"(2S,4R)-tert-butyl 2-((tert-butoxycarbonyl)amino)-4-fluoro-5-oxo-"
"(2S,4R)-tert-butyl 2-((tert-butoxycarbonyl)amino)-4-fluoro-5-oxo-"
"(2S,4R)-tert-butyl 2-((tert-butoxycarbonyl)amino)-4-fluoro-5-oxo-"
"(2S,4R)-tert-butyl 2-((tert-butoxycarbonyl)amino)-4-fluoro-5-oxo-"