A simple and facile iodination method of didechlorotiacumicin B and aromatic compounds

Biosynthetic Diversification of Fidaxomicin Aglycones by Heterologous Expression and Promoter Refactoring

Fidaxomicin (Dificid) is a commercial macrolide antibiotic for treating Clostridium difficile infection. Total synthesis of fidaxomicin and its aglycone had been achieved through different synthetic schemes. In this study, an alternative biological route to afford the unique 18-membered macrolactone aglycone of fidaxomicin was developed. The promoter refactored fidaxomicin biosynthetic gene cluster from Dactylosporangium aurantiacum was expressed in the commonly used host Streptomyces albus J1074, thereby delivering five structurally diverse fidaxomicin aglycones with the corresponding titers ranging from 4.9 to 15.0 mg L^-1. In general, these results validated a biological strategy to construct and diversify fidaxomicin aglycones on the basis of promoter refactoring and heterologous expression.

Flavin-enabled reductive and oxidative epoxide ring opening reactions

Epoxide ring opening reactions are common and important in both biological processes and synthetic applications and can be catalyzed in a non-redox manner by epoxide hydrolases or reductively by oxidoreductases. Here we report that fluostatins (FSTs), a family of atypical angucyclines with a benzofluorene core, can undergo nonenzyme-catalyzed epoxide ring opening reactions in the presence of flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NADH). The 2,3-epoxide ring in FST C is shown to open reductively via a putative enol intermediate, or oxidatively via a peroxylated intermediate with molecular oxygen as the oxidant. These reactions lead to multiple products with different redox states that possess a single hydroxyl group at C-2, a 2,3-vicinal diol, a contracted five-membered A-ring, or an expanded seven-membered A-ring. Similar reactions also take place in both natural products and other organic compounds harboring an epoxide adjacent to a carbonyl group that is conjugated to an aromatic moiety. Our findings extend the repertoire of known flavin chemistry that may provide new and useful tools for organic synthesis.

Epoxide ring opening reactions are important in both biological processes and synthetic applications. Here, the authors show that flavin cofactors can catalyze reductive and oxidative epoxide ring opening reactions and propose the underlying mechanisms.