Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 8, 2015 | http://pubs.acs.org Publication Date: August 25, 1986 | doi: 10.1021/bk-1986-0317.ch011
11 Biosynthesis of Cyclic Monoterpenes Rodney Croteau Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340
C y c l i z a t i o n of an allylic pyrophosphate is a key step in the biosynthesis of most monoterpenes. Early hypotheses concerning the nature of the a c y c l i c precursor and the c y c l i z a t i o n process are first described, and chemical models f o r the c y c l i z a t i o n presented. Following a review of several representative cyclase enzymes and the reactions that they catalyze, a series of stereochemical and mechanistic experiments with p a r t i a l l y p u r i f i e d cyclases are reported. The results of these studies have allowed a detailed description of events at the active s i t e and the formulation of a u n i f i e d stereochemical scheme for the multistep isomerization-cyclization reaction by which the universal precursor geranyl pyrophosphate is transformed to c y c l i c monoterpenes. The monoterpenes constitute a large group of natural products synthesized and accumulated in d i s t i n c t glandular structures by some 50 families of higher plants (1). The vast majority of these compounds are c y c l i c and represent a r e l a t i v e l y small number of s k e l e t a l themes multiplied by a very large range of simple derivatives, p o s i t i o n a l isomers and stereochemical v a r i a n t s . (2). Research on the biochemistry of the monoterpenes can be divided into three general areas; c y c l i z a t i o n reactions, secondary transformations of the parent c y c l i c compounds, and catabolism. These and related topics have been described in a number of comprehensive reviews (3-5.) * the f i e l d is p e r i o d i c a l l y surveyed (6). The focus of t h i s chapter is recent enzyme-level studies directed toward the development of a general model for monoterpene c y c l i z a t i o n . The topic has been b r i e f l y described elsewhere (J_-9). a n
