(2S,3S)-2-(4-methyl-2,6,7-trioxa-bicyclo[2.2.2]oct-1-yl)-5-oxo-3-methyl-pyrrolidine-1-carboxylic acid benzyl ester

(2S)-2-(4-methyl-2,6,7-trioxa-bicyclo[2.2.2]oct-1-yl)-5-oxo-2,5-dihydro-pyrrole-1-carboxylic acid benzyl ester

(2S)-2-(4-methyl-2,6,7-trioxa-bicyclo[2.2.2]oct-1-yl)-5-oxo-pyrrolidine-1-carboxylic acid benzyl ester

(2S,3R)-3-phenyl-5-oxo-pyrrolidine-2-carboxylic acid

(2S,3R)-3-(4-chlorophenyl)-5-oxo-pyrrolidine-2-carboxylic acid