Under a nitrogen atmosphere, at room temperature, to 1-tert-butyl (2S,3S)-3-((E)-8-heptylsulfanyl-oct-1-enyl)-2-hydroxy-2-(2-methoxy-ethyl)-succinate (210.0 mg, 0.430 mmol) obtained in Step C-6b in DMF (4.2 mL), were added methyl (S)-2-amino-3-(4-but-2-ynyloxy-phenyl)-propionate hydrochloride (148.4 mg, 0.516 mmol), 1-[bis(dimethylamino)methyliumyl]-1H-1,2,3-triazolo[4,5-B]pyridine-3-oxide hexafluorophosphate (179.1 mg, 0.473 mmol), and N,N-diisopropylethylamine (299.0 μL, 1.72 mmol) in order. After stirring for 8 hours, the progress of the reaction was stopped by adding water. The mixture was extracted with ethyl acetate. The aqueous layer was extracted with ethyl acetate. The combined organic layer was then washed with water and a saturated brine, dried over anhydrous sodium sulfate, and then filtered. The solvent was distilled out of the filtrate under reduced pressure. The resulting residue was purified with SP1 (SiO2 cartridge, 20% ethyl acetate/n-hexane, Rf=0.35) to obtain tert-butyl (E)-(2S,3S)-3-[(S)-2-(4-but-2-ynyloxy-phenyl)-1-methoxycarbonyl-ethylcarbamoyl]-11-heptylsulfanyl-2-hydroxy-2-(2-methoxy-ethyl)-undec-4-enoate (No. 6804240; 249.3 mg, 2 steps, 80% yield).
