Base- and sugar-modified cytidine monophosphate N-acetylneuraminic acid (CMP-Neu5Ac) analogues - Synthesis and studies with alpha(2-6)-sialyltransferase from rat liver

The reaction of sialyl phosphites 1, 22a-d, 28, 39, and 45 with acyl-protec ted riboside 5-phosphorous acids 2a,b and 23 directly furnished, without ad dition of a catalyst, under phosphite/phosphate exchange the corresponding beta-configured sialyl riboside monophosphates 3a,b, 24a-d, 29, 46, and 47. The synthesis of the starting materials, formation of the products, and th eir treatment with sodium methanolate in methanol and subsequent hydrolysis of the sialic acid ester moiety to provide the unprotected target molecule s 4a,b, 25a-d, 30, 48, and 49 is described. Investigations with alpha(2-6)- sialyl-transferase from rat Liver showed that base replacement in CMP-Neu5A c (4a,b) is not tolerated by the enzyme but that modifications of the 5-, 8 -, or g-position of the neuraminic acid residue (25a-d, 30, 48, 49) are tol erated.