Optimized microwave assisted synthesis of LL37, a cathelicidin human antimicrobial peptide

LL37, a human cathelecidin antimicrobial peptide comprising of 37 amino acids has emerged as one of the vital therapeutic peptides associated with a number of biological applications. In this context, we herein report a highly efficient and optimized methodology for the synthesis of LL37 through SPPS assisted by microwave power. Standard conditions employing uronium coupling reagents was unsatisfactory from the 20th amino acid residue onwards. A segmentation approach revealed that the amide bond formation between the Val and Ile was identified as the problematic coupling. It was found that DIC/Oxyma-Pure in conjunction with THF as the solvent gave best results during manual coupling of 20th position Ile and required double coupling as revealed by HPLC and MALDI-TOF MS. In order to verify the synthesis, antibacterial testing was carried out and the results revealed comparable values with that of literature reported.