Citric Acid → 7-[2-Hydroxy-5-(3-hydroxyoct-1-enyl)-3-(2-tetrahydropyranyloxy)cyclopentyl]heptanoic acid

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Reaction Steps

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 3 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.

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