GENERAL STEPS: (R)-N-Fmoc-2-amino-3-hydroxy-3-methylbutanoic acid was synthesized in the following steps: first, (R)-2-((tert-butoxycarbonyl)amino)-3-hydroxy-3-methylbutanoic acid was stripped of the Boc protecting group in a 1:1 trifluoroacetic acid/dichloromethane solution. Subsequently, the Fmoc protection reaction was carried out using 9-fluorenylmethyl-N-succinimidyl carbonate (Fmoc-OSu) and sodium bicarbonate (NaHCO3) in aqueous acetone solution. After completion of the reaction, the product was purified by silica gel column chromatography (eluent ratio of 1:1:98 methanol/acetic acid/chloroform). Finally, the purified product was freeze-dried from aqueous acetonitrile solution to afford the target compound in 78% yield.
