PROCESS FOR PRODUCING SULFUR- AND PHOSPHORUS-CONTAINING PURINE DERIVATIVES AND PHARMACEUTICAL COMPOSITIONS COMPRISING SAME AS ACTIVE INGREDIENT

摘要

Compounds of formula (I), and pharmaceutically acceptable salts thereof: CHEM wherein R1 is hydroxy or amino; R2 is hydrogen or amino; R3 is hydrogen, hydroxymethyl or acyloxymethyl; R4 is a group of formula: CHEM wherein R5 and R6 are independently selected from hydrogen, C1-6 alkyl and optionally substituted phenyl; or R3 and R4 together are: CHEM wherein R6 is as defined above; having antiviral activity, processes for their preparation and their pharmaceutical use.