(5R,6S)-6-(R)-1-hydroxyethyl-7-oxo-3-(R)-2-tetrahydrofuryl-4-thia-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylate
(5r,6s)-6-(r)-1-hydroxyethyl-7-oxo-3-(r)-2-tetrahydrofuryl-4-thia-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylate