ABSTRACT
Terpenes are derived biosynthetically from units of isoprene, which has the molecular formula C5H8. The in vivo precursors are isopentenyl pyrophosphate and its isomeric dimethylallyl pyrophosphate. In biosynthesis the isoprene units are linked together to build up the skeletons of the terpenes as a multiple of (C5H8)n. (The isoprene rule of Wallach [1887] states that schematic opening of the cyclic skeleton reveals acyclic skeletons that are formally dissected into isoprene units [1].) The isoprene units may be linked together “head to tail” or “tail to tail” (Figure 23.1).
