ACID-CATALYZED AND BASE-CATALYZED DEHYDRATION OF PROSTAGLANDIN-E2 TO PROSTAGLANDIN-A2 AND GENERAL-BASE-CATALYZED ISOMERIZATION OF PROSTAGLANDIN-A2 TO PROSTAGLANDIN-B2

Dehydration of prostaglandin E2(PGE2) to prostaglandin A2 (PGA2) in aqueous solution is catalyzed by hydrogen ion (kdH), hydroxide ion (kdOH)> and quinuclidine (kdA). The values of kdH and kdOH are very similar to those for various known enolization reactions and kdH(H20)/kdn(D20) = 0.6, results that support a mechanism involving rate-determining enolization of PGE2 during dehydration. Isomerization of PGA2 to prostaglandin B2 (PGB2) is general base catalyzed by tertiary amines with kiA(H20)/kiA(D20) = 1.1. The rate constants kiA and kiOH for loss of PGA2 are equal to those for formation of PGB2 and it is suggested that C-12 proton abstraction is rate determining in the reaction sequence PGA2 → PGC2 → PGB2. © 1979, American Chemical Society. All rights reserved.