Practical preparation of unsaturated very-long-chain fatty acids (VLCFAs) and very-long-chain alkene pollinator attractants

TL;DR

This paper presents practical methods to synthesize long-chain fatty acids and alkenes used by orchids to attract pollinators.

Contribution

The study introduces accessible, high-purity synthesis methods for unsaturated very-long-chain fatty acids and alkenes.

Findings

11 VLCFAs were synthesized with >90% isomeric purity in two steps.

17 VLC alkenes were produced with >97% isomeric purity using a single-step Wittig reaction.

The methods require no special reagents or equipment, making them widely applicable.

Abstract

To prepare very-long-chain fatty acids and alkenes (VLCFAs and VLC alkenes) that are known pollinator attractants for sexually deceptive orchids, and biosynthetic precursors thereof, we applied a methodology allowing us to prepare monounsaturated VLCFAs with chain lengths up to 28 carbons and VLC alkenes up to 31 carbons. We implemented a coupling reaction between commercially available terminal alkynes and bromoalkanoic acids to prepare VLCFAs, allowing the products to be formed in two steps. For VLC alkenes, with many alkyltriphenylphosphonium bromides commercially available, we applied a Wittig reaction approach to prepare (Z)-configured monoenes in a single step. Using practical methods not requiring special reagents or equipment, we obtained 11 VLCFAs in > 90% isomeric purity, and 17 VLC alkenes in > 97% isomeric purity. Such general and accessible synthetic methods are essential for chemical ecology and biochemistry research to aid researchers in unambiguously identifying isolated semiochemicals and their precursors.

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