Enantiospecific syntheses of (R)- and (S)-3-methylheneicosane, male-specific cuticular hydrocarbon of the crane fly Tipula autumnalis (Diptera: Tipulidae)

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The chemical ecology of crane flies (Diptera: Tipulidae) has only recently begun to be elucidated, creating a pressing need for enantiomerically pure standards to support structural identification and functional studies. In a previous investigation, the cuticular hydrocarbons ( R )- and ( S )-3-methylheneicosane were identified as male-specific components of Tipula autumnalis , with synthetic samples enabling both confirmation of their stereostructures and assessment of biological activity. Laboratory bioassays revealed that the ( R )-enantiomer elicited an excitatory response in males, whereas the ( S )-enantiomer acted as a repellent. In the present work, we detail the total enantiospecific synthesis of these compounds from methyl ( S )-3-hydroxy-2-methylpropionate precursor. The route employs orthogonal protection, Wittig coupling with a C17 fragment, hydrogenation, and terminal one-carbon homologation, providing efficient access to long-chain methyl-branched hydrocarbons with full stereochemical control. This work establishes a robust and generalizable strategy for the synthesis of enantioenriched methyl-branched hydrocarbons and provides sufficient material to support all future chemical and behavioral studies in this species, paving the way for the development of targeted insect management strategies.