(2R,3S)-1-tert-butyl 2-methyl 2-((S)-1-acetoxy-2-methylpropyl)-3-hydroxy-5-oxopyrrolidine-1,2-dicarboxylate

1-(tert-butyl) 2-methyl (2S,3S,4R)-2-((S)-1-acetoxy-2-methylpropyl)-3-hydroxy-4-methyl-5-oxopyrrolidine-1,2-dicarboxylate

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

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

(2R,3S)-methyl 3-(tert-butyldimethylsilyloxy)-2-((tert-butyldimethylsilyloxy)methyl)-1-(4-methoxybenzyl)-5-oxopyrrolidine-2-carboxylate