The structure and synthesis of malformin A.

A structure (the disulfide form of cyclo-D-cysteinyl-L-valyl-D-cysteinyl-D-leucyl-L-isoleucyl), previously proposed for malformin A, was reexamined. On the basis of chemical degradations, a different structure (the disulfide form of cyclo-D-cysteinyl-D-cysteinyl-L-valyl-D-leucyl-L-isoleucyl) was established. Accordingly, a compound with this structure was synthesized and was found to be identical with malformin A. The synthetic product causes curvatures on corn roots; maximum effect was seen at a concentration of 0.1 mug/ml, the optimal concentration for malformin A.