Tautomerism of the enedione system of 15-oxoprostaglandin D2

Abstract

Oxidation of prostaglandin F_2α methyl ester by chromic acid yielded 15-oxoprostaglandin D₂ methyl ester and the Z- and E-tautomers of the isomeric 12-ene, which were separated by partition chromatography and characterized. After equilibration in acidified water the relative proportions of (Z)-12-ene, (E)-13-ene, and (E)-12-ene were 1.0 : 0.88 : 0.89. In contrast, the proportions of the corresponding isomers of the simpler 1-(2-oxocyclopentyl)oct-1-en-3-one were 1.0 : <0.02 : 5.7, indicating that the side chain at C-8 in the prostaglandin merkedly affects the equilibrium position. In both systems the contribution from enolic forms was small.