New 2-chloro-6beta-fluoropregna-1,4-diene-3,20-diones, specif. those of formula (I) and their pharmaceutically acceptable salts and esters, (X is Br, Cl or OQ; Y is Br, Cl, F or H; R1 and R2 are OQ; R3 is alpha-OQ, alpha- or beta-CH3 or H; each Q is H or acyl, or OQ's at 16/17 or 17/21 can together form a ketal, acetal or alkyl orthoester), are prepd. from e.g. 6 beta-fluoro 3,5alpha, 11alpha, 17alpha, 21-pentahydroxypregn-2-ene-20-one-3,5,17,21-tetraacetate-11-mesyl- ate by 3-stage chlorination-dehydrochlorination to 2-chloro-1,4,9(11) triene then addn. of Cl2 etc. across the 9(11) double bond. (I) are powerful anti-inflammatories with less severe side effects than known steroids, and are administered in usual topical, oral or parenteral forms. They also have good antirheumatic activity. In the cotton pellet granuloma test the most active (I) are effective at 0.5-5 mg/kg orally (c.f. 10-50mg for hydrocortisone acetate or methylprednisolone) and they cause no redn. in the wt. of the adrenal glands; no redn. in thymolytic activity and no wt. loss.
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