Synthesis and Antimicrobial Activity of Furochromone , Benzofuran and Furocoumarin Derivatives Bearing Sulfonyl Moiety

New visnagin-9-sulfonamide derivatives 3 and 4a−c were synthesized through the reaction of visnagin-9-sulfonyl chloride 2 with amino compounds. Acetylation of compounds 4b and 4c gave the monoacetyl and diacetyl derivatives 5 and 6, respectively. Diazotization reaction of compound 4b afforded the corresponding benzotriazole derivative 8. Pyrazole and thiopyrimidine derivatives 9 and 10 were obtained via the opening of pyrone ring upon reaction of compound 3 with hydrazine hydrate and thiourea, respectively. In addition, hydrolysis of compound 3 with potassium hydroxide furnished the visnaginone derivative 11 which used as starting material for synthesize benzofuran derivatives 12−14 and bergaptene derivatives 15−17. The synthesized compounds were tested for antimicrobial activity. Furochromone derivatives 3, 4a−c, 5, 6 and 8 (visnagin-9-sulfonamide derivatives) demonstrate moderate antibacterial and antifungal activities compared with the antibacterial and antifungal activites of the standard drugs. Benzofuran derivatives 11−14 (visnaginone derivatives) showed the lowest antimicrobial activity among all the compounds investigated in this study. Furocoumarin derivatives 15a,b, 16 and 17 (furobenzopyransulfonamide [bergaptensulfonamides]) are moderately active against all the tested strains.


INTRODUCTION
[3] Visnagin (4-methoxy-7-methyl-5H-furo[3,2g] chromen-5-one) is one of the essential chemical constituents of the fruits and seeds of Ammi visnaga, family Umbelliferae and it is known to possess antispasmodic properties to the ureter and bile duct, treats angina, whooping cough, gall bladder and renal colic. [4]It is considered as a potent coronary vasodilator as well as its role in treating bronchial asthma. [5,6]9][10] Chromones represent an attractive source of medicinally interesting compounds due to their low toxicity.Many benzofurans are based on the chromone structure and they have been found to possess several therapeutically interesting biological activities. [11]Sulfonamides are bacteriostatic antimicrobial agents and they are most effective in early stages of acute infections when organisms multiply rapidly.[14] These derivatives are still widely used today for the treatment of various bacterial, protozoal and fungal infections [15] and are the first effective chemotherapeutic agent used in safe therapeutic dosage ranges. [16]Based on the above mentioned observations and D in continuation of our research program on the field of sulfonamide derivatives, [17][18][19][20][21] antimicrobial and antifungal agents, [22][23][24][25] we would like to report the synthesis of furochromone, benzofuran and furocoumarin derivatives containing sulfonamide moiety as a trial to obtain novel class of antibacterial and antifungal agents.

