(3R,3aS,6aR)-tetrahydro-2H-furo[2,3-b]furan-3-yl (2S,3R)-4-(4-amino-N-isobutylphenylsulfonamido)-3-hydroxy-1-phenylbutan-2-ylcarbamate
(3R,3aS,6aR)-hexahydrofuro[2,3-b]furan-3-yl N-((1S,2R)-1-benzyl-2-hydroxy-3-(N1-isobutylsulfanilamido)propyl)carbamate