Microwave-assisted synthesis, biological evaluation and molecular docking studies of new coumarin-based 1,2,3-triazoles.

Coumarin-based 1,4-disubstituted 1,2,3-triazole derivatives were synthesized using a highly efficient, eco-friendly protocol via a copper(i)-catalyzed click reaction between various substituted arylazides and terminal alkynes. The synthetic route was easy to access and gave excellent yields under microwave irradiation conditions compared to the conventional heating route. The structures of all the compounds were characterized by IR, 1H NMR, 13C NMR spectroscopy and mass spectrometry. All the synthesized compounds were screened for their in vitro antimicrobial, antioxidant and anti-inflammatory activities; among all compounds, 8a, 8j, 8k and 8l exhibited better results with respect to standard drugs. Furthermore, molecular docking studies have been carried out with PDB IDs 2VCX (anti-inflammatory), 3VXI (antioxidant), 4GEE (antimicrobial) and 2XFH (antifungal) using the Glide module of the Schrödinger suite. The final compounds 8d, 8e, 8h, and 8k showed the highest hydrogen bond interactions with His-88 and Val-191 proteins and with water in all the proteins. This journal is © The Royal Society of Chemistry.

Introduction

In spite of the extensive use of antibiotic and vaccination programs, infectious diseases continue to be a primary cause of morbidity and mortality worldwide. The continued emergence of antibiotic resistance is one of the utmost global health threats.[1] Multidrug resistant bacterial infections are increasing in frequency and require the use of more aggressive antibiotic therapies.[2] While the continued development of novel antibiotics is crucial, alternative strategies are also needed, such as the development of adjuvants that target bacterial pathways responsible for antibiotic tolerance or resistance.[3] Inflammation is a general condition that occurs during infections in many number of diseases from hay fever, periodontitis, atherosclerosis, rheumatoid arthritis to cancer. The generally used non-steroidal anti-inflammatory drugs (NSAIDs) provide analgesic and antipyretic effects in addition to anti-inflammatory effects in higher doses. The therapeutics are prevailing, but they seriously increase vascular and gastrointestinal risks.[4] Although several drugs exist in the market, there is a serious need to required for the development of new antimicrobial drugs and NSAID (Nonsteroidal Anti-Inflammatory Drugs).

The chemistry of heterocyclic compounds has been an interesting field of study for a long period. Coumarin belongs to the class of flavonoids and are found in many natural as well as synthetic products. Coumarin, a well-known structural motif, shows many pharmacological activities such as anticancer,[5] antioxidant,[6] anti-inflammatory,[7] antimicrobial,[8] and anticoagulant[9] effects; it is also proved to be a promising anti-acetylcholinesterase[10] agent. Some of the marketed drugs like Warfarin,[9] Phenprocoumon,[10] Psoralen[11] and Angelicin[12] contain the coumarin skeleton in their structure and are found to exhibit various pharmacological activities (Fig. 1). Coumarins can be synthesized by using the Perkin,[13,14] Pechmann[15,16] and Knoevenagel[17] reactions. Among the coumarin compounds, the 3-aryl substituted coumarins have gained attention due to their biological activities such as antimicrobial, antioxidant and anti-inflammatory activities. The 3-aryl coumarin derivatives can be synthesized by using reagents such as DCC, DDQ, NaOH, POCl3 and Mukaiyama reagent (2-chloro-1-methylpyridiniumiodide).[18,19] Many of these methods suffer limitations such as the formation of a complex mixture of products, usage of excess reagents and longer reaction times with poor yields. For this reason, a relatively more viable reagent such as 1,1-carbonyldiimidazole[20,21] (CDI) is used for the synthesis of 3-aryl coumarin derivatives, which provides excellent yields by avoiding all the above-mentioned issues. On the other hand 1,2,3-triazole, an important heterocyclic motif, has gained much importance in medicinal chemistry and attracted much attention from organic chemists due to its exceptional pharmacological activities such as antimicrobial,[22-24] anticancer,[25-29] anti-HIV[30] and antitubercular activities.[31] Some of the important drugs like TSAO and Tazobactam contain 1,2,3-triazole in their structure (Fig. 1).

Fig. 1

Marketed drugs containing coumarin and 1,2,3-triazole.

