A colorimetric method for the determination of certain purine antagonists.

The purine antagonists with which this paper is concerned are of interest in the chemotherapy of neoplastic diseases and belong to either of the two groups: the substituted purines such as 6-mercaptopurine (6MP) (1) and isomers of purines such as 4-aminopyrazolo (3,4-d) pyrimidine (4APP) (2). In connection with their pharmacological studies (3), it is essential to have a method available for their estimation in biological fluids. As far as the present authors are aware, such a method has not been described except perhaps for labeled 6MP (4).’ It is the purpose of this communication to describe a calorimetric method developed to meet this need, the principle of which consists in the reduction of the antagonist by zinc amalgam in dilute acid to a diazotizable amine which, after diazotization, couples with N-(1-naphthyl)ethylenediamine (5) to give an intensely colored azo dye.