Fig. 1: Origin of the ambergris odorant (−)-ambrox and its synthesis by polyene cyclizations.
From: The catalytic asymmetric polyene cyclization of homofarnesol to ambrox
a, Polyene cyclization of squalene to (+)-hopene and (+)-ambrein catalysed by class II terpene cyclases and formation of the odorant (−)-ambrox from (+)-ambrein, the main constituent of ambergris. b, Active site of SHC in complex with its inhibitor 2-azasqualene (PDB code: 1UMP) (ref. 13). The conserved DXDD motif required for substrate protonation is highlighted. c, Mechanistic considerations for the polyene cyclization of (3E,7E)-homofarnesol to (−)-ambrox. d, Stork–Eschenmoser hypothesis for the stereospecific antiparallel addition of carbenium ion to an alkene in 1,5-polyolefin cyclizations. e, Catalytic asymmetric concerted polyene cyclization of (3E,7E)-homofarnesol to (−)-ambrox realized in this work. Depictions of SHC and the substrate/catalyst model have been rendered using UCSF Chimera X (refs. 58,59).
