(759f) In Situ Labeling of Natural Products with Alkyne Functionality and Its Applications

The terminal alkyne is a functionality widely used in organic synthesis, pharmaceuticals, and material science. It is a particularly useful moiety in azide-alkyne click chemistry reactions, which have recently emerged as one of the most powerful tools in drug discovery and chemical biology. Despite the importance of the terminal alkyne and its prevalence in synthetic compounds, the biosynthetic routes to terminal alkynes are not well understood. We recently identified and characterized two biosynthetic pathways in microbes that lead to the generation of terminal alkynes through unprecedented carrier protein-dependent pathways. These pathways were further exploited for tagging various natural products with terminal alkyne functionalities through starter unit or extender unit engineering. For example, pyrones (polyketides), antimycins and eponemycins (polyketide-non ribosomal peptide hybrids) have been successfully labeled with alkyne functionality. The natural product tagging strategy also enabled the development of an in situ natural products quantification platform based on bioorthogonal chemistry with the newly installed alkyne tag. Using this quantification platform as a screening method, we applied directed evolution strategy to improve the activity of a membrane-bound bifunctional desaturase/acetylenase. One round of mutagenesis along with the newly developed screening method yielded a desaturase/acetylenase variant conferring ~40-fold increased activity in E. coli. This study not only provides alkyne biosynthetic tools that are useful for chemical biology, but it also has applications in which enzymatic generation of terminal alkynes and in situ bioorthorgonal chemical transformation are required or preferred.