Synthesis and biological evaluation of a pyoverdin‐β‐lactam conjugate: a new type of arginine‐specific cross‐linking in aqueous solution

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Abstract
Arginine specific reagents such as phenylglyoxal and other alpha-dioxo compounds react with arginine side chains by forming adducts with a stoichiometry of 2:1 or a mixture of 2:1 and 1:1. These adducts are labile in neutral and slightly alkaline aqueous solution. We developed a new type of cross-linking reaction with aliphatic beta-dioxo compounds. They can be used for the well-defined, irreversible covalent attachment of molecules carrying a primary amino group to arginyl residues of water soluble peptides. The reaction proceeds under mild conditions in aqueous solution, essentially without the formation of side products. A pyoverdin-cephalexin conjugate was synthesized in order to promote its cellular uptake by Pseudomonas aeruginosa. Preliminary biological investigations of the conjugate indicated that it enters the bacterial cell via the pyoverdin-mediated iron uptake pathway.