, pseudboindoles A (31) and B (32). The other metabolites characterised were 3,3′ -cyclohexylidenebis(1H-indole) (33), 3,3-bis(3-indolyl)butane2-one (34), 2-[2,2-di(1H-indol-3-yl) ethyl] aniline (35), 3,3′ -diindolyl(phenyl) methane
(36), 1,1-(3,3′ -diindolyl)-2-phenylethane (37), perlolyrin (38), pityriacitrin (39), 1-acetylβ-carboline (40), 3-hydroxy-β-carboline (41), 1-(9H-pyrido[3,4-b]indol-1-yl)ethan-1-ol (42)
and Nb -acetyltryptamine (43). These compounds were isolated from the EtOAc extract of
the laboratory-cultured strain after fractionation over Petr Eth and EtOAc. The compounds
were purified using HPLC and a Capcell-Pak C18 UG80 (250 × 20 mm) column with
methanol and purified water as the mobile phase [59].
Pseudoindole A (31) was isolated as an amorphous brown powder, consisting of
one methylene group, six methine groups, three quaternary carbon atoms and is built
of two identical structural moieties comprising an ortho-disubstituted aromatic ring and
3-substituted indole connected at the electronegative carbon C-9 [59]. Chemically, pseudoindole A (31) was deduced as 1,3-di(1H-indol-3-yl)propan-2-ol. Pseudoindole B (32) is
also made up of a similarly identical skeleton connected at the methine carbon C-8, which
bears a chain with a sulfoxide moiety. Compounds 33 to 37 share a common basic structure
comprising two identical groups of ortho-disubstituted aromatic ring and 3-substituted indole joined at carbon C-8, making them a member of the bisindole alkaloid class. Similar to
compound 31 and 32, 3,3′ -cyclohexylidenebis(1H-indole) (33) was also isolated as a brown
amorphous powder [59]. It can be synthesised by reacting an indole with cyclohexanone.
This compound exhibited a 140% enhancing potential towards the Am80-induced HL-60
(myeloid leukemic cell lines) cell. When treated with eight human cancer cell lines (A549,
Molecules 2021, 26, 3227
13 of 27
GLC82, CNE1, CNE2, HONE1, SUNE1, BEL7402 and the human hepatocarcinoma cell line
(SMMC7721)), compound 33 showed cytotoxicity with IC50 values of 22.84, 22.04, 18.69,
20.84, 26.62, 20.54, 27.52 and 22.50 μM, respectively [59]. 3,3-bis(3-indolyl)butane-2-one
(34) was previously reported as a synthesised product but was later isolated as a natural
metabolite from the bacterium Vibrio parahaemolyticus of the North Sea, as a pale yellowish
solid [83]. Another indole reported from the soft-coral-derived fungi is 2-[2,2-di(1H-indol3-yl) ethyl] aniline (35), which was previously isolated from the bacterium Aeromonas sp.
derived from seawater collected from the South China Sea [84]. It is also a common product
produced by various other bacterial sources and exhibits weak toxicity against the A549
cell line with an IC50 value of 22.6 μM [84].
Figure 2. The chemical structures of the types of indole alkaloids isolated from the soft-coralassociated fungi.
The compounds 3,3 ′ -diindolyl(phenyl)-methane (36) and 1,1-(3,3 ′ -diindolyl)-2phenylethane (37) were reported from the bacteria Edwardsiella tarda [85]. 3,3 ′ -diindolyl
Molecules 2021, 26, 3227
14 of 27
(phenyl)-methane (36) was obtained as a red solid, while 1,1-(3,3′ -diindolyl)-2-phenylethane
(37) was reported as a yellowish solid. The compound 3,3′ -diindolyl(phenyl)methane (36)
was found to exhibit weak antibacterial properties against the pathogen Clostridium perfringens [86]. Perlolyrin (38), a type of β-carboline derivative isolated as a yellow powder, was
originally reported as a fluorescent compound from soy sauce. It is also often associated
with plants, such as Ginseng and several Asiatic plants. These derivatives are strongly
associated with its antitumour and anti-oxidative properties [67]. Pityriacitrin (39), on the
other hand, was previously reported from the marine bacterium Paracoccus sp. and the
yeast Malassezia furfur [87]. It appeared as a bright yellow band in thin layer chromatography and was isolated as a yellow solid. Pityriacitrin (39) was characterised as a natural UV
filter in cultures of the yeast Malassezia furfur [88].
Along with the bisindole alkaloids, several β-carboline type indoles were also reported
from the soft-coral associated Pseudallescheria boydii. 1-acetyl-β-carboline (40) is a fluorescent
compound first reported from the marine sponge Tedania ignis [59]. Prior records of this
metabolite were from a terrestrial plant Ailanthus malabarica [67]. Similarly, the other
derivative is 3-Hydroxy-β-carboline (41), which was first obtained in its natural form as
a yellowish amorphous solid from the stems of a medicinal plant Picrasma quassioides
collected in China. This carboline derivative was previously described as a synthesised
product [89]. The final two indoles reported from the investigation of Yuan and team
(2019) [59] were 1-(9H-pyrido[3,4-b]indol-1-yl)ethan-1-ol (42), initially reported from the
heartwood of Dicorynia guianensis as a yellowish powder [90] and Nb -acetyltryptamine
(43), which was isolated from an unidentified marine fungus derived from the red alga
Gracilaria verrucose as a yellowish oil. Previous records on Nb -acetyltryptamine had been as
a bio-transformed product of tryptamine from the fungus Streptomyces staurosporeus [91].
All the chemical structures of these compounds are shown in Figure 3.
Figure 3. The chemical structures of the indoles of type isolated metabolites.
Molecules 2021, 26, 3227
15 of 27
4.3. Anthraquinones Derivates
Anthraquinones are aromatic compounds with the 9,10-anthracenedione core and
are often referred to as 9,10-dioxoanthracene with a keto functionality in its central ring.
There have been nearly 100 naturally occurring anthraquinones, and about 20 have been
identified to be the products of marine fungi derived from the soft-coral genus Sarcophyton.
In 2012, Zheng et al. isolated tetrahydroaltersolanol B (44), five hydroanthraquinone
derivatives named tetrahydroaltersolanols C–F (45–48) and dihydroaltersolanol A (49),
from the liquid culture of Alternaria sp. derived from a Sarcophyton sp. collected from the
Weizhou coral reef in the South China Sea [49]. The crude extract of the cultured fungi was
fractioned using column chromatography with the mobile phase combination between
Petr Eth:EtOAc (1:2). The immunosuppressive potential of the fractions exhibited activity
at concentrations 1.48 ± 0.15 and 11.83 ± 0.83 μg/mL [49]. Repeated Sephadex column
chromatography followed by HPLC over methanol through a Zorbax SB-C18 (9.4 mm ×
25 cm) yielded the above-mentioned metabolites.
