Recently, as the topical anti-inflammatory agents, the 17-esters, 17,21-diesters or 17-ester-21-halides of corticosteroids are used successfully. The mostly favorable and new method on syntheses of these compounds were found on reexamination of several known synthetic methods. It was known that the 17,21-cyclic orthoesters of corticosteroids, which were prepared from the 17,21-dihydroxy compounds by reaction with the orthoester reagent, were converted easily by the weak acid to the 17-monoester compounds. This method was much better than other several direct 17-esterifications, although the 21-ester compound was obtained as by-product. Direct 17-esterifications by known methods did not Rive the desired 17-ester compounds in the satisfactory yield. Also, all direct esterifications of the 16α-methyl corticosteroid, dexamethasone were unsuccessful. Ring opening-reaction of the 17,21-cyclic orthoesters of corticosteroids by employing Ph_3CCl as reagent and DMF as solvent provided the 17-monoester compounds in good yield. Similar reaction of the 17,21-cyclic orthoester compounds by using (CH_3)_3SiCl as reagent and DMF or DMSO as solvent provided directly the 17-ester-21-chloride compounds in good yield. Also, by the use of suitable halide reagents, the corresponding 17-ester-21-halides were obtained. The new route to the 17-ester-21-halides was much industrially better than the known three step method.
