Benzoic acid, 2-[6-[2-(1,1-dimethylethoxy)-2-oxoethoxy]-3-oxo-3H-xanthen-9-yl]-4-[[12 -(9H-fluoren-9-yl)-1,5,10-trioxo-3,11-dioxa-6,9-diazadodec-1-yl]amino]-, ethyl ester