Skip to main content

In vitro antibacterial and in silico docking studies of two Schiff bases on Staphylococcus aureus and its target proteins



Schiff base compounds have extensive applications in various fields such as analytical, inorganic, organic, and biological fields. They have excellent pharmacology application prospects in the modern era and are widely used in the pharmaceutical industry. In the present work in vitro antibacterial and in silico docking studies of two Schiff base compounds 2,2’-(5,5-dimethylcyclohexane-1,3-diylidene)bis(azan-1-yl-1-ylidene)diphenol (DmChDp) and N,N’-(5,5-dimethylcyclohexane-1,3-diylidene)dianiline (DmChDa) were carried out against the bacterial strain Staphylococcus aureus and its target proteins.


The tests proved that the ligands have potential antibacterial activity. In the computational analysis, the drug-like properties of the compounds were first pre-filtered using the Lipinski rule of five. Then, molecular docking study was conducted using the AutoDock 4.2 program, to establish the mechanism by which the molecules inhibit the growth of S. aureus. For this purpose, 6 different target proteins (PDB ID: 1T2P, 3U2D, 2W9S, 1N67, 2ZCO, and 4H8E) of S. aureus were selected. Both the Schiff bases showed a good binding affinity with the target protein dihydrofolate reductase enzyme (PDB ID: 2W9S) but in different sites. Maximum binding energies of about − 10.3 and − 10.2 kcal/mol were observed when DmChDp and DmChDa were docked with 2W9S.


Schiff base compounds DmChDp and DmChDa have appreciable growth-inhibitory power against S. aureus, which can be attributed to the deactivation of the enzyme, dihydrofolate reductase.


The research in the field of therapeutics is of great importance for the improvement of the quality of human life and for reducing human diseases. A vast number of diseases is due to pathogenic organisms. Pathogens are microorganisms that are harmful to the human body. Bacteria, viruses, fungus, prion, protozoan, viroid, etc. are the different types of pathogens. Microbial infections are drastically increased in living beings due to multi-drug-resistant microorganisms even though the human body can defend against potential pathogens [1,2,3].

S. aureus is one of such multi-drug-resistant microorganisms. It is a round-shaped bacterium that is a member of Firmicutes [4]. The cell wall of this species is amorphous and tough. The major component of the cell wall is the peptidoglycan (50% of cell wall mass). The other component that contributes 40% of cell wall mass is teichoic acids and the remaining 10% consist of exoproteins, surface proteins, and peptidoglycan hydrolases. Naturally, this bacterium is found in the nasopharynx of the human body and on the skin. S. aureus can cause infections of the nose, skin, vagina, urethra, and gastrointestinal tract [5, 6]. They are non-sporing, non-motile, and few strains are encapsulated. Nearly 50% of the human population are carriers of S. aureus. Generally, beta (β)-lactum antibiotics such as Penicillin, Carbapenems, Monobactams, and Cephalosporins are used to heal infections caused by Staphylococcus aureus. These drugs bind with proteins in the bacteria and thereby inhibit the bacterial cell wall synthesis [7]. But several studies showed that beta (β)-lactum antibiotics have a low binding affinity with Penicillin-binding proteins and are a major cause for less antibiotic activity [8,9,10]. Even though a large number of antibiotics and chemotherapeutic agents such as linezolid and dalfopristin are available to resist such microorganisms, they are costly and are used only for patients having highly resistant strains [11]. Thus, the development of efficient and novel chemotherapeutic agents in the medical field is of great importance.

Schiff bases are generally prepared by the condensation of carbonyl compounds (aldehyde/ketones) with aromatic or aliphatic primary amines [12]. It is regarded as a nitrogen analogue of an aldehyde or ketone where the imine group substitutes the C=O group. Therefore, it is also known as imine or azomethine. The lone pair of electrons in the sp2 hybrid orbital of N atom in –C=NH- linkage present in Schiff bases enhances their biological and chemical importance [13, 14]. They have widespread use as therapeutic agents and antibacterial agents [15,16,17]. The azomethine group can be seen in drugs like Thiacetazone 5 and Nifuroxazide (INN) 4 available in the market [18].

