We Claim;
1. A process for preparing diacetyl ganciclovir comprising;
a) reacting guanine with 2-acetoxymethoxy-l,3-diacetoxypropane in presence of silylating agents, silylating catalyst and an alkylation catalyst,
b) isolating diacetyl ganciclovir,
c) hydrolyzing of diacetyl ganciclovir in presence of a base,
d) isolating of ganciclovir and,
e) optionally purifying the ganciclovir

2. The process according to claim 1, wherein silylating agent is selected from hexamethyldisilazane (HMDS), trimethylsilyl chloride (TMSCI), and trimethylsilyl triflate (TMST), tert-butyldimethylsilyl chloride, preferably hexamethyldisilazane (HMDS).
3. The process according to claim 1, wherein silylation of guanine is optionally carried out using 0.001-0.005 moles of trifluormethane sulfonic acid
4. The process according to claim 1, wherein silylating catalyst is selected from N,0-bis(trimethylsiIyl)acetamide (BSA), N,0-bis(trimethyIsilyl)trifluoro acetamide (BSTFA), tert-butyldimethylchlorosilane, bis(trimethoxysilyl propylamine, bis(trimethylsiloxy)methylsilane, bis(trimethylsilyl) methane, bis(trimethylsilyl)trifluoroacetamide, preferably N,0-bis(trimethylsilyl) acetamide.
5. The process according to claim 1, wherein alkylation catalyst is selected from the group of quaternary ammonium salts comprising of tetra butyl ammonium bromide, tetra propyl ammonium bromide, tributyl benzyl ammonium chloride, tetra ethyl ammonium chloride, tetra ethyl ammonium bromide, tetra octyl ammonium bromide, tetra butyl ammonium hydrogen sulfate, tetra butyl ammonium acetate, tetrabutyl ammonium iodide, trimethyl benzyl ammonium chloride, triethyl benzyl ammonium chloride, preferably tetra butyl ammonium bromide.

6. The process according to claim 1, wherein the isolation of diacetyl ganciclovir
is carried out in presence of water and acid selected from hydrochloric acid,
sulfuric acid or acetic acid, preferably 1 - 10 % acetic acid and water.
7. The process according to claim 1, wherein the base used is selected from
dimethyl amine, ammonia, triethyl amine, sodium hydroxide, potassium
hydroxide, sodium carbonate & potassium carbonate
8. A process for preparing diacetyl ganciclovir comprising;
a) reacting guanine with 2-acetoxymethoxy-l,3-diacetoxypropane in
presence of silylating agents, silylating catalyst and an alkylation
catalyst,
b) isolating diacetyl ganciclovir in a solvent.
9. The process according to claim 9, wherein silylating catalyst is selected from
N,0-bis(trimethylsilyl)acetamide (BSA), N,0-bis(trimethylsilyl)trifluoro
acetamide (BSTFA), tert-butyldimethylchlorosilane, bis(trimethoxy -
silyIpropyl)amine, bis(trimethylsiloxy)methylsilane, bis(trimethylsilyl)
methane, bis(trimethylsilyl)trifluoroacetamide, preferably N,0-
bis(trimethylsilyl)acetamide.
10. A process for preparing anhydrous Ganciclovir comprising; recrystallizing
Ganciclovir from N, N-dimethylformamide.
Date: 29.05.2008 Place: Hyderabad