5,8,13,17,22,25-Hexaoxanonacosanedioic acid,15-[4-[[(1,1-dimethylethyl)diphenylsilyl]oxy]-1,4-dioxobutoxy]-7,23-bis[[4-[2-hydroxy-1-(hydroxymethyl)ethoxy]-1,4-dioxobutoxy]methyl]-4,9,12,18,21,26-hexaoxo-, bis[2-hydroxy-1-(hydroxymethyl)ethyl] ester