Process for preparing a pharmaceutically active compound (granisetron)

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The invention claimed is:

1. Process for preparing granisetron, or a pharmaceutically acceptable salt thereof, which comprises: a) cyclisation of a compound of formula (I): ##STR00007## in aninert solvent and at a temperature between 0 100.degree. C., in the presence of a strong acid, in order to yield the compound of formula (II): ##STR00008## b) methylation of the compound of formula (II), with an alkylating agent, in the presence of abase, in an inert solvent and at a temperature between 0.degree. C. 160.degree. C. and optionally obtaining a pharmaceutically acceptable salt thereof.

2. Process as claimed in claim 1, wherein step a) is carried out in a protic solvent or mixture of protic solvents.

3. Process as claimed in claim 1, wherein step a) is carried out at a temperature between 10.degree. C. and 40.degree. C.

4. Process as claimed in claim 1, wherein said alkylating agent is dimethyl sulphate.

5. Process as claimed in claim 1, wherein said alkylating agent is dimethyl carbonate.

6. Process as claimed in claim 1, wherein the solvent of step b) is selected from among methylene chloride, toluene or tetrahydrofuran.

7. Process as claimed in claim 1, wherein said base is sodium or potassium hydroxide in concentrated aqueous solution or in solid form.

8. Process as claimed in claim 1, wherein step b) is carried out in the presence of a phase transfer catalyst.

9. Process as claimed in claim 1, wherein the solvent of step b) is a polar aprotic solvent selected from either dimethylformamide (DMF) or N-methyl-2-pyrrolidonone (NMP).

10. Process as claimed in claim 1, wherein said base is an alkaline carbonate.