Kinetics of equilibration of bisulfite and dexamethasone-21-phosphate in aqueous solution

✍ Scribed by George B. Smith; Leonard M. Weinstock; F. Edward Roberts Jr.; Gerald S. Brenner; Alex M. Hoinowski; Byron H. Arison; Alan W. Douglas

• Publisher: John Wiley and Sons
• Year: 1972
• Tongue: English
• Weight: 898 KB
• Volume: 61
• Category: Article
• ISSN: 0022-3549
• DOI: 10.1002/jps.2600610508

✦ Synopsis

Dexamethasone phosphate in aqueous solution is susceptible t o reversible bisulfite addition to form an A-ring-substituted sulfonic acid salt, sodium 16~~-methyl-9~-fluorohydrocortisone-I-sulfonate-21-phosphate. Addition of bisulfite and dissociation of adduct proceed at comparable rates in neutral solution. The addition is a second-order reaction in which sulfite ion and monoanionic dexamethasone phosphate are the major participants; that is, a long-range effect of the steroid phosphate group on the A ring is observed. The adduct dissociation is a second-order general-base-catalyzed reaction in which dianionic adduct is more reactive than trianionic adduct. A large isotope effect was observed for dissociations of protonated and C2-deuterated adducts. Strong dependence of equilibrium steroid composition on temperature was correlated with the temperature dependence of the ionization constant of water.

Keyphrases 0 Dexamethasone phosphate and bisulfite-equilibra-