4'-O-methylpyridoxine (ginkgotoxin) is a neurotoxic antivitamin B6 which occurs in Ginkgo biloba L. seeds. Contrary to a previous report by Wada et al., the toxin was also detected in Ginkgo biloba leaves. The leaves are a source of extracts (e.g. EGb761) employed in the preparation of Ginkgo medications. Consequently the toxin is also present in Ginkgo medications and is even detectable in homoeopathic preparations. The toxin occurs also in boiled Japanese Ginkgo food. However, the amount of the toxin is likely to be too low to exert a detrimental effect after administration of the medication or ingestion of food.

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 B(6) (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-(13)C(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 B(6) biosynthesis. The 4'-O-methyl group of ginkgotoxin (2) was labeled from L-[methyl-(13)C(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 B(6) and/or ginkgotoxin biosynthesis.