All together: A concise strategy for the first diastereoselective total synthesis of (±)‐schindilactone A is reported. The synthesis features a ring‐closing metathesis, a thiourea/cobalt‐catalyzed Pauson–Khand reaction, and a thiourea/palladium‐catalyzed carbonylative annulation reaction. The chemistry can be applied to the synthesis of structures related to schindilactone A.
A total synthesis of aspidophylline A, a pentacyclic akuammiline-type monoterpene indole alkaloid, is described. The synthesis features: 1) rapid access to a fully functionalized dihydrocarbazole through the desymmetrization of readily available 2-allyl-2-(o-nitrophenyl)cyclohexane-1,3-dione; 2) an intramolecular azidoalkoxylation of an enecarbamate to install both the furoindoline ring and the azido functionality; and 3) an intramolecular Michael addition for the construction of the 2-azabicyclo[3.3.1]nonane ring system.
Mechanism-based glycoside hydrolase inhibitors are carbohydrate analogs that mimic the natural substrate’s structure. Their covalent bond formation with the glycoside hydrolase makes these compounds excellent tools for chemical biology and potential drug candidates. Here we report the synthesis of cyclohexene-based α-galactopyranoside mimics and the kinetic and structural characterization of their inhibitory activity toward an α-galactosidase from Thermotoga maritima (TmGalA). By solving the structures of several enzyme-bound species during mechanism-based covalent inhibition of TmGalA, we show that the Michaelis complexes for intact inhibitor and product have half-chair (2H3) conformations for the cyclohexene fragment, while the covalently linked intermediate adopts a flattened half-chair (2H3) conformation. Hybrid QM/MM calculations confirm the structural and electronic properties of the enzyme-bound species and provide insight into key interactions in the enzyme-active site. These insights should stimulate the design of mechanism-based glycoside hydrolase inhibitors with tailored chemical properties.
The total synthesis of strictamine has been achieved in nine steps from a known enol triflate. Characteristic features of our approach included: a) creation of a C7 all-carbon quaternary stereocenter at an early synthetic stage; b) use of an N,N-dimethyl tertiary amine as a surrogate of the primary amine for the rapid build-up of a functionalized 2-azabicyclo[3,3,1]nonan-9-one skeleton (achieved by using a reaction sequence of α-bromination of the ketone, followed by a stereoconvergent intramolecular nucleophilic substitution reaction); and c) a late-stage construction of the indolenine unit.
Let's swap: a scalable, atom-economic, enantio-, and diastereoselective synthetic route to trisubstituted γ-butyrolactones based on a Wagner-Meerwein-type dyotropic rearrangement of cis-β-lactones is described. This methodology was applied in efficient and protecting-group-free formal syntheses and total syntheses of various xanthanolide natural products.
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