The screening of compounds that bind to the target of interest (specific proteins) plays a vital role in drug discovery. Usually, the identification of biologically active compounds is done from a library of structurally known compounds. However, we successfully illustrate here, that NMR techniques including saturation transfer difference (STD), transfer nuclear Overhauser spectroscopy (TrNOESY) and STD-TOCSY (total correlation spectroscopy) in combination with separation methods not only enable the rapid and comprehensive screening of active components, but also their unequivocal structural characterization. Furthermore, a time saving for the recognition of leads is also possible with this application. To probe the binding studies, a hydroethanolic fraction of crude extract (1 mg) from natural product (Rauia resinous) was used for the initial assessment with BSA protein. The docking simulation was performed with BSA in the region of Thr190, Arg198, Arg217, Trp213, Arg256, Ala290 and Tyr451 to further refine the active compound towards the leads. Docking results mimic binding as identified by STD, Tr-NOESY and STD-TOCSY. Isovetexine-2-rhamnosoide (2) was found to be most active through group epitope mapping results as well as the docking simulation with relative free energy of -7.2770. This experiment provided excellent results through the direct NMR screening method. Using Bovine Serum Albumin as a reference, we illustrate that this approach offers an excellent way for the first hand detection of the active constituents/inhibitors from natural remedies used in folk medicinal treatments.

The fall armyworm Spodoptera frugiperda is a polyphagous pest that causes important damage in different regions of America and mainly affects corn crops in both tropical and subtropical areas. Currently, control relies on both transgenic plants and/or chemical pesticides. In this work we describe the preparation of an indexed combinatorial library of amides and its toxic effect by contact against S. frugiperda . (E)-1-(1-Piperidinyl)-3-[4-(trifluoromethoxy)phenyl]-2-propen-1-one was the most active compound with an LD(50) = 0.793 μg mg(-1) of larva. This amide was also evaluated by ingestion and at the lowest concentration (1 mg kg(-1)) achieved 83.3% mortality.

Over the last two decades, new and more advanced strategies that help in the rapid screening and identification of new ligands for a specific macromolecule have become an important domain. From this viewpoint, the effectiveness of STD NMR, Tr-NOESY, and STD-TOCSY has been utilized to evaluate the binding potential of the natural extract of Stryphnodendron polyphyllum, used as a herbal medicine in Brazil, towards human serum albumin. Moreover, 1D-DOSY experiments have also been carried out for the discriminations of different molecular weight compounds present in this extract. Following the STD, Tr-NOESY, and TOCSY analysis, a hyphenated system comprising LC-SPE-NMR was utilized to see the complete structural assignments through 2D spectra. The combined results from NMR spectroscopy and separation methods provided myricetin-3-O-rhamnopyranoside (1), quercetin-3-O-glucopyranoside (2), quercetin-3-O-xylopyranoside (3), and quercetin-3-O-rhamnopyranoside (4) as the active site blockers. Moreover, epitope results and additional Tr-NOESY cross peaks suggested the presence of the flattened conformations of these ligands within the ligand-HSA complex through the edge protons. Similarly, STD competition studies with the ligand-HSA complex were demonstrated by varying the concentration of spy molecule that selectively binds with Sudlow's site II. Finally, docking simulations targeting bothSudlow sites (I and II) were performed, which interestingly mimic the STD competition results and showed that these compounds (1-4) are more prone towards binding site-1 inhibition. Therefore, we suggest that the sequence of techniques presented in this study can be considered as a simple and fast analytical tool for screening natural extracts to get better leads against any specific target.