Mechanism of Photochemical O-Atom Exchange in Nitrosamines with Molecular Oxygen

Author(s)

Oliveira, Marlene Silva ^{[1, 2, 3]} ; Ghogare, Ash-Wini A. ^{[2, 3]} ; Abramova, Inna ^{[2, 3]} ; Greer, Edyta M. ^[4] ; Prado, Fernanda Manso ^[1] ; Di Mascio, Paolo ^[1] ; Greer, Alexander ^{[2, 3]}

Affiliation

^[1] Univ Sao Paulo, Inst Quim, Dept Bioquim, BR-05508000 Sao Paulo - Brazil

^[2] CUNY Brooklyn Coll, Dept Chem, Brooklyn, NY 11210 - USA

^[3] CUNY Brooklyn Coll, Grad Ctr, Brooklyn, NY 11210 - USA

^[4] CUNY, Dept Nat Sci, Baruch Coll, New York, NY 10010 - USA

• Document type: Journal article
• Source: Journal of Organic Chemistry; v. 80, n. 12, p. 6119-6127, JUN 19 2015.
• Web of Science Citations: 2

Abstract

The detection of an oxygen-atom photoexchange process of N-nitrosamines is reported. The photolysis of four nitrosamines (N-nitrosodiphenylamine 1, N-nitroso-N-methylaniline 2, N-butyl-N-(4-hydroxybutypnitrosamine 3, and N-nitrosodiethylamine 4) with ultraviolet light was examined in an O-18(2)-enriched atmosphere in solution. HPLC/MS and HPLC-MS/MS data show that O-18-labeled nitrosamines were generated for 1 and 2. In contrast, nitrosamines 3 and 4 do not exchange the 180 label and instead decomposed to amines and/or imines under the conditions. For 1 and 2, the O-18 atom was found not to be introduced by moisture or by singlet oxygen {[}(18)(O-1(2) (1)Delta(g)] produced thermally by O-18-O-18 labeled endoperoxide of N,N'-di(2,3-hydroxypropyl)-1,4-naphthalene dipropanamide ((DHPNO2)-O-18) or by visible-light sensitization. A density functional theory study of the structures and energetics of peroxy intermediates arising from reaction of nitrosamines with O-2 is also presented. A reversible head-to-tail dimerization of the O-nitrooxide to the 1,2,3,5,6,7-hexaoxadiazocane (30 kcal/mol barrier) with extrusion of O=O-18 accounts for exchange of the oxygen atom label. The unimolecular cyclization of O-nitrowdde to 1,2,3,4-trioxazetidine (46 kcal/mol barrier) followed by a retro {[}2 + 2] reaction is an alternative, but higher energy process. Both pathways would require the photoexcitation of the nitrooxide. (AU)

• FAPESP's process: 12/12663-1 - Singlet molecular oxygen and peroxides in chemical biology
• Grantee: Paolo Di Mascio
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 13/07937-8 - Redoxome - Redox Processes in Biomedicine
• Grantee: Ohara Augusto
• Support Opportunities: Research Grants - Research, Innovation and Dissemination Centers - RIDC