On the biosynthesis of 19,20-dehydroprostaglandin E2.

19,20-Dehydro-PGE1 and 19,20-dehydro-PGE2 were recently identified in human seminal fluid. These prostaglandins might be formed by dehydration of 19(R)-hydroxy-PGE1 and 19(R)-hydroxy-PGE2 or, conceivably, by biosynthesis from precursor fatty acids with a terminal double bond. To examine the latter possibility, 5(Z), 8(Z), 11(Z), 14(Z), 19-eicosapentaenoic acid was prepared by chemical synthesis and incubated with microsomes of ram vesicular glands and glutathione (1 mM). The fatty acid was converted to 19,20-dehydro-PGE2, which was identified by GC-MS, by UV analysis after alkali treatment and by oxidative ozonolysis. The semisynthetic 19,20-dehydro-PGE2 and the corresponding compound in human seminal fluid showed the same polarity on reversed phase HPLC and virtually identical mass spectra. The described method might be used to generate 19,20-dehydro-PGE2 for evaluation of its biological effects.