PURPOSE: To obtain the compd. which is an intermediate useful for nucleoside synthesis in pharmaceutical industry at a good yield with high purity by bringing diacyl guanine into reaction with a halogenating agent in the presence of a base and salt, then hydrolyzing the resulted product.

CONSTITUTION: First, 2,9-diacyl guanine (2-acylamino-6-oxo-acrylpurine) of formula I (R1, R2 are 2 to 10C chain acyl, 7 to 10C aroyl) is borough into reaction with a halogenating agent (e.g.; phosphorous oxychlride, etc.), in the presence of the base (preferably, triethyl amine, etc.), and the salt (preferably, tetraethyl ammonium chloride, etc.). The reaction product is then introduced into water and is hydrolyzed preferably at a reaction temp. of 0 to 5°C and at pH 4 to 7, by which the desired component of formula II (X is Cl, Br) is obtd. The reaction of the compd. of the formula I with the halogenating agent is preferably executed by maintaining the reaction temp. at 15 to 30°C after the addition of the halogenating agent to the compd.