To a solution of 6-O-methylerythromycin A (10 g) in tetrahydrofuran (50 ml ), were added 95 % potassium hydroxide powder (0.87 g ) and 2 - [2 - (2 -ethoxyethoxy ) ethoxy ]ethyl chloroformate (3.60 g) under ice-cooling. After stirring for 3 hours, 95% potassium hydroxide powder (0.24 g ) and 2- [2-(2 -ethoxyethoxy ) ethoxy ]ethyl chloroformate (0.98 g ) were further added thereto and the mixture was stirred for additional 2 days. The post treatment was performed by the same method as the one described in Example 7. The crude product thus obtained was purified by silica gel column chromatography (elution solvent; acetone : n-hexane =7 : 13 - 2 : 3) and then crystallized from chloroform/n-hexane. Thus 6-0-methylerythromycin A 2 '- {2- [2- (2-ethoxyethoxy ) ethoxy]ethyl}carbonate (8.85 g) was obtained as a white powder.
