First total synthesis and biological evaluation of halolitoralin A

A new potent bioactive alanine-rich cyclic hexapeptide halolitoralin A(8), which was previously isolated from the marine sediment-derived bacterial strain Halobacillus litoralis YS3016, has been synthesized by the solution phase technique. All the coupling reactions were performed at room temperature utilizing dicyclohexylcarbodiimide (DCC) as the coupling reagent and N-methylmorpholine (NMM) as the base. The structure of the peptide was characterized by IR, H-1-NMR, C-13-NMR, FAB MS spectral data, as well as elemental analysis and DSC. The synthesized cyclopeptide was also screened for its antimicrobial and anthelmintic activities and found to exhibit potent antifungal activity against the pathogenic fungi Candida albicans and Trichophyton mentagrophytes along with potent antibacterial activity against the gram negative bacteria Pseudomonas aeruginosa and Escherichia coli. Gram negative bacteria were found to be more sensitive than gram positive bacteria towards the newly synthesized peptide. In addition, the peptide was also found to exhibit moderate anthelmintic activity against the earthworms Megascoplex konkanensis and Eudrilus sp.