The use of radioisotopically labelled methyl esters in the determination of the 15-epimer content of prostaglandins

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Abstract
The quantitative determination of the 15-epimer content of prostaglandins by formation of their isotopically-labelled methyl esters is described. Either [3H]dimethyl sulphate or [14C]diazomethane are used as esterification reagents. The reaction products are separated by thin layer chromatography and the epimer ratio determined by scintillation counting of the labelled ester zones. The accuracy of the technique is illustrated by the determination of 15-epimer in ICI 74 205, a close analogue of PGF2α. Evidence for the uncatalysed reaction of diazomethane with the alcoholic hydroxyl groups of prostaglandin molecules, which could be significant in other prostaglandin analysis techniques (e.g. g.l.c.) which depend on quantitative esterification with this reagent, is also presented.