In addition, some of the coumarin-based 1,2,3-triazole (Fig. 2) compounds were reported with considerable anti-Alzheimer's,[32] anticancer,[33] and antibacterial activities[34] and as acetylcholinesterase inhibitors.[35] The coumarin-based triazole compound 2H-chromen-2-one[36] showed antimicrobial activity, 3-[1-(4,5-dicarbomethoxy-1,2,3-triazoloacetyl)]coumarin[37] showed antifungal activity and 2-chromene-3-carboxylate derivative[38] showed good antioxidant activities.

Fig. 2

Synthetic coumarin-based 1,2,3-triazoles reported as antifungal and antioxidant agents.

Microwave-assisted synthesis plays a significant role in synthetic chemistry as it reduces the reaction time with enhanced yields when compared to the conventional method and thus is known to be environmentally friendly.[39,40] In view of the environmental effects, the microwave-assisted synthesis is considered as an alternative for the conventional heating method to approach green synthesis. This technique is also used in medicinal chemistry to develop drug molecules as it offers higher yields in a short reaction time and reduces the waste products when compared to the conventional heating method. Moreover, these reactions are simple, clean, eco-friendly and easy to carry out. The rate of reaction is enhanced due to thermal/kinetic effects, which are significance of high temperatures that can be quickly attained when the reaction mixture is exposed to a microwave field.

Inspired by the diverse pharmacological activities of the coumarin and 1,2,3-triazole derivatives, we synthesized a series of coumarin-based 1,2,3-triazole compounds 8(a–l) using conventional and microwave irradiation methods; they were then evaluated for their in vitro antioxidant, anti-inflammatory, and antimicrobial activities followed by molecular docking studies.

Computational biology and bioinformatics play a major role in designing drug molecules and have the potential to speed up the drug discovery process. Molecular docking of the drug molecules with the receptor (target) gives significant information about drug–receptor interactions and is frequently used to find out the binding orientation of drug candidates to their protein targets in order to calculate the affinity and activity.[39] In view of the pharmaceutical activities of two or more pharmacophore moieties, i.e., coumarin and 1,2,3-triazole, in order to find the combined effects of the newly synthesized scaffolds on biological potency, we herein report a protocol for the design and synthesis of some coumarin-based 1,2,3-triazole compounds.

Results and discussion

Chemistry

The protocol for the synthesis of coumarin-based 1,2,3-triazoles is depicted in Scheme 1. The first step of the synthetic route involves the activation of substituted phenyl acetic acid 1 by using 1,1-carbonyldiimidazole 2 (CDI) using potassium carbonate as the base and acetone as the solvent at room temperature for 1 h to obtain the intermediate 3. In the second step, the alkyne-substituted hydroxy acetophenone 5 is obtained by the selective propargylation of 2,4-dihydroxyacetophenone 4 using K2CO3 in DMF and it is further treated with the intermediate 3 under reflux conditions for 4 h using potassium carbonate and acetone to afford 3-aryl-substituted coumarin compounds 6(a–d). Finally, the alkyne coumarin intermediates 6(a–d) undergo copper(i)-catalyzed Huisgen cycloaddition[41] (click chemistry[42-44]) when treated with different aryl azides 7(a–c) using copper iodide in the presence of DMF/H2O (1 : 1) to obtain coumarin-containing 1,2,3-triazole title compounds 8(a–l).

Scheme 1

Synthetic route for coumarin-based 1,2,3-triazole compounds 8(a–l).

Initially, the activation of phenyl acetic acids was attempted using DABCO as the coupling agent by using a procedure reported in literature,[45] but it could not give promising results. Activation was then performed by treating an acid (1 eq.) with DBU (1 eq.) as a base using two different solvents, namely, dichloromethane and toluene by following a literature protocol.[46] Finally, the reaction conditions were successfully optimized with acid (1 eq.), CDI (1.2 eq.) using K2CO3 as the base and dry acetone as the solvent under inert atmospheric conditions.

The syntheses of alkyne-substituted 3-aryl coumarin intermediates 6(a–d) and coumarin-based 1,2,3-triazole final compounds 8(a–l) were carried out using both conventional and microwave (MW) irradiation methods. Among the two methods, the microwave irradiation method gave good yields (80–90%) when compared to the conventional method (68–79%). The reaction time and yields obtained for the intermediates 6(a–d) and final compounds 8(a–l)via both the methods are summarized in Table 1.

