Keeping in view various pharmacological attributes of indole and coumarin derivatives, a new series of indolindione–coumarin molecular hybrids was rationally designed and synthesized. All synthesized hybrid molecules were evaluated for their antimicrobial potential against Gram-negative bacterial strains ( Escherichia coli and Salmonella enterica ), Gram-positive bacterial strains ( Staphylococcus aureus and Mycobacterium smegmatis ), and four fungal strains ( Candida albicans , Alternaria mali , Penicillium sp., and Fusarium oxysporum ) by using the agar gel diffusion method. Among all synthetics, compounds K-1 and K-2 were found to be the best antimicrobial agents with the minimum inhibitory concentration values of 30 and 312 μg/mL, against Penicillium sp. and S. aureus , respectively. The biological data revealed some interesting facts about the structure–activity relationship which state that the electronic environment on the indolinedione moiety and carbon chain length between indolinedione and triazole moieties considerably affect the antimicrobial potential of the synthesized hybrids. Various types of binding interactions of K-2 within the active site of S. aureus dihydrofolate reductase were also streamlined by molecular modeling studies, which revealed the possible mechanism for potent antibacterial activity of the compound.

Keeping in view various pharmacological attributes of curcumin, coumarin, and isatin derivatives, triazole-tethered monocarbonyl curcumin–coumarin and curcumin–isatin molecular hybrids have been synthesized and evaluated for their antibacterial potential against Gram-positive ( Enterococcus faecalis and Staphylococcus aureus ) and Gram-negative ( Pseudomonas aeruginosa and Escherichia coli ) human pathogenic bacterial strains. Among all hybrid molecules, A-4 and B-38 showed the most potent antibacterial activity with inhibition zones of 29 and 31 mm along with MIC values of 12.50 and 6.25 μg/mL, respectively. Structure–activity relationship that emerged from biological data revealed that the two-carbon alkyl chain between triazole and coumarin/isatin moiety is well tolerable for the activity. Bromo substitution at the fifth position of isatin, para-cholo substitution in the case of curcumin–isatin, and para-methoxy in the case of curcumin–coumarin hybrids on ring A of curcumin are most suitable groups for the antibacterial activity. Various types of binding interactions of A-4 and B-38 within the active site of dihydrofolate reductase (DHFR) of S. aureus are also streamlined by molecular modeling studies, suggesting their capability in completely blocking DHFR.

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