Background:
[1, 3, 4]oxadiazolenone core containing chalcones and nucleosides were synthesized
by Claisen-Schmidt condensation of a variety of benzaldehyde derivatives, obtained from oxidation
of substituted 5-(3/6 substituted-4-Methylphenyl)-1, 3, 4-oxadiazole-2(3H)-one and various substituted
acetophenone. The resultant chalcones were coupled with penta-O-acetylglucopyranose followed
by deacetylation to get [1, 3, 4] oxadiazolenone core containing chalcones and nucleosides. Various
analytical techniques viz IR, NMR, LC-MS and elemental analysis were used to confirm the structure
of the synthesised compounds.The compounds were targeted against Bacillus subtilis, Staphylococcus
aureus and Escherichia coli for antibacterial activity and Aspergillus flavus, Aspergillus niger and
Fusarium oxysporum for antifungal activity.
Methods:
A mixture of Acid hydrazides (3.0 mmol) and N, Nʹ- carbonyl diimidazole (3.3 mmol) in 15
mL of dioxane was refluxed to afford substituted [1, 3, 4]-oxadiazole-2(3H)-one. The resulted [1, 3, 4]-
oxadiazole-2(3H)-one (1.42 mmol) was oxidized with Chromyl chloride (1.5 mL) in 20 mL of carbon
tetra chloride and condensed with acetophenones (1.42 mmol) to get chalcones 4. The equimolar ratio of
obtained chalcones 4 and β -D-1,2,3,4,6- penta-O-acetylglucopyranose in presence of iodine was refluxed
to get nucleosides 5. The [1, 3, 4] oxadiazolenone core containing chalcones 4 and nucleosides 5
were tested to determined minimum inhibitory concentration (MIC) value with the experimental procedure
of Benson using disc-diffusion method. All compounds were tested at concentration of 5 mg/mL,
2.5 mg/mL, 1.25 mg/mL, 0.62 mg/mL, 0.31 mg/mL and 0.15 mg/mL for antifungal activity against
three strains of pathogenic fungi Aspergillus flavus (A. flavus), Aspergillus niger (A. niger) and
Fusarium oxysporum (F. oxysporum) and for antibacterial activity against Gram-negative bacterium:
Escherichia coli (E. coli), and two Gram-positive bacteria: Staphylococcus aureus (S. aureus) and Bacillus
subtilis(B. subtilis).
Result:
The chalcones 4 and nucleosides 5 were screened for antibacterial activity against E. coli, S.
aureus and B. subtilis whereas antifungal activity against A. flavus, A. niger and F. oxysporum. Compounds
4a-t showed good antibacterial activity whereas compounds 5a-t containing glucose moiety
showed better activity against fungi. The glucose moiety of compounds 5 helps to enter into the cell
wall of fungi and control the cell growth.
Conclusion:
Chalcones 4 and nucleosides 5 incorporating [1, 3, 4] oxadiazolenone core were synthesized
and characterized by various spectral techniques and elemental analysis. These compounds were
evaluated for their antifungal activity against three fungi; viz. A. flavus, A. niger and F. oxysporum. In
addition to this, synthesized compounds were evaluated for their antibacterial activity against gram
negative bacteria E. Coli and gram positive bacteria S. aureus, B. subtilis. Compounds 4a-t showed
good antibacterial activity whereas 5a-t showed better activity against fungi.
In vitro antibacterial activity of ethanolic crude extracts of Capsicum annum against Staphylococcus aureus and Escherichia coli isolated from pus and stool samples at Ruhengeri Referral Hospital, Rwanda
