1 g of the compound obtained in Step A is dissolved in 20 ml of anhydrous tetrahydrofuran, followed, at -7° C., by addition of 5 ml of 1M borane solution in tetrahydrofuran, and the mixture is stirred overnight. 0.5 g of potassium carbonate and 10 ml of a mixture of methanol and water (1:1 v/v) are then added. The mixture is maintained at 60° C. for 2 hours and then cooled and evaporated under vacuum. The residue is taken up in water and extracted with ethyl ether, and the organic phase is washed with water, then with saturated aqueous sodium chloride and dried over anhydrous sodium sulphate. It is evaporated to dryness and the residue is taken up in pentane. The expected product is thus obtained.
