Pyridine → HCID 122638429, Verbindung

(2S)-2-[9H-Fluoren-9-ylmethoxycarbonyl(methyl)amino]-3-hydroxypropanoic acid (Compound SP823) (920 mg, 2.70 mmol) was dissolved in dehydrated pyridine (2.5 mL), and the reaction solution was concentrated under reduced pressure. This operation was repeated twice, after which the reaction solution was dissolved in dehydrated pyridine (2.5 mL) under a nitrogen atmosphere, and 4,4′-dimethoxytrityl chloride (931 mg, 2.75 mmol) was added at room temperature. The reaction mixture was stirred at the same temperature for 13 hours and then concentrated under reduced pressure. The resulting residue was dissolved in chloroform (15 mL) and washed with saturated sodium bicarbonate (5 mL). The organic layer was dried over sodium sulfate and then concentrated under reduced pressure, and the resulting crude product was purified by normal-phase silica gel column chromatography (1% diisopropylethylamine-containing dichloromethane/methanol) to afford N-ethyl-N-isopropylpropan-2-aminium (S)-2-((((9H-fluoren-9-yl)methoxy)carbonyl)(methyl)amino)-3-(bis(4-methoxyphenyl)(phenyl)methoxy)propanoate (Compound SP816) (1.92 g, 92%).