Methanesulfonic acid 2-((2R,3S)-1-benzyloxy-3-tert-butoxycarbonylamino-4-oxo-azetidin-2-yl)-ethyl ester
{(3S,4R)-1-Benzyloxy-2-oxo-4-[2-(tetrahydro-pyran-2-yloxy)-ethyl]-azetidin-3-yl}-carbamic acid tert-butyl ester
(1S,5R)-6-Benzyloxycarbonylmethoxy-7-oxo-2,6-diaza-bicyclo[3.2.0]heptane-2-carboxylic acid tert-butyl ester
[(2R,3S)-1-Benzyloxy-2-(2-hydroxy-ethyl)-4-oxo-azetidin-3-yl]-carbamic acid tert-butyl ester
(1S,5R)-6-Benzyloxy-7-oxo-2,6-diaza-bicyclo[3.2.0]heptane-2-carboxylic acid tert-butyl ester