Reactions of cysteine with N-methyl-N-nitroso-p-toluenesulfonamide and N-methyl-N-nitro-N-nitrosoguanidine

The reaction between cysteine and N-methyl-N-nitroso-p-toluenesulfonamide affords almost quantitative yields of cystine and N-methyl-p-toluenesulfonamide. A mechanism based on the intermediacy of the S-nitroso derivative of cysteine and the intermediate formation of nitric oxide is proposed. Nitrous oxide is shown to be a final product. In the reaction of cysteine with N-methyl-N′-nitro-N-nitrosoguanidine a substantial yield of 2-nitramino-4-carboxyl-thiazoline is obtained. Cystine, N-methyl-N′-nitro-guanidine and S-methylcysteine are formed in lesser amounts. The major product arises from nucleophilic attack on the imino carbon of N-methyl-N′-nitro-N-nitrosoguanidine. Concomitant elimination of the methylnitrosamino group accounts for the mathylating ability of the system.