(R*,R*)-N-bis(carboethoxy)methyl-N-tert-butoxycarbonylmethyl-2-bromo-3-acetoxybutylamide

<3α(S*),4α>-1-tert-butoxycarbonylmethyl-3-(1-acetoxyethyl)-4-ethoxycarbonyl-2-azetidinone-4-carboxylic acid

<3α(S*),4β>-1-tert-butoxycarbonylmethyl-3-(1-acetoxyethyl)-4-<1-oxo-2,2-bis(phenylthio)ethyl>-2-azetidinone