Tetrahydroaltersolanol B (44), isolated as a colourless crystal, is a hexahydroanthronol
type anthraquinone isolated only from the fungi Alternaria solani [49]. So far there have
been two records of this metabolite from the fungi. Likewise, tetrahydroaltersolanol C (45)
was also isolated as a colourless crystal. According to the spectroscopic features, compound
45 bears a great deal of structural similarity to the compound tetrahydroaltersolanol B
(44) with differences in the α, β positioning of the proton and hydroxyl at carbon C-3 and
C-9, respectively [49]. Tetrahydroaltersolanol C (45) was isolated as a new metabolite at
the point of report, along with tetrahydroaltersolanols D–F (46–48) from the soft-coral
associated Alternaria sp. It exhibited antiviral activity when screened against the porcine
reproductive and respiratory syndrome virus (PRRSV) [49].
Tetrahydroaltersolanol D (46) was also obtained in the form of colourless crystal.
Though tetrahydroaltersolanol D (46) is structurally identical to tetrahydroaltersolanol
B (44), it varied stereochemically at carbon positions C-1a and C-4a [49]. The relative
configurations of all asymmetric carbons in tetrahydroaltersolanol D (46) were confirmed
as 1aβ, 3β, 4aα, 9β, and 11β, identical to those of tetrahydroaltersolanol B (44). Likewise,
tetrahydroaltersolanol E (47) was isolated as a colourless crystal of similar nature to compounds (45) and (46). Since its chemical shifts resembled tetrahydroaltersolanol B (44), it
was eventually determined as 3-epi-tetrahydroaltersolanol B [49]. Tetrahydroaltersolanol
F (48) was isolated as amorphous pink powder. It shows close structural resemblance to
tetrahydroaltersolanol B (44), despite obvious differences in the presence of a singlet methyl
at 2.14 ppm and the downfield shift of H-3 in 1 H-NMR. The final compound in the set
of hydroanthraquinones reported from the Alternaria sp. was dihydroaltersolanol A (49),
isolated as colourless crystals as well [49]. The relative configurations of all asymmetric
carbons in dihydroaltersolanol A (49) were determined as 1α, 1aα, 3β, 9β, and 11β. None of
these compounds exhibited antimicrobial potential as screened [49].
Further investigation of the marine fungi Alternaria sp. from the Sarcophyton soft coral
yielded six alterporriol-type anthranoid dimers, altersolanols B–C (50–51), altersolanol
L (52), ampelanol (53), macrosporin (54) and alterporriol C (55), together with five more
analogues, alterporriols N–R (56–60) were isolated and characterised [49]. The Alternaria
sp. isolated from the soft coral was cultured in potato glucose liquid medium before
being extracted in EtOAc. Column fractions of extract were subjected to repeated column
chromatography over Sephadex LH-20 and purification via HPLC using a Kromasil C18
preparative HPLC column to yield the reported compounds [49].
Altersolanol B (50), a red needle and altersolanol C (51) were previously reported
from the extract of Alternaria solani, which caused the black spot disease. Both compounds
were potent in inhibiting all the Gram-positive bacteria [71]. Altersolanol L (52), isolated
as a brown powder, and the white crystal macrosporin (54) reported from the soft coral
Alternaria sp. were initially isolated from the endophytic fungus Stemphylium globuliferum
derived from a medicinal plant species [92]. Apart from Alternaria, macrosporin (54) is
known to be produced by several economically important crop-disease-causing fungal
Molecules 2021, 26, 3227
16 of 27
pathogens, such as Cladosporium, Dichotomophthora, Phomopsis, Stemphylium and Dactylaria. Altersolanol L (52) was reported to share a similar skeletal structure to the previously
described dihydroaltersolanol A (49). Ampelanol (53), on the other hand, is another metabolite associated with medicinal plant-derived fungus Ampelomyces sp. It was isolated as
white crystals and determined to exhibit mild cytotoxicity towards mouse lymphoma cells
(L5178Y) [72]. The chemical structures of the anthraquinones compounds 44–54 are shown
in Figure 4.
Figure 4. The chemical structures of compounds 44–54.
Subsequently, several bianthraquinones were isolated from the soft-coral-derived
marine fungi as well. Alterporriol C (55) belongs to a modified bianthraquinone and was
first isolated from the fungus Alternaria porri as red needles [93]. Alterporriol C (55), which
was antibacterial against Escherichia coli and Vibrio parahemolyticus with both MIC values
2.5 μM, is suggested to be made up of the compounds altersolanol A and macrosporin
(54) [49]. Alterporriol N (56) was an amorphous powder in red. 13 C NMR spectrum analysis
suggested that alterporriol N (56) was a symmetrical dimer of altersolanol C (51) with
a C-8 and C-8′ linkage [49]. Another symmetrical dimer to altersolanol C (51) isolated
from Alternaria sp. was alterporriol O (57), which appeared as a red amorphous powder.
Unlike alterporriol N (56), alterporriol O (57) was an anthranoid dimer with a C-4 and
C4’ linkage [49]. Likewise, alterporriol P (58) was also a red, amorphous powder, with
the molecular formula of C32 H26 O12 . Alterporriol P (58), also isolated as a red amorphous
powder, was characterised as a sub-unit of the altersolanol C (51) and macrosporin (54)
linkage via carbon C-4 and C-6’. This compound was cytotoxic against the human prostate
cancer (PC-3) and human colorectal carcinoma (HCT-116) cell lines with the IC50 values 6.4
and 8.6 μM [49]. In contrast, alterporriol Q (59) was obtained as a yellowish amorphous
powder, and the final anthraquinone characterised from Alternaria sp. was alterporriol R
(60), which was determined to be an isomer of alterporriol Q 59 [49]. These compounds
were comprised of two macrosporin (54) sub-units. The two sub-units of alterporriol Q
(59) were linked through carbons C-4 and C-6’, while alterporriol R (60) was connected via
carbons C-4 and C-8′ . Alterporriol Q (59) exhibited antiviral activity against the porcine
reproductive and respiratory syndrome virus (PRRSV), with an IC50 value of 39 μM [49].
Molecules 2021, 26, 3227
17 of 27
All the above-mentioned compounds were isolated via a similar protocol in the choice of
culture conditions, mobile phase in column chromatography and HPLC purification. The
chemical structures of the reported bianthraquinones are shown in Figure 5.
Figure 5. The chemical structures of the reported bianthraquinones.
4.4. Amino Acid Derivates
In 2013, a phenylalanine derivative 4′ -OMe-asperphenamate (61) was isolated from
Aspergillus elegans derived from Sarcophyton sp. [58]. Asperphenamate (62) is another
phenylalanine derivative reported from the same study and has an identical basic skeletal
structure to the white powdered 4′ -OMe-asperphenamate [58]. The only difference observed in the 1 H-NMR spectrum was the presence of a highly electronegative primary
methyl signal at δH 3.74 in 4′ -OMe-asperphenamate (61) instead of an aromatic proton at
Molecules 2021, 26, 3227
18 of 27
δH 7.30 in asperphenamate (62), making it the only detected difference between the two at
the carbon position 4′ [58]. The compounds were isolated in the same manner as the previously mentioned compounds; column chromatography with Petr Ether and EtOAc mobile
phase followed by a Sephadex LH-20 column with chloroform and methanol at a ratio 1:1
and HPLC purification using methanol over a Kromasil C18 preparative column [58]. The
chemical structures of compounds (61) and (62) are shown in Figure 6.
