Characterization of the solution degradation products of etintidine, an H₂‐receptor antagonist

The primary solution degradation products of the antiulcer drug etintidine (1,N″‐cyano‐N‐[2‐[[(5‐methyl‐1H‐imidazol‐4‐yl)methyl]thio]ethyl]‐N′‐2‐propynylguanidine) were determined to be the guanyl urea 2, the guanidine 3, the amine 4a, and the cyanoamine 4b. These products resulted from nitrile hydrolysis and/or intramolecular cyclization of the guanidino and propargyl groups. The amine 4a was found to be a predominant degradation product in aqueous media of pH 4–7 at 70 ± 0.2°C.