Serotonin hydrochloride (1.000 g) and N-phenyl-6-oxo-heptanamide (1.289 g) were stirred in methanol (47 mL) under a nitrogen atmosphere and treated with sodium cyanoborohydride (0.444 g), excluding light from the reaction. After 4 d at ca. 23° C., a solution of sodium bicarbonate (1.00 g) in water (25 mL) was added. One hour later, the reaction was diluted with water (75 mL) and extracted with 1:4 2-propanol:dichloromethane (3×75 mL). The combined extracts were dried (Na2SO4), filtered, and concentrated in vacuo to a foaming oil which was chromatographed using 5:20:80 triethylamine:ethanol:ethyl acetate, isolating the component with an Rf of 0.3. The resulting oil was twice reconcentrated in vacuo from ethanol (100 mL) and then redissolved in ethanol (100 mL). This solution was treated with 1:9 concentrated hydrochloric acid: ethanol (6 mL), concentrated in vacuo reconcentrated from ethanol (100 mL) to an oil, and the oil placed under vacuum to yield the title compound as a solid (1.80 g).
