Side chain of Cefotetan;4-(1-amino-3-tert-butoxy-1,3-dioxopropan-2-ylidene)-1,3-dithietane-2-carboxylic acid;{[4-(carbamoyl)-4-(tert-butyloxycarbonyl)methylene]-1,3-dithiethan-2-yl}carboxylic acid;1,3-Dithietane-2-carboxylic acid, 4-[1-(aminocarbonyl)-2-(1,1-dimethylethoxy)-2-oxoethylidene]-