The Genus Cladosporium: A Prospective Producer of Natural Products

Cladosporium, a genus of ascomycete fungi in the Dematiaceae family, is primarily recognized as a widespread environmental saprotrophic fungus or plant endophyte. Further research has shown that the genus is distributed in various environments, particularly in marine ecosystems, such as coral reefs, mangroves and the polar region. Cladosporium, especially the marine-derived Cladosporium, is a highly resourceful group of fungi whose natural products have garnered attention due to their diverse chemical structures and biological activities, as well as their potential as sources of novel leads to compounds for drug production. This review covers the sources, distribution, bioactivities, biosynthesis and structural characteristics of compounds isolated from Cladosporium in the period between January 2000 and December 2022, and conducts a comparative analysis of the Cladosporium isolated compounds derived from marine and terrestrial sources. Our results reveal that 34% of Cladosporium-derived natural products are reported for the first time. And 71.79% of the first reported compounds were isolated from marine-derived Cladosporium. Cladosporium-derived compounds exhibit diverse skeletal chemical structures, concentrating in the categories of polyketides (48.47%), alkaloids (19.21%), steroids and terpenoids (17.03%). Over half of the natural products isolated from Cladosporium have been found to have various biological activities, including cytotoxic, antibacterial, antiviral, antifungal and enzyme-inhibitory activities. These findings testify to the tremendous potential of Cladosporium, especially the marine-derived Cladosporium, to yield novel bioactive natural products, providing a structural foundation for the development of new drugs.


