Figure 2.

Synthesis of Chol–SIB–PEG conjugates.

Notes: The synthesis of Chol–SIB–PEG can be divided into three steps. Chol–COCl (A) was reacted with para-hydroxy benzaldehyde in anhydrous dichloromethane at room temperature under argon in the presence of N-Ethyldiisopropylamine to synthesize Chol–CHO (B). (II) Chol–CHO (B) and para-phenylenediamine were reacted in the methylbenzene with gentle stirring at 120°C in oil bath overnight to synthesize Chol–SIB–NH₂ (C). Finally, Chol–SIB–PEG (D) was synthesized by conjugating C with HOOC–PEG–COOH in the presence of HATU, DIPEA, and EDC.

Abbreviations: Chol, cholesterol; DIPEA, N,N-diisopropylethylamine; DCM, dichloromethane; HATU, 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b]pyridinium 3-oxide hexafluorophosphate; SIB, Schiff base; EDC, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride; PEG, polyethylene glycol.