Preparation of purines

摘要

A process for the preparation of a compound of formula (A) wherein: X is hydrogen or hydroxy, chloro, C_1-6 alkoxy or pheny C_1-6 alkoxy; and R_a and R_b are hydrogen, or acyl or phosphate derivatives thereof, which process comprises: (i) the preparation of a compound of formula (I) wherein R₁ is C_1-6 alkyl, or phenyl C_1-6 alkyl in which the phenyl group is optionally substituted; R₂ is hydrogen, hydroxy, chlorine, C_1-6 alkoxy, phenyl C_1-6 alkoxy or amino; and R₃ is halogen, C_1-6 alkylthio, C_1-6 alkylsulphonyl, azido, an amino group or a protected amino group, which preparation comprises the reaction of a compound of formula (II) wherein R₂ and R₃ are as defined for formula (I) with a compound of formula (V) wherein L is a leaving group and R₁ is as defined for formula (I), to give a compound of formula (VI), and thereafter converting the intermediate compound of formula (VI) to a compound of formula (I) via decarboxylation, and as necessary or desired, interconverting variables R₁, R₂ and R₃ to further values of R₁, R₂ and R₃; (ii) the conversion of the resulting compound of formula (I) to a compound of formula (A) by converting variable R₃, when other than amino, to amino, reducing the ester groups CO₂R₁ to CH₂OH and optionally forming acyl or phosphate derivates thereof, and as necessary or desired converting variable R₂ in the compound of formula (I) to variable X in the compound of formula (A); characterized in that R₂ is chloro in formula (I)