Triethylamine (29 uL) was added to a solution of tert-butyl (2R)-4-ethyl-2-(piperazin-1-ylcarbonyl)piperazine-1-carboxylate (67.5 mg) in dry dichloromethane (5 ml) followed by 4-chloro phenylisocyanate (35 mg) and the reaction was stirred for 18 h under argon. Methanol (1 ml) was added, the solvent was evaporated and the product purified by chromatography (3-15% MeOH-DCM) to afford the homologated product (91 mg) as a foam. The foam was then dissolved in TFA/DCM (1:1, 6 ml) and stirred for 1 h. The solvent was removed under reduced pressure then taken up in 1M. aqueous sodium hydroxide (30 ml) and extracted with dichloromethane (2×30 ml). The combined organic layers were dried (MgSO4), filtered and evaporated to form the title compound (70 mg) as a white foam.
