Quinolizidines. XV. A racemic synthesis of 10-demethyltubulosine, an alkaloid from Alangium lamarckii.

Abstract

The racemic synthesis of the Alangium lamarckii alkaloid 10-demethyltubulosine (2) has been accomplished for the first time via a lactim ether route, which included the intermediates (±)-7, (±)-8, (±)-10, and (±)-9. The 1'α-H isomers (±)-12 and (±)-11 were also obtained through this synthetic route. The assignments of the configuration at C-1'of (±)-2, (±)-9, (±)-11, and (±)-12 were based on four criteria, namely, the ratio of products from the catalytic reduction of (±)-10, thin-layer chromatographic mobility, and 1H and 13C nuclear magnetic resonance spectral features. The identity of synthetic (±)-2 with (-)-demethyltubulosine from A. lamarckii unequivocally established the structure of this alkaloid.