Structure elucidation of phomopsin A, a novel cyclic hexapeptide mycotoxin produced by Phomopsis leptostromiformis

Abstract

Phomopsin A, the main mycotoxin isolated from cultures of Phomopsis leptostromiformis and the cause of lupinosis disease in animals grazing infected lupins, is a cyclic hexapeptide containing 3-hydroxyisoleucine, 3,4-didehydrovaline, N-methyl-3-(3-chloro-4,5-dihydroxyphenyl)-3-hydroxyalanine, E-2,3-didehydroaspartic acid, E-2,3-didehydroisoleucine, and 3,4-didehydroproline; its ¹³C n.m.r. spectrum was completely assigned and the amino-acid sequence established unambiguously by extensive heteronuclear ¹³C-{¹H} selective population inversion n.m.r. experiments.