Figure 6. The chemical structures of 4′ -OMe-asperphenamate (61) and asperphenamate (62).
4.5. Other Metabolites
In addition to sesquiterpenoid derivates, the marine fungus Chondrostereum sp. associated with Sarcophyton tortuosum has also produced two novel polyacetylenes, chondrosterins G–H (63-64), as well as a known polyacetylene (2E)-decene-4,6,8-triyn-1-ol (64) [68].
Chondrosterin G (63) was isolated in the form of a colourless solid. It was structurally determined as deca-4,6,8-triyn-1,2,3-triol [68]. Chondrosterin H (64) was reported as a white
solid made up of a similar functional group as chondrosterin G (63) [68]. Chondrosterin H
(64) was determined as a 3-chlorodeca-4,6,8-triyn-1,2-diol. Though structurally identical,
the difference between chondrosterins G (63) and H (64) is on the functional group attached
to carbon position C-3 where the chlorin atom was observed in chondrosterin H (64) instead
of a hydroxyl as in chondrosterin G (63). The third metabolite from this investigation was
(2E)-decene-4,6,8-triyn-1-ol (65) (a synonym of dehydromatricarianol), which was common
in basidiomycete-type fungus [68]. Compounds (63–65) can be easily but slowly oxidised
in air, and this process accelerates with heat. Since (2E)-decene-4,6,8-triyn-1-ol (65) was
the main polyacetylenic metabolite in the investigated fungi, it was proposed as a possible
precursor in the biosynthesis for chondrosterins G and H (63–64) [68]. It was suggested
that the double bond of (2E)-decene-4,6,8-triyn-1-ol (65) be epoxidated and hydrolysed to
form a diol as in chondrosterin G (63), while Cl− (a nucleophile) together with H+ reacts
with the epoxidated product to form the halogenated alcohol of chondrosterin H (64) [68].
Structures of the polyacetylenes compound 63–65 are exhibited in Figure 7.
In 2018, three new compounds were isolated from Sarcophyton subviride associated
marine fungus Aspergillus terreus in the South China Sea. The cooked rice cultured fungus
extract yielded luteoride E (66), versicolactone G (67) and (3E,7E)-4,8-di-methyl-undecane3,7-diene-1,11-diol (68). Additionally, nine more metabolites comprising of asterrelenin (69),
methyl 3,4,5-trimethoxy-2-(2-(nicotinamido)benzamido)benzoate (70), 14α-hydroxyergosta4,7,22-triene-3,6-dione (71), territrem A (72), territrem B (73), territrem C (74), lovastatin
(75), monacolin L acid methyl ester (76) and monacolin L (77) were also characterised [52].
Molecules 2021, 26, 3227
19 of 27
Figure 7. Polyacetylenes (63–65) from Sarcophyton tortuosum.
Luteoride E (66), a prenylated tryptophan derivative with a 3,7-disubstituted indole
was obtained as a yellow oil. Careful interpretation of luteoride A chemical data determined the geometry of the oxime functionality of luteoride E (66) to be of E-form [52].
Luteoride E (66) exhibited inhibitory potency against Lipopolysaccharide (LPS)-induced
nitric oxide (NO) production of RAW 264.7 cells with an IC50 value of 24.64 μM. The
butenolide, versicolactone G (67), which was isolated as an amorphous white powder, was
characterised to have a basic skeleton made up of a mono-substituted and a trisubstituted
benzene identical to a previously reported versilactone B. [52]. The difference between
these two metabolites is the presence of a sp3 methylene carbon and oxygenated tertiary
carbon via a methoxy group in versicolactone G (67) instead of the existing δ double bond
in versicolactone B [52]. Alongside luteoride E (66) and versicolactone G (67), (3E,7E)4,8-di-methyl-undecane-3,7-diene-1,11-diol (68), a linear aliphatic alcohol was isolated
as colourless oil and characterised as C13 H24 O2 . When screened for the α-glucosidase
inhibitory activity of versicolactone G of the compounds (66-68), 67 demonstrated potential
inhibitory potency with an IC50 value of 104.8 ± 9.5 μM [52]. None of these metabolites
were antibacterial; however, all three exhibited anti-inflammatory activity against NO production with IC50 values between 15.7 and 24.6 μM. Asterrelenin (69) is a colourless cubic
crystal with infrared peaks detected at 3273, 1691 and 1647 cm−1 wavelengths, and carbon
chemical shifts at 170.0, 168.7 and 166.4 ppm were indications of amides present [52].
Methyl 3,4,5-trimethoxy-2-(2-(nicotinamido)benzamido)benzoate (70) was previously
reported from Aspergillus terreus cultured under high saline conditions (10% salt) [94]. Salt
concentration of 3% and lower did not trigger the production of compound 70. This compound was mildly antibacterial with a minimum inhibition concentration 52.4 μM against
Staphylococcus aureus and Enterobacter aerogenes [95]. Aspergillus terreus also yielded 14αhydroxyergosta-4,7,22-triene-3,6-dione (71), C28 H40 O3 , which was only reported through
synthesis prior to its natural isolation from the soft coral fungi [96].
Additionally, three nitrogen lacking termorgenic mycotoxins territrems A–C (72–74)
were successfully characterised from the CHCl3 of the fungal strain as well [52]. Previous reports on these compounds were from the Aspergillus terreus strain from rice culture. Territrems B and C (73–74) displayed strong anti-acetylcholinesterase inhibition
with IC50 values of 4.2 ± 0.6 and 20.1 ± 3.3, respectively [97]. The lovastatin analogue
(75), C24 H36 O5 , isolated from the soft coral fungi here, is a well-known fungal secondary
metabolite previously reported from Aspergillus sclerotiorum. Lovastatins are an inhibitor
of hydroxymethylglutaryl-coenzyme A reductase (HMGR-CoA). It is also associated with
the cause of reduced cholesterol in humans and is cytotoxic to MCF-7, the human cervical
cancer cell line (HeLa), the human liver cancer cell line (HepG2), and the human skin
melanoma cell line (B16F10). The lovastatin analogue (75) exhibited cytotoxicity towards
Vero (normal kidney) cells with IC50 in the range of 2.2–8.4 μM. It also inhibited the HMGRCoA activity by 42% at 200 μM [98]. The compounds territrem A (72) and lovastatin (75)
were evaluated for their anti-inflammatory activity against NO production and significant
Molecules 2021, 26, 3227
20 of 27
inhibitory potency with IC50 values between 5.48 and 29.34 μM was observed [52]. The last
two compounds reported from the Aspergillus terreus were monacolin L acid methyl ester
(76) and monacolin L (77). These were formerly reported as a byproduct from the fermentation of sterile rice using the fungal strain Monascus purpureus to produce a traditional
Chinese food and medicine called the red yeast rice [99]. The above described compounds
66–77 are shown in Figure 8.
Figure 8. Additional metabolites (66–77) from the soft-coral Sarcophyton-derived marine fungi.
