Design, synthesis and biological evaluation of 5'-C-piperidinyl-5'-O-aminoribosyluridines as potential antibacterial agents.

The discovery of new antibiotics is critical because the emergence of drug-resistant bacteria has posed a serious public health problem. Caprazamycins, which are nucleoside antibiotics, are a promising lead with a novel mode of action, and we have designed simplified analogues containing a piperidine as a scaffold linking the crucial structural units of caprazamycins. These analogues were step-economically synthesized via a sequential aza-Prins-Ritter reaction. Among the tested compounds, the analogue 7 exhibited good MraY inhibitory activity, antibacterial activity against Gram-positive bacterial strains including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci, and metabolic stability. The observed cytotoxicity of 7 against HepG2 cells was overcome by modulating the fatty acyl side chain. The knowledge obtained from our structure-activity relationship studies of the caprazamycins will provide further direction toward the design of potent MraY inhibitors.

Phosphine-olefin ligands based on a planar-chiral (π-arene)chromium scaffold: design, synthesis, and application in asymmetric catalysis.

The NMR and X-ray crystallographic studies clarified that planar-chiral alkenylene-bridged (phosphino-π-arene)(phosphine)chromium complexes 3 were capable of coordinating to a rhodium(I) cation in a bidentate fashion at the (π-arene)-bound phosphorus atom and at the olefin moiety. The P-olefin chelate coordination of 3 constructs the effective chiral environment at the metal center, and thus, these rhodium complexes display high performances in various rhodium-catalyzed asymmetric 1,4- and 1,2-addition reactions with arylboron nucleophiles. The control experiments demonstrated that the (η(2)-olefin)-Rh interaction as well as the bridging structure in 3 played the pivotal roles in the high enantioselectivity of the Rh-catalyzed asymmetric reactions. To enhance the synthetic utilities of these phosphine-olefin ligands, an enantiospecific and scalable synthetic method was developed. The novel synthetic method is flexible in terms of the substituent variation, and a library of the planar-chiral (arene)chromium-based phosphine-olefin ligands was established by the combinatorial approach. Among the newly prepared ligand library, compound 3g, which is with a bis(3,5-dimethylphenyl)phosphino group on the η(6)-arene ring, was found to be a far better chiral ligand in the rhodium-catalyzed asymmetric reactions showing excellent enantioselectivity and high yields.

Synthesis of macrocyclic nucleoside antibacterials and their interactions with MraY.

The development of new antibacterial drugs with different mechanisms of action is urgently needed to address antimicrobial resistance. MraY is an essential membrane enzyme required for bacterial cell wall synthesis. Sphaerimicins are naturally occurring macrocyclic nucleoside inhibitors of MraY and are considered a promising target in antibacterial discovery. However, developing sphaerimicins as antibacterials has been challenging due to their complex macrocyclic structures. In this study, we construct their characteristic macrocyclic skeleton via two key reactions. Having then determined the structure of a sphaerimicin analogue bound to MraY, we use a structure-guided approach to design simplified sphaerimicin analogues. These analogues retain potency against MraY and exhibit potent antibacterial activity against Gram-positive bacteria, including clinically isolated drug resistant strains of S. aureus and E. faecium. Our study combines synthetic chemistry, structural biology, and microbiology to provide a platform for the development of MraY inhibitors as antibacterials against drug-resistant bacteria.