Catalyzes the condensation of L-2,3-diaminopropionyl-citryl-diaminoethane and 2-oxoglutarate to form staphyloferrin B, the fourth and last step in staphyloferrin B biosynthesis. 2-[(L-alanin-3-ylcarbamoyl)methyl]-3-(2-aminoethylcarbamoyl)-2-hydroxypropanoate + 2-oxoglutarate + ATP = AMP + diphosphate + H(+) + staphyloferrin B Siderophore biosynthesis. Forms a mixture of monomer and dimer in solution. Up-regulated under iron-deficient growth conditions. Repressed by Fur under iron-rich growth conditions. Belongs to the IucA/IucC family.