5-Oxa-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid, 7-[(mercaptoacetyl)amino]-7-methoxy-3-[[(1-methyl-1H-tetrazol-5-yl)thio ]methyl]-8-oxo-, 2-(methylsulfonyl)ethyl ester, cis-