Ring-opening metathesis polymerization of steroid-conjugated norbornenes and gradual release of estrone from a polymer film

Steroids (estrone, estradiol, ursodeoxycholic acid, chenodeoxycholic acid, cortisone, prednisone, and dexamethasone) were reacted with either 5-norbornene-2-carboxylic acid chloride or 5-norbornene-2-methanol to form new norbornene derivatives with bioactive and sterically demanding steroid residues bound with an ester linkage. These norbornene-based monomers were polymerized by a ring-opening metathesis polymerization initiated by a ruthenium-carbene complex (Grubbs catalyst) or a ruthenium-vinylidene complex. With a few exceptions, the polymers were soluble in THF, and casting the solution produced films. Solid-state hydrolysis of the estrone-conjugated polymer film showed a slow but steady release of estrone under mild conditions (pH 5.5 or 3.0 at 37 °C).