The chemistry of certain Amaryllidaceae alkaloids

The chemistry of alkaloids of the galanthamine group is reviewed. Oxidation of galanthamine with chromic acid or manganese dioxide to give narwedine and a minor product is described. On the basis of chemical and spectral data this minor product is shown to be keto-aldehyde containing a newly formed pyrrolidine ring. The structure of the phenolic alleloid chlidanthine of the galanthamine group has been determined by NO-dimethylation to give (-)-galanthamine methyl ether methiodide which was in turn prepared from (-)-galanthaminne via (-)-epigalanthamine. The relative stereochemistry of the pair of epimeric allylic alcohols derived from Pummerer's ketone has been determined. The conversion of these alcohols into allylic chlorides with thionyl chloride and with trisdimethylaminophosphine and carbon tetrachloride has been studied in detail. The biosynthesis of chlidanthine has been studied. Tritium-labelled (±)-narwedine, (±)-galanthamine and (±)-epigalanthamine were fed to Chlidanthus fragrans plants. Biosynthetic conversion of tritiated galanthamine and narwedine into chlidanthine was observed. Additionally. narwedine was efficiently converted into galanthamine thus confirming the long-suspected precursor–product relationship of these alkaloids. The observed lack of incorporation of (±)-epigalanthamine into chlidanthine served to confirm the relative configuration of the latter alkaloid.