Synthesis of pseudopeptides based l-tryptophan as a potential antimicrobial agent

Four compounds named l-BTrpPA, l-Trp-o-PA, l-Trp-m-PA and l-Trp-p-PA, pseudopeptides constructed from pyridine and tryptophan units, were synthesized and tested against the Gram-positive, Gram-negative strains of bacteria and human pathogenic fungi. l-Trp-o-PA proved to be a broad-spectrum antimicrobial agent, showing a significant inhibition of the growth of Gram-positive bacteria (Staphylococcus aureus, methicillin-resistant S. aureus, Bacillus subtilis, Micrococcus luteus), and pathogenic fungi (Candida spp., Cryptococcus neoformans, Rhodotorula glutinis, Saccharomyces cerevisiae, Aspergillus spp., Rhizopus nigricans) tested and activity against Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Proteus vulgaris, Enterobacter aerogenes) tested. The in vitro cell cytotoxicity of l-Trp-o-PA was evaluated using haemolytic assay, in which the compound was found to have low lytic property, even up to the concentration of 4000 μg/mL, it only lysed 6–7% of erythrocytes, which was 100-fold greater than the MICs (minimum inhibitory concentration).