Antiinflammatory polymer-bound steroids for topical applications. I: Synthesis and characterization

Covalent binding of hydrocortisone and dexamethasone to hydrophylic biocompatible macromolecular carriers through hydrolizable carbonate linkage was investigated according to two complementary strategies. (a) Radical copolymerization of hydrocortisone-21C-vinylcarbonate with N-vinylpyrrolidone (NVP,60°C), or N-[tris(hydroxymethyl)methyl]acrylamide (THMMA, 50°C) in dimethylacetamide solution: In spite of a nearly zero reactivity ratio for the steroid monomer which behaves as a degradative transfer agent—CT ∼ 5.7 × 10−2 and 6.8 × 10−3 for NVP and THMMA, respectively–this process may afford fairly high molecular weight polymers (Mw ≃ 104–105) with high enough hydrocortisone content (0.03–0.10 mole.fraction). (b) Condensation of the hydrocortisone or dexamethasone-21C-chloroformates onto poly(oxyethylene glycol) (Mn = 6220) or hydroxypropylcellulose (HPC, Mw = 1.35 × 105) in tetrahydrofuran solution (30°C): This straightforward process is of low efficiency (yields >50%), and only HPC derivatives show good chemical homogeneity.