In the present study, the antibacterial activity of the Schiff bases 2,2’-(5,5-dimethylcyclohexane-1,3-diylidene)bis(azan-1-yl-1-ylidene)diphenol (DmChDp) and N,N’-(5,5-dimethylcyclohexane-1,3-diylidene)dianiline (DmChDa) were analysed using disc diffusion method against the pathogenic bacteria S. aureus (Fig. 1). Apart from this, a molecular docking study was also carried out using the AutoDock 4.2 program to predict the best-fit orientation of the drug molecule that binds to a specified protein target of interest to find out the activity and affinity of the drug molecule. This will enable to establish the mechanism by which the Schiff base prevents bacterial growth. Sortase-A (1T2P), DNA gyrase (3U2D), dihydrofolate reductase (DHFR) (2W9S), clumping factor A (ClfA) (1N67) dehydrosqualene synthase (CrtM) (2ZCO), and undecaprenyl diphosphate synthase (UPPS) (4H8E) are the target proteins of S. aureus considered for the study. The two sites of the target 4H8E and four sites of all other targets were selected for docking.

Fig. 1
figure 1

Structure of a DmChDp and b DmChDa


Analar grade samples were used for the synthesis of Schiff bases. 5, 5-dimethylcyclohexanone, 2-aminophenol, and aniline, were purchased from E. Merck. The percentage of elements such as carbon, hydrogen, and nitrogen were analysed by microanalysis using Elementar make Vario EL III model CHNS analyser. KBr disc technique on a Shimadzu model FT-IR Spectrometer (Model IR affinity) were used for recording IR spectra in the region 4000–400 cm−1. Shimadzu UV-Visible-1800 Spectrophotometer was used for recording electronic spectra in DMSO. BRUKER AVANCE III HD was used for 1H NMR and 13C NMR studies in dmso-d6. Mass spectra were recorded using QP 2010 model Shimadzu GCMS.

Synthesis and characterization of Schiff bases

2,2’-(5,5-dimethylcyclohexane-1,3-diylidene)bis(azan-1-yl-1-ylidene)diphenol (DmChDp)

To a stirred ethanolic solution of 2-aminophenol (0 .02 mol), 5,5-dimethyl-1,3-cyclohexanedione (0.01 mol) dissolved in hot ethanol was added, refluxed for 20 min and cooled. Brown-coloured precipitate formed was filtered, washed with ethanol, and recrystallized. Yield was 80%, and M.P. 180 °C [19].

Anal.calcd for C20H22N2O2 was C, 74.53; H, 6.83; and N, 8.69%. Found. was C, 73.91; H, 6.74; and N, 8.52%; IR (KBr) was 3240 cm−1 (OH), 1600 cm−1 (C=N), 1238 cm−1 (C-O), 3080 cm−1 (aromatic C-H), and 2960 and 2877 cm−1 (aliphatic C-H); UV was 22936 cm−1 (n → π*), and 33784 and 39682 cm−1 (π → π*); 1H NMR was δ 0.99 (CH3), δ 2.35 (CH2 between two azomethine group), δ 2.02 (CH2 adjacent to > C(CH3)2), and δ 6.81–7.07 (aromatic H); 13C NMR was 95.88ppm (C=N), 27.84ppm (CH3), 41.52ppm (C containing CH3), 49.78ppm (C between azomethine groups), 32.32ppm (C adjacent to > C(CH3)2), and 116.28–151.55 ppm (aromatic C); mass was M+ peak absent, m/z 216 (base peak) [C14H18NO]+, m/z 231 [C14H19N2O]+, and m/z 178 [C11H16NO]+.

N, N’-(5,5-dimethylcyclohexane-1,3-diylidene)dianiline (DmChDa)

0.01 mol of 5,5-dimethyl-1,3-cyclohexanedione was dissolved in hot ethanol and added to a stirred ethanolic solution of 0.02 mol of aniline. Refluxed for 3h and cooled. Yellow precipitate separated was filtered, washed with ethanol, and recrystallized. Yield was 78%, and M.P. 152 °C [20].

