FTICR MS/MS of 3,4-DHB-SPD and 3,4-DHB-SPD-CT isolated from the B. anthracis ΔasbB mutant and petrobactinBa from the wild type. A, SORI-CAD mass spectrum from 3,4-DHB-SPD; B, SORI-CAD mass spectrum of 3,4-DHB-SPD-CT; C and D, assignments of selected fragments from 3,4-DHB-SPD, suggesting the isomers 2 and 2′; E and F, assignments of selected fragments from 3,4-DHB-SPD-CT, suggesting the isomers 3 and 3′; G, SORI-CAD mass spectrum of petrobactinBa; H, assignments of selected fragments from petrobactinBa.