REACTIVITY-SELECTIVITY PROPERTIES OF REACTIONS OF CARCINOGENIC ELECTROPHILES WITH BIOMOLECULES - KINETICS AND PRODUCTS OF THE REACTION OF BENZO[A]PYRENYL-6-METHYL CATION WITH NUCLEOSIDES AND DEOXYNUCLEOSIDES

The nucleophilicities of the nucleosides and deoxynucleosides toward the carbonium ion generated by solvolysis of the chemical carcinogen 6-(chloromethyl) benzo [a] pyrene were measured by the method of inhibition of the common-ion effect. Nucleosides or deoxynucleosides containing adenine, guanine, or cytosine were able to trap the carbonium ion in competition with water while those containing uracil or thymine were not. Product distribution studies indicated that two products are formed when the carbonium ion is trapped by adenosine, guanosine, or cytidine (or their deoxy analogues). No detectable products were formed with uridine or thymidine. The chemical shifts of the arylmethyl carbon of labeled products prepared by trapping the carbonium ion from solvolysis of 6-(chloromethyl-13C)benzo[a]pyrene indicated that in each case the labeled carbon is bonded to a nitrogen. Consideration of the carbon chemical shifts, pH effects on the UV-vis spectra, chromatographic properties, and chemical properties of the products led to the assignment of structures as follows: (1) from trapping with adenosine, 1-(benzo[o]pyrenyl-6-methyl)adenosine and N6-(benzo[a]pyrenyl-6-methyl)adenosine; (2) from trapping with guanosine, 7-(benzo[o]pyrenyl-6-methyl)guanosine and N2-(benzo[a)pyrenyl-6-methyl)guanosine; (3) from trapping with cytidine, 3-(benzo[a]pyrenyl-6-methyl)cytidine and N4-(benzo[o]pyrenyl-6-methyl)cytidine. The order of nucleophilicity is guanosine > adenosine > cytidine. © 1979, American Chemical Society. All rights reserved.