Comparison of the time and yields of the synthesized compounds 6(a–d) and 8(a–l) using conventional and microwave irradiation methods

Product	Conventional method		Microwave irradiation method
	Time (h)	% yield	Time (min)	% yield
6a	5	75	5	86
6b	5.5	78	6	89
6c	4	79	7	90
6d	4.5	75	6	86
8a	5	72	7	85
8b	4.5	69	7	82
8c	5	75	6	84
8d	4.5	76	8	85
8e	5.5	75	7	85
8f	5	76	6	88
8g	5	70	8	82
8h	5.5	69	8	80
8i	4.5	72	7	85
8j	5	68	5.5	80
8k	6	72	6	85
8l	5.5	68	7	80

The optimized reaction conditions for the synthesis of the final compounds 8(a–l) by the click reaction of different aryl azides 7(a–c) with alkyne intermediates 6(a–d) using copper(i) iodide as a catalyst under different solvent conditions in both conventional and MW irradiation methods are tabulated in Table 2. Among the reaction conditions performed, the best results were achieved when DMF/H2O (1 : 1) was used as the solvent system in both the methods.

Optimization of compound 8a in various methods

Entry	Solvent	Conventional method	Microwave irradiation method
		(% yield)	(% yield)
1	THF	35	40
2	CH3CN	20	27
3	1,4-Dioxane	17	24
4	DMF	58	62
5	DMF/H2O (7 : 3)	60	65
6	DMF/H2O (3 : 2)	68	75
7	DMF/H2O (1 : 1)	72	85

Biological activity

All the synthesized compounds 6(a–d) and 8(a–l) were screened for antioxidant, anti-inflammatory and antimicrobial scavenging activities. Among all the screened compounds 8a, 8j, 8k and 8l showed better results compared with standard drugs.

SAR studies

Antioxidant activity

The in vitro antioxidant[47] activities of intermediates 6(a–d) and final targets 8(a–l) were determined by using two methods, namely, the DPPH[47] radical scavenging assay and HO [48] scavenging assay method[31] with Ascorbic acid taken as the standard drug. All the synthesized compounds, i.e., 6(a–d) and 8(a–l) were screened for in vitro scavenging activity. The IC50 values ranged from 338.48 μM mL−1 to −0.064 μM mL−1 compared with that of standard Ascorbic acid (IC50 value 1.46 μM mL−1). Compounds 8k (IC50 value 0.06146 μM mL−1), 8j (IC50 value 1.11 μM mL−1) and 8d (IC50 value 1.29 μM mL−1) showed excellent activity because the presence of methoxy and other electron releasing groups like methyl maintained the stability of the compounds and also contributed to the improved activity for compound 8k. The presence of two methoxy groups in compound 8d slightly decreased the activity. Further substitution of electron-withdrawing groups like chlorine and methoxy in compound 8l decreased the activity. In addition, 8a (3.50 μM mL−1), 8l (3.52 μM mL−1) and 8f (3.72 μM mL−1) exhibited good activity than the standard drug in the DPPH method. In contrast, in the H2O2 method, compound 8k (IC50 value 0.06146 μM mL−1) exhibited significant results and 8j (IC50 value 1.29 μM mL−1), 8c (IC50 value 1.45 μM mL−1), 8f (IC50 value 1.72 μM mL−1) and 8a (IC50 value 1.76 μM mL−1) revealed good activity than standard Ascorbic acid (IC50 value 1.16 μM mL−1). The antioxidant activity values are shown in Table 3.

Antioxidant activity of compounds 6(a–d) and 8(a–l)

Compound	Antioxidant activity
	DPPH method IC50 (μM mL−1)	H2O2 method IC50 (μM mL−1)
6a	2.24 ± 0.93	3.524 ± 0.47
6b	20.00 ± 0.34	23.57 ± 0.68
6c	293.18 ± 0.25	7.07 ± 0.02
6d	4.5 ± 0.47	1.35 ± 0.45
8a	3.5 ± 0.25	1.76 ± 0.06
8b	338.48 ± 0.47	124.48 ± 0.53
8c	42.50 ± 0.58	1.45 ± 0.45
8d	1.11 ± 0.43	71.21 ± 0.47
8e	343.33 ± 0.58	343.33 ± 0.57
8f	3.72 ± 0.69	1.72 ± 0.47
8g	18.57 ± 0.12	18.57 ± 0.69
8h	2.51 ± 0.36	42.51 ± 0.47
8i	4.8 ± 0.24	4.8 ± 0.56
8j	1.29 ± 0.35	1.269 ± 0.14
8k	0.061 ± 0.38	0.061 ± 0.41
8l	3.524 ± 0.65	3.06 ± 0.32
Ascorbic acid	1.46 ± 0.52	1.16 ± 0.89

