Enzymatic total synthesis of 2,3,4,5-tetrabromopyrrole starting from L-proline

The natural product 2,3,4,5-tetrabromopyrrole (2,3,4,5-TBP) is produced by a marine gammaproteobacterium of the genera Pseudoalteromonas, and has been shown to induce larval settlement in coral. Here we identify the gene cluster encoding the biosynthesis of 2,3,4,5-TBP and report the one-pot seven-enzyme in vitro total synthesis of 2,3,4,5-TBP starting from L-proline. Pyrrolyl-S-ACP halogenases characterized to date catalyze di-chlorination at the 4- and 5- positions of ACP-tethered pyrroles, which subsequently undergo PKS extension and further elaboration prior to offloading of the end product. Our investigation reveals a multifaceted pyrrolyl-S-ACP halogenase selective for bromine that first catalyzes three brominations of pyrrolyl-S-ACP to 3,4,5-tribromopyrrolyl-S-ACP followed by unusual brominative offloading facilitated by a type II thioesterase to yield 2,3,4,5-TBP.