Anal.calcd for C20H22N2 was C, 82.7; H, 7.5; and N, 9.6%. Found. was C, 81.3; H, 6.9; and N, 8.9%; IR (KBr) was 1564 cm−1 (C=N); 1249 and 3234 cm−1 (N-H); 2949, 2879, and 2810 cm−1 (CH3 and CH2); and 3055 cm−1 (aromatic H); UV was 32020 cm−1 (n → π*), and 39463 cm−1 (π → π*); 1H NMR was δ 1.04 (CH3), δ 1.51 (CH2 between two azomethine group), and δ 7.26,7.09 (aromatic H); 13C NMR was 28.35 ppm (CH3); 98.94 ppm (C=N); 32.88, 43.71, and 50.35 ppm (two CH2); and 123.39–138.14 ppm (aromatic C); mass was M+ peak absent, m/z 159 (base peak-[C11H13N]+), m/z 215 [C14H20N2]+, and m/z 198 [C14H18N]+.

In vitro antibacterial studies

Mueller-Hinton agar was used for preparing the medium [21]. Schiff base compounds and the standard antibiotic ampicillin were dissolved in DMSO to prepare the stock solutions. Then, it is diluted to obtain various ranges of concentrations from 100 to 500 μg disc−1. Disc diffusion method was adopted for the drug [22]. The petri dishes were incubated in an air ambiance at 35 °C for 24 h. The diameter of the zone of inhibition was measured and compared with zones produced by the reference antibiotic, ampicillin.

Target proteins in Staphylococcus aureus

Staphylococcus aureus sortase-A (PDB ID: 1T2P)

Sortases are extracellular transpeptidases of Gram-positive bacteria [23, 24]. The function of the enzyme is to sort proteins into the cell wall compartment of Gram-positive bacteria, hence named Sortases. Sortases have a great role in the cell wall envelope assembly and bacterial pathogenicity.

DNA gyrase (PDB ID: 3U2D)

Topoisomerase is an isomerase enzyme that provokes dramatic change in the topology of DNA structure [25, 26]. Topoisomerase is categorized as topoisomerase I and topoisomerase II, based on the number of strands cut in one phase of action. New topoisomerases, type III and IV have also been discovered recently. DNA gyrase subclass of type II topoisomerase is responsible primarily for DNA replication.

Dihydrofolate reductase (DHFR) (PDB ID: 2W9S)

Dihydrofolate reductase (DHFR) is an enzyme that catalyses the formation of tetrahydrofolate (THF) by the reduction of Dihydrofolate (DHF) in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) [27, 28]. Also, it has a great role in the synthesis of thymidylate, purines, methionine, and some other important metabolites. These enzymes are required for cell proliferation. Thus, inhibition of dihydrofolate reductase will results in the destruction of the intracellular tetrahydrofolate pool thereby preventing biosynthesis of RNA, DNA, thymidine, and protein. Due to the wide range of cellular functions, they are targets for anticancer and antimicrobial agents.

Clumping factor A (ClfA) (PDB ID: 1N67)

In blood plasma, there is a glycoprotein called fibrinogen (Fg) which is present at ~ 3 mg/ml concentration and has a significant role in coagulation and haemostasis. Six polypeptide chains are present in fibrinogen such as 2 Aa, 2 Bb, and 2 nd 2 Bb, which are dimeric and symmetrical. The γ-chain has C-terminal residues which are biologically important. In the process of fibrinogen-dependent platelet adherence and aggregation, they interact with platelet integrin aIIb3. This C-terminal residue of γ-chain is also targeted by the pathogenic bacterium Staphylococcus aureus, resulting in fibrinogen-dependent cell clumping and tissue adherence. Clumping factor A (ClfA) [29, 30] was the first Fg γ-chain-binding S. aureus adhesin identified.

Dehydrosqualene synthase (CrtM) (PDB ID: 2ZCO)

The golden carotenoid pigment staphyloxanthin is a virulence factor for S. aureus. Dehydrosqualene synthase [31, 32] is involved in the synthesis of this pigment. The main responsibility of the pigment is to preserve S. aureus against oxidative stress as a result of host immune defence by reactive oxygen species and neutrophils by acting as an antioxidant.

Undecaprenyl diphosphate synthase (UPPS) (PDB ID: 4H8E)

The role of undecaprenyl diphosphate synthase (UPPS) in the biosynthesis of the cell wall of Staphylococcus aureus is very significant [33, 34]. UPPS is important since it is vital for the formation of peptidoglycan. Also, UPPS is not present in humans and is additional merit for the development of good antibacterial agents.

