title: Thiol addition to quinones: model reactions for the inactivation of thymidylate synthase by 5-p-benzoquinonyl-2'-deoxyuridine 5'-phosphate.
abstract: The reaction of methyl mercaptoacetate (5) with phenyl-p-benzoquinone (6) or 5-p-benzoquinonyl-3',5'-di-O-acetyl-2'-deoxyuridine (10) resulted in the formation of the three possible adducts to the quinone rings of 6 and 10; an additional product in the reaction with 10 was the unsubstituted hydroquinone (14). Both reactions were found to be solvent dependent; in buffered aqueous acetonitrile the meta and para adducts of 10 were formed in the ratio of 2:1. In ethyl acetate the ortho adduct and the reduction product of 10 were isolated in a ratio of 2:3. The second-order rate constant for the reaction of 5 with 10 in acetonitrile was 0.53 M-1 s-1; the reaction was accelerated by the addition of water. Although the initially proposed mechanism-based enzyme inactivation cannot be excluded, the results of the model reactions support the alternative mechanism, active-site thiol addition to the quinone ring. If this is true the title compound would be classed as an affinity label, not a mechanism-based inhibitor.
mesh_terms: D016227:Benzoquinones; D055598:Chemical Phenomena; D002621:Chemistry; D003856:Deoxyuracil Nucleotides / Q000494:pharmacology*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D011809:Quinones / Q000494:pharmacology*; D013438:Sulfhydryl Compounds / Q000494:pharmacology*; D013864:Thioglycolates; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors*
chemical_list: D016227:Benzoquinones; D003856:Deoxyuracil Nucleotides; D011809:Quinones; D013438:Sulfhydryl Compounds; D013864:Thioglycolates; C029322:phenylbenzoquinone; C038575:5-(4-benzoquinonyl)-2'-deoxyuridine 5'-phosphate; D013940:Thymidylate Synthase; C037474:methyl thioglycolate