QSAR Studies of some New Synthesized Diacylhydrazine Compounds Derived from Indomethacin as Caspase-1 Inhibitors

Indomethacin (1) reacts with absolute ethanol in presence of conc. sulphuric acid to form the ester (2). This ester was converted into the hydrazide (3) by treatment with hydrazine hydrate. The reaction of the hydrazide (3) with acid chlorides (of indomethacine, dichlofenac, mefenamic acid, aspirin and ibuprofen) in dry xylene afforded the N,N’-diacylhydrazine compounds (4-8). A series of new 2,5-disubstituted-1,3,4-oxadiazoles (9-13) derived from indomethacin (1) was obtained by the dehydrative cyclization of the corresponding N,N’-diacylhydrazines(4-8), in presence of an excess of thionyl chloride. The quantitative structure-activity relationship (QSAR) analysis of the synthesized compounds was also performed to compute the parameters that affect the biological activity (inhibitory activity IC50). Docking analysis was also performed to predict the interactions between the synthesized compounds with Caspase-1 (Interleukin-1 converting enzyme). The study is aimed to predict factor affecting the biological activity of the prepared compounds by employing the QSAR analysis. The structures of the synthesized compounds were confirmed by the spectroscopic methods.


INTRODUCTION
The 2,5-disubstituted-1,3,4-oxadiazole compounds have been reported to be remarkable antidepressive (Almasirad et al., 2004), anticonvulsive (Kashaw et al., 2010), antihypertensive (Bankar et al., 2004), anti-inflammatory (Chandra et al., 2010), antiviral (Wang et al., 2012), antitumor (Savariz et al., 2010, antimicrobial agents (Oliveira et al., 2012), as well as insecticides (Shi et al., 2001). Moreover, they have an interesting electrochemical (Yasuda et al., 2005) and fluorescent properties (Agbaria and Gill, 1994). N,N'-diacylhydrazines are easily accessible starting from acids, acid chlorides or esters and respectively various hydrazides (Dingemans et al., 2001) and are valuable intermediates in the synthesis of cyclic compounds. The most common synthetic strategy for preparing 2,5-substituted-1,3,4-oxadiazoles involves the dehydrative cyclization of N,N'diacylhydrazines using dehydration agents such as POCl 3 (Amir and Kumar, 2007), SOCl 2 (Hernández-Ainsa et al., 2012) or P 2 O 5 (Carlsen and Jorgensen, 1994). The present work is concerned with the preparation of compounds from N,N'-diacylhydrazines containing indomethacin moiety and studying its biological activity as Caspase-1 inhibitor by using quantitative structure activity relationship (QSAR). On the other hand, the QSAR is considered one of the most important field in medicinal chemistry, giving useful information applied to drug design. QSAR models are mathematical equations relating chemical structure to a wide variety of physical, chemical and biological properties. The derived relationship between molecular descriptors and activity is used to estimate the property of other molecules and/or to find the parameters affecting the biological activity (Hansch, 1969).

EXPERIMENTAL
Melting points were determined on an electrothermal IA 9300 Digital-series (1998) apparatus, and they were uncorrected. Infrared spectra were recorded on a Bruker FT-IR spectrophotometer Tensor 27, Germany (College of Education, Mosul University). UV spectra were recorded on a Shimadzu UV/Vis-1650 pc spectrophotometer using chloroform as a solvent (College of Science, Mosul University).
The QSAR study was performed using the previously reported biological activity values (IC 50 nM) (Soper et al., 2006). These values are used as dependent variables. The physicochemical properties [i.e. Lipophilic (CLogP) and Electrostatic (Chemical hardness η)] were calculated using AM 1 as an independent variable in linear regression analysis, then the QSAR models were designed using SPSS (11.5) program. The docking process was carried out using iGEMDOCK v.2.1 program.

Synthesis of [1-(4-chlorobenzoyl)-2-methyl-5-methoxy-1H-indol-3-yl] acetic acid hydrazide (3). General method
To a solution of ester (2) (0.1 mole, 38.55 g) in 100 ml absolute ethanol, hydrazine hydrate (0.5 mole, 7.26 ml) (the hydrazine hydrate (80%) was freshly distilled in presence of sodium hydroxide) was added and the reaction mixture was refluxed for 48 hr. The precipitate was separated on cooling and collected by filtration, then recrystallized from dry benzene to afford the hydrazide (3)  To a solution of an acid (indomethacine, dichlofenac, mefenamic acid, aspirin or ibuprofen) (0.01 mole) in 20 ml of dry benzene, (0.013 mole, 1.53 g) of thionyl chloride was slowly added then the reaction mixture refluxed for 4 hr. The mixture (benzene and excess of thionyl chloride) was evaporated under reduced pressure to dryness. To the solid residue, a solution of acylhydrazine (3) (0.015 mole,5.565 g) in 40 ml of dry xylene and (0.01 mole, 0.82 ml) dry pyridine was added. The reaction mixture was stirred under reflux for 60 min. The resulted precipitate was filtered off and washed with water, dried and recrystallized from a mixture of ethyl acetate and ether or petroleum ether (80-100) o C. The physical properties and spectral data of compounds (4-8) were listed in (Table 1). :

Synthesis of the oxadiazoles (9-13)
To a suspension of (0.01 mole) of N,N'-diacylhydrazine (4-8) in (5 ml) thionyl chloride, (0.5 ml) dry pyridine were added dropwise. The mixture was stirred at room temperature overnight, then refluxed for 30 min. The pyridine and the remained thionyl chloride were removed under vacuum. The remained residue was recrystallized from ethanol to give pure products (9-13). The physical properties and spectral data of compounds (9-13) were listed in (Table 1).
The QSAR study was performed using the calculation of lipophilicity (ClogP) and Electrostatic (Chemical hardness η) as shown in (Table 2) as independent variables in Linear regression analysis which give a QSAR models as shown in equation (1) for 13 compounds described in (Table 2) to obtain inhibitory activity IC 50 toward Caspase-1 (Interleukin-1 converting enzyme) the target is Homo sapiens. IC 50 = -3886.37+ 94.18*CLogP + 911.00*η ……(1) (n =13; correlation coefficient (r) = 0.913) η = (E LUMO -E HOMO)/2 The best biological activity of the synthesized compounds as Caspase-1 inhibitor was exhibited by compound 7 as shown in Table (3), while for the proposed compounds (14-23), the best biological activity as Caspase-1 inhibitor was exhibited by compound 17 as shown in Table  (5). Molecular docking studies have been carried out to get an insight into the inhibitor of Caspase-1 by the selective antagonist of indomethacin derivative compounds. Our investigation has shown that the best docking energy is -138.991 kcal/mol for the synthetic compound (4) with Caspase-1 as shown in Table (  Scheme 1: Synthesis of some N,N'-diacylhydrazines Linked to 2,5-disubstituted-1,3,4oxadiazoles.