Poly(ethylene glycol)-Prodrug Conjugates: Concept, Design, and Applications

Figure 8

Synthesis of PEG-Intron by conjugating activated PEG with free amino groups in the interferon. R is lower alkyl group, R₁, R₂, R₃, R₄, R^1, R^2, R^3, R^4, R₅ is H or lower alkyl; and 𝑥, 𝑦, and 𝑧 are selected from any combination of numbers such that the polymer when conjugated to a protein allows the protein to retain at least a portion of the activity level of its biological activity when not conjugated; with the proviso that at least one of R₁, R₂, R₃, and R₄ is lower alkyl (reproduced from [40].