In 2018, a total of 11 acyclic merohemiterpenes were isolated from the Sarcophyton
subviride-derived fungus Penicillium bialowiezense in the South China Sea [53]. The potato
dextrose agar (PDA) cultured fungus yielded the compounds 8-O-methyl mycophenolic
acid (78), 3-hydroxy mycophenolic acid (79), 6-(5-carboxy-3-methylpent-2-enyl)-7-hydroxy3,5-dimethoxy-4-methylphthalan-1-one (80), 6-(5-methoxycarbonyl-3-methylpent-2-enyl)-3,7dihydroxy-5-methoxy-4-methylphthalan-1-one (81), 6-(3-carboxybutyl)-7-hydroxy-5-methoxy4 -methylphthalan-1-one (82), 6-[5-(2,3-dihydroxy-1-carboxyglyceride)-3-methylpent-2-enyl]7-hydroxy-5-methoxy-4 -methylphthalan-1-one (83), 6-[5-(1-carboxy-4-N-carboxylate)-3-
Molecules 2021, 26, 3227
21 of 27
methylpent-2-enyl]-7-hydroxy-5-methoxy-4-methylphthalan-1-one (84), N-mycophenoyll-valine (85), N-mycophenoyl-l-phenyloalanine (86), N-mycophenoyl-l-alanine (87) and
mycophenolic acid (MPA) (88) [53]. The crude extract of the cultured fungi was fractioned
using column chromatography with the mobile phase combination between petroleum
ether: EtOAc: methanol from the ratio 20:1:0 to 1:1:1. The immunosuppressive potential
of the fractions exhibited activity at concentrations 1.48 ± 0.15 and 11.83 ± 0.83 μg/mL.
Repeated Sephadex column chromatography followed by HPLC over methanol through
a Zorbax SB-C18 (9.4 mm × 25 cm) yielded the above-mentioned metabolites [100]. The
structures of these compounds are shown in Figure 9.
Figure 9. Additional metabolites (78–88) from the soft-coral Sarcophyton-derived marine fungi (cont.).
8-O-methyl mycophenolic acid (78), 3-hydroxy mycophenolic acid (79) and MPA (88),
being white crystals, are part of the mycophenolic acid family where they are mainly found
in the fungal genus Penicillium. They are widely known for their diverse bioactivities, such
as immunosuppressive and antiviral. Compounds (80–84) were newly characterised at
the time of isolation. Compounds (80–81) were isolated as white powders [100]. Based
on structural elucidation, compound (80) was named 6-(5-carboxy-3-methylpent-2-enyl)7-hydroxy-3,5-dimethoxy-4-methylphthalan-1-one, while compound (81) was determined
as 6-(5-methoxycarbonyl-3-methylpent-2-enyl)-3,7-dihydroxy-5-methoxy-4-methylphthalan-1one [100]. 3-hydroxy mycophenolic acid (79) and compound (80) share identical structures,
except that the hydroxyl group at C-3 of (79) is replaced by a methoxy in compound (80).
Comparison between compounds (80) and (81) shows that the carboxyl group at C-6′ in
Molecules 2021, 26, 3227
22 of 27
compound (80) was methyl-esterified in compound (81) [100]. Compound (82) was isolated
as a white powder and closely resembles euparvic acid. Compound (83) was an amorphous white powder known as 2,3-dihydroxypropyl mycophenolate. As for compound
(84), it was identical to 83 in skeleton, except that the 2,3-dihydroxypropyl group in 83 was
replaced by a 4-aminobutanoic acid moiety in 84 [100].
Finally, the compounds N-mycophenoyl-L-valine (85), N-mycophenoyl-L-pheny
loalanine (86) and N-mycophenoyl-L-alanine (87) were colourless solids. [53]. Compounds
(77–88) showed inhibitory potency against inosine-50-monophosphate dehydrogenase
(IMPDH2) with IC50 values between 0.59 and 24.68 μM. When testing their immunosuppressive activity against the proliferation of T-lymphocytes in vitro, the IC50 values of
compounds (78–80) were from 0.84 to 0.95 μM, while the IC50 values of compounds (81–88)
ranged from 3.27 to 24.68 μM [100].
5. Concluding Remarks
The chemical diversity of soft-coral associated symbionts is often limited to bacterial
and fungal isolates cultured under laboratory conditions. Nevertheless, there are still many
unexplored symbionts in terms of their secondary metabolism and natural-product biosynthesis potential. However, the development of new techniques such as metabolomics for
the determination of metabolites produced by specific genes and next generation sequencing creates new dimensions of in-depth investigation of the microbiome. Independent
culture methods, such as the next-generation sequencing on sponges, would reveal novel
microorganisms, and their guild patterns could be analysed in order to know their association with corals. The role of fungi and their respective host can either be symbiotic or
parasitic. As sponges, there have been speculations as to the origin of metabolites isolated
from the soft corals. This review study reveals that no common metabolites were shared
by the host and its fungi. This confirms that the metabolites isolated from the host are
synthesised by the host itself. Due to the diverse bioactivity of the fungal metabolites, we
hypothesise that fungal metabolites perform various functions for additional protection to
their host, presumably similar to the role of constituents, such as the MAAs. The presence
of microorganisms triggers the development of a wide array of secondary metabolites,
which function as mutual defences or for adaptive purposes as well as microbial regulation
of the octocoral holobionts. Recent studies have shown an increasing trend in bioactive secondary metabolites from Sarcophyton-associated marine fungi. However, many compounds
have not been thoroughly evaluated for their bioactivities. In the future, more bioassays
could be conducted on the soft coral and its associated fungal chemical compounds.
Author Contributions: Conceptualisation, K.P.; validation, K.P.; resources, Y.L., K.P.; data curation, Y.L.; writing—original draft preparation, Y.L.; writing—review and editing, Y.L., K.P., J.S.S.S.;
supervision, K.P., S.A.A. All authors have read and agreed to the published version of the manuscript.
Funding: Not applicable for the preparation of this review.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Acknowledgments: This review is an output as part of the University Malaya BKP grant (BK08-2018)
and the Higher Institution Centre of Excellence (HiCoE) grant (IOES-2014G).
Conflicts of Interest: The authors declare no conflict of interest.
