Metabolic pathways of the anti-hypertensive agent, N-(2,5-dimethyl-1H-pyrrol-1-yl)-6-(4-morpholinyl)-3-pyridazinamine hydrochloride. II: Studies in the dog

Metabolic oxidation of the pyrrole ring: structure and origin of some urinary metabolites of the anti-hypertensive pyrrolylpyridazinamine, mopidralazine. III: Studies with the 13C-labelled drug

The metabolism of the anti-hypertensive drug, mopidralazine, N-(2',5'-dimethyl-1H-pyrrol-1-yl)-6-(4"-morpholinyl)-3-pyridazinamine, was reinvestigated in rats using the [2'(5')-13CH3]-labelled drug to determine the significance of the pharmacologically active intermediate 3-hydrazino-6-(4-morpholinyl)pyridazine. The previously proposed mesonic structure of the major metabolite I, i.e., 5'-hydroxy-3',6'-dimethyl-1'-[6-(4"-morpholinyl)-3-pyridazinyl]pyrida zinium hydroxide inner salt, was confirmed by chemical synthesis, X-ray diffraction analysis and 1H n.m.r. of the [3',6'-13CH3]-labelled metabolite I. Metabolite II, 3-methyl-6-(4-morpholinyl)-triazolo [4,3-6 b]pyridazine and metabolite VII, 3-methyl-7-(4-morpholinyl)-3H-pyridazino[1,6-c]pyridazine, were shown to retain the 13CH3 labelling of mopidralazine, whereas metabolite X, 3-acetyl-hydrazino-6-(4-morpholinyl)-pyridazine, loses the labelling, indicating that their formation involves two different pathways. It is hypothesized that the oxidation of the pyrrole leads to ring opening followed by a chemical rearrangement giving rise directly to metabolites II and VII or, with the intermediacy of the pharmacologically active 3-hydrazino-6-(4-morpholinyl) derivative and an enzymic acetylation or conjugation with pyruvic acid, to metabolites X, II and VII.

Metabolic pathways of the anti-hypertensive agent, N-(2,5-dimethyl-1H-pyrrol-1-yl)-6-(4-morpholinyl)-3-pyridazinamine+ ++ hydrochloride. I. Studies in the rat

The metabolic fate of a new anti-hypertensive, 1-pyrrolyl pyridazinamine, was studied in male Wistar rats after both p.o. and i.v. administration (1 mg/kg). The compound undergoes rapid metabolism, disappearing from the central compartment with a half-life of about 0.5 h. Plasma concn. of the parent drug and its major metabolite I following i.v. and p.o. administration suggest a route-dependent first-pass metabolism. Ten metabolites were isolated from the urine and identified by u.v., i.r., mass and 1H-n.m.r. spectroscopy. The structure of some was confirmed by 13C-n.m.r. and chemical synthesis. All biotransformations are restricted to the pyrrole ring which undergoes oxidative cleavage followed by a series of chemical rearrangements. A minor pathway leads to the formation of methyl sulphinyl and methyl sulphonyl pyrroles. It is suggested that, as with natural indoles, the pyrrole might be oxidized by a 2,3-dioxygenase. The three major metabolites, I, II and IX, along with two minor ones, VI and VII, were inactive when tested i.v. for antihypertensive activity.