Stereochemical Studies on Homoterpene Biosynthesis in Higher Plants; Mechanistic, Phylogenetic, and Ecological Aspects

Abstract

Abstract In higher plants, the two homotcrpenes 4,8‐dimethylnona‐l,3,7‐triene ( 1 ) and 4,8,12‐trimethyltrideca‐1,3,7,11‐teiracnc ( 2 ) originate from nerolidol ( 3 ) or geranyllinalool ( 4 ) by anoxidative cleavage of their C‐skele‐lons. The reaction proceeds with exclusive loss of H 8 –C(5) of 3 and formal production of a C 4 fragment. The site specificity of the enzyme(s) is identical for all of the hitherto examined plant families (Agavaceae, Asclepiadaceae, Asteraceae, Leguminosae, Magnoliaceae, and Saxifragaceae). The enzyme tolerates a wide range of structural modifications at the polar head of 3 . Instead of 3 , also gcranylacclone 12 and the secondary alcohol 13 can be cleaved to the homoterpene 1 and as yet unidentified carbonyl fragments. The CC bonds within the aliphatic chain of 3 seem to be essential for the oxidative bond cleavage as well as for recognition and embedding of the substrate into the active center of the enzyme(s). The feed‐induced biosynthesis of 1 and 2 in leaves of the Lima bean Phaseolus lunatm infested with the spider mite Tetranychus urticae probably requires a preceding release of nerolidol ( 3 ) or geranyllinalool ( 4 ) from phylogenic glycosides prior to the fragmentation reaction. The microbial reduction of the trienoic acids 6 and 6a is the key stop for the synthesis of deuterium labelled nerolidol (3 RS ,5 R )‐and (3 RS ,5 S )‐ 9 .