BIOACTIVATION OF THE 3-AMINO-6-CHLOROPYRAZINONE RING IN A THROMBIN INHIBITOR LEADS TO NOVEL DIHYDRO-IMIDAZOLE AND IMIDAZOLIDINE DERIVATIVES: STRUCTURES AND MECHANISM USING 13C-LABELS, MASS SPECTROMETRY, AND NMR

• Published in: Drug metabolism and disposition Vol. 31; no. 11; pp. 1437 - 1447
• Main Authors: SUBRAMANIAN, Raju, LIN, Charles C, HO, Jonathan Z, PITZENBERGER, Steven M, SILVA-ELIPE, Maria V, GIBSON, Christopher R, BRAUN, Matthew P, XIAO YU, YERGEY, James L, SINGH, Rominder
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 01.11.2003
• Subjects: Animals; Bile - chemistry; Bile - metabolism; Biological and medical sciences; Biotransformation; Blood. Blood coagulation. Reticuloendothelial system; Carbon Isotopes - metabolism; Fibrinolytic Agents - analysis; Fibrinolytic Agents - chemistry; Fibrinolytic Agents - metabolism; Imidazoles - analysis; Imidazoles - chemistry; Imidazoles - metabolism; Magnetic Resonance Spectroscopy - methods; Male; Medical sciences; Pharmacology. Drug treatments; Pyrazines - analysis; Pyrazines - chemistry; Pyrazines - metabolism; Rats; Rats, Sprague-Dawley; Spectrometry, Mass, Secondary Ion - methods; Intravenous administration; Serine endopeptidases; Rat; Enzyme; Metabolite; Rodentia; Chemical structure; Thrombin; Anticoagulant; NMR spectrometry; Metabolism; Peptidases; Vertebrata; Mammalia; Animal; Hydrolases; Inhibitor; Pharmacokinetics; Mass spectrometry
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.31.11.1437

Thrombin is a serine protease that plays a key role in the blood coagulation cascade. Compound I [2-[6-chloro-3-[(2,2-difluoro-2-pyridin-2-ylethyl)amino]-2-oxopyrazin-1(2 H )-yl]-N-[(3-fluoropyridin-2-yl)methyl]acetamide] is a potent, selective, and orally bioavailable thrombin inhibitor that is being studied as a possible anticoagulant. Biotransformation studies in rats revealed that 84% of an i.v. dose of I was excreted in the form of two metabolites. Both metabolites were formed by metabolic activation of the pyrazinone ring in I and subsequent rearrangement leading to two novel dihydro-imidazole and imidazolidine derivatives. The structures of these metabolites and their mechanism of formation were elucidated by additional use of two 13 C single labels in the pyrazinone ring of I in combination with mass spectrometry and NMR techniques. The metabolite structures described here illustrate the rich metabolic chemistry of the amino-pyrazinone heterocycle.