Enantioselective Synthesis of Isotopically Labeled Homocitric Acid Lactone

A concise synthesis of homocitric acid lactone was developed to accommodate systematic placement of carbon isotopes (specifically ¹³C) for detailed studies of this cofactor. This new route uses a chiral allylic alcohol, available in multigram quantities from enzymatic resolution, as a starting material, which transposes asymmetry through an Ireland–Claisen rearrangement

Gyramides Prevent Bacterial Growth by Inhibiting DNA Gyrase and Altering Chromosome Topology

Antibiotics targeting DNA gyrase have been a clinical success story for the past half-century, and the emergence of bacterial resistance has fueled the search for new gyrase inhibitors. In this paper we demonstrate that a new class of gyrase inhibitors, the gyramides, are bacteriostatic agents that competitively inhibit the ATPase activity of <i>Escherichia coli</i> gyrase and produce supercoiled DNA in vivo. <i>E. coli</i> cells treated with gyramide A have abnormally localized, condensed chromosomes that blocks DNA replication and interrupts chromosome segregation. The resulting alterations in DNA topology inhibit cell division through a mechanism that involves the SOS pathway. Importantly, gyramide A is a specific inhibitor of gyrase and does not inhibit the closely related <i>E. coli</i> enzyme topoisomerase IV. <i>E. coli</i> mutants with reduced susceptibility to gyramide A do not display cross-resistance to ciprofloxacin and novobiocin. The results demonstrate that the gyramides prevent bacterial growth by a mechanism in which the topological state of chromosomes is altered and halts DNA replication and segregation. The specificity and activity of the gyramides for inhibiting gyrase makes these compounds important chemical tools for studying the mechanism of gyrase and the connection between DNA topology and bacterial cell division

The Synthesis and Antimicrobial Activity of Heterocyclic Derivatives of Totarol

The synthesis and antimicrobial activity of heterocyclic analogues of the diterpenoid totarol are described. An advanced synthetic intermediate with a ketone on the A-ring is used to attach fused heterocycles, and a carbon-to-nitrogen atom replacement is made on the B-ring by de novo synthesis. A-ring analogues with an indole attached exhibit, for the first time, enhanced antimicrobial activity relative to the parent natural product. Preliminary experiments demonstrate that the indole analogues do not target the bacterial cell division protein FtsZ as had been hypothesized for totarol

Comparison of Small Molecule Inhibitors of the Bacterial Cell Division Protein FtsZ and Identification of a Reliable Cross-Species Inhibitor

FtsZ is a guanosine triphosphatase (GTPase) that mediates cytokinesis in bacteria. FtsZ is homologous in structure to eukaryotic tubulin and polymerizes in a similar head-to-tail fashion. The study of tubulin’s function in eukaryotic cells has benefited greatly from specific and potent small molecule inhibitors, including colchicine and taxol. Although many small molecule inhibitors of FtsZ have been reported, none has emerged as a generally useful probe for modulating bacterial cell division. With the goal of establishing a useful and reliable small molecule inhibitor of FtsZ, a broad biochemical cross-comparison of reported FtsZ inhibitors was undertaken. Several of these molecules, including phenolic natural products, are unselective inhibitors that seem to derive their activity from the formation of microscopic colloids or aggregates. Other compounds, including the natural product viriditoxin and the drug development candidate PC190723, exhibit no inhibition of GTPase activity using protocols in this work or under published conditions. Of the compounds studied, only zantrin Z3 exhibits good levels of inhibition, maintains activity under conditions that disrupt small molecule aggregates, and provides a platform for exploration of structure–activity relationships (SAR). Preliminary SAR studies have identified slight modifications to the two side chains of this structure that modulate the inhibitory activity of zantrin Z3. Collectively, these studies will help focus future investigations toward the establishment of probes for FtsZ that fill the roles of colchicine and taxol in studies of tubulin