Methods for isolating crystalline form I of 5-azacytidine

1. A method for isolating crystalline Form I of 5-azacytidine substantially free of other forms, the method comprising:

recrystallizing 5-azacytidine from a solvent mixture comprising at least one polar aprotic solvent and at least one co-solvent selected from the group consisting of:

1,1,2-trichloroethene,

1,2-dichloroethene,

1,2-dimethoxyethane,

1,4-dioxane,

1-butanol,

1-pentanol,

1-propanol,

2-butanol,

2-ethoxyethanol,

2-methoxyethanol,

2-methyl-1-propanol,

2-propanol (isopropyl alcohol),

3-methyl-1-butanol,

acetone,

acetonitrile,

anisole,

butyl acetate,

chlorobenzene,

cumene,

cyclohexane,

dichloromethane,

ethanol,

ethyl acetate,

ethyl ether,

ethyl formate,

ethyleneglycol,

formamide,

isobutyl acetate,

isopropyl acetate,

methyl acetate,

methylbutyl ketone,

methylcyclohexane,

methylethyl ketone,

methylisobutyl ketone,

N,N-dimethylacetamide,

N,N-dimethylformamide,

nitromethane,

propyl acetate,

pyridine,

sulfolane,

tert-butylmethyl ether,

tetrahydrofuran, and

tetralin,

by cooling said solvent mixture from a temperature selected to allow said 5-azacytidine to dissolve completely to about ambient temperature; and

isolating the recrystallized 5-azacytidine.

2. The method of claim 1 wherein said polar aprotic solvent is selected from the group consisting of dimethylsulfoxide, dimethylformamide, dimethylacetamide, and N-methylpyrrolidinone.

3. The method of claim 2 wherein said polar aprotic solvent is dimethylsulfoxide.

4. The method of claim 1 wherein said co-solvent is acetonitrile.

5. The method of claim 1 wherein said co-solvent is ethanol.

6. The method of claim 1 wherein said co-solvent is methylethyl ketone.

7. The method of claim 1 wherein said co-solvent is 2-propanol (isopropyl alcohol).

8. The method of claim 1 wherein said co-solvent is 1-propanol.