Pseudomonic acid (10.00 g, 20 mmole) was dissolved in isobutyl methyl ketone (100 ml) at 40° C. Calcium-2-ethyl-hexanoate (3.32 g, 10 mmole) was suspended in water (50 ml). (It is possible to obtain a solution by using a larger amount of water or an alcohol/water mixture). The solution of pseudomonic acid was added to the calcium-2-ethyl-hexanoate suspension, and the two phase system were stirred for 24 hours. The two phases were then separated, isobutyl methyl ketone (25 ml) was added to the aqueous phase, and stirred for 10 minutes. The two resulting phases were separated, and any traces of isobutyl methyl ketone was evaporated from the aqueous phase. The aqueous mupirocin calcium suspension was cooled in a refrigerator at 5° C. The solid mupirocin calcium dihydrate was filtered, washed with water (20 ml) and dried under vacuum at 35° C. for 14 hours. The mass of product was 7.95 grams. Assay 97.72%, water: 3.45%.