Introduction
The fungus Cladosporium sp.belongs to the Dematiaceae family in the Dothideomycetes order of Ascomycota [1].It was initially classified by Link in 1815 [2].The mycelium of the colonies is well-developed, branched and colored white at the edges.It appears floccose, with a dark center and a white mycelium coating, gradually fading to white margins.In the center, the mycelium is dark and raised, containing conidia in varying shades of olive, along with clear spore scars and umbilicals [3][4][5].The three primary species of the fungi are C. herbarum, C. cladosporioides and C. sphaerospermum [6].It includes many important phytopathogenic bacteria that cause stem rot and leaf spot diseases, such as yellow rot, which is the causal agent of leaf mold in tomato [7].Several species are commonly found as contaminants in clinical laboratories and can prompt allergic lung diseases [8,9].For instance, C. sphaerospermum, a predominantly indoor fungus, has been reported in cases of meningitis, subcutaneous and intra-bronchial infections [8].Besides, C. cladosporioides is a dark mold that can be found on outdoor and indoor materials worldwide.It is one of the most common fungi in outdoor air, and its spores are important in seasonal allergies.
Two new cytotoxic 12-membered macrolides, sporiolide A (11) and sporiolide B (12) (Figure 1), were isolated from the cultured broth of Cladosporium sp.L037, which was separated from an Okinawan marine brown alga Actinotrichia fragilis.Compounds 11 and 12 exhibited cytotoxicity against murine lymphoma L1210 cells with IC 50 values of 0.13 and 0.81 µg/mL, respectively.Compound 11 showed antifungal activity against Candida albicans, Cryptococcus neoformans, Aspergillus niger and Neurospora crassa with IC 50 values of 16.7, 8.4, 16.7 and 8.4 µg/mL, respectively, and compounds 11 and 12 exhibited antibacterial activities against Micrococcus luteus with IC 50 values of 16.7 and 16.7 µg/mL, respectively [37].Additionally, Gesner et al. [34] found one new hexaketide lactone pandangolide 1a (13) and its diastereomer pandangolide 1 (14) (Figure 1) from the ethyl acetate extract of a Cladosporium sp. that was isolated from the Red Sea sponge Niphates rowi.Additionally, cladospolide D (15), cladospolide A (16) and cladospolide B (17) (Figure 1), were isolated from the endophytic fungus Cladosporium sp.FT-0012.Cladospolide D is a new 12-membered macrolide antibiotic that exhibited excellent antifungal activities against Pyricularia oryzae and Muco rracemosus with IC 50 values of 0.15 and 29 µg/mL, respectively [22].On the basis of biosynthetic considerations (Figure 2), a plausible suggestion for compounds 13 and 14 is that they share a common trihydroxydodecanoic acid-polyketide precursor.The absolute structures of C-11 in 13 and 14 are suggested to be S, similar to that of iso-cladospolide B (6), considering the function of type I modular PKS in generating a polyketide chain [34].
The strategy of diverted total synthesis (DTS) (Figure 4) has gained popularity as a method of obtaining compounds otherwise unavailable from nature or through the manipulation of the parent compounds [44,45].The 12-membered macrolactone class of compounds is uniquely well-positioned for exploitation via DTS.These compounds typically have modular synthetic routes, where fragments are synthesized convergently, coupled and cyclized [46][47][48][49].Side-chain decorations can either be carried through as part of a Figure 2. Proposed biosynthesis pathway for compounds 6, 13 and 14 [34].
Two new polyketide metabolites, the 12-membered macrolide 4-hydroxy-12methyloxacyclododecane-2,5,6-trione (25) and 12-methyloxacyclododecane-2,5,6-trione (26) (Figure 1), were isolated from the endophytic fungal Cladosprium colocasiae A801 of the plant Callistemon viminalis.Neither of which exhibited cytotoxic activity, antibacterial activity or α-glucosidase inhibition [39].One new macrolide compound named thiocladospolide E (27) and a novel macrolide lactam named cladospamide A (28), along with cladospolide B (29) (Figure 1), were isolated from mangrove endophytic fungus Cladosporium sp.SCNU-F0001.None of the three compounds showed antitumor cell proliferation activity or antibacterial activity [40].Cladospolide B (30) (Figure 1) was isolated from endophytic fungus Cladosporium sp.IS384.Compound 30 exhibited antibacterial activity against Enterococcus faecalis ATCC 29212 with a MIC value of 0.31 µg/mL [41].Three new macrolides, cladocladosin A (31), thiocladospolide F (32) and thiocladospolide G (33) (Figure 1), were isolated from the marine mangrove-derived endophytic fungus, Cladosporium cladosporioides MA-299 [42].Compounds 31-33 displayed activities against the aquatic pathogenic bacteria Edwardsiella tarda and Vibrio anguillarum with MIC values ranging from 1.0 to 4.0 µg/mL [43].Moreover, compound 31 demonstrated activity against aquatic pathogenic bacterium Pseudomonas aeruginosa, while compound 32 exhibited activity against plant-pathogenic fungus Helminthosporium maydis, both with MIC values of 4.0 µg/mL.A plausible biosynthetic pathway for compounds 31-33 as well as the related congeners such as thiocladospolides A-D and pandangolide 3 was proposed, as shown in Figure 3.Briefly, compounds 32 and 33, thiocladospolides A-D and pandangolide 3 might be derived from the possible precursors dehydroxylated-patulolide C (I), patulolide C (II) or patulolide A (III) through a Michael addition, followed by further oxidation or reduction.The difference was the adding position and attack orientation of the nucleophile (sulfide group) upon the types of the substituent groups at C-4.Generally, when there is no substituent group or the substituent group is only a hydroxyl at C-4, the sulfide group prefers to be added at C-3 to generate compounds 32 and 33, resulting in the sulfide group at C-3 and methyl group at C-11 located on the opposite faces of the molecule.However, when the substituent group at C-4 is a ketone carbonyl at C-4, the adding position of the sulfide group would be at C-2 to yield thiocladospolide A, resulting in the sulfide group at C-2 and methyl group at C-11 located on the same face of the molecule.Adding different sulfide groups such as methyl 2-hydroxy-3-sulfanylpropanoate and methyl 2-sulfanylethanoate to C-2 of the precursor III, would generate thiocladospolides B and C, respectively.Moreover, compound 31 might be derived via oxidation, cyclization and rearrangement from precursor III.
