Synthesis, structure elucidation, and antifungal potential of certain new benzodioxole–imidazole molecular hybrids bearing ester functionalities

Reem I Al-Wabli1 Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia, [email protected]; [email protected]Correspondence[email protected] [email protected]

Alwah R Al-Ghamdi1 Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia, [email protected]; [email protected]

Hazem A Ghabbour2 Department of Medicinal Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura 35516, Egypt

Mohamed H Al-Agamy3 Department of Pharmaceutics, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia;4 Microbiology and Immunology Department, Faculty of Pharmacy, Al-Azhar University, Cairo 11884, Egypt

Mohamed I Attia1 Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia, [email protected]; [email protected];5 Medicinal and Pharmaceutical Chemistry Department, Pharmaceutical and Drug Industries Research Division, National Research Centre, Dokki, Giza 12622, Egypt, [email protected]Correspondence[email protected] [email protected]

Abstract

Background

The incidence of fungal infections is a growing serious global health burden. There is an urgent medical demand to acquire new antifungal drug-like compounds having azole nuclei to get rid of the drawbacks of the currently available azole antifungal agents.

Methods

The target compounds 5a-r were synthesized in a four-step reaction sequence using the appropriate acetophenone derivative as a starting material. The antifungal potential of the title compounds was assessed using DIZ and MIC assays according to the reported standard procedures.

Results

The newly synthesized oximino esters 5a-r were identified with the aid of various spectroscopic approaches. Their assigned chemical structures were confirmed via single-crystal X-ray structure of compound 5o. The molecular structure of compound 5o was crystallized in the triclinic, P–1, a=9.898 (3) Å, b=10.433 (3) Å, c=11.677 (4) Å, α =86.886 (6)°, β =87.071 (7)°, γ =64.385 (6)°, V=1,085.2 (6) Å3, Z=2. The synthesized compounds 5a-r were in vitro evaluated for antifungal potential against four fungal strains. Compounds 5l and 5m bearing a trifluoromethylphenyl moiety showed the best anti-Candida albicans activity with minimum inhibitory concentration (MIC) value of 0.148 μmol/mL, while compound 5b displayed the best activity toward Candida tropicalis with MIC value of 0.289 μmol/mL. Compounds 5o and 5l were the most active congeners against Candida parapsilosis and Aspergillus niger, respectively.

Conclusion

Single-crystal X-ray analysis of compound 5o confirmed without doubt the assigned chemical structures of the title compounds as well as confirmed the (E)-configuration of their oximino group. Compounds 5b, 5l, 5m, and 5o emerged as the most active compounds against the tested fungi and they could be considered as new antifungal lead candidates.

Keywords:

Acknowledgments

The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding of this research through the Research Group Project no RGP-196.

Disclosure

The authors report no conflicts of interest in this work.

Supplementary materials

Antifungal activity

Materials

The reference standard antifungal drug, ketoconazole, was purchased from Sigma-Aldrich Co. (St Louis, MO, USA). Liquid RPMI 1640 medium supplemented with L-glutamine was obtained from Gibco-BRL, Life Technologies (Paisley, Scotland). Sabouraud Dextrose Agar (SDA) was obtained from Merck Co. (Darmstadt, Germany). Dimethyl sulfoxide (100%) was used to dissolve ketoconazole, and/or the tested compound 4 to give an initial concentration of 2,048 mg/L.

Organisms

The used fungal strains are Candida albicans (ATCC 90028), Candida tropicalis (ATCC 66029), Candida parapsilosis (ATCC 22019) and Aspergillus niger (ATCC 16404).

Preparation of fungal inocula

The inocula of the standard mold Aspergillus niger strain have been prepared by removing the sporulated A. niger from the Sabouraud Dextrose agar slant with a microbiological loop and the spores have been suspended in 10 mL of sterile water. The suspension has been filtered through sterile gauze to remove hyphae. The resulting suspension of conidia has been vigorously mixed using a vortex. The suspension has been adjusted to 1×10⁵ CFU/mL using spectrophotometer. This fungal suspension has been diluted 1:5 with RPMI medium to obtain suspensions having 2× of the required final concentration. This conidial suspension had a final concentration of 1×10⁴ CFU/mL when mixed with the tested solution of compound 4. On the other hand, the inocula of the standard yeast strains of C. albicans, C. tropicalis and C. parapsilosis have been prepared by suspending five representative colonies, obtained from 24 to 48 h culture on Sabauraud Dextrose agar medium, in sterile distilled water. The final inoculum concentration must be between 0.5×10⁵ and 2.5×10⁵ CFU/mL.

Preparation of the tested compound solution

Briefly, a twofold dilution series of the tested compounds has been prepared in a double strength RPMI 1640 culture medium. Ten serial dilutions were prepared to give concentrations ranged from 1,024 mg/L to 2 mg/L.

Antifungal susceptibility studies

Minimum Inhibitory Concentrations (MICs) have been determined by broth microdilution testing as described previously by EUCAST.^Citation1 The experiment was carried out in duplicate. Briefly, one mL of RPMI 1640 medium from each of the bottle containing the corresponding concentration of the tested compounds has been transferred into sterile 7 mL Sterilin tubes (Thermo Fisher Scientific, Waltham, MA, USA). The RPMI 1640 medium containing 1,024 mg/L of the tested compounds has been dispensed to tube 1, the medium containing 512 mg/L has been dispensed to tube 2, the medium containing 256 mg/L has been dispensed to tube 3 and so on to tube 10 for the medium containing 2 mg/L of the tested compounds. One mL of the medium has been dispensed in tubes 11 (positive control) and 12 (negative control). One mL of the diluted inoculum suspension has transferred to each tube except tube 12 to bring the tested compounds dilutions to the required final test concentrations. The tubes were incubated at 35°C for 72 h. The MICs of the tested compounds were determined visually by recording the degree of growth inhibition in each tube. The microanalysis results () of the target compounds 5a-r agreed favorably with the proposed structures within ±0.4% of the theoretical values.

Figure S1 ¹H NMR spectrum of compound 5d.

Figure S1 1H NMR spectrum of compound 5d.

Figure S2 ¹³C NMR spectrum of compound 5d.

Figure S2 13C NMR spectrum of compound 5d.

Figure S3 ¹H NMR spectrum of compound 5e.

Figure S3 1H NMR spectrum of compound 5e.

Figure S4 ¹³C NMR spectrum of compound 5e.

Figure S4 13C NMR spectrum of compound 5e.

Figure S5 ¹H NMR spectrum of compound 5k.

Figure S5 1H NMR spectrum of compound 5k.

Figure S6 ¹³C NMR spectrum of compound 5k.

Figure S6 13C NMR spectrum of compound 5k.

Table S1 Microanalysis data of the title compounds 5a–r

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Reference

Rodriguez-TudelaJLArendrupMCBarchiesiFEUCAST Definitive Document EDef 7.1: method for the determination of broth dilution MICs of antifungal agents for fermentative yeasts: Subcommittee on Antifungal Susceptibility Testing (AFST) of the ESCMID European Committee for Antimicrobial Susceptibility Testing (EUCAST)Clin Microbiol Infect20081439840518190574
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