Reber KP, Niner EL. Synthesis of (-)-halichonic acid and (-)-halichonic acid B.
Beilstein J Org Chem 2022;
18:1629-1635. [PMID:
36530535 PMCID:
PMC9727271 DOI:
10.3762/bjoc.18.174]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Accepted: 11/17/2022] [Indexed: 05/31/2024] Open
Abstract
The first syntheses of the amino acids (-)-halichonic acid and (-)-halichonic acid B have been achieved in ten steps starting from commercially available (-)-α-bisabolol. The optimized synthetic route includes a new purification method for isolating (-)-7-amino-7,8-dihydrobisabolene in enantiomerically pure form via recrystallization of its benzamide derivative. The key intramolecular aza-Prins reaction forms the characteristic 3-azabicyclo[3.3.1]nonane ring system of halichonic acid along with the lactonized form of halichonic acid B in an 8:1 ratio. Optical rotation measurements confirmed that these synthetic compounds were in fact the enantiomers of the natural products, establishing both the relative and absolute configurations of the halichonic acids.
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