The strategy of diverted total synthesis (DTS) (Figure 4) has gained popularity as a method of obtaining compounds otherwise unavailable from nature or through the manipulation of the parent compounds [44,45].The 12-membered macrolactone class of compounds is uniquely well-positioned for exploitation via DTS.These compounds typically have modular synthetic routes, where fragments are synthesized convergently, coupled and cyclized [46][47][48][49].Side-chain decorations can either be carried through as part of a Figure 3. Proposed biosynthesis pathway for compounds 31-33 [32].
The strategy of diverted total synthesis (DTS) (Figure 4) has gained popularity as a method of obtaining compounds otherwise unavailable from nature or through the manipulation of the parent compounds [44,45].The 12-membered macrolactone class of compounds is uniquely well-positioned for exploitation via DTS.These compounds typically have modular synthetic routes, where fragments are synthesized convergently, coupled and cyclized [46][47][48][49].Side-chain decorations can either be carried through as part of a coupling fragment or synthesized concurrently and coupled to the macrocycle at a later stage.The ability to synthesize these molecules in such a way offers several advantages.Firstly, individual reactions can be modulated to alter stereochemistry and substitution, thus providing flexibility in the synthesis process.Secondly, by using different coupling partners to generate the core structure, it becomes possible to create structural libraries of analogs.Finally, late-stage manipulation through oxidation and substitution reactions allows for the alteration of specific functional group moieties.
Brefeldin A (34) (Figure 5) was a new macrolide isolated from the liquid fermentation broth of the cork oak endophytic fungus Cladosporium sp.I(R)9-2.Compound 34 was tested for antifungal activity against Aspergillus niger, Candida albicans and Trichophyton rubrum, demonstrating significant antifungal activities with MIC values of 0.97 µg/mL, 1.9 µg/mL and 1.9 µg/mL, respectively [50].Brefeldin A has been touted as a promising lead molecule in the world of drug development because of its potent biological activity in the antitumor [51] and antiviral [52] fields.Two macrolide compounds, 5Z-7-oxozeaenol (35) and zeaenol (36) (Figure 5), were isolated from the fermentation broth of the fungus Cladosporium oxysporum DH14, a fungus residing in the gut of the Chinese rice locust Oxya chinensis.Both compounds exhibited potent phytotoxic activities against the radicle growth of Amaranthus retroflexus L. with IC 50 values of 4.80 and 8.16 µg/mL, respectively, which are comparable to those of the positive control 2,4-dichlorophenoxyacetic acid (IC 50 = 1.95 µg/mL) [53].
at a later stage.The ability to synthesize these molecules in such a way offers several advantages.Firstly, individual reactions can be modulated to alter stereochemistry and substitution, thus providing flexibility in the synthesis process.Secondly, by using different coupling partners to generate the core structure, it becomes possible to create structural libraries of analogs.Finally, late-stage manipulation through oxidation and substitution reactions allows for the alteration of specific functional group moieties.Brefeldin A (34) (Figure 5) was a new macrolide isolated from the liquid fermentation broth of the cork oak endophytic fungus Cladosporium sp.I(R)9-2.Compound 34 was tested for antifungal activity against Aspergillus niger, Candida albicans and Trichophyton rubrum, demonstrating significant antifungal activities with MIC values of 0.97 μg/mL, 1.9 μg/mL and 1.9 μg/mL, respectively [50].Brefeldin A has been touted as a promising lead molecule in the world of drug development because of its potent biological activity in the antitumor [51] and antiviral [52] fields.Two macrolide compounds, 5Z-7-oxozeaenol (35) and zeaenol (36) (Figure 5), were isolated from the fermentation broth of the fungus Cladosporium oxysporum DH14, a fungus residing in the gut of the Chinese rice locust Oxya chinensis.Both compounds exhibited potent phytotoxic activities against the radicle growth of Amaranthus retroflexus L. with IC50 values of 4.80 and 8.16 μg/mL, respectively, which are comparable to those of the positive control 2,4-dichlorophenoxyacetic acid (IC50 = 1.95 μg/mL) [53].
One new dimeric tetralone cladosporone A (54) and three known analogues cladosporones B-D (55-57) (Figure 6) were isolated from fungus Cladosporium sp.KcFL6 ′ derived from mangrove plant Kandelia candel [19].Cladosporone A (54) inhibits colon cancer cell proliferation by modulating the p21 waf1/cip1 expression [62].None of the compounds showed antifungal activity.From a biosynthetic aspect, compounds 54-56 could be generated from hexaketide or pentaketide to form the key monomer tetralone, and then the tetralone coupled to yield the key intermediate 56 (Figure 7).showed antifungal activity.From a biosynthetic aspect, compounds 54-56 could be generated from hexaketide or pentaketide to form the key monomer tetralone, and then the tetralone coupled to yield the key intermediate 56 (Figure 7).6), were isolated from the fermentation of the plant-associated fungus Cladosporium sp.TMPU1621 [58].The chlorinated derivative 63 did not exhibit anti-MRSA activity, whereas the bromine congener 64 inhibited the growth of MRSA ATCC43300 and MRSA ATCC700698 with the same MIC values of 25 μg/mL, suggesting that the presence of a bromine atom affects antimicrobial activity against MRSA.Compound 59 displayed potent anti-MRSA activities against both strains with MIC values of 3.13 and 12.5 μg/mL, respectively, whereas compounds 58 and 60 showed weaker activities.Five new perylenequinone derivatives, altertoxins VIII-XII (65)(66)(67)(68)(69), as well as one known compound cladosporol I (70) (Figure 6), were isolated from the fermentation broth of the marine-derived fungus Cladosporium sp.KFD33 from a blood cockle from Haikou Bay, China.Compounds 65-70 exhibited quorum sensing inhibitory activities against Chromobacterium violaceum CV026 with MIC values of 30, 30, 20, 30, 20 and 30 μg/well, respectively [59].
Compounds 74 and 75 showed potential cytotoxicity against human leukemia cells (K-562) with IC 50 values of 3.97 µg/mL and 3.58 µg/mL, respectively.Compound 75 (40 µg/disc) showed prominent activities against S. aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus megaterium with an average zone of inhibition of 27 mm, 25 mm, 24 mm and 22 mm, respectively, and the activities were compared with kanamycin (30 µg/disc) [60].Compounds 74 and 75 might be useful lead compounds for developing potential cytotoxic and antimicrobial drugs.Anthraquinone (76) (Figure 6) was isolated from the rice medium culture of mangrove-derived fungus Cladosporium sp.HNWSW-1, isolated from the healthy root of Ceriops tagal collected at the Dong Zhai Gang Mangrove Reserve in Hainan.Compound 76 displayed inhibitory activity against α-glycosidase with a IC 50 value of 49.3 ± 10.6 µM [61].