Anti-inflammatory activity

The in vitro anti-inflammatory[49,50] activities of all the synthesized compounds 6(a–d) and 8(a–l) were determined by using two methods, namely, the egg-albumin method and heat-induced hemolytic method by taking Diclofenac as the standard drug. In the egg-albumin method, 8a (IC50 value 15.78 μM mL−1) and 6d (IC50 value 16.50 μM mL−1) exhibited excellent activity than Diclofenac (IC50 value 17.52 μM mL−1). In the heat-induced hemolytic method, compounds 6a (IC50 value 12.06 μM mL−1), 8g (IC50 value 13.16 μM mL−1), 6d (IC50 value 15.00 μM mL−1), 8i (IC50 value 15.35 μM mL−1), 8j (IC50 value 15.90 μM mL−1) and 8f (IC50 value 17.11 μM mL−1) exhibited excellent activity; also, 8a (IC50 value 17.78 μM mL−1) and 8l (IC50 value 18.90 μM mL−1) demonstrated good activity compared to the standard Diclofenac drug (IC50 value 17.52 μM mL−1). The anti-inflammatory activity values are shown in Table 4.

Anti-inflammatory activity of compounds 6(a–d) and 8(a–l)

Compound	Anti-inflammatory
	Egg-albumin method IC50 (μM mL−1)	Heat-induced hemolytic method IC50 (μM mL−1)
6a	42.06 ± 0.57	12.06 ± 0.57
6b	22.91 ± 0.25	22.91 ± 0.25
6c	63.72 ± 0.32	63.72 ± 0.32
6d	16.50 ± 0.91	15.00 ± 0.91
8a	15.78 ± 0.52	17.78 ± 0.42
8b	59.809 ± 0.69	69.809 ± 0.69
8c	76.49 ± 0.14	66.49 ± 0.14
8d	238.13 ± 0.35	138.13 ± 0.35
8e	59.80 ± 0.63	69.80 ± 0.63
8f	31.21 ± 0.47	17.11 ± 0.47
8g	103.26 ± 0.69	13.16 ± 0.69
8h	53.77 ± 0.14	43.77 ± 0.14
8i	45.35 ± 0.87	15.35 ± 0.87
8j	18.90 ± 0.37	15.90 ± 0.37
8k	42.53 ± 0.41	60.67 ± 0.41
8l	28.90 ± 0.65	18.90 ± 0.65
Diclofenac	17.52 ± 0.98	17.52 ± 0.98

Antibacterial activity

The newly synthesized compounds 6(a–d) and 8(a–l) were screened for their antibacterial activity against Gram-positive strains such as Staphylococcus aureus (MTCC 96) and Bacillus subtilis (MTCC 121) and Gram-negative strains such as Escherichia coli (MTCC 43) and Klebsiella pneumonia (MTCC 530) at various concentrations, i.e., 10 μg mL−1 and 20 μg mL−1 by using the agar disc diffusion method.[51] The zone of inhibition was measured in mm and Gatifloxacin was used as the standard drug; the results are shown in Table 5. From the biological evaluation of the activity of the intermediates 6(a–d) to the final compounds 8(a–l), activity further increased due to the presence of 1,2,3-triazole moieties. Among all the prepared compounds, 8a, 8d, 8g and 8j were highly potent due to the presence of the methoxy group in the triazole ring and also, compounds 8b, 8c, 8e, 8f, 8h and 8i showed good activity against all bacterial strains due to the electron-withdrawing groups on the coumarin ring. Compound 8k and compound 8l both showed similar activity to that of the standard drug. The starting compounds 6(a–d) did not show activity. The results also demonstrated that the activity of these compounds 6(a–d) and 8(a–l) was influenced by their structures. In conclusion, 8a and 8j showed very high potential antibacterial activity against tested organisms.

