Biosynthesis of 4′-O-methylpyridoxine (ginkgotoxin) from primary precursors

Cell suspension cultures of Ginkgo biloba and Albizia tanganyicensis were investigated for the presence of 4'-O-methylpyridoxine (ginkgotoxin, 2), the 4'-O-methyl derivative of vitamin B-6 (pyridoxine, 1). The cultures produced the toxin even in the absence of vitamin Be (a common additive to plant cell culture media). This indicates that the pyridoxine ring system of ginkgotoxin is synthesized de novo by the cultured cells. A feeding experiment with D-[U-C-13(6)]glucose revealed that the mode of incorporation of label into the pyridoxine moiety of 2 matched that observed for 1 in Escherichia coli. Thus, the data obtained in this investigation provide independent proof supporting the current hypothesis on vitamin Be biosynthesis. The 4'-O-methyl group of ginkgotoxin (2) was labeled from L-[methyl-C-13(1)]methionine. This indicates that ginkgotoxin is likely to be derived by 4'-O-methylation of pyridoxine (1). The G. biloba cell suspension culture may be a suitable system to get further insight into vitamin Bg and/or ginkgotoxin biosynthesis.