Other Classes of Polyketides
Four new polyketide-derived metabolites, cladoacetal A (84), cladoacetal B (85), 3deoxyisoochracinic acid ( 86) and (+)-cyclosordariolone (87) (Figure 9), were isolated from the solid-substrate fermentation culture of Cladosporium sp.NRRL 29097.Compound 84 inhibited S. aureus, displaying inhibition circles of 13 mm.In addition, compound 86 inhibited the growth of B. subtilis, producing zones of inhibition of 8 mm [27].Alternariol (88) and alternariol 5-O-methyl ether (89) (Figure 9) were isolated from endophytic Cladosporium sp.J6 from endangered Chrysosplenium carnosum from Tibet [63].Compounds 88 and 89 were found to inhibit the photosynthetic electron transport chain in isolated spinach chloroplasts at the same concentrations at which its presence reduced the growth constant of a cyanobacterial (Synechococcus elongatus, strain PCO6301) model.These compounds may represent a novel lead for the development of new active principles targeting photosynthesis [64].

Other Classes of Polyketides
Four new polyketide-derived metabolites, cladoacetal A (84), cladoacetal B (85), 3deoxyisoochracinic acid ( 86) and (+)-cyclosordariolone (87) (Figure 9), were isolated from the solid-substrate fermentation culture of Cladosporium sp.NRRL 29097.Compound 84 inhibited S. aureus, displaying inhibition circles of 13 mm.In addition, compound 86 inhibited the growth of B. subtilis, producing zones of inhibition of 8 mm [27].Alternariol (88) and alternariol 5-O-methyl ether (89) (Figure 9) were isolated from endophytic Cladosporium sp.J6 from endangered Chrysosplenium carnosum from Tibet [63].Compounds 88 and 89 were found to inhibit the photosynthetic electron transport chain in isolated spinach chloroplasts at the same concentrations at which its presence reduced the growth constant of a cyanobacterial (Synechococcus elongatus, strain PCO6301) model.These compounds may represent a novel lead for the development of new active principles targeting photosynthesis [64].Lunatoic acid A (90) (Figure 9) was isolated from the endophytic fungus Cladosporium oxysporum DH14, a locust-associated fungus.Compound 90 exhibited significantly phytotoxic activity against the radicle growth of Amaranthus retroflexus L. with an IC50 value of 4.51 μg/mL, which is comparable to that of the positive control 2,4-dichlorophenoxyacetic acid (IC50 = 1.95 μg/mL).Furthermore, compound 90 showed selective phytotoxic activity with an inhibition rate of less than 22% against the crops of Brassica rapa L., Sorghum durra, Brassica campestris L., Capsicum annucm and Raphanus sativus L. under a concentration of 100 μg/mL.The synthesis pathways of derivative compounds 90a and 90b on the basis of compound 90 are shown in Figure 10.Both derivatives of compound 90 had moderate phytotoxic activity against the radicle growth of A. retroflexus L with inhibition rates of 53.17 and 56.14%, respectively, comparable to that of 2,4-D (87.09%), coassayed as a positive control under a concentration of 100 μg mL -1 .A comparison of the phytotoxic activities of compounds 90, 90a and 90b may provide useful hints for the understanding of the ability of compound 90 to inhibit the radicle growth of A. retroflexus L. These findings suggest that compound 90 has some potential as a new agent for weed control [53].Lunatoic acid A (90) (Figure 9) was isolated from the endophytic fungus Cladosporium oxysporum DH14, a locust-associated fungus.Compound 90 exhibited significantly phytotoxic activity against the radicle growth of Amaranthus retroflexus L. with an IC 50 value of 4.51 µg/mL, which is comparable to that of the positive control 2,4-dichlorophenoxyacetic acid (IC 50 = 1.95 µg/mL).Furthermore, compound 90 showed selective phytotoxic activity with an inhibition rate of less than 22% against the crops of Brassica rapa L., Sorghum durra, Brassica campestris L., Capsicum annucm and Raphanus sativus L. under a concentration of 100 µg/mL.The synthesis pathways of derivative compounds 90a and 90b on the basis of compound 90 are shown in Figure 10.Both derivatives of compound 90 had moderate phytotoxic activity against the radicle growth of A. retroflexus L with inhibition rates of 53.17 and 56.14%, respectively, comparable to that of 2,4-D (87.09%), co-assayed as a positive control under a concentration of 100 µg mL −1 .A comparison of the phytotoxic activities of compounds 90, 90a and 90b may provide useful hints for the understanding of the ability of compound 90 to inhibit the radicle growth of A. retroflexus L. These findings suggest that compound 90 has some potential as a new agent for weed control [53].From the endophytic fungus Cladosporium cladosporioides JG-12, five compounds with different structural types were identified [65].Of these compounds, (5S)-5-hydroxy-7-(4′′-hydroxy-3′′-methoxy-phenyl)-1-phenyl-3-heptanone (91) (Figure 9) showed antibacterial activity against Ralstonia solanacearum and S. aureus.Additionally, this compound exhibited acetylcholinesterase inhibitory activity with an inhibitory rate of 23.54%.
The fungal strains Cladosporium sp.NJF4 and NJF6 were collected from marine sediments in the Gulf of Prydz, and their secondary metabolites were isolated and characterized comprehensively.The results of this study yielded a total of 20 compounds, with two of them, 7-deoxy-7,8-didehydrosydonic acid (92) and sydonic acid (93) (Figure 9), being isolated for the first time from the genus Cladosporium [66].Compound 93 was found to be weakly cytotoxic against HL-60 human promyelocytic leukemia and A-549 human lung carcinoma cell lines.Compound 93 exhibited significant inhibiting activities to four pathogenic bacteria, Bacillus subtilis, Sarcina lutea, Escherichia coli and Micrococcus tetragenus, and uniquely against two marine bacterial strains Vibrio Parahaemolyticus and Vibrio anguillarum [67].These findings suggest that the marine environment in the Gulf of Prydz may harbor diverse fungal species with the potential to produce unique secondary metabolites.The identification of new compounds from these strains could have significant implications for drug discovery and development.
