Figure 2.

Synthetic scheme for PEG-GFL-NH-Ret and PEG-GFL-pNA (a) and ¹H NMR spectra of the PEG-GFL-NH-Ret (b) and PEG-8(PA-GFL-OH) (c) intermediates and the PEG-8PA (d) starting material. Solvents: acetone-d₆ for PEG-PA and PEG-PA-GFL; DMSO-d₆ for PEG-GFL-NH-Ret. The multiplets around 7.25 ppm in (c) and (d) were assigned to phenylalanine aromatic protons with an integral value of five protons. The two methyl protons on Ret-NH₂ in spectrum (c) appeared around 1.0 ppm with an integral value of 3. Methyl protons of leucine in (c) and (d) appeared around 0.9 ppm with an integral value of six protons. Two leucine methyl peaks with an integral value of three protons each were observed in spectrum (c), which confirms the conjugation of four drug molecules to side chains of the polymer.