Synthesis and structure elucidation of potential 6-oxygenated metabolites of (22R)-6alpha,9alpha-difluoro-11beta,21-dihydroxy-1 6alpha,17alpha-propyl methylenedioxypregn-4-ene-3,20-dione, and related glucocorticosteroids

(22R)-6alpha,9alpha-Difluoro-11beta,21-dihydroxy-16 alpha,17alpha-propylmethylenedioxypregn-4-ene-3,20-dione (rofleponide) is a synthetic glucocorticosteroid with high affinity for the rat thymus Glucocorticoid Receptor and a very high biotransformation rate demonstrated through incubation with a human liver S9 subcellular fraction. Because oxidation in the 6-position is an important metabolic pathway of glucocorticosteroids, the potential 6beta-hydroxy and 6-oxo metabolites of rofleponide were synthesized to be used as reference compounds. Three alternative routes were used to reach the 6-hydroxy compound: (a) a one-step procedure involving allylic oxidation of rofleponide by selenium dioxide, (b) selenium dioxide oxidation of the corresponding 1,4-diene followed by selective 1,2-hydrogenation using Wilkinson's catalyst, and (c) autoxidation of a 3-methoxypregna-3,5-diene derivative. All three routes proceeded stereospecifically. Routes (a) and (c) gave approximately the same overall yield of the 6beta-hydroxy epimer, whereas the overall yield from route (b) was much lower, primarily because of incomplete 1,2-hydrogenation. The 6-oxo compound was prepared through Pfitzner/Moffat oxidation of the 6-hydroxy compound. The stereochemistry of the 6-hydroxy substituent is discussed on the basis of 1H-NMR spectroscopy and supplementary 2D NOESY experiments.