title: Theoretical study on the N-demethylation mechanism of theobromine catalyzed by P450 isoenzyme 1A2.
abstract: Theobromine, a widely consumed pharmacological active substance, can cause undesirable muscle stiffness, nausea and anorexia in high doses ingestion. The main N-demethylation metabolic mechanism of theobromine catalyzed by P450 isoenzyme 1A2 (CYP1A2) has been explored in this work using the unrestricted hybrid density functional method UB3LYP in conjunction with the LACVP(Fe)/6-31G (H, C, N, O, S, Cl) basis set. Single-point calculations including empirical dispersion corrections were carried out at the higher 6-311++G** basis set. Two N-demethylation pathways were characterized, i.e., 3-N and 7-N demethylations, which involve the initial N-methyl hydroxylation to form carbinolamines and the subsequent carbinolamines decomposition to yield monomethylxanthines and formaldehydes. Our results have shown that the rate-limiting N-methyl hydroxylation occurs via a hydrogen atom transfer (HAT) mechanism, which proceeds in a spin-selective mechanism (SSM) in the gas phase. The carbinolamines generated are prone to decomposition via the contiguous heteroatom-assisted proton-transfer. Strikingly, 3-N demethylation is more favorable than 7-N demethylation due to its lower free energy barrier and 7-methylxanthine therefore is the optimum product reported for the demethylation of theobromine catalyzed by CYP1A2, which are in good agreement with the experimental observation. This work has first revealed the detail N-demethylation mechanisms of theobromine at the theoretical level. It can offer more significant information for the metabolism of purine alkaloid.
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Tao
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Kang
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China.
authors.forename: Zhiyu
authors.initials: Z
authors.lastname: Xue
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China.
authors.forename: Yongting
authors.initials: Y
authors.lastname: Wang
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China.
authors.forename: Qiu
authors.initials: Q
authors.lastname: Chen
authors.affiliation: College of Chemistry and Chemical Engineering, Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province, China West Normal University, Nanchong 637002, People's Republic of China. Electronic address: chenzeqin@cwnu.edu.cn.
authors.forename: Zeqin
authors.initials: Z
authors.lastname: Chen
authors.affiliation: College of Chemistry, Key Laboratory of Green Chemistry and Technology in Ministry of Education, Sichuan University, Chengdu 610064, People's Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Xue
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D001993:Bronchodilator Agents / Q000737:chemistry*; D019388:Cytochrome P-450 CYP1A2 / Q000737:chemistry*; D006801:Humans; D006859:Hydrogen / Q000737:chemistry*; D006900:Hydroxylation; D007700:Kinetics; D008745:Methylation; D008956:Models, Chemical; D011789:Quantum Theory; D013805:Theobromine / Q000737:chemistry*; D013816:Thermodynamics; D014970:Xanthines / Q000737:chemistry
chemical_list: D000447:Aldehydes; D001993:Bronchodilator Agents; D014970:Xanthines; D006859:Hydrogen; C504573:CYP1A2 protein, human; D019388:Cytochrome P-450 CYP1A2; D013805:Theobromine
keywords: CYP1A2; Density function theory; Dispersion correction; Metabolism; N-demethylation mechanism; Theobromine