Nitrosation and nitrosylation of haemoproteins and related compounds. Part 2. The reaction of nitrous acid with the side chains of α-acylamino-acid esters

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Abstract
The nitrosation of N-acetylcysteine methyl ester with aqueous sodium nitrite and acetic acid furnishes the S-nitroso(thionitrite) derivative as unstable red crystals which decompose in ether to give NN′-diacetylcystine dimethyl ester. Under similar nitrosating conditions N-acetyltyrosine ethyl ester furnishes the 3-nitro-derivative and an unstable product formulated as the corresponding 3-nitroso-derivative. Neither N-acetylhistidine methyl ester nor N-acetylmethionine methyl ester are nitrosated under these conditions. At higher acidities the latter compound gives the N-nitroso-amide and a polar compound regarded as the N-nitrosamide S-oxide. N-Acetyl-N1-nitrosotryptophan methyl ester is solvolysed in aqueous methanolic buffer solutions. The reaction is first order in the N1-nitroso-compound and the rate increases as the pH is lowered in the range 2–8. Solvolysis with n-butyl alcohol gives n-butyl nitrite and N-acetyltryptophan methyl ester. Transnitrosation reactions are also observed with the nitrosothiolcysteine derivative and the N1-nitrosotryptophan derivative as donors and diphenylamine as the acceptor molecule.