Synthesis of sulfated glucuronyl glycosphingolipids; carbohydrate epitopes of neural cell-adhesion molecules

The sulfated glucuronyl glycosphingolipids isolated from the human peripheral nervous system, HO 3S-3-β-Glc pA-(1 → 3)-&[β- d-Gal p-(1 → 4)-β- d-Glc pNAc-(1 → 3)] n-β- d-Gal p-(1 → 4)-β- d-Glc p-(1 → 1)-Cer ( n = 1,2) ( 1 and 2) were synthesized. The glycan part of target molecules was designed to be constructed from glucuronate, lactosamine, and lactose fragments 8, 9 (or 10), and 11, which in turn were synthesized stereo- and/or regio-selectively from readily available compounds. The coupling reaction between 9 and 11 was performed by the action of trimethylsilyl trifluoromethanesulfonate (Me 3SiOTf)), and subsequent manipulation of product 31 gave 33. On the other hand, slight modification of this sequence, including repetitive glycosylation reactions using 10, afforded hexasaccharide 46. These compounds were reacted with nonreducing end glucuronate synthon 8 under the agency of CuBr 2AgOTfBu 4NBr, and the resultant penta- and hepta-saccharides 34 and 47, respectively, were transformed into glycosyl fluorides. Final coupling with the ceramide derivative 7, followed by chemoselective deprotection of the levulinoyl group, sulfation and complete deprotection, afforded the target glycolipids 1 and 2.