Prednisolone-α-cyclodextrin-star poly(ethylene glycol) polypseudorotaxane with delayed pH-sensitivity as a targeted drug delivery system.

The acylation of prednisolone 20-hydrazone with star poly(ethylene glycol) tetracarboxylic acid (M = 20,000) has been used to prepare the corresponding pH-sensitive conjugate. With α-cyclodextrin, this conjugate forms a polypseudorotaxane, which was characterised by means of (1)H NMR spectra, powder X-ray diffraction patterns and STM microscopy. The rate of acid-catalysed hydrolysis of the conjugate was studied under in vitro conditions in model media of hydrochloric acid solutions, phosphate and acetate buffers (pH 2-5.8). The acid-catalysed hydrolysis (at pH 2) of the polypseudorotaxane was ca 3.5 times slower than that of the original conjugate. After 1h in this medium, 86% of the covalently attached prednisolone remained unchanged. The prepared polypseudorotaxane represents a promising peroral transport system of prednisolone with a pH-sensitive linker with delayed acid-catalysed hydrolysis thanks to protection at the molecular level using α-cyclodextrin.