Process for producing erythromycin derivative

#The present invention relates to processes for preparing erythromycin derivatives and to intermediates thereof, and particularly relates to a process for preparing 6-O-substituted ketolide derivatives starting from erythromycin and to intermediates thereof.

#Macrolide antibiotics including erythromycin A have a strong antibacterial activity against Gram-positive bacteria, some Gram-negative bacteria, Mycoplasmas and the like, and have been widely used as agents for the treatment of infections caused by these bacteria. Furthermore, many erythromycin derivatives have been synthesized for the purpose of the improvement of pharmacokinetic properties of erythromycin A, and some of them have already been clinically used as excellent antibiotics. For example, clarithromycin (6-O-methylerythromycin A, U.S. Pat. No. 4,331,803) has been widely used as a therapeutic agent of respiratory tract infections due to its excellent biological properties. There has been recently reported the derivatives which are generically called ketolides and have a potent antibacterial activity against macrolide-resistant bacteria. The structural features of these derivatives are such that the cladinose group at the 3-position of erythromycin A has been removed, and converted into a carbonyl group, the hydroxyl group at the 6-position has been alkylated, and the hydroxyl groups at the 11- and 12-postions have been converted into a cyclic carbamate. Among these ketolides, there is 3-deoxy-3-oxo-6-O-((3-quinol-3-yl)prop-2-enyl)-5-O-desosaminyl erythronolide A 11,12-cyclic carbamate (U.S. Pat. No. 5,866,549, and J. Medicinal Chemistry, vol. 43, pp.1045-1049 (2000)), which has a strong antibacterial activity against both of macrolide-sensitive and macrolide-resistant bacteria that cause respiratory tract infections. As mentioned above, this compound is prepared by modifying at three positions, i.e., at the 6-, 3- and 11,12-positions. The preparation process reported is carried out by once converting the carbonyl group at the 9-position into an oxime derivative, modifying at the 6-position and reproducing a carbonyl group at the 9-position, therefore this manufacturing process needs many steps, and is complicated.

#Problems to be Solved by the Invention

#To a solution of 150 g (0.20 mol) of erythromycin A in 0.5 L of toluene were added 75 g (0.54 mol) of potassium carbonate and 75 g (0.85 mol) of ethylene carbonate, and the resulting solution was stirred at 40° C. for 6 days. The solution was cooled, then to the reaction solution were added 0.2 L of toluene and 0.8 L of water, and the resulting solution was extracted. Then, the toluene layer was washed with a saturated aqueous sodium chloride solution and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The resulting residue was crystallized from ether to obtain 38.0 g of the title compound.

#To a solution of 243 g (0.32 mol) of the compound obtained in Example 1 in 1 L of methanol was added 32.0 g of sodium borohydride under ice cooling. After 1 and 2 hours, sodium borohydride was further added thereto in portions of 30.0 g and 23.0 g, respectively. The resulting solution was stirred for 80 minutes, then the ice-bath was removed, and 500 mL of methanol and 17.3 g of sodium borohydride were added thereto (the total volume of sodium borohydride was 2.7 mol). The resulting solution was stirred for 40 minutes, then 4.5 L of ice water was added thereto, and the precipitate was collected by filtration. The precipitate was dissolved in 2.5 L of chloroform, and washed with a saturated aqueous sodium chloride solution. The washed solution was dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure to obtain 232 g of the title compound.

#To a solution of 232 g (0.30 mol) of the compound obtained in Example 2 in 1.2 L of chloroform was added 34.1 g (0.33 mol) of acetic anhydride at room temperature. After having been stirred for 2 hours, the reaction solution was washed with a saturated aqueous sodium bicarbonate solution and water. Drying the organic layer over anhydrous magnesium sulfate and evaporating the solvent therefrom under reduced pressure gave 239 g of the title compound.