The fungal strains Cladosporium sp.NJF4 and NJF6 were collected from marine sediments in the Gulf of Prydz, and their secondary metabolites were isolated and characterized comprehensively.The results of this study yielded a total of 20 compounds, with two of them, 7-deoxy-7,8-didehydrosydonic acid (92) and sydonic acid (93) (Figure 9), being isolated for the first time from the genus Cladosporium [66].Compound 93 was found to be weakly cytotoxic against HL-60 human promyelocytic leukemia and A-549 human lung carcinoma cell lines.Compound 93 exhibited significant inhibiting activities to four pathogenic bacteria, Bacillus subtilis, Sarcina lutea, Escherichia coli and Micrococcus tetragenus, and uniquely against two marine bacterial strains Vibrio Parahaemolyticus and Vibrio anguillarum [67].These findings suggest that the marine environment in the Gulf of Prydz may harbor diverse fungal species with the potential to produce unique secondary metabolites.The identification of new compounds from these strains could have significant implications for drug discovery and development.
Three new polyketides (97-99) and one known compound (96) (Figure 9) were obtained from the fermentation products of the endophytic fungus Cladosporium sp.OUCMDZ-302, which was derived from the mangrove plant Excoecaria agallocha (Euphorbiaceae) [20].Notably, compound 99 exhibited significant radical scavenging activity against DPPH with an IC 50 value of 2.65 µM, indicating its promising potential as a natural antioxidant agent.Compounds 96 and 97 were postulated to be biosynthesized by the polyketide pathway from acetyl coenzyme A (Figure 11).The pathway involves the condensation, cyclization, dehydration and hydrogenation of acetyl-CoA units.The oxidation and reduction of (S)-12 results in the formation of compound 98.Furthermore, (S)-12 underwent Baeyer-Villiger oxidation, followed by methanolysis and hydrolysis, to yield compound 99.The formations of compounds 75 and 76, on the other hand, are the results of the condensation, reduction, dehydration and decarboxylation of acetyl-CoA units of different lengths.Four new citrinin derivatives, cladosporins A-D (100-103) (Figure 12) were isolated from a culture broth of the deep-sea-derived fungus Cladosporium sp.SCSIO z015.Compounds 100-103 showed weak toxicity toward brine shrimp naupalii with IC50 values of 72.0, 81.7, 49.9 and 81.4 μM, respectively.These values were compared to a positive control, toosendanin, with an IC50 value of 21.2 μM.And 103 also showed significant antioxidant activity against DPPH radicals with an IC50 value of 16.4 μM.This promising compound holds potential for further development as a natural antioxidant agent [70].Four new citrinin derivatives, cladosporins A-D (100-103) (Figure 12) were isolated from a culture broth of the deep-sea-derived fungus Cladosporium sp.SCSIO z015.Compounds 100-103 showed weak toxicity toward brine shrimp naupalii with IC50 values of 72.0, 81.7, 49.9 and 81.4 μM, respectively.These values were compared to a positive control, toosendanin, with an IC50 value of 21.2 μM.And 103 also showed significant antioxidant activity against DPPH radicals with an IC50 value of 16.4 μM.This promising compound holds potential for further development as a natural antioxidant agent [70].One benzofuran derivative (105), one isochroman derivative (106) and two other compounds 104 and 107 (Figure 12) were isolated from the culture extract of Cladosporium sp.JS1-2, an endophytic fungus obtained from the mangrove plant Ceriops tagal.Compounds 105-107 displayed antibacterial activities against S. aureus with the same MIC values of 12.5 µg/mL; the positive control was ciprofloxacin, with a MIC value of 3.12 µg/mL.Compound 107 displayed growth inhibition activity against newly hatched larvae of Helicoverpa armigera Hubner, with the same IC 50 values of 100 µg/mL; the positive control was azadirachtin, with an IC 50 value of 50 µg/mL [56].
A total of 44 alkaloids have been identified from the genus Cladosporium.The structural types of these alkaloids include amines, indoles, pyrrolizidines and quinazolines.Out of the total isolated alkaloids, 36 originated from marine sources.And 21 compounds are newly identified compounds, with marine sources accounting for 66.7% of these newly discovered substances.Furthermore, all of this new material comes from the ocean.In total, there are 27 bioactive compounds, with 22 of them derived from marine sources, making up 81.5% of the bioactive substances.These alkaloids exhibit biological activities, focusing on antiviral, cytotoxicity and enzyme inhibition activities.
A total of 39 steroids and terpenoids have been reported in the genus Cladosporium, with steroids being more common and having keratosteroid skeletons, while terpenoids are more commonly tetracyclic triterpenoids with lanolin steroid skeletons.Out of the total isolated steroids and terpenoids, 17 are derived from marine sources.Additionally, 11 compounds are newly identified, with marine sources accounting for 36.4% of these newly  [21,28,41,55,66].
A total of 39 steroids and terpenoids have been reported in the genus Cladosporium, with steroids being more common and having keratosteroid skeletons, while terpenoids are more commonly tetracyclic triterpenoids with lanolin steroid skeletons.Out of the total isolated steroids and terpenoids, 17 are derived from marine sources.Additionally, 11 compounds are newly identified, with marine sources accounting for 36.4% of these newly discovered substances.These steroids and terpenoids exhibit various biological activities, including antifungal, antiviral, cytotoxicity, and enzyme inhibition activities.In total, there are 10 bioactive compounds, with marine sources contributing to 40% of these bioactive substances.
A total of 17 benzene derivatives were identified from the ferments of Cladosporium sp., with 15 of these compounds originating from marine sources.Among the total isolated benzene derivatives, there are a total of eight bioactive compounds, with seven of them derived from oceanic sources.Notably, the oceanic compounds account for 87.5% of the bioactive substances.These benzene derivatives exhibit biological activities such as antibacterial, phytotoxicity and insecticidal activities.
Eight bioactive compounds with antibacterial, insecticidal, and enzyme inhibitory activities were discovered in the ferments of Cladosporium sp., all originating from the ocean.This further highlights the significance of the ocean as an invaluable resource.Eight bioactive compounds with antibacterial, insecticidal, and enzyme inhibitory activities were discovered in the ferments of Cladosporium sp., all originating from the ocean.This further highlights the significance of the ocean as an invaluable resource.

