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

(1α,4α,5α)-2,6-dioxo-4-methyl-7-tert-butoxycarbonylmethyl-3-oxa-7-azabicyclo(3,2,0)heptane-1-carboxylic acid