Unraveling the Role of Prenyl Side-Chain Interactions in Stabilizing the Secondary Carbocation in the Biosynthesis of Variexenol B

Submitting author affiliation:
University of Yamanashi, Yamanashi, Japan

Beilstein Arch. 2023, 202327. https://doi.org/10.3762/bxiv.2023.27.v1

Published 04 Jul 2023

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Terpene cyclization reactions involve a number of carbocation intermediates. In some cases, these carbocations are stabilized by through-space interactions with π orbitals. Several terpene/terpenoids, such as sativene, satalene, bergamotene, ophiobolin and mangicol, possess prenyl side-chains that do not participate in the cyclization reaction. The role of these prenyl side-chains has been partially investigated, but remains elusive in the cyclization cascade. In this study, we focus on variexenol B that are synthesized from iso-GGPP, as recently reported by Dickschat and co-workers, and investigate the possibility of through-space interactions with prenyl side-chains using DFT calculations. Our calculations show that (i) unstable secondary cation is stabilized by the cation-π interaction from prenyl side-chains, thereby lowering the activation energy, (ii) the four-membered ring formation is completed through bridging from the exomethylene, and (iii) the annulation from the exomethylene proceeds in a barrierless manner.

Keywords: terpene; biosynthesis; secondary carbocation; prenyl side-chain; DFT

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Nakano, M.; Gemma, R.; Sato, H. Beilstein Arch. 2023, 202327. doi:10.3762/bxiv.2023.27.v1

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