Conclusions
From January 2000 to December 2022, a total of 229 natural products were isolated from the genus Cladosporium (Table 1), of which 64.63% of the compounds were isolated from the ocean and 34% of the compounds were found for the first time.These findings strongly suggest that marine-derived Cladosporium has great potential to produce abundant compounds with new structures.Before 2007, there were few studies on the secondary metabolites produced by Cladosporium, and their structural types were mainly concentrated on terpenoids and polyketides.After 2008, studies on the natural products isolated from Cladosporium gradually increased, with the number of compounds isolated each year on overall upward trend, and the structural types of the isolated compounds were gradually diversified, including cyclic peptides, alkaloids and some other types of compounds, indicating that the genus Cladosporium has the potential to produce compounds of multiple structural types (Figure 21).The structures of the isolated compounds with diverse skeletons are mainly concentrated in the classes of polyketides, alkaloids, steroids, terpenoids, benzene derivatives and cyclic peptides (Figure 22).Polyketides, which make up 48% of the natural products derived from this genus, are notably significant among these compounds.

Conclusions
From January 2000 to December 2022, a total of 229 natural products were isolated from the genus Cladosporium (Table 1), of which 64.63% of the compounds were isolated from the ocean and 34% of the compounds were found for the first time.These findings strongly suggest that marine-derived Cladosporium has great potential to produce abundant compounds with new structures.Before 2007, there were few studies on the secondary metabolites produced by Cladosporium, and their structural types were mainly concentrated on terpenoids and polyketides.After 2008, studies on the natural products isolated from Cladosporium gradually increased, with the number of compounds isolated each year on overall upward trend, and the structural types of the isolated compounds were gradually diversified, including cyclic peptides, alkaloids and some other types of compounds, indicating that the genus Cladosporium has the potential to produce compounds of multiple structural types (Figure 21).The structures of the isolated compounds with diverse skeletons are mainly concentrated in the classes of polyketides, alkaloids, steroids, terpenoids, benzene derivatives and cyclic peptides (Figure 22).Polyketides, which make up 48% of the natural products derived from this genus, are notably significant among these compounds.The sources of Cladosporium are distributed in different ecosystems, including the Antarctic, forests and oceans.About 65% of the isolated natural products were separated  The sources of Cladosporium are distributed in different ecosystems, including the Antarctic, forests and oceans.About 65% of the isolated natural products were separated The sources of Cladosporium are distributed in different ecosystems, including the Antarctic, forests and oceans.About 65% of the isolated natural products were separated from marine organism-derived Cladosporium, including sponge, mangrove and gorgonian.
The first marine-derived natural product was isolated from an unidentified sponge-derived Cladosporium in 2001 [22].A larger number of compounds, excluding steroids and terpenoids, have been isolated from Cladosporium in the ocean compared to those obtained from land (Figure 22), which indicates that marine fungi Cladosporium have great potential to produce compounds.
The genus Cladosporium has the potential to produce a great diversity of bioactive secondary metabolites, including antibacterial, cytotoxic, growth inhibitory, enzyme inhibitory, antifungal activity, and quorum sensing inhibitory activity (Figure 22, Tables 2-4).The bioactive compounds isolated from the genus Cladosporium mainly focus on antibacterial activity (26%), cytotoxicity (16%) and antiviral activity (12%), indicating considerable potential for the development of new antibiotics and anticancer compounds from Cladosporium.In addition, many compounds with diverse bioactivities, especially cytotoxic, antibacterial, antiviral and quorum sensing inhibitory compounds are predominantly found in the ocean (Figure 22).These findings emphasize the ocean as a valuable resource and propose that the marine genus Cladosporium has the capacity to generate numerous secondary metabolites with various bioactivities.The genus Cladosporium is capable of producing various secondary metabolites with diverse bioactivities, including antibacterial activity, cytotoxicity, antifungal activity, enzyme inhibition activity, antiviral activity, quorum sensing inhibitory activity and antioxidant activity (Figure 22).Research shows that 63% of the natural products derived from Cladosporium exhibit bioactive activities.Among these compounds, 11, 34, 127, 191, 199 and 203 have demonstrated more than three types of activities (Figure 22, Tables 2-4), highlighting the potential of this genus to produce bioactive natural products.Additionally, it is noteworthy that 59% of these active compounds are isolated from marine-derived fungi, further supporting the development prospects of marine fungi.
