NEW METHOD TO MEASURE THE CARBAMOYLATING ACTIVITY OF NITROSOUREAS BY ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY

A new method for measuring the carbamoylating activity of nitrosoureas and isocyanates using electron paramagnetic resonance (EPR) spectrosc opy is described. The extent and time course of carbamoylation reactio n of chloroethyl isocyanate and a series of 9 nitrosoureas toward amin o group of 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl were examined with both the EPR method and the HPLC method which has been proposed b y Brubaker et al. [Biochem. Pharmacol. 35:2359 (1986)]. Spin-labeled n itrosoureas we synthesized are included in this study since they have less toxicity or more efficiency than commercially available drug in s ome cases. The concentration of carbamoylated product was easily deter mined with the EPR spectra. There is a very high correlation (r = 0.98 2, t = 2.58, N = 10, p < 0.001) between the EPR and HPLC methods. Spin -labeled nitrosoureas showed lower carbamoylating activity than non-la beled analogues. The carbamoylating activity for these nitrosourea dep ended on the reactivity of isocyanate intermediate and almost independ ent of their half life. This rapid and simple EPR method is suitable f or the detailed investigation of the rate and extent of carbamoylation reaction.