(4R,10aR)-4-Methyl-3,4,10,10a-tetrahydro-1H-pyrazino[1,2-a]indole-2,7-dicarboxylic acid 2-tert-butyl ester (300 mg, 0.9 mmol) was dissolved in dichloromethane (5 mL). N-Butylamine (0.45 mL, 4.5 mmol), 4-ethylmorpholine (0.57 mL, 4.5 mmol) and BOP (0.42 g, 0.95 mmol) was added and the mixture was stirred for 16 h at room temperature. The mixture was added to 1 N hydrochloric acid (20 mL) and extracted with diethylether (2×50 mL). Organic phases were pooled, washed with water, 2 N sodium bicarbonate, water and brine to be finally dried with MgSO4. The solvents were removed in vacuo to yield the title compound as colorless foam (346 mg, 98%); ISP-MS: m/e=332.3 (M+H+).