Molecules 2021, 26, 3227
23 of 27
Abbreviations
The following abbreviations are used in this manuscript:
UV
MNP
MAA
Petr Eth
EtOAc
MeOH
RP-HPLC
HPLC
NMR
ROS
PDB
PDA
MeCN
ODS
A549
CNE2
LoVo
IC50
EC50
GPY
COSY
HMBC
SUNE1
MCF-7
CNE1
Bel7402
KB
HONE1
GLC-82
SMMC-7721
HL7702
GLC82
HL 7702
HL-60
Am-80
L5178Y
HCT-116
HeLa
PRRSV
DEPT
HMBC
B16F10
HeLa
HepG2
B16F10
Vero
HRESIMS
CHCl3
OH
MIC
LPS
NO
HMGR-CoA
MPA
IMPDH2
Ultra violet
Marine natural product
Mycosporin amino acid
Petroleum Ether
Ethyl Acetate
Methanol
Reverse Phased High-Performance Liquid Chromatography
High-Performance Liquid Chromatography
Nuclear Magnetic Resonance
Reactive Oxygen Species
Potato Dextrose Broth
Potato Dextrose Agar
Acetonitrile
Octadecylsilyl
Human lung adenocarcinoma cell line
Human nasopharyngeal carcinoma cell line
Human colon cancer cell line
Half maximal inhibition concentration
Half maximal effective concentration
Glucose peptone yeast
Homonuclear correlation spectroscopy
Heteronuclear Multiple Bond Correlation
Human Nasopharyngeal carcinoma cell line
Human breast cancer cell line
Human nasopharyngeal carcinoma cell line
Human hepatic cancer cell line
Human epidermoid carcinoma cell line
Epithelial tumour cell line
Gejiu Lung Carcinoma-82
Human hepatocarcinoma cell line
Normal human liver cell
Human lung adenocarcinoma cell line
Normal Human Liver Cells
Myeloid leukemic cell lines
RARα Specific Synthetic Retinoid
Mouse lymphoma cells
Human colorectal carcinoma cell line
Human cervical cancer cell line
porcine reproductive and respiratory syndrome virus
Distortionless enhancement by polarisation transfer
Heteronuclear multiple bond correlation
Human skin melanoma cell line
Human cervical cancer cell line
Human liver cancer cell line
Human skin melanoma cell line
Normal kidney cells
High-Resolution Electrospray Ionisation Mass Spectrometry
Chloroform
Hydroxyl
Minimum inhibition activity
Lipopolysaccharide
Nitric oxide
Hydroxymethylglutaryl-coenzyme A reductase
Mycophenolic acid
inosine-50-monophosphate dehydrogenase
Molecules 2021, 26, 3227
24 of 27
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
Lau, Y.W.; Poliseno, A.; Kushida, Y.; Quere, G.; Reimer, J.D. The Classification, Diversity and Ecology of Shallow Water Octocorals.
Encycl. World’s Biomes 2020, 4, 597–611.
Yesson, C.; Taylor, M.L.; Tittensor, D.P.; Davies, A.J.; Guinotte, J.; Baco, A.; Black, J.; Hall-Spencer, J.M.; Rogers, A.D. Global habitat
suitability of cold-water octocorals. J. Biogeogr. 2012, 39, 1278–1292. [CrossRef]
Samimi-Namin, K.; van Ofwegen, L. The Octocoral Fauna of the Gulf. In Coral Reefs of the Gulf; Riegl, B.M., Purkis, S.J., Eds.;
Springer: Dordrecht, The Netherlands, 2012; pp. 225–252.
Williams, G.C. The global diversity of sea pens (cnidaria: Octocorallia: Pennatulacea). PLoS ONE 2011, 6, e22747. [CrossRef]
[PubMed]
Fabricius, K.; Alderslade, P. Soft Corals and Sea Fans: A Comprehensive Guide to the Tropical Shallow Water Genera of the Central-West
Pacific, the Indian Ocean and the Red Sea; Fabricius, K., Alderslade, P., Eds.; Australian Institute of Marine Science: Queensland,
Australia, 2001; p. 264.
Zapata-Guardiola, R.; Lopez-Gonzalez, P.J. Two new gorgonian genera (Octocorallia: Primnoidae) from Southern Ocean waters.
Polar Biol. 2010, 33, 313–320. [CrossRef]
McFadden, C.S.; Ofwegen, L.P. A second, cryptic species of the soft coral genus Incrustatus (Anthozoa: Octocorallia: Clavulariidae)
from Tierra del Fuego, Argentina, revealed by DNA barcoding. Helgol. Mar. Res. 2013, 67, 137–147. [CrossRef]
Perez, C.D.; de Moura Neves, B.; Cordeiro, R.T.; Williams, G.C.; Cairns, S.D. Distribution of Octocorallia. In The Cnidaria, Past,
Present and Future; Goffredo, S., Dubinsky, Z., Eds.; Springer International Publishing: Cham, Switzlerland, 2016; pp. 109–123.
McFadden, C.S.; Sanchez, J.A.; France, S.C. Molecular phylogenetic insights into the evolution of Octocorallia: A review. Integr.
Comp. Biol. 2010, 50, 389–410. [CrossRef] [PubMed]
Fadden, C.S.; van Ofwegen, L.P. Stoloniferous octocorals (Anthozoa, Octocorallia) from South Africa, with descriptions of a new
family of Alcyonacea, a new genus of Clavulariidae, and a new species of Cornularia (Cornulariidae). Invertebr. Syst. 2012, 26,
331–356.
McFadden, C.S.; France, S.C.; Sanchez, J.A.; Alderslade, P. A molecular phylogenetic analysis of the Octocorallia (Cnidaria:
Anthozoa) based on mitochondrial protein-coding sequences. Mol. Phylogenet. Evol. 2006, 41 513–527. [CrossRef]
Aratake, S.; Tomura, T.; Saitoh, S.; Yokokura, R.; Kawanishi, Y.; Shinjo, R.; Reimer, J.D.; Tanaka, J.; Maekawa, H. Soft Coral
Sarcophyton (Cnidaria: Anthozoa: Octocorallia) Species Diversity and Chemotypes. PLoS ONE 2012, 7, e30410. [CrossRef]
Raimundo, I.; Silva, S.G.; Costa, R.; Keller-Costa, T. Bioactive secondary metabolites from octocoral-Associated microbes—New
chances for blue growth. Mar. Drugs 2018, 16, 485. [CrossRef]
Verselveldt, J. A revision of the genus Sarcophyton Lesson (octocorallia, Alcyonacea). Zool. Verh. 1982, 192, 1–91.
Feussner, K.-D.; Waqa, T. Five new species of Sarcophyton (Coelenterata: Octocorallia) from the Fiji Islands. South Pac. J. Nat. Appl.
Sci. 2013, 31, 1–26. [CrossRef]
van der Land, J. UNESCO-IOC Register of Marine Organisms (URMO). 2008. Available online: http://www.marinespecies.org/
urmo (accessed on 4 March 2021).
Simpson, W.M. Descriptions of some of the new marine invertebrata from the Chinese and Japanese Seas. Acad. Nat. Sci. 1855, 7,
375–378.
Verseveldt, J.; Benayahu, Y. Descriptions of one old and five new species of Alcyonacea (Coelenterata: Octocorallia) from the Red
Sea. Zool. Meded. 1978, 53, 57–74.
Verseveldt, J. Alcyonaceans (Coelenterata: Octocorallia) from some Micronesian Islands. Zool. Meded. 1978, 53, 49–55.
Liu, R. Checklist of Marine Biota of China Seas. In Checklist of Marine Biota of China Seas; Liu, R., Ed.; Science Press: Beijing, China,
2008; p. 1267
Lin, M.-C.; Dai, C.-F. Drag, morphology and mechanical properties of three species of octocorals. J. Exp. Mar. Bio. Ecol. 1996, 201,
13–22. [CrossRef]
Tixier-Durivault, A. Octocoralliaires de Madagascar et des iles avoisinantes. Faune de Madagascar 1966, 21, 1–456.
Tixier-Durivault, A. Les octocoralliaires de Nha-Trang (Viet-Nam). Cah du Pacifique 1970, 14, 115–236.
