Modification of sialic acid carboxyl group of ganglioside.

A simple and quantitative method for the modification of sialic acid carboxyl group in ganglioside is described. Methyl iodide was added to the ganglioside in dimethylsulfoxide. The reaction was completed quickly at room temperature, giving the methyl ester with practically no by-products. Reduction of the methyl ester was achieved by sodium borohydride. These modified gangliosides were chemically characterized. Reduced GM1 has a strong antigenicity compared with the original GM1, and it raised high titer antisera which did not crossreact with the original GM1 nor with its methyl ester. Peanut agglutinin, which binds strongly to asialo GM1 but weakly to GM1, bound to the methyl ester of GM1 and reduced GM1. Cholera toxin, which is specific for GM1, also reacted with the methyl ester of GM1 and reduced GM1 to a certain extent.