A solution of 7-[2-oxo-5-(3-oxooct-1-enyl)-3-(2-tetrahydropyranyloxy)cyclopentyl]heptanoic acid [0.45 g.; prepared as described above in Example 2(g)] in methanol (10 ml.) was added to a stirred 2% w/v aqueous solution of sodium citrate (100 ml.) at -5° C. Potassium borohydride (1.6 g.) was then added portionwise, allowing the pH to change to pH 8 and then maintaining at pH 8 by the addition, when necessary, of quantities of 10% w/v aqueous citric acid solution. When the addition of the potassium borohydride was complete, the solution was stirred for 90 minutes, meanwhile maintaining the pH at pH 8 by means of the addition of further quantities of the citric acid solution, and allowing it to attain room temperature. The solution was then treated with acetone (50 ml.), treated with a further quantity of the citric acid solution to bring the pH to pH 4, saturated with sodium chloride and extracted three times with diethyl ether. The combined ethereal extracts were washed with a saturated solution of sodium chloride in 2N hydrochloric acid, and then with a saturated aqueous solution of sodium chloride, and dried over magnesium sulphate. The solvent was removed in vacuo to give crude 7-[2-hydroxy-5-(3-hydroxyoct-1-enyl)-3-(2-tetrahydropyranyloxy)cyclopentyl]heptanoic acid (0.34 g.), νmax 1700 cm-1, 980 cm-1, which was used as starting material in the following preparation (i) of 7-[2,3-dihydroxy-5-(3-hydroxyoct-1-enyl)cyclopentyl]heptanoic acid without further purification being necessary.