Imahara, Y. Report on the Octocorallia from the Ryukyu Islands of Japan. Bull. Inst. Ocean Res. Dev. Tokai Univ. 1991, 11, 59–94.
Verseveldt, J. Octocorallia from north-western Madagascar (Part II). Zool. Verh. Leiden 1971, 117, 1–73.
Roxas, H.A. Two new species of Sarcophyton Less. from the Philippines. Univ. Philipp. Nat. Appl. Sci. Bull. 1932, 4, 73–80.
Verseveldt, J. Octocorallia from New Caledonia. Zool. Meded. 1974, 48, 95–122.
Benayahu, Y. Corals of the South-west Indian Ocean: I. Alcyonacea from Sodwana Bay, South Africa. Invest. Rep. Oceanogr. Res. Inst.
1993, 67, 1–15.
Macfadyen, L.M.I. Alcyonaria (Stolonifera, Alcyonacea, Telestacea and Gorgonacea). Gt Barrier Reef Exped 1928–1929. Sci. Rep.
1930, 5, 17.
Utinomi, H. On some alcyonarians from the West-Pacific islands (Palau, Ponape and Bonins). Publ. Seto. Mar. Biol. Lab. 1956, 5,
221–242. [CrossRef]
Morton, B.; Morton, J. The Sea Shore Ecology of Hong Kong; Hong Kong University Press: Hong Kong, China, 1983.
Roxas, H.A. Philippine Alcyonaria, II. The families Alcyoniidae and Nephthyidae. Philipp. J. Sci. 1933 50, 1–5
van der Land, J. UNESCO-IOC Register of Marine Organisms, a common base for biodiversity inventories. In Families and
Bibliography of Keyworks; van der Land, J., Ed.; NNM, Leiden and ETI: Amsterdam, The Netherlands, 1994.
Molecules 2021, 26, 3227
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
25 of 27
Verseveldt, J. Report on the Octocorallia (Stolonifera and Alcyonacea) of the Israel south Red Sea expedition 1962, with notes on
other collections from the Red Sea. Sea Fish Res. Stn Haifa Bull. 1965, 14, 27–47.
Verseveldt, J.; Benayahu, Y. On two old and fourteen new species of Alcyonacea (Coelenterata, Octocorallia) from the Red Sea.
Rijksmuseum van Natuurlijke Historie 1983, 208, 3–33
Verseveldt, J. Biological results of the Snellius expedition. XX. Octocorallia from the Malay Archipelago (Part I). Temminckia 1960,
10, 209–251.
Verseveldt, J.; Tursch, A. Octocorallia from the Bismarck Sea (Part I). Zool. Meded. 1979, 54, 133–147.
Samimi, N.K.; van Ofwegen, L.P. Some shallow water octocorals (Coelenterata: Anthozoa) of the Persian Gulf. Zootaxa 2009, 2058
1–52.
Benayahu, Y.; Perkol-finkel, S. Soft Corals (Octocorallia: Alcyonacea) from Southern Taiwan. I. Zool Stud. 2004, 43, 537–547.
Pratt, E.M. The Alcyonaria of the Maldives. Part II. The genera Sarcophytum, Lobophytum, Sclerophytum and Alcyonium. Fauna
Geogr. Maldive Laccadive Arch. 1903, 2, 503–509.
Alderslade, P.; Shirwaiker, P. New species of soft corals (Coelenterata: Octocorallia) from the Laccadive Archipelago. Beagle 1991,
8, 189–233.
Benayahu, Y.; Ofwegen, L.P. Van. New species of Sarcophyton and Lobophytum (Octocorallia: Alcyonacea) from Hong Kong.
Zool. Meded. 2009, 83, 863–876.
van de Water, J.A.J.M.; Allemand, D.; Ferrier-Pages, C. Host-microbe interactions in octocoral holobionts—Recent advances and
perspectives. Microbiome 2018, 6, 1–28. [CrossRef]
Pernice, M.; Raina, J.B.; Radecker, N.; Cardenas, A.; Pogoreutz, C.; Voolstra, C.R. Down to the bone: The role of overlooked
endolithic microbiomes in reef coral health. ISME J. 2020, 14, 325–334. [CrossRef]
Peixoto, R.S.; Rosado, P.M.; Leite, D.C.D.A.; Rosado, A.S.; Bourne, D.G. Beneficial microorganisms for corals (BMC): Proposed
mechanisms for coral health and resilience. Front. Microbiol. 2017, 8, 341. [CrossRef]
Toledo-Hernandez, C.; Zuluaga-Montero, A.; Bones-Gonzalez, A.; Rodríguez, J.A.; Sabat, A.M.; Bayman, P. Fungi in healthy and
diseased sea fans (Gorgonia ventalina): Is Aspergillus sydowii always the pathogen? Coral Reefs 2008, 27, 707–714. [CrossRef]
Zuluaga-Montero, A.; Ramírez-Camejo, L.; Rauscher, J.; Bayman, P. Marine isolates of Aspergillus flavus: Denizens of the deep or
lost at sea? Fungal Ecol. 2010, 3, 386–391. [CrossRef]
Soler-Hurtado, M.M.; Sandoval-Sierra, J.V.; Machordom, A.; Dieguez-Uribeondo, J. Aspergillus sydowii and other potential fungal
pathogens in gorgonian octocorals of the Ecuadorian Pacific. PLoS ONE 2016, 11, e0165992. [CrossRef] [PubMed]
Zheng, C.J.; Shao, C.L.; Guo, Z.Y.; Chen, J.F.; Deng, D.S.; Yang, K.L.; Chen, Y.Y.; Fu, X.M.; She, Z.G.; Lin, Y.C. Bioactive
hydroanthraquinones and anthraquinone dimers from a soft coral-derived Alternaria sp. fungus. J. Nat. Prod. 2012, 75, 189–197.
[CrossRef] [PubMed]
Koh, L.L.; Tan, T.K.; Chou, L.M.; Goh, N.K.C. In Proceedings of the The 12th International Coral Reef Symposium (ICRS 2012),
Queensland, Australia, 9–13 July 2012; Volume 1, pp. 521–526.
Zhang, X.-Y.; Bao, J.; Wang, G.-H.; He, F.; Xu, X.-Y.; Qi, S.-H. Diversity and antimicrobial activity of Culturable fungi isolated from
six species of the South China Sea gorgonians. Microb. Ecol. 2012, 64, 617–627. [CrossRef] [PubMed]
Liu, M.; Sun, W.; Wang, J.; He, Y.; Zhang, J.; Li, F.; Zhang, Y. Bioactive secondary metabolites from the marine-associated fungus
Aspergillus terreus. Bioorg. Chem. 2018, 80, 525–530. [CrossRef]
El-Demerdash, A.; Kumla, D.; Kijjoa, A. Chemical Diversity and Biological Activities of Meroterpenoids from Marine DerivedFungi: A Comprehensive Update. Mar. Drugs 2020, 18, 317. [CrossRef]
Li, H.-J.; Xie, Y.-L.; Xie, Z.-L.; Chen, Y.; Lam, C.-K.; Lan, W.-J. Chondrosterins A–E, Triquinane-Type Sesquiterpenoids from Soft
Coral-Associated Fungus Chondrostereum sp. Mar. Drugs 2012, 10, 627–638. [CrossRef]
Huang, L.; Lan, W.J.; Li, H.J. Two new hirsutane-type sesquiterpenoids chondrosterins N and O from the marine fungus
Chondrostereum sp. Nat. Prod. Res 2018, 32, 1578–1582. [CrossRef]
Zhang, X.Y.; Hao, H.L.; Lau, S.C.K.; Wang, H.Y.; Han, Y.; Dong, L.M.; Huang, R.M. Biodiversity and antifouling activity of fungi
associated with two soft corals from the South China Sea. Arch. Microbiol. 2019, 201, 757–767. [CrossRef]
Agrawal, S.; Adholeya, A.; Barrow, C.J.; Deshmukh, S.K. In-vitro evaluation of marine derived fungi against Cutibacterium acnes.
