Modification of Sialic Acid Carboxyl Group of Ganglioside

Abstract

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.