Nitrosating properties of bis-methylthio-diiron-tetranitrosyl (Roussin's red methyl ester), a nitroso compound isolated from pickled vegetables consumed in northern China.

Bis-methylthio-diiron-tetranitrosyl (Roussin's red methyl ester, RRME), recently identified in pickled vegetables consumed in a high incidence area of oesophageal cancer in Northern China, was examined for its activity as a nitrosating agent in vivo and in vitro. Freshly synthesized RRME nitrosated secondary amines (morpholine and pyrrolidine) slowly in the presence of air; it failed to nitrosate these amines under strictly anaerobic conditions. In experiments in rats, a fresh sample of RRME was found to be a weak nitrosating agent, whereas partially decomposed RRME showed a strong nitrosating activity comparable to that of nitrite. Possible mechanisms for nitrosation by RRME are discussed.