Anaerobe 2018, 49, 5–13. [CrossRef]
Zheng, C.J.; Shao, C.L.; Wu, L.Y.; Chen, M.; Wang, K.L.; Zhao, D.L.; Sun, X.P.; Chen, G.Y.; Wang, C.Y. Bioactive phenylalanine
derivatives and cytochalasins from the soft coral-derived fungus, Aspergillus elegans. Mar. Drugs 2013, 11, 2054–2068. [CrossRef]
Yuan, M.X.; Guo, Q.; Ran, Y.Q.; Qiu, Y.; Lan, W.J.; Li, H.J. New Aromadendrane Sesquiterpenoid Pseuboydone F from the
Marine-derived Fungus Pseudallescheria boydii F44-1. Rec. Nat. Prod. 2019, 14, 166–170. [CrossRef]
Carroll, A.R.; Copp, B.R.; Davis, R.A.; Keyzers, R.A.; Prinsep, M.R. Marine natural products. Nat. Prod. Rep. 2019, 36, 122–173.
[CrossRef]
Jimenez, C. Marine natural products in medicinal chemistry. ACS Med. Chem. Lett. 2018, 9, 959–961. [CrossRef]
Changyun, W.; Haiyan, L.; Changlun, S.; Yanan, W.; Liang, L.; Huashi, G. Chemical defensive substances of soft corals and
gorgonians. Acta Ecol. Sin. 2008, 28, 2320–2328. [CrossRef]
Bourne, D.G.; Morrow, K.M.; Webster, N.S. Insights into the Coral Microbiome: Underpinning the Health and Resilience of Reef
Ecosystems. Annu. Rev. Microbiol. 2016, 70, 317–40. [CrossRef]
Molecules 2021, 26, 3227
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
26 of 27
Glasl, B.; Herndl, G.J.; Frade, P.R. The microbiome of coral surface mucus has a key role in mediating holobiont health and
survival upon disturbance. ISME J. 2016, 10, 2280–2292. [CrossRef]
Li, Z.; Hentschel, U.; Webster, N.; Olson, J.; Haggblom, M. Editorial: Special issue on sponge microbiome. FEMS Microbiol. Ecol.
2020, 96, fiaa075. [CrossRef]
de la Coba, F.; Aguilera, J.; Korbee, N.; de Galvez, M.V.; Herrera-Ceballos, E.; Álvarez-Gomez, F. UVA and UVB Photoprotective
Capabilities of Topical Formulations Containing Mycosporine-like Amino Acids (MAAs) through Different Biological Effective
Protection Factors (BEPFs). Mar. Drugs 2019, 17, 55. [CrossRef]
Li, H.-J.; Lan, W.-J.; Lam, C.-K.; Yang, F.; Zhu, X.-F. Hirsutane Sesquiterpenoids from the Marine-Derived Fungus Chondrostereum
sp. Chem. Biodivers. 2011, 8, 317–324. [CrossRef]
Li, H.J.; Chen, T.; Xie, Y.L.; Chen, W.D.; Zhu, X.F.; Lan, W.J. Isolation and structural elucidation of chondrosterins F–H from the
marine fungus Chondrostereum sp. Mar. Drugs 2013, 11, 551–558. [CrossRef]
Li, H.J.; Jiang, W.H.; Liang, W.L.; Huang, J.X.; Mo, Y.F.; Ding, Y.Q.; Lam, C.K.; Qian, X.J.; Zhu, X.F.; Lan, W.J. Induced marine
fungus Chondrostereum sp. as a means of producing new sesquiterpenoids chondrosterins I and J by using glycerol as the carbon
source. Mar. Drugs 2014, 12, 167–175. [CrossRef]
Huang, L.; Lan, W.J.; Deng, R.; Feng, G.K.; Xu, Q.Y.; Hu, Z.Y.; Zhu, X.F.; Li, H.J. Additional new cytotoxic triquinane-type
sesquiterpenoids chondrosterins K–M from the marine fungus Chondrostereum sp. Mar. Drugs 2016, 14, 157. [CrossRef]
Yagi, A.; Okamura, N.; Haraguchi, H.; Abot, T.; Hashimoto, K. Antimicrobial tetrahydroanthraquinones from a strain of Alternaria
solani. Phytochemistry 1993, 33, 87–91. [CrossRef]
Aly, A.H.; Edrada-Ebel, R.; Wray, V.; Muller, W.E.; Kozytska, S.; Hentschel, U.; Proksch, P.; Ebel, R. Bioactive metabolites from the
endophytic fungus Ampelomyces sp. isolated from the medicinal plant Urospermum picroides. Phytochemistry 2008, 69, 1716–1725.
[CrossRef] [PubMed]
Wang, G.Y.S.; Abrell, L.M.; Avelar, A.; Borgeson, B.M.; Crews, P. New hirsutane based sesquiterpenes from salt water cultures of a
marine sponge-derived fungus and the terrestrial fungus Coriolus consors. Tetrahedron 1998, 54, 7335–7342. [CrossRef]
Yang, F.; Chen, W.D.; Deng, R.; Li, D.D.; Wu, K.W.; Feng, G.K.; Zhu, X.F. Hirsutanol A induces apoptosis and autophagy via
reactive oxygen species accumulation in breast cancer MCF-7 cells. J. Pharmacol. Sci. 2012, 119, 214–220. [CrossRef]
Hellwig, V.; Dasenbrock, J.; Schumann, S.; Steglich, W.; Leonhardt, K.; Anke, T. New triquinane-type sesquiterpenoids from
Macrocystidia cucumis (basidiomycetes). Eur. J. Org. Chem. 1998, 1998, 73–79. [CrossRef]
Etchri, A.; William, A.A.; Lois, M.B. Antifungal sesquiterpenoids from an arthroconidial fungus. J. Nat. Prod. 1989, 52, 1042–1054.
