(S-(E))-1-(5-((2-amino-5-O-(aminocarbonyl)-2-deoxy-L-xylonoyl)amino)-1,5-dideoxy-1-(3,4-dihydro-5-(hydroxymethyl)-2,4-dioxo-1(2H)-pyrimi dinyl)-beta-D-allofuranuronoyl)-3-ethylidene-2- azetidinecarboxylic acid