Process for preparing N6,9-disubstituted adenine

A process for preparing a N.sup.6,9-disubstituted adenine having the general formula (I):

• ##STR10## wherein R.sup.1 is hydrogen, a lower alkyl group having 1 to 4 carbon atoms, benzyl group or furfuryl group, R.sup.2 is a lower alkyl group having 1 to 4 carbon atoms, benzyl group or furfuryl group, Y and Z are the same or different and each is hydrogen, chlorine, bromine or fluorine, which comprises reacting a metal salt of N.sup.6 -substituted adenine having the general formula (II):
• ##STR11## wherein R.sup.1 and R.sup.2 are the same as defined above, M is an alkali metal or an alkaline earth metal and n is an integer of 1 or 2, with a benzyl halide compound having the general formula (III):
• ##STR12##
• wherein Y and Z are the same as defined above, and X.sup.1 is chlorine or bormine, in the presence of a phase transfer catalyst selected from the group consisting of polyethylene glycol or its alkyl ether having the general formula (VII):
• R.sup.9 O(CH.sub.2 CH.sub.2 O).sub.m R.sup.9 (VII)
• wherein R.sup.9 is hydrogen or an alkyl group having 1 to 4 carbon atoms and m is an integer of not less than 3;
• and diethylene glycol or its alkyl ether having the general formula (VIII):
• (R.sup.10 OCH.sub.2 CH.sub.2).sub.2 O (VIII)
• wherein R.sup.10 is hydrogen or an alkyl group having 1 to 4 carbon atoms, whereby formation of the 3-isomer is suppressed.