[2S-(2α,3β,4β)]-1-[(1,1-dimethylethoxy)carbonyl]-2-[[[(1,1-dimethylethyl)dimethylsilyl]oxy]methyl]-4-(1-methylethenyl)-3-pyrrolidineacetic acid ethyl ester

ethyl (4S)-N-(t-butyloxycarbonyl)amino-5-hydroxypentanoate

(S)-2-((tert-butoxycarbonyl)amino)-5-ethoxy-5-oxopentanoic acid

ethyl (S)-4-((tert-butoxycarbonyl)(3-methylbut-2-en-1-yl)amino)-5-((tert-butyldimethylsilyl)oxy)pentanoate