Antibacterial activity of compounds 6(a–d) and 8(a–l) at different concentrations

Compound	Zone of inhibition (mm)
	Gram positive bacteria				Gram negative bacteria
	Staphylococcus aureus		Bacillus subtilis		Escherichia coli		Klebsiella pneumonia
	10 μg mL−1	20 μg mL−1	10 μg mL−1	20 μg mL−1	10 μg mL−1	20 μg mL−1	10 μg mL−1	20 μg mL−1
6a	12	18	11	21	08	11	06	10
6b	09	19	12	19	10	12	04	11
6c	10	20	10	22	11	15	07	09
6d	12	17	09	18	09	12	12	14
8a	22	32	23	40	16	21	14	20
8b	15	24	16	32	13	16	08	14
8c	18	36	16	34	14	18	09	16
8d	23	32	22	42	18	23	13	20
8e	16	23	15	32	12	16	08	13
8f	18	25	19	38	15	19	11	17
8g	24	34	22	42	18	25	12	22
8h	15	24	16	28	14	17	06	13
8i	16	27	19	39	12	20	09	17
8j	26	34	27	39	21	29	14	22
8k	19	26	16	32	12	14	06	12
8l	19	27	18	37	14	25	08	15
Gatifloxacin	20	30	20	40	15	20	10	18

Antifungal activity

All the synthesized compounds 6(a–d) and 8(a–l) were screened for their in vitro antifungal activity against three fungal organisms, namely, Aspergillus niger, Aspergillus flavus and Fusariumoxy sporum at a concentration of 50 μg mL−1 by using the disc diffusion method[51] and the results were compared with that of Clotrimazole, used as a standard drug. The study of antifungal activity is shown in Table 6; it was observed that among all the synthesized compounds, 8a, 8b, and 8c showed better activity against the three pathogenic fungi due to the presence of fluorine group on coumarin. Compounds 8j, 8k and 8l showed better activity due to the presence of the methoxy group in the triazole ring. The remaining compounds exhibited similar activity to that of the standard drug. Due to the methoxy group of the triazole compounds 8d and 8g, they showed poor activity. It was observed that the intermediate-to-product activity increased due to the presence of the 1,2,3-triazole moiety. Overall, the antifungal activities of the compounds were good against the tested fungal strains.

Antifungal activities of the compounds 6(a–d) and 8(a–l) at a concentration 50 μg mL−1

Compound	Zone of inhibition (mm) at 50 μg mL−1 concentration
	Aspergillus niger	Aspergillus flavus	Fusariumoxy sporum
6a	07.2	06.4	07.3
6b	08.8	07.2	06.6
6c	07.2	08.6	09.2
6d	08.2	07.9	06.5
8a	18.8	17.6	18.6
8b	17.9	16.8	17.8
8c	18.2	16.3	18.9
8d	10.6	11.8	11.6
8e	13.6	14.2	14.8
8f	15.2	14.8	16.2
8g	10.3	12.5	12.6
8h	14.6	13.8	14.6
8i	15.9	14.5	15.8
8j	18.6	16.7	19.0
8k	16.5	15.8	16.2
8l	15.9	14.8	14.3
Clotrimazole	17.3	16.4	18.2

Molecular docking studies

To gain more insights into the interactions of coumarin-based 1,2,3-triazole derivatives 8(a–l), molecular docking studies were performed. Molecular docking was carried out using the Glide module of the Schrödinger suite using PDB IDs 2VCX (anti-inflammatory),[52]3VXI (antioxidant),[53]4GEE (antimicrobial)[54] and 2XFH (antifungal)[55] to correlate the binding mode of the synthesized compounds with the proteins. The above-mentioned proteins were selected on the basis of the reference compound that existed as a co-crystal ligand on the target protein. In the current work, we have considered 2VCX for its anti-inflammatory activity since it is a prostaglandin D2 synthase[56] protein involved in the cyclooxygenase pathway.[57] Similarly, 3VXI was used for its anti-oxidant activity due to its dye decolourising peroxidase (DyP) complex with Ascorbic acid as the crystal ligand.[58] The protein 4GEE was considered because of its DNA–gyrase B and topoisomerase IV-mediated broad spectrum activity.[59] For the identification of antifungal activity, we thereby considered 2XFH Cytochrome P450 EryK cocrystallized with the inhibitor Clotrimazole.[60] The potential binding free energies (ΔG) were evaluated and the rationality of the compounds was further evaluated through QikProp for their drug likeness.

