An NMR study of the lactonization of alpha-N-acetylneuraminyl-(2 -> 3)-lactose

The composition of the products formed by treatment of commercial alpha -Ne u5Ac-(2 --> 3)-beta -D-Galp-(1 --> 4)-D-Glc (3'-sialyllactose) with glacial acetic acid was investigated by H-1-C-13 one- and two-dimensional NMR spec troscopy and fast atom bombardment-mass spectrometry. The data confirmed th at the major product of the reaction was alpha -Neu5Ac-(2 --> 3)-beta -D-Ga lp-(1 --> 4)-D-Glc-(1c --> 2b)-lactone, which reverted to the starting mate rial on standing in aqueous solution at ambient temperature, but for which complete NMR assignments are reported. The NMR data led to the tentative co nclusion that the reaction also yielded small amounts of lactose, and alpha -Neu5Ac-(2 --> 3)-beta -D-Galp-(1 --> 4)-D-Glc-(1c --> 4b)-lactone which w as stable in aqueous solution. (C) 2000 Elsevier Science Ltd. All rights re served.