Chemistry
The starting material, visnagine-9-sulfonyl chloride 2 [26] was prepared from the reaction of visnagine 1 with chlorosulfonic acid.The reactivity of sulfonylchloride derivative 2 towards nitrogenous compounds was discussed.Thus, interaction of 2 with piperazine as secondary amine and o-phenatidine, o-phenylenediamine and 4,4'-diaminobiphenyl gave the corresponding sulfonamide derivatives 3 and 4a−c, respectively (Scheme 1).The structures of 3 and 4 have been assigned as a reaction product on the basis of analytical and spectral data.IR spectrum of 4a as an example displayed absorption bands at 3239 and 1661 cm −1 due to NH and C=O functional groups, respectively. 1H NMR spectrum exhibited two sharp singlet signals at 2.40 ppm and 3.89 ppm assignable to CH3 and OCH3 protons, another triplet and quartet signals at 1.21 and 4.22 ppm specific for ethoxy protons.Other singlets were observed at 6.07 ppm corresponding for chromone-H proton, multiplet signals in 6.69−7.95ppm region owing to aroma c protons, two doublets for furan protons as well as a broad signal at 8.61 ppm due to NH proton.Mass spectrum showed a molecular ion peak at m/z = 429, corresponding to a molecular formula C21H19NO7S.
Compounds 4b and 4c are considered as key intermediates for the synthesis of some sulfonamide derivatives.Thus, treatment of 4b and 4c with acetic anhydride produced the corresponding acetyl and diacetyl derivatives 5 and 6, respectively (Scheme 2).Spectral data of the isolated product was in complete agreement with the expected structures.IR spectrum of compound 6 showed absorption bands at 3121, 1710 and 1662 cm −1 corresponding to NH and 2C=O functional groups, respectively. 1H NMR spectrum showed five singlet signals at 1.99, 2.32, 4.06 and 6.19 ppm characteristic for 3CH3, OCH3 and chromone-H protons, respectively.In addition, treatment of 4b with nitrous acid produced benzotriazole derivative 8 through the formation of diazonium chloride salt 7 followed by intramolecular cyclization via HCl elimination (Scheme 2).The structure of 8 was confirmed by elemental analysis and spectral data.IR spectrum exhibited band at 1668 cm −1 corresponding for C=O group.
The reactivity of sulfonamide derivative 3 against binucleophilic reagents was investigated.Thus, treatment of 3 with hydrazine hydrate in ethanol under reflux afforded in good yield a product that was identified as pyrazole derivative 9. Formation of compound 9 is assumed to take place via nucleophilic attack of hydrazine which caused ring opening of -pyrone which readily undergo interamolecular cyclization by water elimination (Scheme 3).IR spectrum showed lack the band corresponding for carbonyl functional group and showed broad band around 3392 cm −1 due to OH and NH functional groups. 1 H NMR spectrum revealed a singlet signal at 6.45 ppm characteristic for pyrazole proton also, another broad singlet signals at 10.41, 11.14 ppm due to NH and OH protons.Similarly, interaction of 3 with thiourea in ethanol containing anhydrous potassium carbonate led to ring opening.The thiopyrimidine derivative 10 was assigned for the reaction product on the basis of its elemental analysis and spectral data obtained.IR spectrum lacked an absorption band due to a carbonyl functional group and revealed absorption bands at: 3443 and 3221 cm −1 characteristic for OH and NH functional groups, respectively. 1H NMR spectrum displayed signals at 7.34, 9.59 and 13.05 ppm assignable to pyrimidine-H, NH and OH protons, respectively.
It is interesting in this connection that the hydrolysis of sulfonamide derivative 3 with potassium hydroxide caused opening -pyrone ring and the product of this reaction was identified on the basis of its spectral data as visnaginone derivative 11.IR spectrum revealed the presence of OH and NH stretching bands at: 3165 and 3124 cm −1 and C=O band at: 1666 cm −1 .Also, its 1 H NMR spectrum supported its structure, as it revealed the piperazine ring protons at 2.68−3.33 and two broad signals at 10.26 and 13.13 ppm assignable to NH and OH protons, respectively.Treatment of 11 with dimethylformamide-dimethylacetal (DMF-DMA) in toluene under reflux afforded the corresponding enaminone derivative 12. IR spectrum displayed broad absorption

Antibacterial and Antifungal Activities
The synthesized compounds were tested in vitro for antibacterial and antifungal activities by the agar diffusion method against the following strains: two Gram-positive bacteria, Staphylococcus aureus NCTC-7447 and Bacillus cereus ATCC-14579; two Gram-negative bacteria, Pseudomonas oeruginosa IMRU-70, and Esherichia coli NCTC-289; and three Fungi, Aspergillus ochraceus Wilhelm AUCC-230, Penicillium chrysogenum thom AUCC-530 and Candida albicans AUCC-420.The results were summarized in Table 1.Most of the synthesized compounds exhibited various antimicrobial activity towards all the micro-organisms used.
Certain aspects of the structure activity relationships of the prepared compounds were clearly highlighted.The results of the antimicrobial screening demonstrated the following assumptions about the structural activity relationship (SAR).Incorporating piperazin-1-ylsulfonyl moiety in position 9 of visnagine as in structure 3 had a detrimental effect on antimicrobial activity.Visnagin-9-piperazin-1-ylsulfonyl 3 showed moderately active against all the tested strains.Changing the substituent on sulfonamide at position C-9 of visnagine from 2-ethoxyphenyl to 2-aminophenyl to 4aminobiphenyl (4a → 4b → 4c) to show the difference between each substituent on the effect of the antimicrobial activity was carried out.Compound 4c showed more activity than its analogues and showed high activities against all the tested strains.Incorporating sulfonamide-phenyl-acetamide moiety in position 9 of visnagine as in structure 5 did not improve the antimicrobial activity.Compound 5 showed moderately active against all the tested strains.Similarly, incorporating sulfonamide-biphenyl-4-yl-acetamide moiety in position 9 of visnagine as in structure 6 showed little improvement on antimicrobial activity.Compound 6 showed moderate activity against all the tested organisms.Surprising, incorporating 1H-benzo[d][1,2,3]triazol-1-ylsulfonyl moiety in position 9 of visnagine as in structure 8 did not showed remarkable improvement on the antimicrobial activity.Compound 8 showed moderately activity against all the tested bacteria and no activity against all the tested fungi.Broken -pyrone ring of visnagine as in structure 11 resulted in the lowest antimicrobial activity among all the investigated compounds.Visnaginone derivative 11 showed no activity against most of the tested bacteria and fungi.Treatment of 11 with dimethylformamide-dimethylacetal did not improve the antimicrobial activity.Compound 12 showed no activity against most of the tested bacteria and fungi.In addition, condensation of visnaginone 11 with 4-chlorobenzaldeyde did not improve the antimicrobial activity.Styryl derivative 13 showed no activity against most of the tested bacteria and fungi.Moreover, condensation of styryl derivative 13 with phenylhydrazine did not improve the antimicrobial activity.Pyrazole derivative 14 showed high activity against C. albicans only and no activity against most of the tested bacteria and fungi.Formation of fuorocoumarin (furobenzopyransulfonamide [bergaptensulfonamides]) 15a,b showed moderately active against all the tested strains.Treatment of 15b with sulfur or aryledine did not improve the antimicrobial activity.