Gebhardt, K.; Schimana, J.; Hoeltzel, A.; Dettner, K.; Draeger, S.; Beil, W.; Rheinheimer, J.; Fiedler, H.P. Aspochalamins AD and
Aspochalasin Z Produced by the Endosymbiotic Fungus Aspergillus niveus LU 9575 II. Structure Elucidation. J. Antibiot. 2004, 57,
715–720. [CrossRef] [PubMed]
Tomikawa, T.; Shin-Ya, K.; Seto, H.; Okusa, N.; Kajiura, T.; Hayakawa, Y. Structure of aspochalasin H, a new member of the
aspochalasin family. J. Antibiot. 2002, 55, 666–668. [CrossRef]
Zhou, G.X.; Wijeratne, E.K.; Bigelow, D.; Pierson, L.S.; VanEtten, H.D.; Gunatilaka, A.L. Aspochalasins I, J, and K: Three new
cytotoxic cytochalasans of Aspergillus f lavipes from the rhizosphere of Ericameria laricifolia of the Sonoran Desert. J. Nat. Prod.
2004, 67, 328–332. [CrossRef]
Zhang, Y.; Wang, T.; Pei, Y.; Hua, H.; Feng, B. Aspergillin PZ, a novel isoindole-alkaloid from Aspergillus awamori. J. Antibiot. 2002,
55, 693–695. [CrossRef]
Fujii, Y.; Tani, H.; Ichinoe, M.; Nakajima, H. Zygosporin D and two new cytochalasins produced by the fungus Metarrhizium
anisopliae. J. Nat. Prod. 2000, 63, 132–135. [CrossRef]
Xiao, L.; Liu, H.; Wu, N.; Liu, M.; Wei, J.; Zhang, Y.; Lin, X. Characterization of the high cytochalasin E and rosellichalasin
producing-Aspergillus sp. nov. F1 isolated from marine solar saltern in China. World J. Microbiol. Biotechnol. 2013, 29, 11–17.
[CrossRef]
Veluri, R.; Oka, I.; Wagner-Dobler, I.; Laatsch, H. New indole alkaloids from the North Sea bacterium Vibrio parahaemolyticus
Bio249. J. Nat. Prod. 2003, 66, 1520–1523. [CrossRef]
Cai, S.X.; Li, D.H.; Zhu, T.J.; Wang, F.P.; Xiao, X.; Gu, Q.Q. Two New Indole Alkaloids from the Marine-Derived Bacterium
Aeromonas sp. CB101. Helv. Chim. Acta 2010, 93, 791–795. [CrossRef]
Yang, C.L.; Han, Y.; Wang, Y.; Zhang, X.H.; Zhu, W.M. Bis- and tris- indole alkaloids from Edwardsiella tarda. Microbiol. China 2010,
37, 1325–1330.
Yuan, M.-X.; Qiu, Y.; Ran, Y.-Q.; Feng, G.-K.; Deng, R.; Zhu, X.-F. Exploration of Indole Alkaloids from Marine Fungus
Pseudallescheria boydii F44-1 Using an Amino Acid-Directed Strategy. Mar. Drugs 2019, 17, 77. [CrossRef]
Liew, L.P.; Fleming, J.M.; Longeon, A.; Mouray, E.; Florent, I.; Bourguet-Kondracki, M.L.; Copp, B.R. Synthesis of 1-indolyl
substituted β-carboline natural products and discovery of antimalarial and cytotoxic activities. Tetrahedron 2014, 70, 4910–4920.
[CrossRef]
Machowinski, A.; Kramer, H.J.; Hort, W.; Mayser, P. Pityriacitrin—A potent UV filter produced by Malassezia furfur and its effect
on human skin microflora. Mycoses 2006, 49, 388–392. [CrossRef]
Jiao, W.H.; Gao, H.; Li, C.Y.; Zhou, G.X.; Kitanaka, S.; Ohmura, A.; Yao, X.S. β-Carboline alkaloids from the stems of Picrasma
quassioides. Magn. Reson. Chem. 2010, 48, 490–495. [PubMed]
Molecules 2021, 26, 3227
90.
27 of 27
Anouhe, J.B.S.; Adima, A.A.; Niamke, F.B.; Stien, D.; Amian, B.K.; Blandinieres, P.A.; Virieux, D.; Pirat, J.L.; Kati-Coulibaly, S.;
Amusant, N. Dicorynamine and harmalan-N-oxide, two new β-carboline alkaloids from Dicorynia guianensis Amsh heartwood.
Phytochem. Lett. 2010, 12, 158–163. [CrossRef]
91. Li, Y.; Li, X.F.; Kim, D.S.; Choi, H.D.; Son, B.W. Indolyl alkaloid derivatives, N b-acetyltryptamine and oxaline from a marinederived fungus. Arch. Pharm. Res. 2003, 26, 21–23. [CrossRef] [PubMed]
92. Debbab, A.; Aly, A.H.; Edrada-Ebel, R.; Wray, V.; Muller, W.E.; Totzke, F.; Zirrgiebel, U.; Schachtele, C.; Kubbutat, M.H.; Lin, W.H.
Bioactive metabolites from the endophytic fungus Stemphylium globuliferum isolated from Mentha pulegium. J. Nat. Prod. 2009, 72,
626–631. [CrossRef]
93. Suemitsu, R.; Ueshima, T.; Yamamoto, T.; Yanagawase, S. Alterporriol C: A modified bianthraquinone from Alternaria porri.
Phytochemistry 1988, 27, 3251–3254. [CrossRef]
94. Wang, Y.; Zheng, J.; Liu, P.; Wang, W.; Zhu, W. Three new compounds from Aspergillus terreus PT06-2 grown in a high salt medium.
Mar. Drugs 2011, 9, 1368–1378. [CrossRef]
95. Wang, F.Z.; Wei, H.J.; Zhu, T.J.; Li, D.H.; Lin, Z.J.; Gu, Q.Q. Three New Cytochalasins from the Marine-Derived Fungus Spicaria
elegans KLA03 by Supplementing the Cultures with L-and D-Tryptophan. Chem. Biodivers. 2011, 8, 887–894. [CrossRef]
96. Bladon, P.; Sleigh, T. Photo-oxygenation of 3-acetoxyergosta-3,5,7,22-tetraene and related compounds. J. Chem. Soc. 1965,
6991–7000. [CrossRef]
97. Nong, X.H.; Wang, Y.F.; Zhang, X.Y.; Zhou, M.P.; Xu, X.Y.; Qi, S.H. Territrem and butyrolactone derivatives from a marine-derived
fungus aspergillus terreus. Mar. Drugs 2014, 12, 6113–6124. [CrossRef]
98. Phainuphong, P.; Rukachaisirikul, V.; Saithong, S.; Phongpaichit, S.; Bowornwiriyapan, K.; Muanprasat, C. Lovastatin Analogues
from the Soil-Derived Fungus Aspergillus sclerotiorum PSU-RSPG178. J. Nat. Prod. 2016, 79, 1500–1507. [CrossRef]
99. Ma, J.; Li, Y.; Ye, Q.; Li, J.; Hua, Y.; Ju, D. Constituents of red yeast rice, a traditional Chinese food and medicine. J. Agric. Food
Chem. 2000, 48, 5220–5225. [CrossRef]
100. Zhang, Q.; Yang, B.; Li, F.; Liu, M.; Lin, S.; Wang, J. Mycophenolic acid derivatives with immunosuppressive activity from the
coral-derived fungus penicillium bialowiezense. Mar. Drugs 2018, 16, 230. [CrossRef]