ice the mixture was stirred at room temperature for 30 minutes and then diluted with ethyl acetate it was then washed with water and then with an aqueous solution of sodium thiosulfate after which it was dried over anhydrous sodium sulfate and evaporated to dryness under reduced pressure the residue was purified by column chromatography through silica gel eluted with chloroform and methanol in proportions ranging from pure chloroform to a 95 5 by volume mixture it was then further purified by chromatography through a silica gel lobar column merck size b eluted with a 90 7 3 by volume mixture of chloroform isopropanol and methanol to give 530 mg of the title compound 1 47 g of 2 2 dimethyl 1 3 dioxolan 4 ylmethyl chloroformate prepared as described in the preparation was added dropwise in two portions to an ice cooled solution of 0 60 g of milbemycin d and 1 ml of pyridine in 10 ml of ethyl acetate the mixture was allowed to react at the same temperature for 1 hour at the end of which time ethyl acetate was added the mixture was then washed in turn with water an aqueous solution of potassium bisulfate an aqueous solution of sodium bicarbonate and an aqueous solution of sodium chloride and.