Introduction
Treatment for bacterial infections is becoming complicated day by day due to the ability of bacteria to develop resistance to antimicrobial agents,1 Microorganisms have become resistant to currently used antibiotics due to over-prescription of antibiotics, and their inappropriate use by patients. This challenges the treatment even though previously used antibiotics or antimicrobial drugs are no longer effective, and infections become progressively difficult to treat.2 Hence, it is essential to design and discover new and safer as well as more effective antimicrobial drugs,3 Literature survey revealed that 1, 3, 4-oxadiazole possess diverse pharmacological activities such as anticancer,4 antimicrobial,5, 6 anti-hypertensive,7 anticonvulsant,8 antimalarial,9 antiviral,10 anti-inflammatory.11 Some of 2, 5-disubstituted 1, 3, 4- oxadiazole based entities have emerged as most potent antimicrobial activities.12, 13, 14 CYP51 is one of the key enzyme of ergosterol biosynthesis in different biological kingdoms and is found in eukaryotes (including humans). Inhibition of ergosterol synthesis, as the new structures fit very well in the active site of the lanosterol 14α-demethylase enzyme. It takes part in the synthesis of ergosterol, the main sterol component of the fungal cell membrane and serves the metabolic function such as membrane permeability, membrane fluidity, enzyme activity, cell morphology, and cell cycle progression. Inhibition of this enzyme causes loss of cell continuity and cell dysfunction.15 1, 3, 4-Oxadiazole block the 14α-demethylation of lanosterol into ergosterol, which is a major component of fungal cytoplasmic membranes and a bioregulator of membrane asymmetry, fluidity and integrity.16, 17, 18, 19, 20, 21, 22, 23, 24, 25
Materials and Methods
In silico ADME (Absorption, Distribution, Metabolism and Excretion Studies)
ADME describes the pharmacokinetics of the molecules within the body of organisms. It evaluates the risk of a pharmacological compound being administered to the human body or other organisms. These pharmacokinetic properties are identified in silico using an online tool such as SwissADME (http://www.swissadme.ch/),24 preADMET (https://preadmet.bmdrc.kr/). According to the Lipinski’s rule of 5, the two or more violation makes the molecules orally inactive. Drug likeness is the complicated balance of multiple chemical characteristics and structure features that determines whether a molecule is similar to the medications that are already on the market. These properties include hydrophobicity, hydrogen bonding characteristics, electronic distribution, flexibility, molecule size, and the presence of several pharmacophoric features all influence a molecule's behavior in a living organism, including transport properties, bioavailability, reactivity, affinity to proteins, toxicity, metabolic stability, and many other factors.20
Molecular docking studies
To predict the binding interaction of designed 2,5 disubstituted 1,3,4-Oxadiazole derivatives with targeted protein, molecular docking is performed. The targeted protein is the CYP51 (PDB ID: 6AYC). Molecular docking is performed using Autodock Vina software. Before docking, the protein was prepared using the Discovery visual studio tool. The protein is downloaded from PDB and the unwanted atoms such as water molecules, hetero atoms, unwanted chains, cofactors are removed, making the protein ready for interaction. The designed 2, 5 disubstituted 1, 3, 4-Oxadiazole derivatives are optimized by using Chem 3D software to minimize the energy of the structure.
Result and Discussion
To be a successful medicine, the chemical must have high biological activity at low effective concentrations, low toxicity, and the ability to remain active until the intended result occurs. As the 1, 3, 4-Oxadiazole nucleus is reported widely to treat microbial infection, new derivatives containing 2, 5 disubstituted 1, 3, 4-Oxadiazole are designed for its antimicrobial activity, targeting the ergosterol biosynthesis inhibitor activity. From the Pass online (http://way2drug.com/PassOnline/predict.ph). All the designed compounds are given in Figure 2. It was found that the designed compound shows ergosterol biosynthesis inhibitor activity with a minimal adverse drug reaction.
