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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.


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.