[C:1]([OH:9])(=[O:8])[CH2:2][CH2:3][CH2:4][CH2:5][C:6]#[CH:7].O[N:11]1[C:15](=[O:16])[CH2:14][CH2:13][C:12]1=[O:17].Cl.CN(C)CCCN=C=NCC.C(=O)(O)[O-].[Na+]>C(Cl)Cl>[C:12]1(=[O:17])[N:11]([O:8][C:1](=[O:9])[CH2:2][CH2:3][CH2:4][CH2:5][C:6]#[CH:7])[C:15](=[O:16])[CH2:14][CH2:13]16-heptynoic acid (5) (≧97%, TCI, Portland, Oreg.) (1 g, 7.9 mmol, 1 equiv.) was dissolved in 100 ml of anhydrous methylene chloride. N-hydroxysuccinimide (NHS) (98+%, Acros, New Jersey) (2.3 g, 19.8 mmol, 2.5 equiv.) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) (98+%, Alfa Aesar) (2.3 g, 11.9 mmol, 1.5 equiv.) was added to the above solution. The resulting reaction mixture was stirred at room temperature overnight (18 hours) before 500 ml of a saturated sodium bicarbonate aqueous solution was added to it. The aqueous phase was extracted with 500 ml of ether. The ether extract was combined with the methylene chloride phase, washed with 500 ml of water and 500 ml of brine, and then dried with anhydrous magnesium sulfate. After magnesium sulfate was filtered away and the solvent was removed by rotary evaporation, an off-white solid (1.3 g, 72% yield) was obtained after being further dried overnight under vacuum. This solid was then used directly in the next step.
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