Trifluoroacetic acid → 1-(Piperidine-3-carbonyl)piperidine-2-carboxylic acid [4-phenyl-1-(3-phenyl-propyl)-butyl]-amide

1-(1-tert-butoxycarbonylpiperidine-3-carbonyl)-piperidine-2-carboxylic acid [4-phenyl-1-(3-phenyl-propyl)-butyl]-amide (81) (1.35 g; 2.29 mmol) is dissolved in methylene chloride (40 mL) at ambient temperature. Trifluoroacetic acid (20 mL) is added in a slow stream, and the solution is stirred for 4 hours at ambient temperature. The solution is concentrated in vacuo at 40° C. The residue is dissolved in methylene chloride (200 mL) and poured onto saturated sodium bicarbonate solution. The pH is adjusted to 9 with saturated potassium carbonate solution. The mixture is shaken the layers separated. The water layer is extracted with methylene chloride (3×50 mL). The combined organic extracts are washed with water, dried over MgSO4, filtered, and concentrated in vacuo affording the desired product (1.09 g) as an oil.