Total Synthesis and Structure Revision of (-)-Avicennone C

Natural epoxyquinoids: isolation, biological activity and synthesis. An update

Epoxyquinoids are of continuing interest due to their wide natural distribution and diverse biological activities, including, but not limited to, antibacterial, antifungal, anticancer, enzyme inhibitory, and others. The last review on their total synthesis was published in 2017. Since then, almost 100 articles have been published on their isolation from nature and their biological profile. In addition, the review specifically considers synthesis, including total and enantioselective, as well as the development of shorter approaches for the construction of epoxyquinoids with complex chemical architecture. Thus, this review focuses on progress in this area in order to stimulate further research.

Total Synthesis of Floyocidin B: 4,5-Regioselective Functionalization of 2-Chloropyridines

The recently discovered natural product (NP) (+)-floyocidin B with antimicrobial activity against Mycobacterium tuberculosis displays a hitherto unknown dihydroisoquinolinone scaffold in the class of the epoxyquinone NPs. The 4,5-regioselective functionalization of 2-chloropyridines was identified as a suitable strategy leading to the total syntheses of (+)-floyocidin B and analogs. In this paper, we present the long and winding evolution process to the final synthetic pathway, including model systems for route scouting and elucidation of side products, which enabled us to understand the unique reactivity of this unprecedented scaffold. A special focus was laid on method studies with different 2-chloropyridines, disclosing an unexpected effect of the 2-chloro substituent on the regioselectivity compared to 2-unsubstituted or carbon-substituted pyridines. Finally, a head-to-head comparison with the previously described synthesis of all four stereoisomers of the NP (−)-avicennone C revealed significant differences in the reactivity of these structurally closely related scaffolds.

The Discovery and Structure-Activity Evaluation of (+)-Floyocidin B and Synthetic Analogs

Tuberculosis represents one of the ten most common courses of death worldwide and the emergence of multidrug‐resistant M. tuberculosis makes the discovery of novel anti‐tuberculosis active structures an urgent priority. Here, we show that (+)‐floyocidin B representing the first example of a novel dihydroisoquinoline class of fungus‐derived natural products, displays promising antitubercular hit properties. (+)‐Floyocidin B was identified by activity‐guided extract screening and its structure was unambiguously determined by total synthesis. The absolute configuration was deduced from a key synthesis intermediate by single crystal X‐ray diffraction analysis. A hit series was generated by the isolation of further natural congeners and the synthesis of analogs of (+)‐floyocidin B. Extensive biological and physicochemical profiling of this series revealed first structure‐activity relationships and set the basis for further optimization and development of this novel antitubercular scaffold.