In silico molecular docking studies

Lipinski rule of five

Lipinski rule envisages that an orally active drug will be small and slightly lipophilic. This rule depicts molecular properties rather than pharmacological activity and states that a drug has good oral activity if it satisfies the five conditions such as the following [35]:

  1. 1.

    Molecular weight < 500

  2. 2.

    Octanol-water partition coefficient logP < 5

  3. 3.

    Less than 5 hydrogen bond donors (total number of NH and OH bonds)

  4. 4.

    Less than 10 hydrogen bond acceptors (total number of N and O atoms)

  5. 5.

    Molar refractivity between 40 and 130

Molecular docking

Docking studies were carried out to establish the mechanism by which the Schiff base compounds prevent bacterial growth. Binding affinity and interactions of the Schiff bases with different target proteins in S. aureus were derived from docking studies [36,37,38]. The steps involved in the docking process are as follows.

Preparation of ligands and proteins

The structure of the Schiff bases in MOL format was derived using ChemSketch software and converted to PDB format using open babel software. The structures of the proteins were downloaded in PDB format from RCSB PDB. Using Pymol software, water molecules and ligands already present in the proteins were removed; hydrogen atoms were added and saved in PDB format. Six target proteins of Staphylococcus aureus were utilized to check the interaction with synthesized Schiff bases.

Prediction of active site

Prediction of the active site is important in structure-based drug design. Co-ordinates of binding sites of the proteins were identified using the software BIOVIA Discovery Studio.


Molecular docking calculations were carried out with the aid of the software AutoDock 4.2 and binding energy of the protein—Schiff base adducts were obtained [39].

Visualization of protein-ligand complexes

The protein-ligand complexes were visualized using the software BIOVIA Discovery Studio and their 3D and 2D interaction plots were derived. Hydrogen bond interactions such as conventional and non-conventional H bonds, hydrophobic interactions such as amide-pi stacked, pi-pi stacked, pi-sigma, pi-pi T-shaped, alkyl and pi-alkyl interactions, electrostatic interactions such as pi-anion and pi-cation interactions, van der Waals interaction, and unfavourable donor-donor and acceptor-acceptor interactions are commonly seen between protein and ligand. The binding affinity of the compound with the target protein is the resultant of all the interactions and binding energy existing between them.


The antibacterial activity of the Schiff base compounds is shown in Table 1. Results showed that they have appreciable growth-inhibitory power. The compounds were first pre-filtered using Lipinski rule of five to check the drug-like properties. The parameters such as mass, number of hydrogen bond donors, number of hydrogen bond acceptors, log P (octanol-water partition coefficient), and molar refractivity of both Schiff bases were evaluated by the rule and are given in Table 2.

Table 1 Antibacterial activity of the Schiff bases and ampicillin
Table 2 Lipinski rule of five

In vitro antibacterial study showed that the ligands DmChDp and DmChDa have the potential to act as good antibacterial agents. Now, it is necessary to understand the mechanism by which the compounds inhibit the growth of bacteria. For that, molecular docking studies were conducted, by the aid of which we get an idea about the protein target in bacteria with which the ligands have more binding affinity. The stability of the protein-ligand complex was evaluated on the basis of two essential criteria: (1) the highest binding energy and (2) the number of interactions of the ligand with the active site residues. The highest binding energies (BE) and the number of interactions of the ligands with protein models under study were enlisted in Table 3. A ligand can mainly undergo interactions such as van der Waals, hydrogen bonding, hydrophobic, and electrostatic while docking into the active site. From literature, it is clear that binding energy has a great role than the number of interactions to predict the best binding mode. Among the interactions, conventional H bond (HB) (more prominent) and hydrophobic interactions are more effective than the others. Table 4 indicates the amino acid residues of different binding pockets interacted with the Schiff base molecules.

Table 3 Binding energy and number of interactions of Schiff bases docked with target proteins in S. aureus
Table 4 Interactions of Schiff bases with amino acid residues of target proteins in S. aureus

Binding energy and number of interactions clearly establish that both the Schiff bases have more binding affinity towards the enzyme dihydrofolate reductase (2W9S). The structure of the protein target dihydrofolate reductase (2W9S) is shown in Fig. 2.

