(2R,3S,8S)-8-ethoxycarbonyl-2-hydroxymethyl-5,6-dimethyl-9-oxo-1-aza-bicyclo[4.3.0]non-5-ene

(2S,3S,4S)-4-Benzyl-3-tert-butoxycarbonylmethyl-4-carboxy-2-hydroxymethyl-5-oxopyrrolidine

(2R,5R,6R,7R)-6,7-epoxy-7-ethoxycarbonyl-8-oxo-2-phenyl-1-aza-3-oxabicyclo[3.3.0]octane

(2R,5S,6S,7S)-7-Benzyl-6-tert-butoxycarbonylmethyl-7-ethoxycarbonyl-3-oxa-8-oxo-2-phenyl-1-azabicyclo[3.3.0]octane

(2R,5S,6S,7R)-7-Benzyl-6-tert-butoxycarbonylmethyl-7-ethoxycarbonyl-3-oxa-8-oxo-2-phenyl-1-azabicyclo[3.3.0]octane