Biosynthesis of γ-bisabolene in tissue cultures of Andrographispaniculata

Abstract

Experiments with intact callus cultures of Andrographispaniculata and a derived cell-free system have established that: (1) the biosynthesised γ-bisabolene has the Z-configuration 6; (2) the biosynthetic intermediate is a 6-trans-13 and not a 6-cis-15 farnesyl pyrophosphate; (3) in paniculide B 17, and probably also in γ-bisabolene 14, the ring carbon derived from C-2 of mevalonate is anti to the side chain; (4) mevalonolactone and trans,trans-famesyl pyrophosphate are incorporated into γ-bisabolene without hydrogen loss respectively from C-5 and C-1; cyclisation to the bisabolenyl cation therefore does not involve prior trans to cis isomerisation of the terminal double bond of farnesol by a redox mechanism; (5) taken together with our previous findings, it is established that Andrographis cultures contain two independently functioning enzymes: (i) a trans,trans- to cis,trans-farnesol isomerase, and (ii) a trans,trans-farnesyl pyrophosphate isomerase-cyclase. The absolute configuration of paniculide B has been established by an X-ray cristallographic analysis of its bis-p-bromobenzoate.