Absolute Configuration of Scopolamine N-Oxide and of Related Compounds

Abstract

Structure analysis of (−) scopolamine N-oxide (1) hydrobromide monohydrate by X-ray crystallography has proven that the N-methyl group is axial and the amineoxide function is equatorial. The absolute configuration of the tropic acid residue has also been determined by anomalous scattering as being S, in complete agreement with chemical correlation experiments.The N-stereoisomer of 1 has also been detected as a minor product 2 for the first time, as a result of using 100 MHz n.m.r. spectroscopy in the product analysis of the oxidation of (−) scopolamine with hydrogen peroxide in ethanol. A similar n.m.r. study was undertaken with atropine and tropine and correlation of chemical shifts with N-configuration in the N-oxides, 3–6, was attempted. N-oxidation of scopolamine, and by analogy of related tropane bases, has taken a preferentially equatorial course, similar to other quaternization reactions.