Diazole and triazole derivatives of castor oil extract: synthesis, hypoglycemic effect, antioxidant potential and antimicrobial activity ; Diazoles y triazoles derivados del extracto de aceite de ricino: síntesis, efecto hipoglucémico, potencial antioxidante y actividad antimicrobiana

F. Taieb Brahimi , F. Belkhadem, B. Trari and A.A. Othman Département de classe préparatoire, Ecole Supérieure en Génie Electrique et Energétique d’Oran, Bp. 64 CH2 Achaba Hanifi USTO 31003 Oran, Algérie. Laboratoire de Synthèse Organique Bioactive, Département de Chimie Organique Industrielle, Faculté de Chimie, Université des Sciences et de la Technologie d’Oran, Mohamed Boudiaf-USTO-MB, BP. 1505, El-M’naouer, 31003 Oran, Algérie. Laboratoire scientifique et technique régional de police ORAN 31000, Algérie. Corresponding author: fawziatb@yahoo.fr


INTRODUCTION
Castor oil is a natural production of the castor plant (Ricinus Communis) (Mubofu, 2016). Castor oil plants are widespread throughout the globe, particularly in tropical regions such as India, the southeastern Mediterranean Basin of North Africa (Trochain, 1930), Los Angeles, California (Witchard, 1997) and elsewhere. Castor oil has many uses; for example, it remains of commercial importance as a non-freezing, antimicrobial, pressure-resistant lubricant for special purposes, either for latex or metals, or as a lubricating component in fuels (Imankulov, 2012). Castor oil has long been used on the skin to prevent dryness. Whether pure or processed, it is still a component of many cosmetics (Bianchi et al., 2011;Rachapudi et al., 2017).
The high percentage of ricinoleic acid residues in castor oil and their derivatives inhibit virus, bacteria or fungi (Ghosh et al., 2013). The literature has revealed several synthetic modifications and utilization of ricinoleic acid. These modifications vary between ethylenic bond (Godard et al., 2013) hydroxyl group (Thames et al., 2006) and carboxylic acid group (Dutta et al., 2011;Lavanya et al., 2012).
Heterocyclic-fatty acid hybrids such as oxadiazole, thiadiazole and triazole derivatives of vegetable oils are a new class of fatty acid derivatives with a wide range of biological activities and significance in the field of medicinal chemistry. They possess a broad spectrum of therapeutic uses such as analgesic, antimicrobial, anti HIV activity, antitumor, antimalarial, anticancer, anticonvulsant, anti-diabetic, antioxidant (Cao et al., 2014;Ahmad et al., 2017).
This work is mainly concerned with the extraction of castor oil from seeds of the plant and the isolation of ricinoleic acid. The latter was subjected to synthetic modifications focused on the carboxylic group to ultimately give six diazole derivatives. The synthetic intermediates and final products were studied to determine the biological evaluation of their α-amylase inhibitory, antimicrobial and antioxidant activities.

General
All reactions were monitored by TLC, silica gel F254, made by Merck, Germany. Melting points (ºC) were measured in open glass capillaries using a Branstead 9001 Electrothermal melting point apparatus and were not corrected. The UV visible electron spectroscopy was recorded on an Optisen View 4.2 spectrometer. The IR spectra were recorded using KBr disks in a GENESISIIFTIR spectrophotometer, in ν units of cm −1 . The 1 H and 13 C-NMR spectra (1D) were recorded on a Bruker AC 400 MHz spectrometer (University of Lyon 1, France) in DMSO-d 6 and referenced to TMS. Symbols δ were used for chemical sifts in ppm, s = singlet, d = doublet, dd = double doublet and m = multiplets. Mass spectra were obtained using a GC-MS CLARIS 500 (Laboratoire Régional de Police Scientifique d'Oran, Algeria). The microorganisms in this study were supplied and identified by the laboratory of microbiology by the university hospital of Oran1. The Mueller Hinton medium was supplied by (Difco).

