ABSTRACT
Nucleoside hydrolases are a strategic target for the development of drugs to treat leishmaniasis, a neglected disease that affects 700 thousand to one million people annually. The present study aimed to identify Leishmania donovani nucleoside hydrolase (LdNH) inhibitors from the leaves of Ormosia arborea, a tree endemic to Brazilian ecosystems, through a strategy based on 1H NMR analyses and chemometrics. The aqueous EtOH extract of O. arborea leaves inhibited LdNH activity by 95%. The extract was fractionated in triplicate (13 in each step, making a total of 39 fractions). Partial least squares discriminant analysis (PLS-DA) was used to correlate the 1H NMR spectra of the fractions with their LdNH inhibitory activity and thus to identify the spectral regions associated with the bioactivity. The strategy aimed at isolating the probable bioactive substances and led to two new A-type proanthocyanidins, linked to a p-coumaroyl unit (1 and 2), which appeared as noncompetitive inhibitors of LdNH (IC50: 28.2 ± 3.0 µM and 25.6 ± 4.1 µM, respectively). This study confirms the usefulness of the NMR-based chemometric methods to accelerate the discovery of drugs from natural products.
Subject(s)
Fabaceae/chemistry , Leishmania donovani/chemistry , N-Glycosyl Hydrolases/antagonists & inhibitors , Brazil , Ecosystem , Fabaceae/metabolism , Humans , Magnetic Resonance Spectroscopy , Molecular Structure , N-Glycosyl Hydrolases/chemistry , N-Glycosyl Hydrolases/metabolismABSTRACT
This study presents new inhibitors of the nucleoside hydrolase from Leishmania donovani (LdNH) with in vitro leishmanicidal activity. Biological screening of 214 Brazilian plant extracts was performed to select plants with enzyme inhibitory activity. Two plants were selected for their results, and for their lack of prior phytochemical description: Leandra amplexicaulis DC. (Melastomataceae) and Urvillea rufescens Cambess (Sapindaceae). Three flavonoids were isolated by bioguided fractionation of the hydroethanolic extracts: kaempferol 3-O-α-l-rhamnopyranoside (1) and kaempferol 3-O-ß-d-xylopyranosyl-(1â2)-α-l-rhamnopyranoside (2) from L. amplexicaulis, as well as tricetin-4'-O-methyl flavone (3) from U. rufescens. These flavonoids showed inhibitory activities (IC50) of 197.4 µM (1), 74.7 µM (2) and 1.1 µM (3) on the LdNH. Their binding mode was proposed based on molecular docking with LdNH and by NMR Saturation Transfer Difference studies. Kinetic studies demonstrate that the most potent inhibitor (3) acts by uncompetitive inhibition. This study reports for the first time the inhibition of LdNH by naturally sourced flavonoids.
