The trans-3-amino-2-piperidineacetic acid derivative (I), obtained as a 5:1 mixture of (2S,3R)- and (2R,3S)-isomers, was condensed with cyclohexyl isocyanate (II) to produce urea (III). Base-catalyzed cyclization of (III) gave rise to the dioxo pyridopyrimidine (IV). Acid cleavage of the Boc group of (IV) afforded the corresponding mixture of enantiomeric trans-amines (V). Acylation of amines (V) with N-Boc-L-tryptophan (VI) by means of BOP as the coupling reagent furnished the corresponding mixture of diastereomeric amides from which the target isomer was isolated by preparative TLC.