3-(7-Oxo-4-oxa-1-azabicyclo[3.2.0]heptan-3-yl)-2-[3-(7-oxo-4-oxa-1-azabicyclo[3.2.0]heptan-3-yl)-3-hydroxypropanoylamino]-3-hydroxypropionic acid [ 103059-93-4 ]