(-)-1β-methoxycarbonylethyl-1α-ethyl-1,2,3,4,6,7,12,12bα-octahydroindolo[2,3-a]quinolizine

(3R)-1-(2-(1H-indol-3-yl)ethyl)-3-ethyl-4-hydroxy-3-(3-hydroxypropyl)piperidin-2-one

(S)-3-ethyl-1-{2-[1-(tert-butoxycarbonyl)-1H-indol-3-yl]ethyl}-3-(3-hydroxypropyl)-2-piperidinone

(S)-3-ethyl-1-[2-(1H-indol-3-yl)ethyl]-3-(3-{[(1,1-dimethylethyl)diphenylsilyl]oxy}propyl)-2-piperidinone

(3R)-3-ethyl-1-([2-(1H-indol-3-yl)ethyl]-3-{[3-(1,1-dimethylethyl)diphenylsilyl]oxy}propyl)-4-hydroxy-2-piperidinone