合成路线1

Protection of ethyl piperidine-3-carboxylate (I) with di tert-butyl dicarbonate gave carbamate (II), which was alkylated with 4-(bromomethyl)thiazole (III) in the presence of potassium hexamethyldisilazide to afford racemic (IV). Acid deprotection of the Boc group of (IV) yielded amine (V). This was resolved by coupling with (R)-O-acetyl mandelic acid (VI), followed by chromatographic separation of the diastereoisomers. Then, acid hydrolysis of the desired isomer (VII) provided the (S)-piperidine (VIII). Subsequent coupling of (VIII) with N-Boc-D-tryptophan (IX) in the presence of EDC and HOBt gave amide (X). After Boc deprotection of (X), the resulting amine (XI) was coupled with N-Boc-2-aminoisobutyric acid (XII) to produce (XIII). Finally, acid removal of the Boc group of (XIII) furnished the title compound.