title: Explanation through density functional theory of the unanticipated loss of CO₂ and differences in mass fragmentation profiles of ritonavir and its rCYP3A4-mediated metabolites.
abstract: In the present study, the metabolism of ritonavir was explored in the presence of rCYP3A4 using a well-established strategy involving liquid chromatography-mass spectrometry (LC-MS) tools. A total of six metabolites were formed, of which two were new, not reported earlier as CYP3A4-mediated metabolites. During LC-MS studies, ritonavir was found to fragment through six principal pathways, many of which involved neutral loss of CO2, as indicated through 44-Da difference between masses of the precursors and the product ions. This was unusual as the drug and the precursors were devoid of a terminal carboxylic acid group. Apart from the neutral loss of CO2, marked differences were also observed among the fragmentation pathways of the drug and its metabolites having intact N-methyl moiety as compared to those lacking N-methyl moiety. These unusual fragmentation behaviours were successfully explained through energy distribution profiles by application of the density functional theory.
authors.affiliation: Department of Pharmaceutical Analysis, National Institute of Pharmaceutical Education and Research (NIPER), S.A.S. Nagar, Punjab, India.
authors.forename: Shalu
authors.initials: S
authors.lastname: Jhajra
authors.forename: Tarun
authors.initials: T
authors.lastname: Handa
authors.forename: Sonam
authors.initials: S
authors.lastname: Bhatia
authors.forename: P V
authors.initials: PV
authors.lastname: Bharatam
authors.forename: Saranjit
authors.initials: S
authors.lastname: Singh
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis* / Q000737:chemistry* / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000378:metabolism*; D006801:Humans; D013058:Mass Spectrometry; D008958:Models, Molecular; D008970:Molecular Weight; D011994:Recombinant Proteins / Q000378:metabolism; D019438:Ritonavir / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D011994:Recombinant Proteins; D002245:Carbon Dioxide; D051544:Cytochrome P-450 CYP3A; D019438:Ritonavir
keywords: CO2 neutral loss; density functional theory; group substitution effect; mass fragmentation; metabolism; rCYP3A4; ritonavir