Antioxidant activity (DPPH radical scavenging assay)
The DPPH solution was prepared in advance by dissolving 4 mg of DPPH in 100 mL of absolute methanol. 0.1 mL of each sample at different concentrations (65.5; 125; 250; 500; 1000) μg/mL were added to 3.9 mL of DPPH. Reference antioxidant solutions (ascorbic acid) were also prepared under the same conditions to serve as a positive control. The negative control consisted only of DPPH and methanol. The mixture was left in the dark for 30 min until discoloration. The presence of the DPPH radicals gave a dark purple color to the solution and which was absorbed rapidly at 517 nm when reduced. The color became pale yellow. During the reaction, the layer of this radical became saturated on contact with an antioxidant, which explained the disappearance of its coloring. This discoloration highlighted the trapping power of the free radical by the tested product. The percentage of the anti-free radical activity was estimated according to the equation below (Vijayalaxmi et al., 2015): PI % = (Abs control -Abs product /Abs control) *100 PI: Percentage inhibition Abs control: Absorbance at the 517 nm wavelength of the negative control (DPPH + methanol).

α-Amylase inhibition activity
The α-amylase inhibitory activity of the synthetic compounds was determined using the chromogenic DNSA method with a few modifications (Adegboye et al., 2018). 300 μl of 0.02 M sodium phosphate buffer (pH 6.9) containing α-amylase solution (0.5 mg/ mL) and 300 μl of sample at different concentrations (62.5; 125; 250; 500; 1000) μg/mL were incubated at 37 °C for 30 min. Afterwards, 300 μl of a 1% starch solution in 0.02 M sodium phosphate buffer were added to each tube at timed intervals. The reaction mixtures were then incubated at 37 °C for 15 min. The reaction was stopped with 0.5 mL of dinitrosalicylic acid (DNSA) color reagent. The reaction mixture was then diluted after adding 5 mL of distilled water, and absorbance was measured at 540 nm. The α-amylase inhibitory activity was calculated as follows: Where A samp and A cont were defined as absorbance of the sample and the control, respectively.
site of action of the products tested on bacterial cells was the plasma membrane. This was directly related to the amphiphilic nature of the tested products which facilitated their insertion between the membrane phospholipids and ensured their solubilization in the lipid bilayer (Soliman et al., 2015). The good activity was attributed to the presence of pharmacologically active groups NH-CS-NH, C = O and C = S attached to the heterocyclic nuclei (triazoles, oxadiazoles and thiadiazoles). The presence of amine functions (NH 2 ) provided the tested molecules a higher activity on mushrooms than those of other products.

Antioxidant activity
From a methodological point of view, the free radical test, 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) is recommended for compounds containing the SH, NH and OH (Barbuceanu et al., 2014) groups and was carried out at ambient temperature. This made it possible to eliminate any risk of thermal degradation of labile molecules (Li et al., 2018). This test consisted of the reduction of an alcoholic solution of the radical species DPPH • in the presence of a hydrogen donor antioxidant (AH), which resulted in the formation of a non-radical form of DPPH-H. Based on the experimental results (see Figure 4), the starting ricinoleic triglyceride (1), ester (2) and diazoles (4, 5, 7, 9, 10 and 11) showed high activity at different concentrations. Indeed, the structure-activity relationship of the heterocycle showed that the scavenging activity of the radicals increased with the presence of the hydrogen donor groups (-NH 2 , -NH, -SH, -OH). The conjugation between the free radicals of the hetero atoms (Nitrogen, Oxygen, Sulfur) and the π electrons of the aromatic ring represented an additional factor to increase the stability of the radical structure.
IC 50 (Inhibitory concentration 50), also referred to as EC 50 (Efficient Concentration 50), is the concentration of the test sample needed to reduce 50% of the DPPH radical. The IC 50 are calculated graphically by percent inhibition as a function of different concentrations of the tested product. From the value shown in Table 3, we noted a strong antiradical power for castor oil, which resulted in a fairly low IC 50 , comparable to that of the standard compound ascorbic acid.