What is "-perdesonide"

(R)-Perdesonide is one of the two isomers of perdesonide, a glucocorticoid steroid. There is a dioxolane moiety with a chiral carbon at position 3; this was introduced to reduce mineralocorticoid activity. The (R)-isomer of the acetal has been shown to be the most potent in this class of steroid. Perdesonide resembles clocortolone in that both have two halide atoms; perdesonide has two fluorine atoms and clocortolone has one chlorine atom and one fluorine atom.