Eudesmyl cation

Protonation-induced cychzation of germacrene A generates the cis-decalin skeleton of the eudesmyl cation, an intermediate in the biosynthesis of the phytoalexin capsidiol (79). The eudesmane skeleton is converted to the 5-epi-aristolochene (80) skeleton by Wagner-Meerwein rearrangements of a hydride and a methyl group (Cane 1990). Hydroxylation of 80 then produces capsidiol. The entire process of formation of epi-aristolochene from FPP is mediated by a single synthase which has been purified from tobacco (Starks et al. 1997). The intermediacy of germacrene A in the biosynthesis was demonstrated by mutation of... 

GuaiyI cation Eudesmyl cation Cadinyl cation Trichodienyl cation Artemisinyl cation (13) (14) (15) (16) (17)... 

Artemisia maritima is a drug that was widely used in the past as anthelmintic and was later removed based on its severe side effects. Its biosynthesis is based on the methylene reduction of costunolide (23) and its proton activation and cyclization of germacrane core to provide eudesmyl cation (14). Sequential oxidative steps at C-1 and C-3 positions, followed by elimination of water, complete the route to a-santonin [19]. 

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