Fig. 2
figure 2

Structure of the target protein dihydrofolate reductase (PDB ID: 2W9S)


In vitro antibacterial studies

Even though both compounds (DmChDp and DmChDa) have less activity than the standard antibiotic ampicillin, they showed appreciable growth-inhibitory power. The diameter of the zone of inhibition exhibited by ampicillin in S. aureus was 30 mm, while the Schiff bases DmChDp and DmChDa exhibited 26 mm and 25 mm respectively, at 500 μg disc−1 concentration. The zone of inhibition was found to be increasing with the concentration of the compounds. Thus, they can be considered good antibacterial agents for S. aureus.

Lipinski rule of five

According to this rule, an orally active drug must have less than two violations [35]. Results showed that the Schiff bases DmChDp and DmChDa have only one violation and hence they obey the Lipinski rule, suggesting that these compounds have the potential to behave as an orally active drug.

Docking studies of Schiff bases with targets in Staphylococcus aureus

Docking studies of DmChDp with 2W9S

From Table 3, it is clear that the Schiff base is more effective in sites 2 and 3 of the target 2W9S with a maximum binding energy of − 9.9 and − 10.3 kcal/mol, respectively. The interaction pattern showed that DmChDp interacted with the target 2W9S through 2 hydrogen bonds in active site 2 (LEU20, SER49 residues) and 1 hydrogen bond in active site 3 (ALA7 residue). In active site 2, the first hydrogen bond is formed between the nitrogen atom of the Schiff base (-C=N-) and H of LEU20. The second was originated from phenolic H to the N of SER49. In site 3, the hydrogen bond is formed between phenolic oxygen of the ligand and the H atom of ALA7 (2.24 Å).

The other interactions present in site 2 were carbon H bond (GLN19), alkyl interaction (LEU20, ILE50), pi-alkyl interaction (LYS29), and unfavourable acceptor-acceptor interaction (ILE14). In site 3, apart from conventional H bond, non-classical H bond, van der Waals, and hydrophobic interactions were also observed.

PHE92 and ILE5 residues present in site 3 of 2W9S interacted by means of pi-pi T-shaped and amide-pi stacked interactions, respectively. The amino acid residues LEU20 and ILE50 formed two alkyl interactions each and the residues ALA7, ILE31, ILE5, and PHE92 form pi-alkyl interactions. Considering binding energy and interactions, it is derived that DmChDp has more binding affinity towards site 3 of the protein target 2W9S. Thus, the inhibition mechanism of S. aureus by DmChDp may involve deactivation of the function of the dihydrofolate reductase enzyme.

Docking studies of DmChDa with 2W9S

DmChDa is also more effective in sites 2 and 3 of the target 2W9S with a maximum binding energy of − 10.5 and − 9.5 kcal/mol, respectively. In site 2, there is a conventional hydrogen bond interaction with SER49 residue (imine N with H of SER49, 2.06 Å), whereas in site 3, hydrogen bond interaction was absent. In both sites, there are three alkyl interactions (ILE50, LEU20), three pi-alkyl interactions (ILE14, ALA7, ILE5) and a pi-sigma interaction (ILE31). The van der Waals interaction is with ILE14 and PHE92 residue in sites 2 and 3, respectively. In addition to these interactions, there is an amide-pi stacked interaction with ASN18 in site 2. Based on the values of binding energy and interactions, it can be stated that DmChDa has more binding affinity towards site 2 of the target 2W9S. Thus, DmChDa also deactivates the dihydrofolate reductase enzyme preferentially than the other five enzymes.

In brief, out of the 6 target proteins selected for docking study, the Schiff base compounds are more active against dihydrofolate reductase enzyme and the growth-inhibitory power against S. aureus is attributed to the high binding affinity towards this enzyme. Also, the amino acid residues LEU20, ILE50, and PHE92 interacted with the cyclohexanone ring when both the compounds docked with the target 2W9S. 3D and 2D interaction diagrams of Schiff bases are shown in Figs. 3 and 4, respectively.

