**Acknowledgements**

Knowing the absolute stereochemistry of the congeners and their fungal origin, they belong to the "antipodal" set of compounds and they can be regarded as a result of extensive oxidative reactions of (−)-γ-cadinene **74**. Recently, Rabe *et al.* [35] have reported isolation of several sesquiterpenes including (−)-γ-cadinene, [α]D-32.3° by incubation of FPP with six purified bacterial terpene cyclases. The results were further supported by labeling experiments with 13C labeled isotopomers of FPP. Interestingly, antipodal cadinenic sesquiterpenes with known absolute configurations have been isolated from Indian vetiver oil (*Vetiveria zizanioides*) [36]. Isolation of (−)-γ-cadinene **74**, khusinol **75** and khusinol oxide **76** could be regarded as the precursors for the metabolites of *Xylaria* sp. A very clean sequence indicating a plausible order of formation of *Xylaria sp.* metabolites associated with the termite nest is presented (**Scheme 22**). We believe that this presentation will be useful while investigating the biosyn-

This chapter gives overview of some of the interesting molecular rearrangements of sesquiterpenes reported over last decade. Further biosynthesis of albaflavenone, caryol-1(11)-ene-10-ol, (+)-koraiol, pogostol, patchouli alcohol and valerenadiene are also presented. The recent trends in the biosynthesis of natural products is focused on enzymatic synthesis using isotopic labeling, nevertheless discussions on structural interrelationships of various congeners provides insights in to natural occurrence of these molecules and finding their biosynthetic links.

**Scheme 22.** Proposed plausible order of formation of *Xylaria* sp. metabolites from FPP.

thetic pathways using isotopic labeling studies.

106 Terpenes and Terpenoids

**3. Conclusions**

We wish to dedicate this review to Professor R. B. Bates on his retirement from Research. We thank Dr. Asha D'Souza, Prof. Shailesh Shah and Rahul Chowgule for their valuable help in providing many research articles required for this review.
