Biosynthesis of mangostin. Part 1. The origin of the xanthone skeleton

Abstract

The biosynthesis of mangostin (3) has been studied by wick-feeding of ¹⁴C- and ¹³C-labelled precursors to young Garcinia mangostana plants. Radioactive mangostin was isolated as 3,6-di-O-methylmangostin (4), which was subsequently degraded to phloroglucinol and isovaleric acid to aid location of the label. Although results from feeding of ¹⁴C-labelled precursors suggested two alternative malonate–shikimate routes to compound (3), experiments with ¹³C-labelled compounds clearly demonstrated that mangostin (3) originates from a C₆C₁ unit (benzoate) and three C₂ units (malonates). [1,2,3-¹³C₃]malonic acid was incorporated solely into ring A of compound (4) and two different arrangements of C₂ units in compounds (17a and b) were evident, indicating that mangostin (3) derives via ring closure of a symmetrical intermediate (18).