(4S)-4-[(4R)-4-benzyl-5-oxotetrahydrofuran-(2R)-2-yl]-4-[bis(tert-butoxycarbonyl)amino]butyric acid

[(1S)-1-[(4R)-4-benzyl-5-oxotetrahydrofuran-(2R)-2-yl]-4-(tert-butyldimethylsilanyloxy)butyl]carbamic acid tert-butyl ester

[4-butylcarbamoyl-(1S)-1-[3-(tert-butyldimethylsilanyloxy)propyl]-(2R)-2-hydroxybutyl]carbamic acid tert-butyl ester

(2S)-N'-(2-tert-butoxycarbonylamino-5-hydroxy-pentanoyl)-N-methyl-hydrazinecarboxylic acid benzyl ester