Indole-5-carboxylic acid (57 mg, 0.35 mmol) was dissolved in THF(2 ml) and DMF (1 drop), then oxalyl chloride (37 μl, 54 mg, 0.42 mmol) was added. The mixture was stirred at room temperature for 3 hours, the solvent was evaporated under reduced pressure and the residue was dissolved in DMF (2 ml) and added to a stirred solution of 1-phenethylpiperazine (66 mg, 0.35 mmol) and diisopropylethylamine (91 μl, 68 mg, 0.52 mmol) in dichloromethane (1 ml). The mixture was stirred at room temperature for 24 hours, then the solvent was evaporated under reduced pressure. The residue was purified by flash column chromatography on silica gel, eluting with CH2Cl2 /CH3OH/NH3 ; 95:5:0.5 and crystallized from EtOAc/hexane to give the piperazine as microcrystals (32 mg, 27%), mp 105°-108° C.
