8-(tert-butyl) 3-methyl (1R,5S)-2-hydroxy-8-azabicyclo[3.2.1]oct-2-ene-3,8-dicarboxylate

(2R,5S)-N-(tert-butyloxycarbonyl)-5-[1'-(2'-methoxycarbonyl)ethyl]proline methyl ester

(3aS,4R,7S,8aS)-9-(tert-butoxycarbonyl)-3a,5,6,7,8,8a-hexahydro-4H-4,7-epiminocyclohepta[d]isoxazole-3-carboxylic acid

(1R,2S,6S,8S)-5-Oxa-4,11-diaza-tricyclo[6.2.1.02,6]undec-3-ene-3,11-dicarboxylic acid 11-tert-butyl ester 3-ethyl ester

(1R,2R,3S,5S)-tert-butyl 3-(benzoyloxy)-2-carbamoyl-8-azabicyclo[3.2.1]octane-8-carboxylate