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

(2R,3R,4R)-4-Hydroxymethyl-3-(4-methoxy-benzylsulfanyl)-oxetane-2-carboxylic acid dimethylamide

(2R,3R,4R)-4-Hydroxymethyl-3-mercapto-oxetane-2-carboxylic acid methyl ester

(2R,3R,4R)-3-Acetylsulfanyl-4-hydroxymethyl-oxetane-2-carboxylic acid methyl ester