Investigation On The Bioactive Metabolites From Two Marine Fungi

Marine natural products are rich sources for drug discovery.Due to the special marine environment,such as hypertonicity,high pressure,and hypoxia,marine organisms can produce active metabolites which have incomparable skeleton diversity and novelty relative to terrestrial organisms,and the probability of discovering new drugs is much higher than that of terrestrial organisms.Aiming at searching for active compounds with novel structures and unique mechanisms,two marine fungi were cultivated to investigate their secondary metabolites.Colletotrichum gloeosporioides BB4 was isolated from the inner tissues of Meretrix meretrix collected from Hailing Island,Yangjiang,Guangdong Province,China,and identified by ITS sequence.Using the Amino Acid-Directed Strategy proposed by our team,a variety of amino acids were added to the rice solid medium,and the fungus was cultured on a large scale,22 compounds were isolated from the extract,including 10new compounds.The structures of these compounds were identified by NMR,HR-ESI-MS,¹³C NMR calculations,OR calculations,and chemical synthesis.To determine the absolute configurations of new compounds 2-1 to 2-4,we synthesized all eight configurations through five to seven steps;similarly,we synthesized two configurations of compound 2-7 to determine the absolute configuration;The absolute configuration of compounds 2-9a/2-9b was established via OR calculation and ¹³C NMR calculation.The lipid-lowering activity test showed that compounds 2-1a,2-2,and 2-6 significantly reduced triglyceride（TG）levels with EC₅₀ values of 5.78,9.00,and 1.31μM,respectively.The cytotoxicity test showed that these compounds had no obvious cytotoxic activity against human breast cancer cell line MDA-MB-435 and human lung cancer cell line A549.Lecanicillium fusisporum was isolated from the inner tissues of sea cucumbers collected from the Xisha Islands in China and identified by ITS sequence.Using a similar strategy by adding a variety of amino acids to the glucose-yeast extract-peptone（GYP）medium for a small-scaled cultivation,six alkaloids were isolated,including a new indole alkaloid lecasporinoid（3-1）.The absolute configuration of 3-1 was determined by OR calculation,¹³C NMR calculation combined with chemical synthesis.In addition,the isolated compounds were screened for anti-Dengue Virus activity.In conclusion,a total of 28 compounds,including 11 new compounds,were isolated from the marine fungi Colletotrichum gloeosporioides BB4and Lecanicillium fusisporum,indicating that the amino acid-directed strategy can induce marine fungi to produce active compounds with novel structures.At the same time,according to the configuration assignment of colletotrichindole A,we creatively synthesized colletotrichindole A by efficient chemical synthesis methods such as asymmetric hydrogen transformation,Mitsunobu reaction,and Yamaguchi esterification.In addition,compounds 2-1a,2-2,and 2-6 were able to significantly reduce the activity of triglyceride levels,and have the potential to treat diseases related to abnormal lipid metabolism.