Incorporation of deuterium-labelled analogs of isopentenyl diphosphate for the elucidation of the stereochemistry of rubber biosynthesis

Abstract

A series of six deuterium-labelled analogs of isopententyl diphosphate (IPP) was prepared to investigate the detailed stereochemical course of addition of C₅ units during rubber biosynthesis in Hevea brasiliensis and Parthenium argentatum. These analogs were incorporated into the cis-polyisoprene chain by rubber transferase in rubber particles, and the stereochemistry was determined by ²H-NMR analysis of the polymer or of levulinic acid derivatives obtained from its ozonolytic degradation. Results indicate that rubber chain elongation occurs with loss of the pro-S hydrogen of IPP, addition of the allylic diphosphate to the si face of IPP and inversion of stereochemistry at the carbon bearing the diphosphate.