Betamethasone: Betamethasone is 9a-fluoro-16/-methyl-11 /,17,21-trihydroxypregna-1,4-dien-3,20-dione, or simply 9a-fluoro-16/-methylprednisolone (27.1.52). As seen from the chemical name of the drug, betamethasone only differs from dexamethasone in the orientation of the methyl group at C16. The proposed method of synthesis differs from the other method in a number of details and successive reactions besides the first stage, in particular concerning the addition of the methyl group at C16 of the steroid ring. Betamethasone, like dexamethasone, is synthesized from 3a-acetoxy-16-pregnen-11,20-dione; however, the methyl group at C16 of the steroid ring is not reacted with methylbromide, but rather is reacted with diazomethane followed by hydrogenation of the double bond between carbon atoms C16-C17 of the steroid ring using a palladium on carbon catalyst, which results in the corresponding /-orientation of the introduced methyl group .
As an isomer of dexamethasone, betamethasone is primarily used locally to treat dermatitis and eczema, and also as an anti-itch agent. Synonyms of this drug are betacor, celestan, supercortene, and others.
Triamcinolone: Triamcinolone, 9a-fluoro-11b,16a,17,21-tetrahydroxypregna-1, 4-dien-3,20-dione (27.1.61), differs from dexamethsone in terms of chemical structure in that the a methyl group at C16 is replaced with a hydroxyl group. It is synthesized from the 21-O-acetate of hydrocortisone 27.1.17. In the first stage, both carbonyl groups of this compound undergo ketalization by ethylene glycol. Next, the hydroxyl group in the resulting diketal 27.1.53 is replaced with chlorine using thionyl chloride, and the product undergoes dehydrochlorination using an alkaline, during which the 21-O-acetyl group also is hydrolyzed. Acetylating the hydroxyl group once again with acetic anhydride gives a triene 27.1.54. Reacting this with osmium tetroxide gives the vicinal diol 27.1.55. The secondary hydroxyl group at C16 of this product undergoes acetylation by acetic anhydride in pyridine, which forms the diacetate 27.1.56. Treating the product with N-bromoacetamide in chloric acid gives a bromohydrin
(27.1.57), which upon reaction with potassium acetate is transformed to an epoxide
(27.1.58). Opening of the epoxide ring, using hydrofluoric acid, gives the corresponding 9-fluoro-11-hydroxy derivative 27.1.59. Upon microbiological dehydrogenation, the C1-C2 bond is oxidized to a double bond, forming triamcinolone acetate (27.1.60), the acetyl group of which is hydrolyzed, forming the desired triamcinolone (27.1.61) [30-32].
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