The kinetics of decomposition of N-alkyl derivatives of nitrosoguanidine.

formation of the active alkylating species, i.e., the alkyldiazonium ion, has been described by Shapiro (3), and the alkylation of DNA has been described by Lawley and Thatcher (1). In order, however, to compare the effects of higher alkyl homologs on the properties of the DNA, the kinetics of formation of the active alkylating species are required. The TV-methyl, TV-ethyl,TV-propyl, and TV-butyl derivatives of nitrosoguanidine were obtained from Aldrich Chemical Company (Milwaukee, Wis.), and the authenticity was determined by infrared and mass spectroscopy. For kinetic studies, 0.4 ml of the stock solutions of the TV-methyl, TV-ethyl, and TV-propyl derivatives (100 mM in absolute ethyl alcohol) was diluted into 2.6 ml of either Tris, pH 9.0, or sodium phosphate, pH 7.5, buffer to give a final concentration of 13.4 mM. Spectra were scanned in the range of 440 to 380 nm at 10-min intervals on a Beckman DB-GT spectrophotometer. Decomposition of the alkylating agents is shown in Chart 1, and the rate constants are shown in Table 1. From these data it may be seen that the rate of decomposition of the homologs is 1st order and varies as a function of the increasing carbon number in the alkyl portion of the molecule. In addition, the rate is, with the exception of the TV-ethyl derivative, pH dependent. Because of insolubility of the TV-butyl derivative, no kinetic data were obtained. The establishment of these rate constants provides a method of ensuring that the results of alkylation studies involving the various TV-alkyl derivatives and DNA will be comparable on a reasonable basis. When the rate constants are utilized, the reaction times of each alkylating species can be adjusted to provide equimolar release of alkylating equivalents. For example, comparison of the extent of alkylation of a DNA solution containing 2X 10~3 M phosphorus would require