Diisopropylethylamine → C20-Otbu-glu(otbu)-aeea-aeea-osu

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To a solution of 19-{(S)-1-tert-Butoxycarbonyl-3-[2-(2-{[2-(2-carboxymethoxyethoxy)ethyl-carbamoyl]methoxy}ethoxy)ethylcarbamoyl]propylcarbamoyl}nonadecanoic acid tert-butyl ester (3.1 g) in acetonitrile (50 ml) was added TSTU (1.39 g) and DIPEA (0.91 ml). The mixture was stirred at room temperature over night and then concentrated in vacuo. To the residue was added aqueous 0.1 N HCl (100 ml) and ethyl acetate (200 ml). The layers were separated and the aqueous layer was extracted with ethyl acetate (50 ml). The combined organic layers were washed with water and brine, dried (magnesium sulphate) and concentrated in vacuo to give an oil. Yield 99% (3.4 g).

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