A flexible approach for the asymmetric syntheses of hyacinthacines A2, A3 and structural confirmation of hyacinthacine A3

Abstract

A concise and flexible approach for the asymmetric syntheses of polyhydroxylated pyrrolizidine alkaloids hyacinthacines A₂ and A₃ has been developed using iterative reductive alkylation of O,O′-dibenzyltartarimide (5) as key steps. The ambiguity about the structure of synthetic hyacinthacine A₃ due to the differences in the NMR data of the synthetic material (2) and the natural product (hyacinthacine A₃) was eliminated jointly by comprehensive 1D and 2D-NMR studies, and by analysis of the ¹H and ¹³C NMR spectra of a mixed synthetic product and natural hyacinthacine A₃. The latter method also allowed a confirmation of the structure of the natural hyacinthacine A₃, and may be useful for structural confirmation of other hydroxylated alkaloids.