Table 1
Druglikeness analysis of designed 2, 5 disubstituted 1,3,4-Oxadiazole derivatives
Absorption, distribution, metabolism and excretion (ADME results)
All the designed compounds violate only one rule, so we can say that the molecules are orally active. The results of ADME studies are given in Table 1, Table 2. From the designed compounds follow the rule of 5 having octanol-water partition coefficient (mol log P) not greater than 5 except C4 and C6,24
Table 2
In silico ADME properties of 2, 5 disubstituted 1,3,4-Oxadiazole designed derivatives.
Table 3
Docking study of the designed2, 5 disubstituted 1,3,4-Oxadiazole derivatives.
it is predicted that the molecules have good oral bioavailability. (Table 1) The water solubility is given as the logarithm of molar concentration. The water solubility of designed compounds is typically in the range of -5.00 to -6.00. (Table 1) Because of the presence of lipophilic functionalities aimed at improving cell permeability, the designed compounds are moderately water-soluble. The percent absorption of the compounds was calculated since the absorption of an orally administered medication occurs mostly through the small intestine. Because Caco2 cells from human colon cancer resemble intestinal epithelial cells, their permeability can predict drug intake. The compound having high permeability should have Papp > 8 x10-6 246 cm/s. Interestingly, all the designed compounds show high Caco-2 permeability. Also, all the compounds showed high intestinal absorption. (Table 2)
The distribution of the drug in the body was predicted using a volume of distribution (VDss), blood-brain barrier permeability, and fraction unbound. Higher value VDss implies better drug distribution in the tissues than in plasma, and Log VDss> 0.45 suggests more tissue distribution. All the compounds show the moderate distribution in tissues. The percent bound efficacy of medicine suggests that it is less bound to blood proteins and hence more free to distribute. The plasma protein binding model predicts whether a substance will bind strongly to blood carrier proteins. The percent PPB of the designed compound ranges from 92 to 100%. As a result of the designed compound, there's a high probability of these compounds can reach the desired targets. SwissADME and preADMET tools were used to calculate the permeability of the blood-brain barrier (BBB). All the designed compounds interact with cytochromes either as substrates or as inhibitors. The compounds are likely to have hepatotoxicity hence further study is necessary to determine the hepatotoxic dose level. All the designed compounds have good ADME and toxicity properties and can be considered as the probable lead candidate.
Molecular docking results
Molecular docking is a method for predicting the major binding mode of a ligand with a target protein of known 3D structure, which is an important tool in structure-based computer-assisted drug design.25 The designed 2, 5 disubstituted 1,3,4-Oxadiazole derivatives are docked well into the active site of the target protein (PDB ID: 6AYC) using autodock software. The designed compound C4, C8, C9 shows appropriate binding to the target protein by hydrogen bond and hydrophobic interaction whereas C1, C2, C3, C5, C6, C7, C10 shows hydrophobic bonding. Among this, C3, C7, C8, and C9 shows other interaction. The interactions established by the active compounds were within the 5 Å radius to the binding site of CYP51 protein. Almost all the compounds were active and C9 is the most active compound with minimum binding affinity are selected as potent inhibitors. Hydrophobic interaction of C9 with TYR, ILE and ALA are distinguished. There is also the formation of the hydrogen bonds between molecules TYR and HIS are fully recognized as indicated which have observed Table 2, Table 3. Docking studies revealed that the binding mode of the most active compounds with designed compound and target protein.
Conclusion
The 2, 5 disubstituted 1,3,4-Oxadiazole derivatives were designed and it's in silico parameter was studied. According to ADME studies all the designed compounds can be considered as lead molecules. Among the derivatives, C9 show the most potent inhibitor according to a molecular docking study. They interact with TYR, ILE and ALA to form hydrophobic interaction and with TYR and HIS form hydrogen bonding. The ADME study of these compounds reveals that they are suitable for drug-likeness. These derivatives have good PPB and intestinal absorption properties. Overall, the studies reveal that C9 compounds show potent inhibitors against CYP51 as an antimicrobial agent.
