2(1H)-Isoquinolinecarboxylic acid,3-[6,11-bis[(1,1-dimethylethoxy)carbonyl]-18,18-dimethyl-1,16-dioxo-17-oxa-2,6,11,15-tetraazanonadec-1-yl]-3,4-dihydro-6-hydroxy-,9H-fluoren-9-ylmethyl ester