Fig. 3
figure 3

3D interaction diagrams of a DmChDp in site 3 of 2W9S and b DmChDa in site 2 of 2W9S

Fig. 4
figure 4

2D interaction diagrams of a DmChDp in site 3 of 2W9S and b DmChDa in site 2 of 2W9S


Schiff base compounds DmChDp and DmChDa have appreciable growth-inhibitory power on comparing with the inhibitory power of the standard antibiotic ampicillin against the pathogenic bacteria S. aureus. Maximum zone of inhibition of about 26 mm and 25 mm were shown by DmChDp and DmChDa, respectively, at a concentration of 500 μg disc−1. Both of them obeyed Lipinski’s rule of five and possess drug-like property. Among the target proteins selected for study, both the Schiff bases showed good binding affinity in sites 2 and 3 of the target protein dihydrofolate reductase enzyme (PDB ID: 2W9S). Maximum binding energies of − 10.3 and − 10.2 kcal/mol were observed for DmChDp and DmChDa docked with 2W9S, respectively, which clearly establish that the appreciable growth-inhibitory power of these Schiff bases against the pathogenic bacteria S. aureus is mainly due to deactivation of the enzyme, dihydrofolate reductase.

Availability of data and materials

Data and material are available upon request.







  1. Takeuchi A, Sprinz H, LaBrec EH, Formal SB (1965) Experimental bacillary dysentery. An electron microscopic study of the response of the intestinal mucosa to bacterial invasion. Am J Pathol 47(6):1011–1044

    CAS  PubMed  PubMed Central  Google Scholar 

  2. Mel D, Gangarosa EJ, Radovanović ML, Arsić BL, Litvinjenko S (1971) Studies on vaccination against bacillary dysentery. 6. Protection of children by oral immunization with streptomycin-dependent Shigella strains. Bull World Health Organ 45(4):457–464

    CAS  PubMed  PubMed Central  Google Scholar 

  3. Kaur S, Modi NH, Panda D, Roy N (2010) Probing the binding site of curcumin in Escherichia coli and Bacillus subtilis FtsZ–a structural insight to unveil antibacterial activity of curcumin. Eur J Med Chem 45(9):4209–4214.

    Article  CAS  PubMed  Google Scholar 

  4. Ogston A (1984) Classics in infectious diseases. Rev Infect Dis 6(1):122–128.

    Article  Google Scholar 

  5. Kluytmans J, Belkum AV, Herbrugh V (1997) Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks. Clin Microbiol Rev 10(3):505–520.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  6. Cole AM, Tahk S, Oren A, Yoshioka D, Kim YH, Park A, Ganz T (2001) Determinants of Staphylococcus aureus nasal carriage. Clin Diagn Lab Immunol 8(6):1064–1069.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Llarrull LI, Fisher JF, Mobashery S (2009) Molecular basis and phenotype of methicillin resistance in Staphylococcus aureus and insights into new β-lactams that meet the challenge. Antimicrob Agents Chemother 53(10):4051–4063.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  8. Sainsbury S, Bird L, Rao V, Shepherd SM, Stuart DI, Hunter WN, Owens RJ, Ren J (2011) Crystal structures of penicillin-binding protein 3 from Pseudomonas aeruginosa: comparison of native and antibiotic-bound forms. J Mol Biol 405(1):173–184.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  9. Turk S, Verlaine O, Gerards T, Zivec M, Humljan J, Sosic I, Amoroso A, Zervosen A, Luxen A, Joris B, Gobec S (2011) New noncovalent inhibitors of penicillin-binding proteins from penicillin-resistant bacteria. Plos One 6:1–9

    Article  Google Scholar 

  10. Yoshida H, Kawai F, Obayashi E, Akashi S, Roper DI, Tame JR, Park S-Y (2012) In silico study on penicillin derivatives and cephalosporins for upper respiratory tract bacterial pathogens. J Mol Biol 423(3):351–364.

    Article  CAS  PubMed  Google Scholar 

  11. Rayner C, Munckhof WJ (2005) Antibiotics currently used in the treatment of infections caused by Staphylococcus aureus. Intern Med J 36:142–143

    Google Scholar 

  12. Schiff H (1864) Mittheilungen aus dem Universitätslaboratorium in Pisa: Eine neue Reihe organischer Basen. Justus Liebigs Ann Chem 131(1):118–119.

