title: Identification of oleamide in Guatteria recurvisepala by LC/MS-based Plasmodium falciparum thioredoxin reductase ligand binding method.
abstract: Our current research on applications of mass spectrometry to natural product drug discovery against malaria aims to screen plant extracts for new ligands to Plasmodium falciparum thioredoxin reductase (PfTrxR) followed by their identification and structure elucidation. PfTrxR is involved in the antioxidant defense and redox regulation of the parasite and is validated as a promising target for therapeutic intervention against malaria. In the present study, detannified methanol extracts from Guatteria recurvisepala, Licania kallunkiae, and Topobea watsonii were screened for ligands to PfTrxR using ultrafiltration and liquid chromatography/mass spectrometry-based binding experiments. The PfTrxR ligand identified in the extract of Guatteria recurvisepala displayed a relative binding affinity of 3.5-fold when incubated with 1 μM PfTrxR. The ligand corresponding to the protonated molecule m/z 282.2792 [M+ H]+ was eluted at a retention time of 17.95 min in a 20-min gradient of 95% B consisting of (A) 0.1%formic acid in 95% H₂O-5% ACN, and (B) 0.1% formic acid in 95% ACN-5% H₂O in an LC-QTOF-MS.Tandem MS of the protonated molecule m/z 282.2792 [M + H]+, C₁₈H₃₆NO (DBE: 2; error: 1.13 ppm) resulted in two daughter ions m/z 265.2516[M + H-NH₃]+ (DBE: 3; error: 0.35 ppm) and m/z 247.2405 [M + H-NH₃-H₂O] +, (DBE: 4; error:2.26 ppm). The PfTrxR ligand was identified as oleamide and confirmed by comparison of the retention time, molecular formula, accurate mass,and double bond equivalence with the standard oleamide. This is the first report on the identification of oleamide as a PfTrxR ligand from Guatteria recurvisepala R. E. Fr. and the corresponding in vitro activity against P. falciparum strain K1 (IC₅₀ 4.29 μg/mL).
authors.affiliation: Department of Pharmacal Sciences, Harrison School of Pharmacy, Auburn University, Auburn, Alabama, USA.
authors.forename: Ranjith
authors.initials: R
authors.lastname: Munigunti
authors.forename: Nicholas
authors.initials: N
authors.lastname: Nelson
authors.forename: Vanisree
authors.initials: V
authors.lastname: Mulabagal
authors.forename: Mahabir P
authors.initials: MP
authors.lastname: Gupta
authors.forename: Reto
authors.initials: R
authors.lastname: Brun
authors.forename: Angela I
authors.initials: AI
authors.lastname: Calderón
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000737:chemistry* / Q000302:isolation & purification; D002460:Cell Line; D002470:Cell Survival; D002853:Chromatography, Liquid; D045469:Chrysobalanaceae / Q000737:chemistry; D055808:Drug Discovery; D031043:Guatteria / Q000737:chemistry*; D020128:Inhibitory Concentration 50; D008024:Ligands; D013058:Mass Spectrometry; D035322:Melastomataceae / Q000737:chemistry; D009829:Oleic Acids / Q000737:chemistry* / Q000302:isolation & purification; D010176:Panama; D010936:Plant Extracts / Q000737:chemistry* / Q000302:isolation & purification; D010963:Plasmodium falciparum / Q000201:enzymology*; D051381:Rats; D012015:Reference Standards; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism*; D014462:Ultrafiltration
chemical_list: D000962:Antimalarials; D008024:Ligands; D009829:Oleic Acids; D010936:Plant Extracts; C029407:oleylamide; D013880:Thioredoxin-Disulfide Reductase