Patent ID: 7601835

Claim:
A method for preparation of a purine derivative of formula I, comprising (a) reacting a compound of formula VI with X—R 3 —X to form a compound of formula V wherein R 1 is selected from the group consisting of amino, protected amino, hydroxyl, protected hydroxyl, R 2 is halo, R 3 is selected from the group consisting of C 1-6 alkyl and C 1-6 alkyl substituted by one or more substituents independently selected from the group consisting of amino, protected amino, hydroxyl, protected hydroxyl and C 1-6 alkyl, each R 5 is selected from the group consisting of C 1-6 alkyl carbonyl and C 1-6 alkyl carbonyl substituted by one or more substituents independently selected from the group consisting of halo, hydroxyl, protected hydroxyl and C 1-6 alkyl, and each X is independently a leaving group, subsequently (b) converting a compound of formula V to a compound of formula IV by reacting the compound of formula V with CH 2 (COOR 4 ) 2 , wherein R 4 is selected from the group consisting of C 1-6 alkyl and C 1-6 alkyl substituted by one or more substituents independently selected from the group consisting of halo, amino, protected amino, hydroxyl, protected hydroxyl and C 1-6 alkyl, wherein the compound of formula V is converted to the compound of formula IV in a polar solvent in the presence of base, (c) reducing a compound of formula IV to yield a compound of formula III, (d) hydrogenating a diol of formula III so as to yield a compound of formula II, and (e) reacting the compound of formula II obtained in (d) with (R 5 ) 2 O to form the compound of formula I.