- Potent Mechanism-Based Inhibition of Human CYP2B6 by Clopidogrel and Ticlopidine
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The thienopyridine derivatives ticlopidine and clopidogrel are inhibitors of ADP-induced platelet aggregation. Pharmacological activity of these prodrugs depends on cytochrome P450 (P450)-dependent oxidation to the active antithrombotic agent. In this study, we investigated the interaction potential of clopidogrel and ticlopidine by using human liver microsomes and recombinantly expressed P450 isoforms. Both clopidogrel and ticlopidine inhibited CYP2B6 with highest potency and CYP2C19 with lower potency, Clopidogrel also inhibited CYP2C9, and ticlopidine also inhibited CYP1A2, with lower potency. Inhibition of CYP2B6 was time- and concentration-dependent, and as shown by dialysis experiments, it was irreversible and dependent on NADPH, suggesting a mechanism-based mode of action. Inactivation was of nonpseudo-first-order type with maximal rates of inactivation (K inact) for clopidogrel and ticlopidine in microsomes (recombinant CYP2B6) of 0.35 (1.5 min-1) and 0.5 min-1 (0.8 min -1), respectively, and half-maximal inactivator concentrations (KI) were 0.5 μM (1.1 μM) for clopidogrel and 0.2 μM (0.8 μM) for ticlopidine. Inhibition was attenuated by the presence of alternative active site ligands but not by nucleophilic trapping agents or reactive oxygen scavengers, further supporting mechanism-based action. A chemical mechanism is discussed based on the known metabolic activation of clopidogrel and on the finding that hemoprotein integrity of recombinant CYP2B6 was not affected by irreversible inhibition. These results suggest the possibility of drug interactions between thienopyridine derivates and drug substrates of CYP2B6 and CYP2C19.
- Richter, Tanja,Muerdter, Thomas E.,Heinkele, Georg,Pleiss, Juergen,Tatzel, Stephan,Schwab, Matthias,Eichelbaum, Michel,Zanger, Ulrich M.
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p. 189 - 197
(2007/10/03)
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- Base Catalysed Rearrangements involving Ylide Intermediates. Part 18. Competing , , and Rearrangements of Ammonium Ylides
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The rearrangements of acyl stabilised ammonium ylides are, in several cases, accompanied by competing rearrangements and in one case by a rearrangement.For examples involving migrating benzyl or phenylethyl groups the mechanism of these rearrangements has been studied.Thus the competing , , and rearrangements of the ylide (12) are largely intramolecular, but the intermolecularity is as high as 28percent for the and rearrangements and 14percent for the rearrangement in methanol at 55 deg C.The competing and rearrangements of the optically active (29a) give products with predominant retention of the configuration of the migrating phenylethyl group, but the intramolecular stereoselectivity of the rearrangement is significantly greater than that of the rearrangement.These results are consistent with a radical pair pathway for all three modes of rearrangement.Suitably substituted acyl stabilised allylammonium ylides (55) rearrange by competing , and processes.
- Chantrapromma, Kan,Ollis, W. David,Sutherland, Ian O.
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p. 1049 - 1062
(2007/10/02)
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- Absorption Spectra and Photochemical Rearrangements in Phenylalkene Cations in Solid Argon
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Matrix photoionization experiments with phenylalkenes produced and trapped the parent molecular cations in solid argon at 20 K.In the substituted styrene cation cases, structure was resolved in red and ultraviolet absorption bands and assigned to Ph-C stretching and Ph-C=C bending modes.Molecular ion rearrangements were observed during sample formation and upon the photolysis of the cold sample; allylbenzene cation rearranged to β-methylstyrene cation and indan cation with 290 nm irradiation.The matrix absorption bands were substantially sharper than photodissociati on spectra, which suggests that excess internal energy may contribute substantially to the bandwidth of gaseous molecular ions produced by electron impact.
- Andrews, Lester,Harvey, James A.,Kelsall, Benuel J.,Duffey, Donald C.
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p. 6415 - 6422
(2007/10/02)
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