Substituted thiobenzoic acid S-benzyl esters as potential inhibitors of a snake venom phospholipase A 2 : Synthesis, spectroscopic and computational studies I.C. Henao Castañeda a,⇑ , J.A. Pereañez a,b , J.L. Jios c a Programa de Ofidismo y Escorpionismo, Departamento de Farmacia, Facultad de Química Farmacéutica, Universidad de Antioquia, Calle 67, No. 53 108, Apartado Aéreo 1226, Medellín, Colombia b Facultad de Medicina, Universidad Cooperativa de Colombia, Medellín-Colombia, Calle 48 # 28-00, Medellín, Colombia c Unidad LaSeISiC-PlaPiMu, Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 esq. 115, 1900 La Plata, Argentina highlights " Substituted thiobenzoic acid S-benzyl esters were synthesized and characterized. " Thioesters inhibited the enzymatic activity of a venom phospholipase A 2. " Molecular docking study suggests that compounds could interact with His48 at the active site of PLA 2. " Further in vivo studies are required to confirm the antiophidic potential of thioesters. article info Article history: Received 2 May 2012 Received in revised form 13 June 2012 Accepted 14 June 2012 Available online 20 June 2012 Keywords: Thioesters Phospholipase A 2 Docking Snake venom DFT calculations Conformational analysis abstract 4-Chlorothiobenzoic acid S-benzyl ester (I), 3-nitrothiobenzoic acid S-benzyl ester (II), 4-nitrothiobenzoic acid S-benzyl ester (III) and 4-methylthiobenzoic acid S-benzyl ester (IV) were prepared and character- ized by 1 H and 13 C NMR, Mass spectrometry and IR spectroscopy. Quantum chemical calculations were performed with Gaussian 09 to calculate the geometric parameters and vibrational spectra. Phospholi- pase A 2 (PLA 2 ) was purified from Crotalus durissus cumanensis venom by molecular exclusion chromatog- raphy, followed by reverse phase-high performance liquid chromatography. Two studies of the inhibition of phospholipase A 2 activity were performed using phosphatidilcholine and 4-nitro-3-octanoyloxybenzo- ic acid as substrates, in both cases compound II showed the best inhibitory ability, with 74.89% and 69.91% of inhibition, respectively. Average percentage of inhibition was 52.49%. Molecular docking was carried out with Autodock Vina using as ligands the minimized structures of compounds (I–IV) and as protein PLA 2 (PDB code 2QOG). The results suggest that compounds I–IV could interact with His48 at the active site of PLA 2 . In addition, all compounds showed Van der Waals interactions with residues from hydrophobic channel of the enzyme. This interaction would impede normal catalysis cycle of the PLA 2 . Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Snakebites represent a relevant public health issue in many regions of the world, particularly in tropical and subtropical countries of Africa, Asia, Latin America and Oceania [1]. The path- ophysiological effects observed in ophidian bites combine the action of several enzymes, proteins and peptides, which include phospholipases A 2 , hemorrhagic metalloproteases and other prote- olytic enzymes, coagulant components, neurotoxins, cytotoxins and cardiotoxins, among others [2]. Phospholipases A 2 (PLA 2 ; EC 3.1.1.4) are enzymes that abundantly occur in snake venoms with crucial action in the hydrolysis of phospholipids. PLA 2 can also induce several pharmacological effects such as edema, modulation of platelet aggregation, as well as neurotoxic, anticoagulant and myotoxic effects [3,4]. The structure of PLA 2 s is composed of three long helixes (two of them are antiparallel), two antiparallel b sheets and a calcium- binding loop. These proteins have a variable length from 119 to 134 amino acids. Their antiparallel a helixes (residues 37–57 and 90–109, respectively) together with the N-terminal helix (residues 1–12), define the hydrophobic channel. This structure leads the substrate to the active site, which is formed of four residues: His48, Asp49, Tyr52 and Asp99. Asp49 in combination with Tyr28, Gly30 and Gly32 form the calcium-binding loop, which is responsible for coordinating the Ca 2+ required during catalysis [5]. In addition, there is an interfacial binding surface, which medi- ates the adsorption of the enzyme onto the lipid–water interface of 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.06.031 ⇑ Corresponding author. Tel.: +57 4 2195476. E-mail address: ihenao@farmacia.udea.edu.co (I.C. Henao Castañeda). Journal of Molecular Structure 1028 (2012) 7–12 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc