合成路线1

Condensation of 2(S)-aminobutyramide (I) with Meldrum’s acid derivative (II) in refluxing acetonitrile affords a mixture of two pyrrolidonecarboxylic acid regioisomers, (III) and (IV), which, without isolation, are subjected to decarboxylation in methyl isobutyl ketone at 120 °C, and then separated by column chromatography .
Alternatively, 2(S)-aminobutyramide (I) –obtained by basification of either its tartrate salt with NH4OH/i-PrOH or its hydrochloride salt with NH3/i-PrOH (2)– is reductively condensed with 5-hydroxy-4-propyl-2-furanone (V) by means of NaBH4 and NaOH in H2O/toluene, yielding the dihydropyrrol-2-one (VI) . Transfer hydrogenation of compound (VI) with ammonium formate and Pd/C in H2O at 50 °C provides the diastereomeric mixture of pyrrolidinones (VII) , which are finally separated by column chromatography or recrystallization .
The intermediate dihydropyrrolone (VII) is alternatively obtained by direct condensation of furanone (V) with 2(S)-aminobutyramide (I) in the presence of H2 and Pd/C in AcOH/i-PrOH or by cyclization of aminoamide (I) with 3-(iodomethyl)hexanoyl chloride (VIII) by means of KOH and tetrabutylammonium bromide in CH2Cl2 .
Amide (VII) is also prepared from 2-(2-oxo-4-propylpyrrolidino)-butyric acid (IX) via activation as the corresponding mixed anhydride with ethyl chloroformate and Et3N in THF, followed by quenching with liquid ammonia .
Similarly, alkylation of optically pure 4(R)-propyl-2-pyrrolidinone (X) with racemic methyl 2-bromobutyrate (XI) in the presence of NaH in THF affords pyrrolidinone butyrate methyl ester (XII) as a diastereomeric mixture. Subsequent ammonolysis of ester (XII) with aqueous ammonia gives the corresponding mixture of amides (XIII) separated using column chromatography .