(4R,5S,6S)-6-((R)-1-Hydroxy-ethyl)-3-{(2S,3S,4R)-2-iodomethyl-4-[(4-nitro-benzyloxycarbonylamino)-methyl]-oxetan-3-ylsulfanyl}-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitro-benzyl ester

(4R,5S,6S)-6-((R)-1-Hydroxy-ethyl)-3-{(2R,3S,4R)-2-hydroxymethyl-4-[(4-nitro-benzyloxycarbonylamino)-methyl]-oxetan-3-ylsulfanyl}-4-methyl-7-oxo-1-aza-bicyclo[3.2.0]hept-2-ene-2-carboxylic acid 4-nitro-benzyl ester

((2R,3S,4S)-4-Iodomethyl-3-mercapto-oxetan-2-ylmethyl)-carbamic acid 4-nitro-benzyl ester

((2R,3S,4R)-4-Hydroxymethyl-3-mercapto-oxetan-2-ylmethyl)-carbamic acid 4-nitro-benzyl ester

[(2R,3S,4R)-4-Hydroxymethyl-3-(4-methoxy-benzylsulfanyl)-oxetan-2-ylmethyl]-carbamic acid 4-nitro-benzyl ester