Synthesis of Anabaenopeptins With a Strategic Eye Toward N‐Terminal Sequence Diversity

A divergent synthesis strategy was developed for producing various anabaenopeptins (AP) for harmful algal bloom monitoring. The synthesis involved on-resin stepwise pentapeptide assembly on a MeDbz linker then N-α-ureido amino acid attachment and cyclization. To manage N-methylated amino acids, modified coupling conditions were employed. Lysine's ε-amino group reacted with the activated MeDbz linker in a self-cleaving head-to-side chain cyclization. Cyclization conditions were optimized by screening different pH levels to control lysine α-amine cyclization and prevent hydrolysis. Global cleavage and purification afforded the pure anabaenopeptins. This approach proved effective as a general platform for anabaenopeptin synthesis, allowing rapid access to anabaenopeptins A, B, F, and oscillamide Y.