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

Abstract

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.