The general procedure for the synthesis of 1-(9H-fluoren-9-yl)-3-oxo-2,7,10,13,16-pentaoxa-4-azaoctadecan-18-oic acid from 14-amino-3,6,9,12-tetraoxatetradecane-1-oic acid and compounds (CAS: 102774-86-7) was as follows: 14-amino-3,6,9,12-tetraoxatetradecane -1-acid (0.79 g, 3.14 mmol) and K2CO3 (1.04 g, 7.50 mmol) were dissolved in 5.8 mL of water and stirred at room temperature for 15 minutes. Subsequently, N-(9-fluorenylmethoxycarbonyl)succinimide (Fmoc-OSu, 1.28 g, 3.79 mmol) was added, and stirring of the reaction mixture was continued for 24 h, during which the reaction progress was monitored by thin-layer chromatography (TLC, with unfolding agent ratio of CHCl3/MeOH/AcOH, 5:1:0.06). Upon completion of the reaction, the salts were removed by filtration and the filtrate was washed with ether (Et2O) and then acidified with 3N hydrochloric acid to pH 1. The acidified solution was used to extract the target compounds with dichloromethane (DCM). After the extraction was completed, the solvent was removed by distillation under reduced pressure and the resulting crude product was purified by reversed-phase high performance liquid chromatography (RP-HPLC). The fraction containing the target product was collected and lyophilized to give compound 11a (1.08 g, 73% yield). Compound 11a has the chemical formula C25H11NO8, theoretical mass-to-charge ratio [M + H]+ = 474.2, measured mass-to-charge ratio [M + H]+ = 474.9, [M + Na]+ = 496.9.
