REDUCTION OF 3'-AZIDO-3'-DEOXYTHYMIDINE (AZT) AND AZT NUCLEOTIDES BY THIOLS - KINETICS AND PRODUCT IDENTIFICATION

3'-Azido-3'-deoxythymidine (AZT), AZT 5'-monophosphate, and AZT 5'-tri phosphate (AZTTP) were reduced by dithiothreitol with second-order rat e constants of 2.30 x 10(-3), 1.50 x 10(-3), and 7.46 x 10(-4) M(-1) s (-1), respectively. Handlon and Oppenheimer reported that AZT is quant itatively reduced by thiols to 3'-amino-3'-deoxythymidine (Handlon, A. L., and Oppenheimer, N. J. (1988) Pharm. Res. (N. Y.) 5, 297-299). In the present report, multiple products of this reaction were identifie d by the techniques of UV spectroscopy, phosphate analysis, coelution with authentic standards from reversed-phase high pressure liquid chro matography, two-dimensional NMR spectroscopy, and mass spectrometry. T he product mixture from reduction of AZT 5'-monophosphate at pH 7.1 an d 25 degrees C was composed of 2,3'-anhydro-beta-D-threo-thymidine 5'- monophosphate (6.4%), 3'-amino-3'-deoxythymidine 5'-monophosphate (19. 6%), beta-D-threo-thymidine 5'-monophosphate (6.8%), thymine and 3-ami no-2,3-dideoxyribal 5-monophosphate (8.9%), beta-D-threo-thymidine 3', 5'-cyclic monophosphate (9.1%), 3'-deoxy-2',3'-didehydrothymidine 5'-m onophosphate (31.5%), and 3',5'-anhydro-beta-D-threo- hymidine (17.8%) . Thymine and 3',5'-anhydro-beta-D-threo-thymidine were also products of reduction of AZT and AZTTP. Furthermore, the nucleosides of the abo ve monophosphates were products of reduction of AZT, and the correspon ding triphosphates were products of reduction of AZTTP. The product ra tios were dependent on the level of phosphorylation of AZT and on the pH of the reaction. Mechanisms for formation of these products are pro posed.