Certain prostaglandin type C compounds and processes for their preparation have been disclosed in the literature. PGC.sub.2 is disclosed by R. L. Jones, Brit. J. Pharmacol. 45, 144P - 145P (1972) and Biochim. Biophys. Acta, 280 (1972) 588-601, wherein PGC.sub.2 is reported to have 3-fold greater depressor activity than its precursors, the corresponding PGA.sub.2 compound, and 50-fold greater activity than the corresponding PGB.sub.2 compound. Crabbe et al., Tetrahedron Letters No. 32, pp 3021-3022 (1973) have reported the synthesis of the corresponding 9.alpha.-hydroxy PGC.sub.2 (9.alpha.,11.alpha.-dihydroxyprosta-5-cis-11,13-trans-trienoic acid) and certain of the intermediates disclosed herein.
Each of the above-mentioned known prostaglandins is a derivative of prostanoic acid which has the following structure and atom numbering: ##SPC1##
See, for example, Bergstrom et al., Pharmacol, Rev. 20, 1 (1968), and references cited therein. A systematic name for prostanoic acid is 7-[(2.beta.-octyl)-cyclopent-1.alpha.-yl]-heptanoic acid.
PGA.sub.1 has the following structure: ##SPC2##
PGA.sub.2 has the following structure: ##SPC3##
PGB.sub.1 has the following structure: ##SPC4##
PGB.sub.2 has the following structure: ##SPC5##
PGC.sub.1 has the following structure: ##SPC6##
PGC.sub.2 has the following structure: ##SPC7##
In the above formulas, as well as in the formulas given hereinafter, broken line attachments to the cyclopentane ring indicate substituents in alpha configuration, i.e., below the plane of the cyclopentane ring. Heavy solid line attachments to the cyclopentane ring indicate substituents in beta configuration, i.e., above the plane of the cyclopentane ring.
The side-chain hydroxy at C-15 when drawn with a broken line as in the above formulas and some of those which follow hereinafter is in the S configuration, although .alpha. is preferred as a designation for this configuration. The side chain hydroxy at C-15 when drawn with a heavy solid line as in some of the formulas which follow hereinafter is in the R configuration. This configuration is also known as epi, although .beta. is preferred as a designation. See Nature, 212, 38 (1966), Hamberg, European J. Biochem, 6, 147 (1968), and Weinheimer et al., Tetrahedron letters 49, 5185 (1969), and references cited in those, for discussions of the stereochemistry of these prostaglandins.
Molecules of the known prostaglandins each have several centers of asymmetry, and can exist in racemic (optically inactive) form and in either of the two enantiomeric (optically active) forms, i.e., the dextrorotatory and levorotatory forms. As drawn, the above formulas represent optically active compounds each with the same absolute configuration as optically active prostaglandin E.sub.1 (PGE.sub.1) obtained from certain mammalian tissues, for example, sheep vesicular glands or human seminal plasma. See, for example, Bergstrom et al., J. Biol. Chem, 238, 3555 (1963), Horton, Experientia, 21, 113 (1965), Bergstrom et al., Pharmacol. Rev. 20, 1 (1968), and references cited in those. The mirror image of each of above formulas represents the other enantiomer of that prostaglandin, The racemic form of a prostaglandin contains equal numbers of both enantiomeric molecules, and one of the above formulas and the mirror image of that formula is needed to represent correctly the corresponding racemic prostaglandin. For convenience hereinafter, use of the term PGC.sub.2 and the like, will mean the optically active form of that prostaglandin with the same absolute configuration as PGE.sub.1 obtained from mammalian tissues. When reference to the racemic form of one of those prostaglandins is intended, the word "racemic" of "dl" will preceed the prostaglandin name.