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.
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(2H)-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 13C 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.
Subramanian
Raju
R
Department of Drug Metabolism, WP75-100, Merck Research Laboratories, West Point, PA 19486, USA. raju_subramanian@merck.com
Lin
Charles C
CC
Ho
Jonathan Z
JZ
Pitzenberger
Steven M
SM
Silva-Elipe
Maria V
MV
Gibson
Christopher R
CR
Braun
Matthew P
MP
Yu
Xiao
X
Yergey
James L
JL
Singh
Rominder
R
D000818:Animals; D001646:Bile / Q000737:chemistry / Q000378:metabolism; D001711:Biotransformation; D002247:Carbon Isotopes / Q000378:metabolism; D005343:Fibrinolytic Agents / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D007093:Imidazoles / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008297:Male; D011719:Pyrazines / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods
D002247:Carbon Isotopes; D005343:Fibrinolytic Agents; D007093:Imidazoles; D011719:Pyrazines