4-Methylmorpholine → methyl 2-{[(1R,10R,11S,16S)-3-hydroxy-1,11,15,15-tetramethyl-8,8-dioxo-8lambda6-thiatetracyclo[8.8.0.02,7.011,16]octadeca-2,4,6-trien-5-yl]formamido}acetate

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A mixture of (1R,10S,11S,16S)-3-methoxy-11,15,15-trimethyl-8,8-dioxo-8λ6-thiatetracyclo[8.8.0.02,7.011,16]octadeca-2,4,6-triene-5-carboxylic acid (61) (0.20 g, 0.49 mmol), HATU (0.37 g, 0.98 mmol), N-methylmorpholine (0.20 mL, 3.0 mmol) and glycine methyl ester hydrochloride (0.18 g, 1.5 mmol) in THF (10 mL) and DMF (2.0 mL) was stirred at room temperature for 18 h. The THF was evaporated under reduced pressure, the residue was quenched with water and the resulting solid was collected by filtration. The crude product was purified by flash column chromatography on silica gel (CH2Cl2/MeOH, 10:1) to give methyl 2-{[(1R,10R,11S,16S)-3-hydroxy-1,11,15,15-tetramethyl-8,8-dioxo-8λ6-thiatetracyclo[8.8.0.02,7.011,16]octadeca-2,4,6-trien-5-yl]formamido}acetate (92) (0.10 g, 42%) as a white solid. 1H NMR (CDCl3): δ 8.16 (s, 1H), 7.81 (d, 1H), 7.71 (d, 1H), 7.18 (m, 1H), 4.24 (m, 2H), 3.32 (m, 3H), 2.30 (d, 1H), 1.76-1.00 (m, 16H), 0.97 (s, 3H), 0.88 (s, 3H), 0.84 (s, 3H). MS m/z 478 (C25H35NO6S+H+).

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