In conclusion, comparative docking studies from all the proteins revealed that compound 8l showed a high docking score of −7.792 and a binding energy of −117.95 in the protein 2VCX; also, their predicted activities were found to be slightly higher than that of the standard (provided in the ESI Table†). This clearly indicated that compound 8l showed an explicit effect as a potential anti-inflammatory, antimicrobial and antioxidant molecule. The intermediate compounds 6b and 6d showed best H-bond interactions with water in all the proteins (2XFH, 4GEE and 3VXI) as the standard Ascorbic acid and Gatifloxacin predominantly (as illustrated in Fig. 1 and 3 of the ESI†), stating that these compounds could be further exploited to newer chemical agents possessing antioxidant and antimicrobial activities, as depicted in Fig. 4. The standard antifungal agent Clotrimazole shows hydrogen bond interactions with Arg-293 (depicted in Fig. 2 provided in the ESI†). The final compounds 8d, 8e, 8h and 8k showed hydrogen bond interactions with His-88 (Fig. 4a) and Val-191 (4b) amino acids and with water (4c) in all the proteins 2VCX, 3VXI, 4GEE and 2XFH. This signifies that the synthesized compounds possess antibacterial and antifungal activities in addition to antioxidant and anti-inflammatory activities. Docking scores along with the binding free energies for all the synthesized compounds have been quantified and tabulated in Table 7. The average predicted activities of different chemical methods have been calculated for the synthesized compounds (provided in the ESI from Tables 3d to 6d†). The pharmacokinetic properties (ADME) of the compounds exhibited excellent 100% human oral absorption and were found to be in the acceptable range, as shown in Table 2d (provided in the ESI†).

Fig. 3

Docking pose images of intermediate compounds 6b and 6d showing H-bond interaction with water in Gram positive bacteria by the protein 4GEE.

Fig. 4

Docking pose images of final compounds 8d, 8h and 8k showing H-bond interaction with His-88 in 2VCX protein (a), Val-191 in 3VXI (b) and water in 2XFH and 4GEE proteins (c), respectively.

Quantified active site binding free energies along with the docking scores of the synthesized compounds and standard molecules

Compounds	Docking scores				Binding free energies
	Anti-inflammatory activity (2VCX)	Anti-oxidant activity (3VXI)	Anti-microbial		Anti-inflammatory activity (2CVX)	Anti-oxidant activity (3VXI)	Anti-microbial
			Anti-bacterial (4GEE)	Anti-fungal (2XFH)			Anti-bacterial (4GEE)	Anti-fungal (2XFH)
6a	−5.984	−4.882	−5.760	−6.657	−83.72	−54.41	−69.13	−77.31
6b	−6.315	−4.826	−6.748	−5.148	−86.94	−55.04	−70.79	−61.08
6c	−6.177	−4.559	−6.585	−4.857	−86.36	−55.68	−71.29	−61.61
6d	−6.232	−3.801	−6.580	−4.791	−83.57	−46.00	−78.56	−57.66
8a	−6.928	−3.355	−5.756	−3.180	−94.07	−52.26	−68.97	−52.0
8b	−6.587	−3.636	−4.994	−4.096	−88.37	−53.29	−57.01	−52.6
8c	−6.165	−2.949	−5.122	−5.676	−88.66	−59.42	−53.52	−69.37
8d	−6.962	−2.438	−5.970	−2.927	−92.74	−54.29	−71.94	−45.55
8e	−6.927	−3.740	−5.796	−2.368	−92.26	−60.44	−71.17	−38.23
8f	−6.051	−3.528	−4.818	−4.339	−92.16	−47.36	−62.39	−67.33
8g	−6.972	−3.720	−5.554	−2.792	−106.36	−57.00	−67.63	−44.93
8h	−6.725	−3.778	−5.654	−3.594	−92.263	−47.41	−72.09	−51.41
8i	−6.575	−2.823	−5.659	−4.112	−94.63	−53.35	−71.45	−68.46
8k	−6.587	−3.240	−5.006	−2.587	−94.638	−54.15	−62.72	−37.15
8l	−7.792	−2.868	−4.869	−3.984	−117.95	−50.68	−61.15	−47.79
Diclofenac	−5.553	—	—	—	−91.55	—	—	—
Ascorbic acid	—	−6.184	—	—	—	−85.23	—	—
Gatifloxacin	—	—	−5.553	—	—	—	−56.38	—
Clotrimazole	—	—	—	−6.288	—	—	—	−89.15

Conclusion

We herein, reported the new scaffolds 6(a–d) and 8(a–l) were synthesized by using a microwave irradiation method to obtained better yield as compared to conventional heating method. The use of a DMF : water (1 : 1) solvent system helped in increasing the product yield through traditional, conventional and microwave irradiation routes. However, we observed greater yields via the microwave irradiation route in lesser duration. Biological evaluations and molecular docking studies revealed an increase in the activity of the target compounds from their intermediates. Compounds 8d, 8e, 8h and 8k showed excellent hydrogen bonding interactions with His-88, Val-191 and water.

Conflicts of interest

There are no conflicts to declare.