    Article  Google Scholar 

  13. Singh P, Goel RL, Singh BP (1975) 8-acetyl-7-hydroxy-4- methyl coumarin as a gravimetric reagent for Cu2+ and Fe3+. J Indian Chem Soc 52:958–959

    CAS  Google Scholar 

  14. Elmali KM, Elerman Y (2000) Keto-enol tautomerism, conformations and structure of N-(2-hydroxy-5- methylphenyl), 2-hydroxybenzaldehydeimine. J Mol Struct 477:151–158

    Google Scholar 

  15. da Silva CM, da Silva DL, Modolo LV, Alves RB, de Resende MA, Martins CVB, de Fathima A (2011) Schiff bases: a short review of their antimicrobial activities. J Adv Res 2(1):1–8.

    Article  Google Scholar 

  16. Naeimi H, Nazifi ZS, Amininezhad SM, Amouheidari M (2013) Synthesis, characterization and in vitro antimicrobial activity of some new Schiff bases and their complexes. J Antibiot 66(11):687–689.

    Article  CAS  Google Scholar 

  17. Nayak SG, Poojary B (2019) Synthesis of novel Schiff bases containing arylpyrimidines as promising antibacterial agents. Heliyon 5:1–7

    Article  Google Scholar 

  18. Hassan AS, Askar AA, Nossier ES, Naglah AM, Moustafa GO, Al-Omar MA (2019) Antibacterial evaluation, in silico characters and molecular docking of schiff bases derived from 5-aminopyrazoles. Molecules 24:1–12

    Google Scholar 

  19. Ragi K, Joby TK, Vinod PR, Sini VC, Binsi MP (2019) Synthesis, cyclic voltammetric, electrochemical and gravimetric corrosion inhibition investigations of Schiff base derived from 5-5-dimethyl cyclohexanone and 2-aminophenol on mild steel in 1 M HCl and 0.5 M H2SO4. Int J Electrochem 2019:1–13

    Google Scholar 

  20. Ragi K, Joby TK, Vinod PR, Binsi MP, Reeja J (2020) Corrosion inhibition of mild steel by N,N’-(5,5-dimethylcyclohexane-1,3-diylidene)dianiline in acid media: Gravimetric and electrochemical evaluations. Curr Chem Lett 9:1–14

    Google Scholar 

  21. Mueller JH, Hinton JA (1941) Protein-free medium for primary isolation of the Gonococcus and Meningococcus. Proc Soc Exp Biol Med 48:3330–3333

    Article  Google Scholar 

  22. Bauer AW, Kirby WM, Sherris JC, Turck M (1966) Antibiotic susceptibility testing by a standardized single disk method. Am J Clin Pathol 45(4_ts):493–496.

    Article  CAS  PubMed  Google Scholar 

  23. Zong Y, Bice TW, Ton-That H, Schneewind O, Narayana SLV (2004) Crystal structures of Staphylococcus aureus sortase A and its substrate complex. J Biol Chem 279(30):31383–31389.

    Article  CAS  PubMed  Google Scholar 

  24. Raman N, Sobha S, Mitu L (2012) Synthesis, structure elucidation, DNA interaction, biological evaluation, and molecular docking of an isatin-derived tyramine bidentate Schiff base and its metal complexes. Monatsh Chem 143(7):1019–1030.

    Article  CAS  Google Scholar 

  25. Eakin AE, Green O, Hales N, Walkup GK, Bist S, Singh A, Mullen G, Bryant J, Embrey K, Gao N, Breeze A, Timms D, Andrews B, Uria-Nickelsen M, Demeritt J, Loch JT 3rd, Hull K, Blodgett A, Illingworth RN, Prince B, Boriack-Sjodin PA, Hauck S, MacPherson LJ, Ni H, Sherer B (2012) Pyrrolamide DNA gyrase inhibitors: fragment-based nuclear magnetic resonance screening to identify antibacterial agents. Antimicrob Agents Chemother 56(3):1240–1246.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  26. Gomathi G, Gopalakrishnan R (2016) A hydrazone Schiff base single crystal (E)-methyl N(')-(3,4,5-trimethoxybenzylidene) hydrazine carboxylate: physicochemical, in vitro investigation of antimicrobial activities and molecular docking with DNA gyrase protein. Mater Sci Eng C 64:133–138.

    Article  CAS  Google Scholar 

  27. Heaslet H, Harris M, Fahnoe K, Sarver R, Putz H, Chang J, Subramanyam C, Barreiro G, Miller JR (2009) Structural comparison of chromosomal and exogenous dihydrofolate reductase from Staphylococcus aureus in complex with the potent inhibitor trimethoprim. Proteins. 76(3):706–717.

