(R)-Piperazinecarboxylic acid (I) is sequentially protected with 2-(t-butoxycarbonyloxy)imino-2-phenylacetonitrile to produce the 4N-Boc-piperazine (II), and then with cyclohexyl chloroformate, yielding the 1N-cyclohexyl carbamate (III). Selective N-Boc group cleavage in (III) under acidic conditions provides piperazine (IV). This is condensed with the tricyclic chloride (V) to furnish, after chromatographic separation of the isomers, the required intermediate (VI).
Reduction of (R)-ethyl nipecotate (VII) with LiAlH4 yields 3-piperidinemethanol (VIII), which is further protected as the N-Boc derivative (IX) by using Boc2O. Treatment of the piperidine alcohol (IX) with p-toluenesulfonyl chloride and pyridine leads to tosylate (X). Condensation of the sodium derivative of 4-methylimidazole (XI) with tosylate (X) gives rise to a mixture of regioisomeric N-alkylated imidazoles, which are chromatographically separated after derivatization with trityl chloride. The desired isomer (XII) is then deprotected under acidic conditions, giving piperidine (XIII). Finally, EDC-mediated coupling between piperidine (XIII) and the piperazinecarboxylic acid (VI) furnishes the title amide.