Abstract
In order to transform an optical integrity of L-lysine (L-5c) into simple piperidine alkaloids in a biomimetic sence, optically active pipecolic acids (D- or L-10c) or their derivatives ((R) - or (S) -11) were chosen as synthetic intermediates. It was found that deamination of L-5c-HC1 with a combination of sodium nitrite and aqueous hydrochloric acid, followed by the treatment with aqueous base, could give D-10c being more than 90% optically active. On the other hand, deamination of L-5c-1/2H2SO4 with sodium nitrite-aqueous sulfuric acid, followed by chlorination with thionyl chloride and pyridine and by cyclization with aqueous base, could afford L-10c which was about 80% optically pure. Precise estimation of retention for optical activity was carried out by isolating formed D- or L-10c as their derivatives ((R) (+)-11a, b or (S) (-)-11b). Exploitations for other synthetic routes to L-10c from L-5c were also undertaken. Based on the above-mentioned experimental results, almost optically pure (S) (+)-coniine, one of the simplest piperidine alkaloids, could be prepared from L-5c-HC1 via D-10c and (R) (+)-11a or b.
