Ang Li

Scholarisine A (1) represents a structurally distinct and synthetically intriguing subfamily of the echitamine/akuammiline-type alkaloids. Inspired by its postulated biogenetic logic, we developed a radical cyclization strategy that retains the key bond-forming site while replacing the aldol reaction. This reaction-altering biomimetic strategy, combined with expeditious preparation of a tetracyclic precursor, enabled a 13-step, scalable synthesis of 1. Moreover, facile access to its congeners, scholarisines I, T, and W (2-4), was achieved. Compound 2 impairs lysosomal degradative capacity and thus inhibits late-stage autophagy in cancer cells.

Paxdaphnine A (1) and daphlongamine B (2) are two heptacyclic Daphniphyllum alkaloids, each containing eight consecutive stereogenic centers. We achieved the first synthesis of these molecules in racemic form by using a biomimetic aza-Prins cyclization strategy. Paxdaphnine B (3), a putative biogenetic precursor of 1 and 2, was also obtained in the synthesis. A pentacyclic analogue of 3 was prepared in a scalable manner and served as a common intermediate. The sterically congested cyclopentane moiety of this intermediate was constructed via a nitrone-olefin cycloaddition reaction, and the assembly of its diquinane motif relied on an intramolecular Pauson-Khand reaction. Despite the unsatisfactory outcome of the initial biomimetic aza-Prins reaction of 3 with HCHO, we utilized the N-cyanomethyl derivative of 3 as an alternative substrate in combination with AgTFA as a promoter to rescue the biomimetic route to 1. On the basis of a similar strategy, an aza-Prins cyclization-lactonization cascade, involving a different terminating nucleophile, was developed for the synthesis of 2.

Ambiguine P (5) is a synthetically challenging representative of the hapalindole-type natural products. Inspired by the biosynthesis of this indole terpenoid family, we developed a Cope/Prins/Friedel-Crafts cascade, achieving a six-step synthesis of 5 from 2,2-dimethylcycloheptanone. Altered from the biosynthetic pathway, this cascade strategically commenced with a tricyclic indolenine derivative bearing a seven-membered ring, enabling efficient construction of the pentacyclic scaffold of 5. The oxidation state was elevated through chlorination and hydroxylation in the final stage.

Autophagy is a conserved catabolic process crucial for maintaining cellular homeostasis and has emerged as a promising therapeutic target for many diseases. Mechanistically novel small-molecule autophagy regulators are highly desirable from a pharmacological point of view. Here, we report the macroautophagy-inhibitory effect of hapalindole Q, a member of the structurally intriguing but biologically understudied hapalindole family of indole terpenoids. This compound promotes the noncanonical degradation of Yes-associated protein 1 (YAP1), the downstream effector of the Hippo signaling pathway, via chaperone-mediated autophagy, disrupting proper distribution of Rab7 and suppressing autophagosome−lysosome fusion in macroautophagy. Its binding to YAP1 is further confirmed by using biophysical techniques. A preliminary structure−activity relationship study reveals that the hapalindole Q scaffold, rather than the isothiocyanate group, is essential for YAP1 binding and degradation. This work not only identifies a macroautophagy inhibitor with a distinct mechanism of action but also provided a molecular scaffold for direct targeting of YAP1, which may benefit the development of therapeutics for both autophagy-related and Hippo−YAP-related diseases.

α-synuclein (α-syn) assembles into structurally distinct fibril polymorphs seen in different synucleinopathies, such as Parkinson’s disease and multiple system atrophy. Targeting these unique fibril structures using chemical ligands holds diagnostic significance for different disease subtypes. However, the molecular mechanisms governing small molecules interacting with different fibril polymorphs remain unclear. Here, we investigated the interactions of small molecules belonging to four distinct scaffolds, with different α-syn fibril polymorphs. Using cryo-electron microscopy, we determined the structures of these molecules when bound to the fibrils formed by E46K mutant α-syn and compared them to those bound with wild-type α-syn fibrils. Notably, we observed that these ligands exhibit remarkable binding adaptability, as they engage distinct binding sites across different fibril polymorphs. While the molecular scaffold primarily steered the binding locations and geometries on specific sites, the conjugated functional groups further refined this adaptable binding by fine-tuning the geometries and binding sites. Overall, our finding elucidates the adaptability of small molecules binding to different fibril structures, which sheds light on the diagnostic tracer and drug developments tailored to specific pathological fibril polymorphs.

While natural terpenoid cyclases generate complex terpenoid structures via cationic mechanisms, alternative radical cyclization pathways are underexplored. The metal-catalysed H-atom transfer reaction (M-HAT) offers an attractive means for hydrofunctionalizing olefins, providing access to terpenoid-like structures. Artificial metalloenzymes offer a promising strategy for introducing M-HAT reactivity into a protein scaffold. Here we report our efforts towards engineering an artificial radical cyclase (ARCase), resulting from anchoring a biotinylated [Co(Schiff-base)] cofactor within an engineered chimeric streptavidin. After two rounds of directed evolution, a double mutant catalyses a radical cyclization to afford bicyclic products with a cis-5-6-fused ring structure and up to 97% enantiomeric excess. The involvement of a histidine ligation to the Co cofactor is confirmed by crystallography. A time course experiment reveals a cascade reaction catalysed by the ARCase, combining a radical cyclization with a conjugate reduction. The ARCase exhibits tolerance towards variations in the dienone substrate, highlighting its potential to access terpenoid scaffolds.

While natural terpenoid cyclases generate complex terpenoid structures via cationic mechanisms, alternative radical cyclization pathways are underexplored. The metal-catalyzed hydrogen-atom-transfer (M-HAT) reaction offers an attractive means for hydrofunctionalizing olefins, providing access to terpenoid-like structures. Artificial metalloenzymes offer a promising strategy for introducing M-HAT reactivity into a protein scaffold. Herein, we report our efforts towards engineering an artificial radical cyclase (ARCase), resulting from anchoring a biotinylated [Co(Schiff-base)] cofactor within an engineered chimeric streptavidin. After two rounds of directed evolution, a double mutant catalyzed a radical cyclization to afford bicyclic products with a cis-5-6-fused ring structure and up to 97% enantiomeric excess. The involvement of a histidine ligation to the Co-cofactor was confirmed by crystallography. A time-course experiment revealed a cascade reaction catalyzed by the ARCase, combining a radical cyclization with a conjugate reduction. The ARCase exhibited tolerance towards variations in the dienone substrate, highlighting its potential to access terpenoid scaffolds.