A Nitrile Glucoside and Biflavones from the Leaves of Campylospermum excavatum (Ochnaceae).

The study of the MeOH extract of the leaves of Campylospermum excavatum led to the isolation of a nitrile glucoside, named campyloside C (1) and an original derivative of ochnaflavone, 7-O-methylochnaflavone (2), along with three known biflavonoids, amentoflavone, sequoiaflavone, and sotetsuflavone (3 - 5). The linkage site of the sub-units of 2 was confirmed by chemical correlation, after semi-synthesis of a trimethoxylated derivative of ochnaflavone (2a). The structures of these compounds as well as their relative and absolute configurations were assigned by 1D- and 2D-NMR experiments, HR-ESI-MS and Electronic Circular Dichroism (ECD) calculations. A low-pass J filter HMBC experiment was performed in order to define the configuration of the double bond of 1. All of the biflavonoids were evaluated against protozoan parasites. Amentoflavone moderately inhibited the promastigote form of Leishmania infantum.

NASCA-HMBC, a new NMR methodology for the resolution of severely overlapping signals: application to the study of agathisflavone.

INTRODUCTION: Standard NMR 2D heteronuclear HMBC spectra have a low resolution in the indirect carbon dimension, making it very difficult to assign signals to individual carbons when their chemical shifts are < 0.3 ppm apart. OBJECTIVE: To establish spectral aliasing for HMBC experiments to improve the resolution in the carbon dimension without increasing the total experimental time and avoiding ambiguities in the observed chemical shifts. METHODOLOGY: The NASCA-HMBC (Non-ambiguous Assignment by Superposition of Coupled Aliased HMBC) methodology combines a pair of HMBC spectra recorded with slightly different carbon windows to provide typically one order of magnitude increase in the resolution and unambiguous chemical shifts. RESULTS: The application of this methodology to a biflavonoid found in Ouratea gilgiana resulted in spectra with a sufficiently high resolution to make the assignment straightforward and report, for the first time, the full assignment of agathisflavone. CONCLUSION: The methodology should find many applications in dimeric and oligomeric compounds such as peptides, carbohydrates, polyketides and other cases where signal clustering is expected.

Spectral aliasing: a super zoom for 2D-NMR spectra. Principles and applications.

The NMR methodology based on spectral aliasing developed at the University of Geneva is reviewed. Different approaches aimed at increasing the resolution in the indirect carbon dimension of 2D heteronuclear experiments are presented with their respective advantages. Applications to HSQC, HMBC and other 2D heteronuclear experiments to the study of natural products and synthesis intermediates are shown. HSQC-based experiments for diffusion measurements, kinetics studies and titrations experiments all take advantage of spectral aliasing to reduce the experimental time from unrealistically long acquisition times to overnight experiments. The roles of computational methods such as DFT/GIAO and Logic for Structure Determination (LSD) in structure determination are discussed.