An
N-methylated analog of a marine bacteria-derived natural proline-rich tetracyclopeptide was synthesized by coupling the deprotected dipeptide fragments Boc-
l-prolyl-
l-
N-methylleucine-OH and
l-prolyl-
l-
N-methylphenylalanine-OMe. A coupling reaction was accomplished utilizing
N,
N′-Dicyclohexylcarbodidimde
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An
N-methylated analog of a marine bacteria-derived natural proline-rich tetracyclopeptide was synthesized by coupling the deprotected dipeptide fragments Boc-
l-prolyl-
l-
N-methylleucine-OH and
l-prolyl-
l-
N-methylphenylalanine-OMe. A coupling reaction was accomplished utilizing
N,
N′-Dicyclohexylcarbodidimde (DCC) and 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC·HCl) as coupling agents and Triethylamine (TEA) or
N-methylmorpholine (NMM) as the base in the presence of the racemization suppressing agent. This was followed by the cyclization of the linear tetrapeptide fragment under alkaline conditions. The structure of the synthesized cyclooligopeptide was confirmed using quantitative elemental analysis, FTIR (Fourier-transform infrared spectroscopy),
1H NMR (Nuclear magnetic resonance spectroscopy),
13C NMR, and mass spectrometry. From the bioactivity results, it was clear that the newly synthesized proline-rich tetracyclopeptide exhibited better anthelmintic potential against
Megascoplex konkanensis,
Pontoscotex corethruses, and
Eudrilus eugeniae at a concentration of 2 mg/mL as well as improved antifungal activity against pathogenic dermatophytes
Trichophyton mentagrophytes and
Microsporum audouinii at a concentration of 6 μg/mL, as compared to non-methylated tetracyclopeptide. Moreover,
N-methylated tetracyclopeptide displayed significant activity against pathogenic
Candida albicans.
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