A Simplified Process for the Manufacture of Imagabalin Hydrochloride (PD-0332334), an α2δ-Ligand for the Treatment of Generalised Anxiety Disorder

The development of a highly efficient two-step process for the manufacture of the α2δ-ligand imagabalin hydrochloride 1 is described in 50% overall yield from (R)-3-methylhexanoic acid 2. Key aspects of this route include the development of a one-pot process for the synthesis of β-enamine ester 7 and its subsequent diastereoselective hydrogenation with a Ru-(S)-BINAP catalyst. The use of a combination of TFA, ammonium trifluoroacetate, and relatively low pressures in the asymmetric hydrogenation are novel conditions reported for this type of transformation. The simplified process described realised a 4-fold reduction in cost of goods compared with the previously described enabling route.