ABSTRACT: Cyanobactins are ribosomally derived peptide natural products that are extensively posttranslationally modified. In exploring the biosynthesis of diverse cyanobactins in nature, we found that the enzyme sequences are highly similar (often, identical) despite producing diverse substrates. We have been working to understand these multistep pathways, where the enzymes are relatively fixed while the substrates undergo substantial modification. In so doing, we have also examined the chemical mechanisms underlying some of the posttranslational tailoring steps and synthesized diverse derivatives in vivo and in vitro for drug discovery.