Structure activity relationships (SARs) can be used to predict biological activity from molecular structure.Wang et al. [54] reported an evaluation of the relationships between structure and bioactivity for cladosporin (37) and its analogues (38)(39)(40)(41).After an overall evaluation of the relationship between the structures and antifungal activity of the compounds at 30 µM, several essential positions were identified as potential determinants of their antifungal activity.The absolute configuration of C-6 ′ in the structures of compounds 37 and 38 was found to have a significant impact on the antifungal activity of the parent compound.Specifically, the R configuration of C-6 ′ in structure 38 led to a marked decrease in antifungal activity against Colletotrichum species, while slightly increasing the antifungal activity against Phomopsis species.Comparing the structures of compounds 37 and 39 revealed that he introduction of a hydroxyl group at the C-5 ′ position results in a complete loss of antifungal activity against Colletotrichum species and decreased selectivity against Phomopsis species, highlighting the importance of maintaining an unsubstituted C-5 ′ for antifungal activity.Furthermore, by comparing the structures of compounds 37 and 40, it was observed that the replacement of the hydroxyl group with a methoxy group at C-8 caused a broad loss of antifungal activity against all tested fungi, suggesting that this position might be the active site where hydrogen bonds are formed.Additionally, when compounds 39 and 41 were compared, the replacement of the hydrogen of the hydroxyl group at C-6 and the hydrogen at C-5 ′ with acetyl groups greatly increased the selectivity toward the two Phomopsis species.Therefore, the differences in activity indicated that the S configuration of C-6 ′ , the openness of C-5 ′ , the presence of a hydroxyl group at C-8 and the introduction of functional groups at C-6 influence the antifungal properties of these compounds [54].
Compounds 9, 78, 79 and 80 exhibit potent lipid-lowering activities in HepG2 hepatocytes (Figure 23, Table 4), suggesting that they can be developed into hypoglycemic agents (Figure 23).Compound 34 displays significant antifungal activity (Figure 23, Table 4), declaring the potential of 34 to be applied in agricultural fungicide.Compounds 35, 36 and 90 demonstrate potent phytotoxic activities against the radicle growth of Amaranthus retroflexus L (Figure 23, Table 4).This indicates the potential for developing compounds 35, 36 and 90 as new herbicides.Compound 59 demonstrates a stronger antibacterial activity against MRSA than the positive control (Figure 23, Table 2), highlighting the challenge of bacterial drug resistance.Compounds 75, 93, 156 and 168 display potent antibacterial activities compared to the positive control (Figure 23, Table 2), which means they could be valuable starting points for the development of new antibiotics.Compounds 115, 118, 120-122 and 124 show noteworthy antiviral activities (Figure 23, Table 4), which support their potential use as antibiotics.Compound 133 exhibits potent cytotoxicity against a series of cancer cell lines (Figure 23, Table 4), including cervical cancer HeLa, mouse lymphocytic leukemia P388, human colon adenocarcinoma HT-29 and human lung carcinoma A549 with IC 50 values of 0.76, 1.35, 2.48 and 3.11 µM, respectively, which suggests that it might have potential to be developed as an antitumor agent.Compound 177 exhibits potent anti-inflammatory activity (Figure 23, Table 4), declaring the potential of 177 to be applied in adjuvant drugs for anticancer therapy.Compound 184 displays potential antiviral activity against RSV (Figure 23, Table 4), which demonstrates that 184 could be employed in developing vaccines and antiviral drugs.Compound 196 exhibits noteworthy antibacterial activity (Figure 23, Table 2), making it a promising candidate for developing a strong fungicide.Compound 203 displays significant inhibitory effects against Candida albicans, and also showed inhibitory activities against Panagrellus redivivus and acetylcholinesterase (Figure 23, Tables 2-4).This finding suggests that compound 203 may have potential therapeutic applications for the treatment of fungal infections, nematode infestations and neurodegenerative diseases.Compounds 226 and 229 exhibit strong inhibition against α-glucosidase (Figure 23, Table 4), indicating their potential use in antidiabetic therapy.These results further suggest that the genus Cladosporium holds promise as a source of bioactive compounds.In this review, we comprehensively summarized the chemical structure types, biosyntheses, bioactivities, sources, and distributions of secondary metabolites isolated from Cladosporium in the period from January 2000 to December 2022.The literature survey indicates that the genus Cladosporium, especially marine-derived Cladosporium, has great potential as a producer to generate abundant and diverse new bioactive natural products.Some potent antibacterial and cytotoxic compounds isolated from Cladosporium have the The secondary metabolites of Cladosporium may play crucial roles in the ecosystem and have specific ecological effects.Some secondary metabolites, such as compounds 115, 120-122, 124 and 156, have antifungal and antiviral effects, which can be utilized for biological control, managing the growth and reproduction of pests and pathogenic microorganisms and safeguarding crops and forest vegetation [13,21,26,44].Some compounds, like compounds 35, 36 and 90, exhibit potent phytotoxicity and show promise as new herbicides (Figure 23) [53].Volatile organic compounds can influence plant communication, aid in defense against pathogens and enhance plant growth and development.They can also bolster plant immunity and stress resistance, improve soil quality, increase soil fertility and contribute to vegetation recovery and ecosystem stability [95].
In this review, we comprehensively summarized the chemical structure types, biosyntheses, bioactivities, sources, and distributions of secondary metabolites isolated from Cladosporium in the period from January 2000 to December 2022.The literature survey indicates that the genus Cladosporium, especially marine-derived Cladosporium, has great potential as a producer to generate abundant and diverse new bioactive natural products.Some potent antibacterial and cytotoxic compounds isolated from Cladosporium have the potential to be developed into new drugs.Additionally, all the natural products isolated from Cladosporium provide a structural foundation for drug design.

