From monomer to pentamer, diverse antimicrobial benzofuran polyketides from the marine-derived Striaticonidium cinctum

Chemical investigation of the mangrove sediment-derived fungus Striaticonidium cinctum SCSIO 41432 resulted in the isolation of 27 new benzofuran polyketides, including diverse monomeric (1−21), dimeric (22 and 23), trimeric (24), tetrameric (25 and 26) and pentameric (27) derivates. Their structures including absolute configurations were confirmed by extensive analysis of the spectroscopic data, Mosher’s method, Mo2(OAc)4-induced circular dichroism, ECD calculations and single-crystal X-ray diffraction. Structurally, di-stribenfurans A and B (22 and 23) were deduced as rare nonsymmetric C–C linked benzofuran dimers, while trimeric to pentameric benzofurans (24−27) were unprecedent polymers with sulfinyl and ether bridges. The antimicrobial assay against twelve plant pathogenic fungi and four bacterial strains revealed that most of the monomers showed better antibiotic activities than monomeric glycosides and polymers. Sulfinyl moiety in monomers lead stronger antibacterial effects instead of antifungal activities. Remarkably, stribenfuran U (21) displayed strongest antifungal activity against Colletotrichum gloeosporioides with MIC value of 0.78 μg/mL. Further microscopic analysis showed that 21 could destroy the cell membrane structure of the hyphae of C. gloeosporioides, cause the surface to exhibit obvious pits and folds. This study expanded the structural variety of natural benzofuran derivates and laid a robust foundation for the development of benzofurans as antifungal lead drugs.