4.5 Article

Betulin-containing bioactive amphiphilic copolymers: Synthesis, characterization and self-assembly

Journal

POLYMERS FOR ADVANCED TECHNOLOGIES
Volume 34, Issue 8, Pages 2529-2540

Publisher

WILEY
DOI: 10.1002/pat.6069

Keywords

betulin; bioactive copolymer; oligo(ethylene glycol) methacrylate; RAFT polymerization; self-assembly; self-folding; thermoresponsive polymer

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Betulin, a natural triterpene, has been modified to increase its solubility in water by incorporating it into an amphiphilic copolymer. Well-defined biocompatible copolymers with high betulin content have been synthesized. These copolymers exhibit thermoresponsive behavior and have potential applications in targeted drug delivery.
Betulin, a natural triterpene possessing a wide range of biological activities, has been modified via Steglich esterification to produce a methacrylate derivative capable of participating in radical polymerization. The modification is intended to increase the solubility of betulin, which is almost insoluble in water, by incorporating into the composition of an amphiphilic copolymer. The resulting solubility of betulin in water increased from 8.10(-5) mg/mL to more than 10 mg/mL per betulin. For this, well-defined biocompatible thermoresponsive copolymers with high betulin content have been synthesized through the conventional and RAFT copolymerizations of betulin methacrylate (BeMA) with methoxy oligo(ethylene glycol) methacrylate (MOEGMA). BeMA was more reactive in the BeMA-MOEGMA pair; the resulting copolymers were slightly enriched with BeMA units (r(1) = 1.70, r(2) = 0.93). The copolymers exhibited LCST-type behavior. LCST was tuned by balancing the hydrophobic betulin and hydrophilic OEG fragments. The molecular weight characteristics of polymers and their behavior in aqueous and organic solutions have been studied. Copolymers obtained by conventional polymerization had lower cloud points than RAFT copolymers of the same composition. The copolymers are characterized by low critical micelle concentrations that decrease as the BeMA fraction in the copolymers increases. RAFT copolymers were shown to form unimolecular micelles resistant to dissociation, which is promising for their use in targeted drug delivery.

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