Figure 21 .
Figure 21.Structural types of compounds isolated from Cladosporium over different years.

Figure 22 .
Figure 22.(a) Structural types of compounds isolated from Cladosporium from January 2000 to December 2022; (b) Bioactivities of natural products isolated from Cladosporium discovered from January 2000 to December 2022; (c) Activities of compounds isolated from marine and terrestrial Cladosporium from January 2000 to December 2022; (d) Structural types of compounds of marine and terrestrial isolated from Cladosporium from January 2000 to December 2022.

Figure 21 . 39 Figure 21 .
Figure 21.Structural types of compounds isolated from Cladosporium over different years.

Figure 22 .
Figure 22.(a) Structural types of compounds isolated from Cladosporium from January 2000 to December 2022; (b) Bioactivities of natural products isolated from Cladosporium discovered from January 2000 to December 2022; (c) Activities of compounds isolated from marine and terrestrial Cladosporium from January 2000 to December 2022; (d) Structural types of compounds of marine and terrestrial isolated from Cladosporium from January 2000 to December 2022.

Figure 22 .
Figure 22.(a) Structural types of compounds isolated from Cladosporium from January 2000 to December 2022; (b) Bioactivities of natural products isolated from Cladosporium discovered from January 2000 to December 2022; (c) Activities of compounds isolated from marine and terrestrial Cladosporium from January 2000 to December 2022; (d) Structural types of compounds of marine and terrestrial isolated from Cladosporium from January 2000 to December 2022.

39 Figure 23 .
Figure 23.Bioactive molecular network of natural products isolated from Cladosporium from January 2000 to December 2022.

Figure 23 .
Figure 23.Bioactive molecular network of natural products isolated from Cladosporium from January 2000 to December 2022.
Int. J.Mol.Sci.2023, 24, x FOR PEER REVIEW 11 of 39 isolated from the rice medium culture of mangrove-derived fungus Cladosporium sp.HNWSW-1, isolated from the healthy root of Ceriops tagal collected at the Dong Zhai Gang Mangrove Reserve in Hainan.Compound 76 displayed inhibitory activity against α-glycosidase with a IC50 value of 49.3 ± 10.6 μΜ [61].

Table 1 .
Compounds isolated from Cladosporium from January 2000 to December 2022.

Table 4 .
Other activities of compounds isolated from Cladosporium during 2000-2022.