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Route to the synthesis of enantiomerically pure ethyl ( S )-3-cyano-5-methylhexanoate, ( S )- 5 , a key chiral intermediate for Pregabalin has been improved. The racemic β-cyano diester,  3  was prepared in 98% purity via gelatine catalysed Knoevenagel condensation of diethylmalonate with isovaleraldehyde followed by hydrocyantion of α,β-unsaturated diester  14  using acetone cyanohydrin and K 2 CO 3 . Racemic diethyl 2-(1-cyano-3-methylbutyl)malonate,  rac - 3 , has been resolved using lipase from  Thermomyces lanuginosus  immobilised in form of crosslinked enzyme aggregates, CLEAs. The CLEAs were made by employing commercial soymilk as an additional protein source and a reaction was carried out in a moving basket reactor. The immobilised enzyme was found to be stable in many organic solvents and temperature up to 50 °C. The resolution reaction was studied in a basket reactor at 50% substrate loading in calcium acetate buffer, pH 7.5 at 30 °C by using 20% w/w enzyme loading. The apparent kinetic parameters were Vmax,app= (8.74 ± 0.43) mM/h/g and Km,app= (1.5 ± 0.07) M (correlation coeff.  r  = 0.98). The desired ethyl ( S )-3-cyano-5-methylhexanoate, ( S )- 5  is obtained in 90-92% theoretical yield and  e.e  &gt; 99%. The advantages of this improved process are mild reaction conditions; an alternate method for hydrocyanation step avoiding the use of highly toxic potassium cyanide at large scale operation and an immobilised enzyme that can be reused for at least 11 recycles.

Preparation of enantiopure pregabalin intermediate using cross linked enzyme aggregates (CLEAs) in basket reactor