Phenylalanine-independent biosynthesis of 1,3,5,8-tetrahydroxyxanthone. A retrobiosynthetic NMR study with root cultures of Swertia chirata.

Root cultures of Swertia chirata (Gentianaceae) were grown with supplements of [1-13C]glucose, [U-13C6]glucose or [carboxy-13C]shikimic acid. 1,3,5,8-Tetrahydroxyxanthone was isolated and analysed by quantitative NMR analysis. The observed isotopomer distribution shows that 1,3,5,8-tetrahydroxyxanthone is biosynthesized via a polyketide-type pathway.

Seven imidazole alkaloids from Lepidium sativum.

The seeds of Lepidium sativum afforded five new dimeric imidazole alkaloids lepidine B, C, D, E and F in addition to the known imidazole alkaloid lepidine and two new monomeric imidazole alkaloids semilepidinoside A and B. Their structure were elucidated on the basis of spectroscopic evidence.