BIOSYNTHESIS OF ACYCLIC HOMOTERPENES IN HIGHER-PLANTS PARALLELS STEROID-HORMONE METABOLISM

The irregular C-11 homoterpene 4,8-dimethylnona-1,3,7-triene 1 originates in higher plants (Angiospermae) from nerolidol 3 by sequential oxidative degradation. The degradative pathway is established by feeding of deuterium labelled precursors to plantlets of the lima bean Phaseolus lunatus followed by mass spectrometric analysis of the collected volatile metabolites. The successful conversion of nerolidol 3, geranylacetone 4, 2,3-dihydroxy-3,7,11-trimethyldodeca-6,10-diene 6, 1,2-epoxinerolidol 7 and 1,2,3-trihydroxy-3,7,11-trimethyldodeca-6,10-diene 8 into 1 may be indicative for a sequential degradation in the order 3 --> 7 --> 8 --> 4 --> 1 or 3 --> 6 --> 4 --> 1. The chiral centres of the putative intermediates have been characterized and a high degree of enantioselectivity of the involved enzymes has been found. The sequence exhibits a formal analogy to cytochrome P-450 linked dealkylation reactions in the field of steroids.