CONCLUSIONS
Derivatives of furochromone, benzofuran and furocoumarin which bearing sulfonyl moiety were synthesized in order to evaluate their antibacterial and antifungal activities.Regarding the effect of each derivative against bacterial and fungal strains, results of antimicrobial activity in this study revealed that: Derivatives of visnagine with piperazin-1-ylsulfonyl moiety in position 9 showed moderate activity against all the tested strains.Changing the substituent at position C-9 of visnagine from N-(2-ethoxyphenyl)-sulfonamide to N-(2-aminophenyl)-sulfonamide or N-(4-aminobiphenyl)-sulfonamide improved the antimicrobial activity.Besides, N-(4-aminobiphenyl)-sulfonamide moiety showed higher activity against all the tested strains.Incorporating sulfonamide-phenyl-acetamide, sulfonamide-biphenyl-4-yl-acetamide or 1H-benzo[d] [1,2,3]triazol-1-ylsulfonyl moieties in position 9 of visnagine did not improve the antimicrobial activity.Broken -pyrone ring of visnagine resulted in the lowest antimicrobial activity among all the compounds investigated in this study.Formation of fuorocoumarin (furobenzopyran-sulfonamide [bergaptensulfonamides]) showed moderate activity against all the tested strains.

EXPERIMENTAL
Melting points were determined on a digital Gallen-Kamp MFB-595 instrument and were uncorrected.IR spectra (KBr) were measured using a Jasco FT/IR-300E spectrometer. 1 H NMR were recorded on a Brucker (500 MHz) spectrometer using TMS as an internal standard; chemical shifts are reported as δ/ppm units.Mass spectra were performed on a Shimadzu GSMS-QP 1000 Ex mass spectrometer at 70 eV.The elemental analyses were carried out at the Microanalytical Center, Cairo University, Cairo, Egypt.Antimicrobial screening was carried out in Biochemistry Department Faculty of Agriculture, Al-Azhar University.

General Procedure for Acetylation of Compounds 4b and 4c
The solution of 4b or 4c (0.01 mol) in acetic anhydride (10 mL) was heated under reflux for 2h.The reaction mixture was cooled and the solid product collected and crystallized from proper solvent to give 5 and 6, respectively.

Antimicrobial Assay
The synthesized compounds were screened in vitro for their antimicrobial activities against strains of bacteria and strains of fungi by the agar diffusion technique. [1]A 1 mg/mL solution in dimethylformamide was used.The bacteria and fungi were maintained on nutrient agar and Czapek's-Dox agar media, respectively.DMF showed no inhibition zones.The agar media were inoculated with different microorganisms culture tested.After 24h of incubation at 37 °C for bacteria and 48h of incubation at 28 °C for fungi, the diameter of inhibition zone (mm) was measured.Chloramphenicol and Terbinafin used as references for antibacterial and antifungal activities, respectively.

Table 1 .
Antimicrobial activity of the synthesized compounds against the pathological organisms expressed as inhibition diameter zones in millimeters (mm) based on well diffusion assay