Tricyclic β-lactams: total synthesis and antibacterial activity of 5α- and 5β-methoxy-tribactams

My 50-Plus Years of Academic Research Collaborations with Industry. A Retrospective

A retrospective is presented highlighting the synthesis of selected "first-in-kind" natural products, their synthetic analogues, structure elucidations, and rationally designed bioactive synthetic compounds that were accomplished because of collaborations with past and present pharmaceutical and agrochemical companies. Medicinal chemistry projects involving structure-based design exploiting cocrystal structures of small molecules with biologically relevant enzymes, receptors, and bacterial ribosomes with synthetic small molecules leading to marketed products, clinical candidates, and novel drug prototypes were realized in collaboration. Personal reflections, historical insights, behind the scenes stories from various long-term projects are shared in this retrospective article.

Bypassing the stereoselectivity issue: transformations of Kinugasa adducts from chiral alkynes and non-chiral acyclic nitrones

An approach to β-lactams via a reaction between chiral copper acetylides and acyclic nitrones is reported. Electronic circular dichroism (ECD) in combination with NMR spectroscopy was used to determine the absolute configuration of all components of complex mixtures of azetidinones. Stereochemical preferences observed in the studied reactions are discussed and a model of a new reaction pathway supported by DFT conformational analysis is proposed. Subsequent transformations of the synthesized Kinugasa adducts followed by epimerization at the C-3 carbon atom led to trans-substituted azetidinones with improved stereoselectivity, mimicking a variety of important β-lactam structures. On the other hand, the oxidation of the furyl residue to the carboxylic group followed by oxidative decarboxylation with lead tetraacetate afforded the more thermodynamically stable trans-substituted 4-acetoxy azetidinone. The latter strategy is particularly attractive for the diastereomeric mixture in which isomers with the same configuration at the C-3 carbon atom dominate.

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

A review of the synthesis of natural products and bioactive compounds adopting phosphonamide anion technology is presented highlighting the utility of phosphonamide reagents in stereocontrolled bond-forming reactions. Methodologies utilizing phosphonamide anions in asymmetric alkylations, Michael additions, olefinations, and cyclopropanations will be summarized, as well as an overview of the synthesis of the employed phosphonamide reagents.

Preparation of aromatic β-Selenolactams and their bioactivities as agricultural chemicals

The purpose of this study was to investigate the possibility of aromatic beta-selenolactams being used in agricultural chemicals. A series of beta-selenolactams with aromatic substituents at the 1-, 2- and 3-positions were synthesized and their bioactivities were evaluated. Acarianicidal and insecticidal activity against common destructive insects, antibacterial activity against seven common plant pathogens, and plant growth activity of typical food crops were investigated. We found that introduction of 4-chloro and 4-methyl groups on 2- or 3-phenyl groups of the beta-selenolactam ring brought about acarianicidal activity against adults and eggs of Plutella xylostella. However, except for moderate to weak effect on fatality of Culex pipiens molestus Forskal, insecticidal activity against two other kinds of insects, antibacterial activity against plant pathogens, and activity on plant growth regulation were not detected among the beta-selenolactam derivatives.

3-N,N-Dimethylamino-3-deoxy lincomycin: A structure-based hybrid between lincomycin and the desosamine unit of erythromycin

The observation that the desosamine sugar unit in erythromycin and the methyl thiolincosaminide portion of lincomycin occupy virtually identical sites on the 23S rRNA according to X-ray crystallograpaic data, instigated the synthesis of 3-N,N-dimethylamino-3-deoxy lincomycin as a hybrid structure. The synthesis in eight steps from lincomycin, involving a trans-diequatorial opening of an intermediate epoxide as the key step, is described.

Design and synthesis of a novel class of constrained tricyclic pyrrolizidinone carboxylic acids as carbapenem mimics

A series of tricyclic pyrrolizidinone carboxylic acids harboring an angular methano group were synthesized as mimics of carbapenems and carbapenams. A key reaction involved a novel intramolecular cyclopropanation mediated by a trimethylstannylmethyl group and an adjacent iminium ion. Enolate chemistry on a tricyclic lactam ring unit allowed the introduction of various substituents. Further elaboration afforded tricyclic pyrrolidinone carboxylic acids, which were found to be inactive as inhibitors against a panel of bacterial strains. However, the antibacterial activity of ceftazidine was enhanced in the presence of the tricyclic analogues.

Design, synthesis and bioactivity evaluation of tribactam beta lactamase inhibitors

Known carbapenem compounds with inhibitory effect towards beta-lactamase enzymes are formed from bicyclical beta lactam structural scaffolds. On the basis of results from theoretical computational methods and molecular modelling we have designed and developed a synthetic route towards novel, biologically active tricyclic derivatives of carbapenems.