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A solution of 20 mL of a 1.0 M solution of sodium hexamethyldisilamide in tetrahydrofuran was cooled to -78° C. in an ice bath under nitrogen. Then a solution of 3.00 g (20 mmole) of benzyl acetate in 10 mL of dry THF was added and the solution was stirred at 0° C. under nitrogen. After 15 min., 4.5 g (5 mmole) of 17-ethyl-1-hydroxy-12-[2'-(4"-oxo-3"-methoxycyclohexyl)-1'-methylvinyl]-14-t-butyldimethylsilyloxy-23,25-dimethoxy-13,19,21,27-tetramethyl-11,28-dioxa-4-azatricyclo[22.3.1.04,9 ]octacos-18-ene-2,3,10, 16-tetraone (Example 9) in 10 mL of dry tetrahydrofuran was added dropwise over 5 minutes and the solution was stirred at -78° C. under nitrogen. After 3 h, the reaction was quenched by addition of 2 mL of glacial acetic acid in 10 mL of dry tetrahydrofuran. Diethylether was added and the mixture was partitioned between ether and water and the aqueous layer was washed with ether. The organic fraction was sequentially washed with saturated KHCO3 solution and brine, dried over MgSO4, filtered and concentrated. The oily residue was purified by flash chromatography (silica gel, 6 cm×20 cm) using ethyl acetate-hexane to afford 2.58 g (49%) of the title compound as a colorless foam; MS (FAB) 1060 (M+Li).

1. stirringthe solution was stirred at -78° C. under nitrogen
2. waitAfter 3 h
3. customthe reaction was quenched by addition of 2 mL of glacial acetic acid in 10 mL of dry tetrahydrofuran
4. additionDiethylether was added
5. customthe mixture was partitioned between ether and water
6. washthe aqueous layer was washed with ether
7. washThe organic fraction was sequentially washed with saturated KHCO3 solution and brine
8. dry with materialdried over MgSO4
9. filtrationfiltered
10. concentrationconcentrated
11. customThe oily residue was purified by flash chromatography (silica gel, 6 cm×20 cm)