Chemical synthesis to access rare heterocycles and tool compounds to probe bacterial polysaccharide metabolism - Abstract Two emphasis areas are proposed which are underpinned by synthetic organic chemistry. First, new synthetic methodology to access exceptionally rare nitrogen-rich compounds will be developed to expand the availability of medicinally relevant, densely functionalized heterocycles. We pioneered new methodology to synthesize the rare diazacyclobutene (DCB) heterocycle. Less than ten examples of stable DCBs where previously known. The dearth of examples has prevented their application in any biological or synthetic context. Nevertheless, preliminary biological investigations show that some DCBs exhibit potent anti-parasitic activity, suggesting that further development of the scaffold may unlock additional biological activity relevant to human disease. Accessing new examples of DCBs will enable biological evaluation and expansion of the synthetic utility of the heterocycle. Exploiting new reactivity of DCBs and related intermediates will provide new methods to synthesize a large variety of medicinally relevant, richly functionalized heterocycles through the development of cascade reactions of labile monocyclic DCB intermediates. Similarly, the intentional diversion of key reactive intermediates with Lewis Acids will access additional rare heterocycles through novel mechanisms. The second emphasis area will develop new non-microbicidal tool compounds to interrogate the polysaccharide metabolism of gut bacteria of the Bacteroides genus. The enzymatic machinery deployed by the Bacteroides genus serves as a model system to understand glycan foraging strategies deployed by the entire Bacteroidetes phylum, which represents over half of the constituents of a normal healthy microbiota). Presently, our lab has uncovered the only known chemical probes to interrogate this fundamental system governing carbohydrate utilization by prominent gut microbes. Additionally, Bacteroides spp. are associated with common anaerobic bacterial infections affecting multiple organ systems, sepsis, gut inflammatory and autoimmune diseases, and colorectal cancer. Building on our prior discovery that the natural product acarbose shuts down the Starch Utilization System (Sus) of Bacteroides spp., we will synthesize useful chemical probes to interrogate this fundamental metabolic pathway deployed by prominent gut microbes for eventual therapeutic gain. Thus, we will provide tools to clarify the mechanism of action of acarbose-induced arrest of bacterial starch metabolism by deploying synthetic analogs bearing fluorophores and photoaffinity tags. This will also provide key fundamental knowledge about the promiscuity of the probe with other Sus-like constructs. We will uncover potential downstream effects on virulence factors (i.e. biofilm formation, antibiotic resistance, and toxin production) in the organisms upon acarbose-mediated shutdown of the Sus. This work will lay important groundwork toward providing versatile tools to understand gut microbial metabolism as it pertains to human disease. We will also significantly expand synthetic access to new probe molecules capable of interrogating the Sus as well as other related enzyme suites that are leveraged by a majority of human gut microbes.
