Patent ID: 7629457

Claim:
A method for producing a cytosine nucleoside compound comprising reacting a sugar phosphate and cytosine or a derivative of cytosine in the presence of an enzyme preparation obtained from a bacterial mass of Escherichia coli or culture thereof having a purine nucleoside phosphorylase, which acts also as a cytosine nucleoside phosphorylase, to obtain the cytosine nucleoside compound, wherein, before the step of reacting a sugar phosphate and cytosine or a derivative of cytosine, the activity of cytosine deaminase and/or the activity of cytidine deaminase of said bacterial mass, or culture thereof or said enzyme preparation are lost or reduced by at least one of the following steps: (i) contacting the bacterial mass, culture thereof or an enzyme preparation having the activity of purine nucleotide phosphorylase and at least one of the activities of cytosine deaminase and cytidine deaminase with water containing N,N-dimethylformamide or N,N′-dimethylimidazolidinone as an organic solvent at a concentration of 50 volume % to 90 volume %, for an effective time of at least 1 hour, in the presence of a pentose- 1-phosphate, to eliminate or reduce selectively at least one of the activities of cytosine deaminase and the activity of cytidine deaminase; and (ii) heating the bacterial mass, culture thereof or enzyme preparation at a temperature from 60° C. to 90° C. for an effective time of at least 30 minutes, in the presence of a pentose- 1-phosphate, to eliminate or reduce selectively at least one of the activities of cytosine deaminase and the activity of cytidine deaminase, wherein the enzyme preparation is obtained from the bacterial mass or culture thereof thus treated by at least one of steps (i) and (ii) wherein said derivative of cytosine is a compound expressed by formula (I) wherein X is carbon or nitrogen, Y is hydrogen, a halogen or a lower alkyl; and wherein the purine nucleoside phosphorylase has an activity of catalyzing a reaction between a compound of formula (I) and a sugar phosphate to produce a corresponding cytosine nucleoside compound.