BIOSYNTHESIS OF ACYCLIC HOMOTERPENES - ENZYME SELECTIVITY AND ABSOLUTE-CONFIGURATION OF THE NEROLIDOL PRECURSOR

The acyclic homoterpene 4,8-dimethylnona-1,3,7-triene is a metabolite of (3S)-nerolidol. The absolute configuration of the precursor was established by GC-MS analysis of the molecular ion of the homoterpene produced after feeding a mixture consisting of equal amounts of (3S)-[12-H-2(3), 13-H-3(3)]- and (3R)-[4-H-2(2), 15-H-2(3)]nerolidol to various plants. The degree of the enantioselectivity of the converting enzyme was found to be characteristic for the selected plant or the plant cultivar. Thus leaves of Phaseolus lunatus and leaves of Spatiphyllum wallisii convert specifically (3S)-nerolidol, whereas leaves of Fragaria x magna and leaves of Gossypium herbaceum exhibit only a moderate degree of enantioselectivity (3S:3R, 66:34). The isotope distribution of the homoterpene emitted from leaves of G. herbaceum (herbivore inducible biosynthesis) and that of the homoterpene released from the blossoms (endogeneously controlled biosynthesis) of the plant is identical (S:R, 66:34) suggesting that the same enzyme is active within the different tissues or organs of the plant. A highly enantioselective synthesis of (3S)-[12-H-2(3), 13-H-3(3)]- and (3R)-[C4-H-2(2), 15-H-2(3)]-nerolidol is described.