Synthesis and Biological Investigation of Antifungal Peptides and Benzimidazoles

Abstract

Candida albicans exists as a harmless commensal pathogen but for those immunocompromised individuals can become a life-threating problem. Its high level of resistance that exhibits against most clinically used antifungal drugs, plus their many similarities that share with the host, makes it quite challenging the development of effective antifungal drugs and therapies. “Scaffold hopping” is a valuable tool in drug development to generate focused compound collections by modifying the core structure of known active compounds. The design and synthesis of novel lead compounds based on focused target-family design carried out in this dissertation, was supported by solid phase and solution phase combinatorial organic chemistry. Our main starting hits have been LL-37 peptide and EMC120B12, a benzimidazole compound previously found to be active with an IC50 and CC50 of 0.75 μM and 97.5 μM, respectively. Analogues of peptide LL-37 and EMC120B12 were synthesized. Besides, based on scaffold hopping approach, indoles, triazoles and imidazo[1,2-a]pyridines were designed and synthesized as well. All compounds were isolated and analyzed by HPLC-ESI-MS. Representative products were characterized using NMR. All synthesized compound collections were evaluated for its antifungal properties. A primary high-throughput screening at 10 μM, eight out of fifteen benzimidazole analogues and two LL-37 analogues were active against Candida albicans. Further biological studies like dose-response assay, minimum inhibitory concentration (MIC) and screening of clinical Candida spp isolates, confirmed that two benzimidazole analogues: (S)-2-(1-Aminobutyl)-1-(3-fluorobenzyl)benzimidazole (BE10) and (S)-2- (1-Aminobutyl)-1-(3-chlorobenzyl)benzimidazole (BE9) were more active than the principle hit. However, BE9 was finally discarded due to its toxic effect on the host cells. Unfortunately, the rest of the indole, triazole, imidazo[1,2-a]pyridine and LL-37 analogues were not active against the several Candida species tested. Although preliminary biological data for BE10 is doubtlessly promising, additional biological experiments, like in vivo studies are necessary to confirm a clinical candidate or to further optimize the structure.