1) The condensation of 3-methyl-1-[2-(1-piperidinyl)phenyl)butylamine (I) with 2-[3-ethoxy-4-(ethoxycarbonyl)phenyl]acetic acid (II) by means of triphenylphosphine, triethylamine and CCl4 gives the corresponding amide-ester (III), which is then hydrolyzed with NaOH in ethanol/water to the racemic repaglinide. 2) The condensation of amine (I) with 2-[4-(ethoxycarbonyl)-3-hydroxyphenyl]acetic acid (IV) by means of triphenylphosphine as before yields the corresponding amide-ester (V), which is then submitted to ethoxylation with NaH and ethyl bromide in DMF to afford the racemic amide-ester (III), already obtained.
The addition of glycine ethyl ester (I) to 2-propenenitrile (II) by means of KOH in water gives N-(2-cyanoethyl)glycine ethyl ester (III), which is cyclized by means of di-tert-butyl dicarbonate yielding the protected pyrrolidinone (IV). The reduction of (IV) with NaBH4 in ethanol affords the pyrrolidinol (V), which is further reduced with LiAlH4 in THF and protected with di-tert-butyl dicarbonate to give the fully N-protected compound (VI). The oxidation of (VI) with pyridine/SO3 complex yields the pyrrolidinone (VII), which is treated with O-methylhydroxylamine (VIII) to afford the correponding oxime (IX). The deprotection of (IX) with acetyl chloride in cool methanol gives 4-(aminomethyl)pyrrolidin-3-one O-methyloxime (X), which is finally condensed with 7-chloro-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylic acid (XI) by means of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in acetonitrile.