Synthesis and pharmacological evaluation of new topical anti-inflammatory steroids.

The purpose of this research was to develop new topical steroid derivatives showing reduced systemic effects. Pregna-16 alpha,17-carboxycyclic acetal derivatives have been recently synthesized by reacting triamcinolone with methyl acetylalkanoate in the presence of a catalytic amount of perchloric acid. In testing for the anti-inflammatory activity of the compounds, rat cotton-pellet granuloma inhibition bioassay and mouse croton-oil-induced ear oedema inhibition bioassay were employed. One of the synthesized compounds, (22R)-9 alpha-fluoro-11 beta,21-dihydroxy-3,20-dioxo-16 alpha, 17-(methyl, methoxycarbonylmethyl)methylenedioxy-1,4-pregnadiene (I), showed more or less the same activity as shown by prednisolone in the granuloma inhibition test. However, compound I showed higher activity in the ear oedema inhibition test when applied topically (ID50 = 0.002 mg), as compared to prednisolone (ID50 = 0.006 mg) and triamcinolone (ID50 = 0.026 mg). When compound I was applied to mice, and thymus involution was measured for judging systemic effects, it was found that compound I did not show any significant thymus involution up to 0.1 mg/mouse (systemic administration) and 0.5 mg/mouse (topical administration). Because of its significantly reduced systemic effects, this compound is a promising topical anti-inflammatory steroid.