From pregabalin to rac-3-cyano-5-methylhexanoic acid : an easy conversion which valorizes waste pregabalin enantiomer

(S)-(+)-3-Aminomethyl-5-methylhexanoic acid (pregabalin) was converted in one-pot to (S)-(-)-3-cyano-5-methylhexanoic acid (pregabalin nitrile) by N-dichlorination and double dehydrochlorination. The (S) β-cyanoacid was racemized under mild conditions by treatment with a base. This very simple and efficient procedure, applied to (R)-(-)-3-aminomethyl-5-methylhexanoic acid, would enable the recycling of the undesired enantiomer of pregabalin, an anticonvulsant drug manufactured by the synthesis of rac-3-aminomethyl-5- methylhexanoic acid and subsequent classical resolution.