Purine derivative and pharmaceutical composition

A purine derivative of the formula:

• ##STR7## wherein R is a hydrogen atom, C.sub.1-8 alkyl group or a phenyl group which may be substituted by at least one substituent selected from a halogen atom, a C.sub.1-4 alkyl group and a C.sub.1-4 alkoxy group;
• each of R.sup.1 and R.sup.2 is a hydrogen atom, a C.sub.1-8 alkyl group, a C.sub.3-7 cycloalkyl group, a hydroxy-C.sub.1-8 alkyl group, a di-C.sub.1-8 alkylamino-C.sub.1-8 alkyl group, a cyclic amino-C.sub.1-8 alkyl group wherein the cyclic amino is selected from 1-pyrrolidinyl, piperidino, morpholino, thiomorpholino, 1-piperazinyl, 4-methyl-1-piperaznyl, 4-(2-hydroxyethyl)-1-piperazinyl and 4-methyl-1-homopiperazinyl, a C.sub.2-8 alkenyl group or a phenyl-C.sub.1-3 alkyl group, or R.sup.1 and R.sup.2 together with the adjacent nitrogen atom form a heterocycle selected from 1-pyrrolidinyl, piperidino, 1-piperazinyl, 4-methyl-1-piperazinyl, 4-(2-hydroxyethyl)-1- piperazinyl, 1-homopiperazinyl, 4-methyl-1-homopiperazinyl, morpholino and thiomorpholino, and each of R.sup.3 and R.sup.4 is a hydrogen atom or a C.sub.1-4 alkyl group, or
• a pharmaceutically acceptable acid addition salt thereof.