    Article  CAS  PubMed  Google Scholar 

  28. Dinari M, Gharahi AP (2018) Synthesis, spectroscopic characterization, antimicrobial evaluation and molecular docking study of novel triazine-quinazolinone based hybrids. J Mol Struct 1156:43–50.

    Article  CAS  Google Scholar 

  29. Deivanayagam CCS, Wann ER, Chen W, Carson M, Rajashankar KR, Hook M, Narayana SVL (2002) A novel variant of the immunoglobulin fold in surface adhesins of Staphylococcus aureus: crystal structure of the fibrinogen-binding MSCRAMM, clumping factor A. EMBO J 21(24):6660–6672.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. Wadapurkar RM, Shilpa MD, Katti AKS, Sulochana MB (2018) In silico drug design for Staphylococcus aureus and development of host-pathogen interaction network. Inform Med Unlocked 10:58–70.

    Article  Google Scholar 

  31. Liu C-I, Liu GY, Song Y, Yin F, Hensler ME, Jeng W-Y, Nizet V, Wang AH-J, Oldfield E (2008) A cholesterol biosynthesis inhibitor blocks Staphylococcus aureus virulence. Science 319(5868):1391–1394.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. Kahlon AK, Roy S, Sharma A (2013) Molecular docking studies to map the binding site of squalene synthase inhibitors on dehydrosqualene synthase of Staphylococcus aureus. J Biomol Struct Dyn 28:201–210

    Article  Google Scholar 

  33. Zhu W, Zhang Y, Sinko W, Hensler ME, Olson J, Molohon KJ, Lindert S, Cao R, Li K, Wang K, Wang Y, Liu Y-L, Sankovsky A, de Oliveirac CAF, Mitchell DA, Nizete V, McCammonc JA, Oldfield E (2013) Antibacterial drug leads targeting isoprenoid biosynthesis. Proc Natl Acad Sci 110(1):123–128.

    Article  PubMed  Google Scholar 

  34. Anitha P, Lavanya P, Anbarasu A, Ramaiah S (2014) Molecular docking study of catechins compounds from Camellia sinensis against UPPS in Staphylococcus aureus. J Comput Biol 3:3–9

    Google Scholar 

  35. Lipinski CA, Lombardo F, Dominy BW, Feeney PJ (2001) Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings. Adv Drug Deliv Rev 46(1-3):3–26.

    Article  CAS  PubMed  Google Scholar 

  36. Schneider G, Bohm H-J (2002) Virtual screening and fast automated docking methods. Drug Discov Today 7(1):64–70.

    Article  CAS  PubMed  Google Scholar 

  37. Ferreira LG, dos Santos RN, Oliva G, Andricopulo AD (2015) Molecular docking and structure-based drug design strategies. Molecules 20(7):13384–13421.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  38. Hecht D, Fogel GB (2009) A novel in silico approach to drug discovery via computational intelligence. J Chem Inf Model 49(4):1105–1121.

    Article  CAS  PubMed  Google Scholar 

  39. Forli S, Huey R, Pique ME, Sanner MF, Goodsell DS, Olson AJ (2016) Computational protein-ligand docking and virtual drug screening with the AutoDock suite. Nat Protoc 11(5):905–919.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

Download references


The authors acknowledge Dr. Deepu Mathew and Dr. Ravi Shankar, Bioinformatics Centre (DIC), Kerala Agricultural University, for the advice given to carry out the docking study and Mr. Naijil George and Ms. Kavya, Biotechnology Department St. Joseph’s College for the successful completion of the antimicrobial studies.


Authors are grateful to Council of Scientific & Industrial Research (CSIR) for providing financial assistance for the research work.

Author information

Authors and Affiliations



RK carried out in vitro and in silico studies and drafted the manuscript. The author JTK and VPR designed the study and edited the manuscript. RJ and VTK helped to carry out the work. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Joby Thomas Kakkassery.

Ethics declarations

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

K, R., Kakkassery, J.T., Raphael, V.P. et al. In vitro antibacterial and in silico docking studies of two Schiff bases on Staphylococcus aureus and its target proteins. Futur J Pharm Sci 7, 78 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: