2.3. The synthesis of DSPE-PEG-LA

To offer an active liver targeting function in liposomes, DSPE-PEG-LA was synthesized by acylation reaction of DSPE-PEG-NH₂ and LA under the catalysis of EDC·HCl and NHS. White powders of DSPE-PEG-NH₂ (50 mg, 0.018 mmol) and LA (64.5 mg, 0.18 mmol) were dissolved in 2 mL DMSO, respectively, and stirred at room temperature for 2 h. And then, EDC·HCl (34.5 mg, 0.18 mmol), NHS (20.7 mg, 0.18 mmol), and triethylamine (TEA, 3 μL) were added into the mixture to stirred overnight at room temperature. The reaction solution was dialyzed (MWCO 2000 Da) against deionized water for 24 h. The product was lyophilized to obtain white powder (47.5 mg, yield 84.7%). ¹H NMR (DMSO-d₆): δ 0.85 (s, 6H), 1.23 (s, 64H), 3.31–3.51 (m, 180H, broad), 3.74 (s, 4H), 3.86 (s, 2H), 4.72 (s, 1H), 7.90 (s, 2H). IR (KBr): υ_max 3407, 2917, 2888, 1740, 1660, 1547, 1334, 1111, 721 cm⁻¹.