Isolation, ECD assisted structural analyses, biosynthetic discussions, and biological activities of epi-cochlioquinones D and its derivatives

epi-Cochlioquinone D (1) and its 12-α-hydroxyderivative (2) were isolated from Helminthosporium velutinum TS28 based on antifungal screening against Cochliobolus miyabeanus. Relative configurations were established by the NMR analyses except for C5 locating far from the other asymmetric centers. ECD discussions involving spectral comparison with those of other related molecules as well as those based on theoretical calculations disclosed not only the C5 configuration but also the chirality for C12-C22 polycyclic moiety. H. velutinum TS28 also afforded precochlioquinol D (3), just the side chain component, which led us to discuss their biosynthetic pathway. Although 1 and 2 inhibit C. miyabeanus effectively, the C-14 epimeric cochlioquinones scarcely inhibited in spite of very close structures. Present study further revealed that C. miyabeanus tightly recognizes both the polycyclic moiety and the side chain. In contrast, both cochlioquinones and epi-cochlioquinones exhibited potent cytotoxicity against human colon adenocarcinoma (COLO 201) cells regardless of the C14 configuration as well as type of side chains.