Secondary Metabolites Of Marine-derived Fungal Strains Acrostalagmus Luteoalbus And Penicillium Coffeae And Their Bioactivity

The study of secondary metabolites from marine endophytic fungi has received extensive attention in recent two decades.Compared to terrestrial fungi,marine fungi live in very different environments.Mangrove plants,algae,sponges and seabed sediments are the main sources of marine fungi.On the one hand,marine fungi have to adapt to the pressure brought by environments.On the other hand,they need to coexist with competitors peacefully.Secondary metabolites are important tools for fungi to communicate with each other,so it`s interesting to research on fungal metabolites to get structure unique and biological active natural products.In this thesis,through screening of endophytic fungi from alga and mangrove plants by TLC,HPLC and bioactivity test,the chemical diversity of secondary metabolites of two fungi,Acrostalagmus luteoalbus TK-43 and Penicillium coffeae MA-314,was selected for chemical investigation.As a result,a total of 60 metabolites,including 15 new compounds were isolated through a variety of separation methods,and their bioactivity was evaluated.Briefly,fouty-two compounds(AL1a–AL39),including a series of new N-methoxy-containing indolediketopiperazines(AL1a–AL7),a new sulfide indolediketopiperazine(AL9)and a new xanthone(AL19),were isolated from the culture extract of Acrostalagmus luteoalbus TK-43,an endophytic fungus obtained from the marine green alga Codium fragile.And the crystal structures of compounds AL1–AL6 and AL19 were obtained by single crystal culture.At present,there are few reports on indolediketopiperazines with N-methoxy,and only two compounds of the same type have been found before.Compounds AL1–AL3 were three pairs of indolediketopiperazine enantiomers and the optical resolution by chiral HPLC successfully afforded individual enantiomers AL1a/AL1b,AL2a/AL2b and AL3a/AL3b,respectively.The absolute configurations of these compounds were determined by TDDFT-ECD calculations.The structures of these compounds obtained by chiral resolution are stable and the absolute configuration can not spontaneous change.Therefore,the generation of isomerism should be in the biosynthesis stage,and not be affected by the later separation and purification process.Eighteen metabolites(PC1–PC18),including a new?-lactone(PC1)and two pairs of new isocoumarin derivatives(PC2 and PC3)were isolated from Penicillium coffeae MA-314,an endophytic fungus obtained from the fresh inner tissue of the leaf of marine mangrove plant Laguncularia racemosa.According to the structural features of the isolated compounds,different bioactivity models,such as antimicrobial,anti-acetylcholinesterase(anti-AChE)and antioxidant activities were selected to evaluate the activity of the metabolites.In the antimicrobial activity experiment,compound AL2b showed weak inhibitory activity against Fusarium solani(MIC=32?g/mL),but its enantiomer AL2a showed no obvious activity.Compound AL4 showed weak inhibitory activity against Alternaria solani(MIC=32?g/mL),while its epimers AL3a and AL3b showed no activity.Compounds PC1 exhibited potent activity against Fusarium oxysporum f.sp.momordicae nov.f.and Colletotrichum gloeosporioides,with MIC values of 1?g/mL,which was close to that of the positive control,amphotericin B(MIC=0.5?g/mL).In the anti-acetylcholinesterase(anti-AChE)activity test,compound AL1a exhibited superior activity with IC₅₀ value of 2.3?M to its enantiomer AL1b(IC₅₀=13.8?M)and its epimers AL2a(IC₅₀=78.8?M)and AL2b(IC₅₀=49.2?M).It suggests that compounds of those having different absolute configurations at C-3 and C-6 generally showing better anti-AChE activity than those possessing same absolute configuration at C-3 and C-6.In addition,the 3R derivative usually has stronger activity than that of the 3S-isomer.In the antioxidant activity test,the new compounds PC2 and PC3showed no significant antioxidant activity,but the known compound PC4 showed moderate activity with IC₅₀ value of 656?M.This phenomenon indicates that the hydroxyl substitution at the C-4 of these compounds can effectively weaken their antioxidant activity.In summary,the secondary metabolites and their bioactivity of the above two strains of marine endophytic fungi were studied in detail.A series of novel compounds with bioactivities obtained from these fungi provided the research foundation for the future research on natural products of marine fungi and the development of new marine drugs.