Structure elucidation of a novel antibiotic of the vancomycin group. The influence of ion-dipole interactions on peptide backbone conformation

Tailoring the nuclear Overhauser effect for the study of small and medium-sized molecules by solvent viscosity manipulation

The nuclear Overhauser effect (NOE) is a consequence of cross-relaxation between nuclear spins mediated by dipolar coupling. Its sensitivity to internuclear distances has made it an increasingly important tool for the determination of through-space atom proximity relationships within molecules of sizes ranging from the smallest systems to large biopolymers. With the support of sophisticated FT-NMR techniques, the NOE plays an essential role in structure elucidation, conformational and dynamic investigations in liquid-state NMR. The efficiency of magnetization transfer by the NOE depends on the molecular rotational correlation time, whose value depends on solution viscosity. The magnitude of the NOE between ¹H nuclei varies from +50% when molecular tumbling is fast to -100% when it is slow, the latter case corresponding to the spin diffusion limit. In an intermediate tumbling regime, the NOE may be vanishingly small. Increasing the viscosity of the solution increases the motional correlation time, and as a result, otherwise unobservable NOEs may be revealed and brought close to the spin diffusion limit. The goal of this review is to report the resolution of structural problems that benefited from the manipulation of the negative NOE by means of viscous solvents, including examples of molecular structure determination, conformation elucidation and mixture analysis (the ViscY method).

Catalytic site-selective thiocarbonylations and deoxygenations of vancomycin reveal hydroxyl-dependent conformational effects

We have examined peptide-based catalysts for the site-selective thiocarbonylation of a protected form of vancomycin. Several catalysts were identified that either enhanced or altered the inherent selectivity profile exhibited by the substrate. Two catalysts, one identified through screening and another through rational design, were demonstrated to be effective on 0.50-g scale. Deoxygenations led ultimately to two new deoxy-vancomycin derivatives, and surprising conformational consequences of deoxygenation were revealed for one of the new compounds. These effects were mirrored in the biological activities of the new analogues and support a structural role for certain hydroxyls in the native structure.

The structural biology of molecular recognition by vancomycin

Vancomycin is the archetype among naturally occurring compounds known as glycopeptide antibiotics. Because it is a vital therapeutic agent used world-wide for the treatment of infections with gram-positive bacteria, emerging bacterial resistance to vancomycin is a major public health threat. Recent investigations into the mechanisms of action of glycopeptide antibiotics are driven by a need to understand their detailed mechanism of action so that new agents can be developed to overcome resistance. These investigations have revealed that glycopeptide antibiotics exhibit a rich array of complex cooperative phenomena when they bind target ligands, making them valuable model systems for the study of molecular recognition.