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Communication | Special issue | Vol 56, No. 1-2, 2002, pp.51-58
Published online, 1st January, 1970
DOI: 10.3987/COM-01-S(K)17
■ Short Stereoselective Syntheses of (-)-Ajmalicine, (-)-3-Iso-ajmalicine and Their 5-Methoxycarbonyl Derivatives from Secologanin

Richard T. Brown,* Bukar E. N. Dauda, Simon B. Pratt, and Paul Richards

*Department of Chemistry, The University of Manchester, Oxford Road, Manchester, M13 9PL, U.K.

Abstract

Enzymatic hydrolysis of secologanin ethylene acetal at pH 5.0 resulted in stereoselective rearrangement of its aglucone to a dihydropyran aldehyde, which on reductive amination with tryptamine and cyclisation afforded 3-iso-ajmalicine, subsequently inverted to ajmalicine; analogous use of methyl S-tryptophanate gave 5S-methoxycarbonyl-3-iso-ajmalicine, whereas the R-enantiomer rather surprisingly yielded the ajmalicine derivative, whose anomalous CD spectrum has been rationalised.