An improved process for the preparation of a compound of formula, which comprises the steps of: (a) reacting isovaleraldehyde of formula and alkyl cyanoacetate of formula optionally in presence of salts of weak acid and weak base or weak base in a suitable solvent to get 2-cyano-5-methyl-hex-2-enoic acid alkyl ester of formula; wherein R 1 = Linear or branched alkyl C 1 -C 4 (b) reacting 2-cyano-5-methyl-hex-2-enoic acid alkyl ester of formula with a suitable cyanide source in water or in an organic solvent or mixture thereof to get 2-isobutylsuccinonitrile of formula; (c) obtaining optionally 2-isobutylsuccinonitrile of formula by reacting isovaleraldehyde of formula and alkyl cyanoacetate of formula in presence of suitable cyanide source in water or in an organic solvent or mixture thereof in a single step; (d) converting 2-isobutylsuccinonitrile of formula to racemic 3-cyano-5-methyl-hexanoic acid or salt thereof of formula with the genetically modified nitrilase enzyme Nit 9N_56_2 in water or optionally with an organic co-solvent at appropriate pH and temperature; wherein R 2 = Cationic counter ion, hydrogen, alkali metal salt, alkaline earth metal salt, ammonium salt, alkyl ammonium salt, and organic amine salt (e) converting racemic 3-cyano-5-methyl-hexanoic acid or salt thereof of formula to racemic alkyl 3-cyano-5-methyl-hexanoate of formula by treatment with alcohol (R 3 OH) and acidic catalyst or alkyl halide (R 3 X) in presence of a base in a suitable solvent or a mixture of solvents thereof; wherein R 3 = Linear or branched alkyl C 1 to C 4, or C 7 to C 10 aryl or alkyl aryl (f) obtaining -alkyl 3-cyano-5-methyl-hexanoate of formula (VIII) and -3-cyano-5-methyl-hexanoic acid or salt thereof of formula by enzymatic enantioselective hydrolysis in water or organic solvent or a mixture thereof from racemic alkyl 3-cyano-5-methyl-hexanoate of formula; wherein R 2 = Cationic counter ion hydrogen, alkali metal salt, alkaline earth metal salt, ammonium salt, alkyl ammonium salt, and organic amine salt and R 3 = Linear or branched alkyl C 1 to C 4 or C 7 to C 10 aryl or alkyl aryl (g) obtaining optionally the compound of formula by racemizing unwanted -3-cyano-5-methyl-hexanoic acid or salt thereof of formula or substantially enriched -3-cyano-5-methyl-hexanoic acid salt thereof of formula in presence of a base in solvent or a mixture thereof; (h) converting -alkyl 3-cyano-5-methyl-hexanoate of formula (VIII) to pregabalin of formula by hydrolyzing ester group with suitable alkali or alkaline earth metal base followed by hydrogenation optionally in one pot in a solvent selected from water or organic solvents or a mixture thereof in presence of a suitable hydrogenation catalyst. (a) reacting isovaleraldehyde of formula and alkyl cyanoacetate of formula optionally in presence of salts of weak acid and weak base or weak base in a suitable solvent to get 2-cyano-5-methyl-hex-2-enoic acid alkyl ester of formula; wherein R 1 = Linear or branched alkyl C 1 -C 4 (b) reacting 2-cyano-5-methyl-hex-2-enoic acid alkyl ester of formula with a suitable cyanide source in water or in an organic solvent or mixture thereof to get 2-isobutylsuccinonitrile of formula; (c) obtaining optionally 2-isobutylsuccinonitrile of formula by reacting isovaleraldehyde of formula and alkyl cyanoacetate of formula in presence of suitable cyanide source in water or in an organic solvent or mixture thereof in a single step; (d) converting 2-isobutylsuccinonitrile of formula to racemic 3-cyano-5-methyl-hexanoic acid or salt thereof of formula with the genetically modified nitrilase enzyme Nit 9N_56_2 in water or optionally with an organic co-solvent at appropriate pH and temperature; wherein R 2 = Cationic counter ion, hydrogen, alkali metal salt, alkaline earth metal salt, ammonium salt, alkyl ammonium salt, and organic amine salt (e) converting racemic 3-cyano-5-methyl-hexanoic acid or salt thereof of formula to racemic alkyl 3-cyano-5-methyl-hexanoate of formula by treatment with alcohol (R 3 OH) and acidic catalyst or alkyl halide (R 3 X) in presence of a base in a suitable solvent or a mixture of solvents thereof; wherein R 3 = Linear or branched alkyl C 1 to C 4, or C 7 to C 10 aryl or alkyl aryl (f) obtaining -alkyl 3-cyano-5-methyl-hexanoate of formula (VIII) and -3-cyano-5-methyl-hexanoic acid or salt thereof of formula by enzymatic enantioselective hydrolysis in water or organic solvent or a mixture thereof from racemic alkyl 3-cyano-5-methyl-hexanoate of formula; wherein R 2 = Cationic counter ion hydrogen, alkali metal salt, alkaline earth metal salt, ammonium salt, alkyl ammonium salt, and organic amine salt and R 3 = Linear or branched alkyl C 1 to C 4 or C 7 to C 10 aryl or alkyl aryl R 2 = Cationic counter ion hydrogen, alkali metal salt, alkaline earth metal salt, ammonium salt, alkyl ammonium salt, and organic amine salt and R 3 = Linear or branched alkyl C 1 to C 4 or C 7 to C 10 aryl or alkyl aryl (g) obtaining optionally the compound of formula by racemizing unwanted -3-cyano-5-methyl-hexanoic acid or salt thereof of formula or substantially enriched -3-cyano-5-methyl-hexanoic acid salt thereof of formula in presence of a base in solvent or a mixture thereof; (h) converting -alkyl 3-cyano-5-methyl-hexanoate of formula (VIII) to pregabalin of formula by hydrolyzing ester group with suitable alkali or alkaline earth metal base followed by hydrogenation optionally in one pot in a solvent selected from water or organic solvents or a mixture thereof in presence of a suitable hydrogenation catalyst.