Total synthesis of an immunosuppressive glycolipid, (2S, 3S, 4R)-1-O-(α-D-galactosyl)-2-tetracosanoylamino-1,3,4-nonanetriol

A practical and efficient total synthesis of (2S,3S,4R)-1-O-(α-d-galactosyl)-2-tetracosanoylamino-1,3,4-nonanetriol, OCH 1b, a potential therapeutic candidate for Th1-mediated autoimmune diseases, is described. The synthesis incorporates direct alkylation onto epoxide 5 and stereospecific halide ion catalyzed α-glycosidation reaction. A key intermediate 10 was obtained in only eight steps and 37% overall yield from commercially available d-arabitol 2, and the total synthesis of 1b was accomplished in 12 steps and 19% overall yield. This method will enable the synthesis of a variety of phytosphingolipids, especially that with the shorter sphingosine side chain than 1a, in a highly stereoselective manner.