(3S)-methyl 3-(tert-butyldimethylsilyloxy)-2-((S)-1-hydroxy-2-methylpropyl)-1-(4-methoxybenzyl)-5-oxopyrrolidine-2-carboxylate

(2R,3S)-methyl 3-(tert-butyldimethylsilyloxy)-2-((tert-butyl-dimethylsilyloxy)methyl)-5-oxopyrrolidine-2-carboxylate

(2R,3S)-methyl 2-((S)-1-acetoxy-2-methylpropyl)-3-(tert-butyldimethylsilyloxy)-5-oxopyrrolidine-2-carboxylate

(2R,5R)-1-aza-2-(tert-butyl)-5-methoxycarbonyl-6,8-dioxo-3-oxabicyclo[3.3.0]octane

(2R,4S)-2-tert-Butyl-3-ethoxycarbonylacetyl-4-methoxycarbonyl-1,3-oxazolidine