It had been found by our research group that the D-5 strain of Cochliobolus spicifer produces phytotoxins, i.e.spiciferones A,B,C,and spiciferinone, and a plant growth regulator, i.e.spicifernin. We also clarified that these metabolites are biosynthesized from a common polyketide precursor. In the course of our search for the structurally-related metabolites, we found a new metabolite related to spiciferinone, named it cochliospicin A and determined its structure. From the structure elucidated, cochliospicin A was supposed to form from spiciferinone and a C3 unit. Previously, we isolated a new phytotoxin, sorokinianin from Bipolaris sorokiniana OB-25-1 and sorokinianin was supposed to be formed from prehelminthosporol, a sesquiterpene, and a C3 unit. We attempted to clarify the biogenetic origin of the C3 unit using B.sorokiniana OB-25-1. Based on the results from the feeding experiments and the replacement culture experiments, the biogenetic origin of the C3 unit was found to be oxaloacetic acid, a memeber of the TCA cycle.
Neocosmospora vasinfecta NHL 2298 produces phytotoxins ; neovasinin and neovasifuranones. To clarify the biosynthetic pathway of these phytotoxins, we searched for the structurally related metabolites and found neovasipyridones. From the structure of neovasipyridones determined, neovasipyridones are biosynthesized through the Schiff base formation reaction of the aldehyde precursor of neovasifuranones with alkyl amines, followed by dehydration of the Schiff base.