Induction of Three New Secondary Metabolites by the Co-Culture of Endophytic Fungi DHS-48 and sp. DHS-11 Isolated from the Chinese Mangrove Plant .

Co-cultivation is a powerful emerging tool for awakening biosynthetic gene clusters (BGCs) that remain transcriptionally silent under artificial culture conditions. It has recently been used increasingly extensively to study natural interactions and discover new bioactive metabolites. As a part of our project aiming at the discovery of structurally novel and biologically active natural products from mangrove endophytic fungi, an established co-culture of a strain of DHS-48 with another genus fungus DHS-11, both endophytes in mangrove , proved to be very efficient to induce the production of new metabolites as well as to increase the yields of respective target metabolites. A detailed chemical investigation of the minor metabolites produced by the co-culture of these two titled fungal strains led to the isolation of six alkaloids (-), two sterols (, ), and six polyketides (-). In addition, all the compounds except and , as well as three new metabolites phomopyrazine (), phomosterol C (), and phomopyrone E (), were not present in discrete fungal cultures and only detected in the co-cultures. The structures were elucidated on the basis of spectroscopic analysis, and the absolute configurations were assumed by electronic circular dichroism (ECD) calculations. Subsequently, the cytotoxic, immunosuppressive, and acetylcholinesterase inhibitory properties of all the isolated metabolites were determined in vitro. Compound exhibited moderate inhibitory activity against ConA-induced T and LPS-induced B murine splenic lymphocytes, with IC values of 35.75 ± 1.09 and 47.65 ± 1.21 µM, respectively.