THE STRUCTURE OF ANNOTININE

Abstract

Annotinine is hydrolyzed by aqueous barium hydroxide to annotininic acid, C16H23O4N, which with diazomethane forms methyl annotininate. Treatment of this ester (or of annotinine) with potassium methoxide in methanol produces epimerization and gives rise to methyl epiannotininate, also produced by methanolysis of annotinine. Whereas under the action of barium hydroxide methyl annotininate regenerates annotininic acid, methyl epiannotininate is converted to annotinine hydrate. Hydrolysis of annotinine with dilute sulphuric acid gives rise to annotinine diol, which is oxidizable to an amino acid, whereas the isomeric annotinine hydrate on oxidation gives rise to a hydroxyketo lactone. This corroborates the evidence already in the literature indicating that the γ-lactone ring in annotinine hydrate is not the same as that originally present in the alkaloid. The relevant chemical reactions of annotinine are reviewed in the light of a tentative structure suggested for annotinine.