4-Amino-(4S)-4,11-diethyl-3,4,12,14-tetrahydro-4-hydroxy-3,14-dioxo-1H-pyrano[3,4:6,7]indolizino[1,2-b]quinolin-9-yl 1-Piperidinecarboxylic Acid Ester [ 185304-42-1 ]