Nitrogenous bases-heme reactions

The spontaneous reaction of nitric oxide with thiols is slow at physiological pH and the final product under anaerobic conditions is not a nitrosothiol (Pryor et al., 1982). The reaction is slow because it involves the conjugate base of the thiol (R—S"). At pH 7.0, the oxidation of cysteine by nitric oxide required 6 hr to reach completion and yields RSSR and N 2O as the products. The synthetic preparation of nitrosothiols usually involves the addition of nitrosonium ion from acidified nitrite to the thiol, or oxidation of the thiol with nitrogen dioxide under anaerobic conditions in organic solvents. Nitric oxide will form nitrosothiols by reaction with ferric heme groups, such as found in metmyoglobin or methemoglobin (Wade and Castro, 1990). It is also possible that nitrosyldioxyl radical also reacts with thiols to form a nitrosothiol. 

There are several related reactions involving probable formation of episulfonium ions from aikenes, with subsequent addition of various nitrogen nucleophiles giving products of net rraru-1,2-(N + S) addition (ref. 197 and references cited therein). In a recent example ( heme 64) the sulfur reagent also provides the nitrogen nucleophile yields were best with styrene. Related cyclizations are known in the 3-lactam area, e.g. Scheme 65 compounds (43) and (44) are also available by related but base-catalyzed cyclizations. ... 

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