The reaction of 4-[1-(4-chlorophenyl)-1-(2-pyridyl)methoxy]piperidine (I) with ethyl 4-bromobutyrate (II) by means of K2CO3 in refluxing acetone gives the corresponding condensation product (III), which is then hydrolyzed with NaOH in ethanol/water yielding compound (IV).
A new synthesis of betotastine has been developed: The racemic 4-[1-(4-chlorophenyl)-1-(2-pyridyl)methoxy]piperidine (I) is submitted to optical resolution with N-acyl amino acids such as N-acetyl-L-phenylalanine (preferred), N-acetyl-L-leucine, N-(benzyloxycarbonyl)-L-phenylalanine, N-(benzyloxycarbonyl)-L-valine, N-(benzyloxycarbonyl)-L-threonine, N-(benzyloxycarbonyl)-L-serine or with (2R,3R)-3-(5-chloro-2-nitrophenylsulfanyl)-2-hydroxy-3-(4-methoxyphenyl)propionic acid (preferred) or (2R,3R)-2-hydroxy-3-(4-methoxyphenyl)-3-(2-nitrophenylsulfanyl)propionic acid as chiral intermediates, yielding the (S)-isomer (II). The condensation of (II) with ethyl 4-bromobutyrate (III) by means of a base such as Na2CO3, NaHCO3, K2CO3 or KHCO3 gives the expected 4-(1-piperidinyl)butyric acid ester (IV), which is finally hydrolyzed with NaOH or KOH in aqueous ethanol or methanol.