Total synthesis of α-galactosyl cerebroside Original Research Article

A highly convergent synthetic approach was developed to obtain α-galactosyl cerebroside O-(α-d-galactopyranosyl)-2-hexacosylamino-d-ribo-1,3,4-octadecantriol, which has previously been demonstrated to have immunostimulatory activity. Known 4,6-O-benzylidene galactose was the starting material for both the required α-galactosyl and the phytosphingosine building blocks O-(2,3-di-O-benzyl-4,6-O-benzylidene-d-galactopyranosyl) trichloroacetimidate (4) and 2-O-methanesulfonyl-d-arabino-1,2,3,4-octadecantetrol (5). The key step of the synthetic strategy is the highly regio- and stereoselective O-galactosylation of 1,3,4-O-unprotected phytosphingosine acceptor 5 using known 4 as donor. The total synthesis required only 11 synthetic steps starting from galactose.