Results and discussions

:H and 13 C NMRs showed the complete removal of the ethyl and TFA groups and also consistent with structure (Figures 1, 2). Measured specific viscosity in

Figure 1: :H NMR of copolymer-1.

water, 1% solution at 25°C and calculated the viscosity molecular weight [15].

Also analyzed the polymer by light scattering (GPC MALLS) and determined molecular weight (Mw) (Figure 3). Molecular weight profile and polydispersity are similar to that of the old method. Measured specific rotation in water (1% solution) at 25°C and the results are comparable. Amino acid ratios are determined by amino acid analysis and are within the expected range (Table 1).

Figure 2: C NMR of copolymer-1.
Table 1: Molecular Weights, Polydispersity, Specific Rotation, Amino Acid Analysis and Yield for Copolymer-1.

Viscosity Molecular Weight

GPC MALLS Molecular Weight

Polydispersity (Mw/Mn)

Specific Rotation

Amino Acid Analysis

% Yield





Ala: 5.70 Glu: 1.90 Lys: 4.80 Tyr: 1.00


Figure 3 shows the GPC MALLS profile for copolymer-1 and is consistent with the expected molecular weight and polydispersity.

The main purpose of the synthesis of copolymer-1 described above was to eliminate the usage of hazardous reagents (HBr/acetic acid and piperidine) and make the process more greener and less labor intensive. Aqueous alkaline condition is used in the deprotection step of Poly (L-Ala, y-Et-L-Glu, Ne-TFA-L-Lys, L-Tyr) copolymer to remove the TFA group from lysine and the ethyl group from glutamic acid in a single reaction. No racemization occurs during the removal of these protecting groups, as is apparent from a comparison of the specific rotation of copolymer-1 prepared via benzyl protected glutamic acid (-65° + 5°) with that of ethyl protected (Table 1).




Figure 3: GPC MALS analysis instrument type: DAWN EOS; Cell type: K5;

Laser wavelength: 690.0 nm; Solvent: 20mM Sodium Phosphate +130mM Sodium Chloride.

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