The synthesis of four bipodal dihydroxamic acids containing an apical C atom and amide linkages is described, where Ia,b represent "normal" and "retro" hydroxamate isomers: (R)CH[C(=O)NH(CH2)(2)NHC(=O)(CHZ)(n)R'](2) (Ia, R = CH3, R' = N(OH)(C=O)CH3, n = 2; Ib, R = CH3, R' = (C=O)N(OH)CH3, n = 2; Ic, R = CH3, R' (C=O)N(OH)CH3, n = 3; Id, R = C4H9, R' = (C=O)N(OH)CH3, n = 2.). The pK(a1) and pK(a2) values in aqueous solution are reported, and some degree of cooperativity is noted. Complexation equilibria with Fe-aq(3+) are described, and values for stepwise and overall equilibrium constants are reported. log beta (230) values for Ia-d are 59.22, 59.45, 58,91, and 58.46, slightly lower than for rhodotorulic acid, although the pFe values for the. synthetic siderophores are comparable to that for rhodotorulic acid.