Abstract
Objective: The aim of this study was to examine in vitro antimicrobial activity of a series of 7-benzamidocoumarin derivatives against three Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, and Bacillus pumilus), three Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia, and Salmonella typhi), and three fungi (Candida albicans, Candida tropicalis, and Aspergillus niger) by 2-fold serial dilution method.
 Materials and Methods: The compounds were synthesized by amide coupling of 7-amino-4-methyl coumarin 5 and 7-amino-4-chloromethyl coumarin 6 with different aromatic acids 7 (a-h) and heteroaromatic acids 8 (i-j) in the presence of phosphorous trichloride as an acid catalyst in acetonitrile. The synthesized compounds were evaluated for antimicrobial and chitinase inhibitory activity.
 Results: Compounds 9, 11, 12, 21, and 23 showed good antibacterial activity with minimum inhibitory concentration (MIC) ranging from 6.25 to 50 μg/mL. Among them, compound 21 was the most active molecule with MIC 6.25 μg/mL against S. aureus and 6.25 μg/mL against, B. pumilus and S. typhi. Compounds 11 and 21 were the most potent antifungal candidates with MIC 6.25–25 μg/mL against C. albicans and C. tropicalis. All the compounds were also evaluated for their chitinase inhibitory property and among them; compound 9 emerged as strong inhibitor of the enzyme.
 Conclusion: Some of the compounds showed very good antimicrobial activities. Among these, compound 21 showing potent antimicrobial activities against five of the nine microbial strains examined in this study, was the most active compound of the series. Some of the compounds also showed chitinase inhibitory properties. This study also provides a starting point for investigating the structure-activity relationships (SARs) of synthetic 7-benzamidocoumarins.
Highlights
Over the past decade, the incidence of bacterial infections has increased worldwide, in Indian subcontinent, portions of South America, and tropical fraction of Africa [1,2]
With the desired amino coumarins 5 and 6 in hand, the synthesis of 7-benzamidecoumarins was undertaken. 7-benzamido-4-methyl-coumarins 9–11 were obtained by reaction between 7-amino-4-methyl coumarin 5 and substituted salicylic acids 7 a-c in CH3CN in the presence of PCl3 under reflux condition while compounds 12–14 and 15 were prepared by the reaction of 7-amino-4-chloromethyl coumarin 6 with substituted salicylic acids 7a-c and unsubstituted salicylic acid 7d, respectively
Doublet appeared at δ 7.81 with coupling constant of 2.4 Hz was due to the H-8 proton of the benzamide ring, whereas doublets at δ 7.61 and δ 7.50 with a coupling constant of 8.7 Hz were due to the H-5 and H-6 protons of benzopyrone ring, respectively
Summary
The incidence of bacterial infections has increased worldwide, in Indian subcontinent, portions of South America, and tropical fraction of Africa [1,2]. In spite of the availability of a large number of antibiotics and chemotherapeutics, the treatment of bacterial diseases still remains a challenging problem due to a number of factors such as the emergence of drug-resistant strains, severe adverse effects, narrow antibacterial spectrum, and association of microbial infections with other diseases mainly in immunocompromised patients [3,4,5]. The opportunistic fungal pathogens belonging to Candida spp., Cryptococcus spp., and Aspergillus spp. account for the majority of documented invasive fungal infections in humans. These infections are responsible for high morbidity and mortality in immune-compromised patients such as those undergoing organ transplants or anticancer chemotherapy and patients with AIDS [8]. There is a pressing need for the development of alternative antimicrobial drugs involving new molecules with a broader spectrum and less side effects
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