Synthesis, Characterization and In vitro Antimicrobial Activity of Aspartoyl Derivatives

Aims: This research focused on synthesizing antifungal N-tosyl-L-aspartoyl derivatives with the aim of relating the structure with the expected biological activities. Elucidation of compounds that had good yiel and were active was done.

Study Design: The antimicrobial activities of aspartic acid derivatives was determined against five fungal isolates using the in vitro model.

Place and Duration of Study: The experiments were carried out in Makerere University, Department of Chemistry and Department of Botany, between 2012 and 2014.

Methodology: Synthesis N-tosyl-L-aspartic acid was prepared by reacting p-tosyl chloride with L-aspartic acid in sodium hydroxide-ether mixture. The anhydride was prepared by refluxing N-Tosyl-L-aspartic acid with acetic anhydride. N-tosyl-L-aspartoylamino acids were obtained using 1:1 mole of the tosyl derivatives with amino acids: glycine, L- alanine, L-Leucine, L-valine and L-tyrosine. N-tosyl-L-aspartoylamino acid methyl esters were prepared by the action of thionyl chloride in methanol on N-tosyl-L-aspartoylamino acid derivatives. N-tosyl-L-aspartoylaniline derivatives and N-tosyl-L-aspartoyl-p-amino benzoic acid were achieved by refluxing the amines and p-amino benzoic acid in glacial acetic acid with the anhydride. The acid chloride was synthesized by refluxing N-tosyl-L-aspartoyl-p-amino benzoic acid in thionyl chloride. Stirring the acid chloride with appropriate amino acid in triethylamine-benzene mixture yielded the N-tosyl-L-aspartoyl-p-aminobenzoylamino acids. Esterifying these derivatives with Methanol in thionyl chloride afforded the methyl esters. The acid azide was prepared by stirring sodium azide in dry benzene with N-tosyl-L-aspartoyl-p-aminobenzoyl chloride. N-tosyl-L-aspartoylamino phenyl ureas were obtained by Curtius rearrangement by coupling of acid azides with appropriate amino acids in dry benzene. The structures of the products were elucidated using micro- and IR-spectral analyses. Confirmation of the structures was done by 1H NMR (Nuclear Magnet Resonance) spectroscopy at 60 MHz with TMS (Tetramethylsaline) as internal standard and elemental analysis.

Results: Thirty three compounds were tested for their biological activity against five fungal isolates, Candida albicans, Fusarium solani, Fusarium moniliforme, Penicillium expansum and Cladosporium cladosporioides. Eighteen compounds showed activity on either Candida albicans or Fusarium, while all the derivatives showed no antimicrobial activity on the three fungal isolates Fusarium moniliforme, Penicillium expansum and Cladosporium cladoporioides. All the synthesised compounds were tested against selected micro-organisms. These included: Candida albicans, Fusarium solani, Fusarium moniliforme, Penicillin expansum, Cladosporium cladosporioides. The antimicrobial properties of derivatives were assayed in vitro by agar disc diffusion method. The fungal isolates were locally isolated from rice porridge, milled Pakistan rice and from millet powder while the culture media was prepared using Potato Dextrose Agar (PDA).

Conclusion: The study showed that changing the chemical structures of the synthesized compounds (1-33) resulted in change of biological activity, when the structure of the compound was altered. This proves that they could be of practical pharmaceutical application.