ABSTRACT
The cylindrocyclophanes are a family of macrocyclic natural products reported to exhibit antibacterial activity. Little is known about the structural basis of this activity due to the challenges associated with their synthesis or isolation. We hypothesised that structural modification of the cylindrocyclophane scaffold could streamline their synthesis without significant loss of activity. Herein, we report a divergent synthesis of the cylindrocyclophane core enabling access to symmetrical macrocycles by means of a catalytic, domino cross-metathesis-ring-closing metathesis cascade, followed by late-stage diversification. Phenotypic screening identified several novel inhibitors of methicillin-resistant Staphylococcus aureus. The most potent inhibitor has a unique tetrabrominated [7,7]paracyclophane core with no known counterpart in nature. Together these illustrate the potential of divergent synthesis using catalysis and unbiased screening methods in modern antibacterial discovery.
Subject(s)
Anti-Bacterial Agents/pharmacology , Methicillin-Resistant Staphylococcus aureus/drug effects , Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/chemistry , Dose-Response Relationship, Drug , Microbial Sensitivity Tests , Molecular Structure , Stereoisomerism , Structure-Activity RelationshipABSTRACT
We describe semi-syntheses of the 11-hydroxyrotenoids sumatrol (1) and villosinol (2), starting from rotenone (5), using an oxime-directed C11-H functionalisation approach. Thus, rotenone (5) was converted into rotenone oxime (6), which gave dimeric palladacycle 7 following reaction with Na2PdCl4·3H2O. Controlled, divergent, oxidation of palladacycle 7 with either Pb(OAc)4 or K2Cr2O7 afforded the 11-acetoxylated intermediates 9 and 13, respectively, which were transformed into sumatrol (1) and villosinol (2).
ABSTRACT
We describe stereocontrolled semi-syntheses of deguelin and tephrosin, anti-cancer rotenoids isolated from Tephrosia vogelii. Firstly, we present a new two-step transformation of rotenone into rot-2'-enonic acid via a zinc-mediated ring opening of rotenone hydrobromide. Secondly, following conversion of rot-2'-enonic acid into deguelin, a chromium-mediated hydroxylation provides tephrosin as a single diastereoisomer. An Étard-like reaction mechanism is proposed to account for the stereochemical outcome. Our syntheses of deguelin and tephrosin are operationally simple, scalable and high yielding, offering considerable advantages over previous methods.
