Synthesis of sphingosines, 11. Convenient synthesis of phytosphingosine and sphinganine from D ‐galactal and D ‐arabitol

Abstract 3,4,6‐Tri‐O‐benzyl‐D‐galactal (3) was directly converted into 3,4,6‐tri‐O‐benzyl‐2‐deoxy‐D‐galactose (5). Wittig reaction of 5 with alkyltriphenylphosphonium salts in the presence of n‐butyllithium as the base afforded olefins 6a, b which could be readily transformed into phytosphingosines 1a, b via different routes: (i) at first azido group introduction and then double bond and protective group removal, and azido group generation via hydrogenation; (ii) 2‐O‐mesylation, then double bond and benzyl group removal via hydrogenation, and finally nitrogen introduction; (iii) selective double bond hydrogenation, then nitrogen introduction, and finally benzyl group removal and amino group generation via hydrogenation. Wittig reaction of 5 with alkyltriphenylphosphonium salt in the presence of potassium tert‐butoxide as the base afforded diene 7a which proved to be a convenient precursor for sphinganine syntheses; thus, 2‐O‐mesylation, then double bond and benzyl group removal via hydrogenation and 1,3‐O‐acetylation, and finally nitrogen introduction and de‐O‐acetylation afforded 23a. Based on the convenient transformation of D‐arabitol into the 1,3‐O‐benzylidene derivative 25 a further phytosphingosine synthesis is outlined.