Biochemical Properties of N-Methylamides of Sialic Acids in Gangliosides1

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Abstract
A simple and rapid method for the preparation of N-methylamides (-CONHCH3 of sialic acids in gangliosides and biochemical properties of the modified gangliosides are described. The sialic acid carboxyl groups of gangliosides were esterified with CH3I-dimethylsulfoxide, followed by heating with monomethylamine. The modified gangliosides were chemically identified by TLC, IR spectroscopy, GLC-mass spectrometry and NMR spectroscopy. The N-methylamide derivative of GM1 produced a high titer IgG antibody. The antibody weakly cross-reacted with the methylester of GM1 and its reductive derivative but did not react with the intact GM1. A monoclonal antibody (M2590) specific for GM3 did not react with carboxylmodified GM3 (methylester, N-methylamide, and reduced GM3), but it reacted with modified GM3 which contains the C7-analog of the sialic acid. Clostridium perfringens and Arthrobacter ureafaciens sialidases did not hydrolyze the N-methylamide derivatives, methylesters or reductive derivatives of the gangliosides and, furthermore, these derivatives did not inhibit the actions of these sialidases.