Journal of the American Chemical Society p. 8023 - 8029 (1985)
Update date:2022-08-12
Topics:
Rice, Scott
Ichinotsubo, Dana
Mower, Howard
Mandel, Morton
The antiulcer drug cimetidine is nitrosated by using NaNO2 and aqueous HCl to generate a mononitroso product which is isolated in up to 80percent yield as either the free base or nitrate salt.The structures of both the free base and nitrate salt were elucidated by using spectral methods.It was found that nitrosation of cimetidine causes a shift in the guanidine ?-electron distribution from predominantely conjugated cyanimino-type bonding to a more delocalized arrangement typically observed for unsubstituted guanidines.The free base of nitrosocimetidine in CHCl3 or Me2SO forms a hydrogen bond between the uncharged imidazole and guanidine moieties.The hydrogen bond can be intramolecular, and its formation is followed by the gradual appearance of charge transfer (CT) between the hydrogen-bonded moieties.Similar CT complexes are formed in CHCl3 from equal molar amounts of 1-methylimidazole and N,N'-dimethyl-N''-cyano-N-nitrosoguanidine (DCNG) or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).The charge-transfer transitions for these systems are similar to those of the n->?* transitions normally observed for the nitrosoguanidines, suggesting that nearly equivalent orbital energies are occupied by the ? electrons of the guanidine and imidazole moieties in the charge-transfer complex.The greater mutagenic activity reported for nitrosocimetidine as the free base compared to its nitrate salt may be related to the presence of an intramolecular complex in the neutral compound.
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