Bicyclic enol cyclocarbamates inhibit penicillin-binding proteins.

Natural products form attractive leads for the development of chemical probes and drugs. The antibacterial lipopeptide Brabantamide A contains an unusual enol cyclocarbamate and we used this scaffold as inspiration for the synthesis of a panel of enol cyclocarbamate containing compounds. By equipping the scaffold with different groups, we identified structural features that are essential for antibacterial activity. Some of the derivatives block incorporation of hydroxycoumarin carboxylic acid-amino d-alanine into the newly synthesized peptidoglycan. Activity-based protein-profiling experiments revealed that the enol carbamates inhibit a specific subset of penicillin-binding proteins in B. subtilis and S. pneumoniae.

Enzyme-Mediated Modification of Single-Domain Antibodies for Imaging Modalities with Different Characteristics.

Antibodies are currently the fastest-growing class of therapeutics. Although naked antibodies have proven valuable as pharmaceutical agents, they have some limitations, such as low tissue penetration and a long circulatory half-life. They have been conjugated to toxic payloads, PEGs, or radioisotopes to increase and optimize their therapeutic efficacy. Although nonspecific conjugation is suitable for most in vitro applications, it has become evident that site specifically modified antibodies may have advantages for in vivo applications. Herein we describe a novel approach in which the antibody fragment is tagged with two handles: one for the introduction of a fluorophore or (18)F isotope, and the second for further modification of the fragment with a PEG moiety or a second antibody fragment to tune its circulatory half-life or its avidity. Such constructs, which recognize Class II MHC products and CD11b, showed high avidity and specificity. They were used to image cancers and could detect small tumors.

The use of 18F-2-fluorodeoxyglucose (FDG) to label antibody fragments for immuno-PET of pancreatic cancer.

We generated 18F-labeled antibody fragments for PET imaging using a sortase-mediated reaction to install a transcyclooctene (TCO)-functionalized short peptide onto proteins of interest, followed by reaction with a tetrazine-labeled-18F-2-deoxyfluoroglucose (FDG). The method is rapid, robust, and site-specific (radiochemical yields >25%, not decay corrected). The availability of 18F-2-deoxyfluoroglucose avoids the need for more complicated chemistries used to generate carbon-fluorine bonds. We demonstrate the utility of the method by detecting heterotopic pancreatic tumors in mice by PET, using anti-Class II MHC single domain antibodies. We correlate macroscopic PET images with microscopic two-photon visualization of the tumor. Our approach provides easy access to 18F-labeled antibodies and their fragments at a level of molecular specificity that complements conventional18F-FDG imaging.