Construction of a Protoberberine Alkaloid Skeleton via the Palladium-Catalyzed α-Arylation-Amide Formation Cascade

Quick Access to Protoberberine and Tetrahydroprotoberberine Derivatives/Analogues with One-Pot Sequential Isochromenylium-Mediated Annulation

A one-pot access to the protoberberine and tetrahydroprotoberberine scaffold has been developed from easily available primary amine-functionalized o-alkynylbenzaldehydes. The core skeleton of protoberberine was afforded via in situ generation of isochromenylium by Ag(I) catalysis, subsequent cyclization to isoquinolinium, and final hydride reduction by a continuous operation procedure. The newly developed step-economic protocol shows excellent regio- and stereoselectivity and is capable of achieving those previously unavailable derivatives/analogues with electron-deficient substituents, providing a robust tool for medicinal investigations of protoberberines and derivatives.

Palladium-Catalyzed Allylation of Endocyclic 1-Azaallyl Anions

Endocyclic 1-azaallyl anions engage allyl acetates in a palladium-catalyzed allylation followed by reduction to give unprotected 2-(hetero)aryl-3-allylpiperidines and 2-allyl-3-arylmorpholines, products not easily accessible by other means. The allyl group is then readily transformed into a variety of functional groups. Preliminary studies on the asymmetric variant of the reaction using an enantiomerically pure BI-DIME-type ligand provide the product with moderate enantioselectivity. Computational studies suggest that energy barriers of inner-sphere reductive elimination and outer-sphere nucleophilic substitution are almost the same, which makes both of them possible reaction pathways. In addition, the inner-sphere mechanism displays an enantiodiscriminating C-C bond forming step, while the outer-sphere mechanism is much less selective, which combined to give the asymmetric variant of the reaction moderate enantioselectivity.

Recent advances in total synthesis of protoberberine and chiral tetrahydroberberine alkaloids

Covering: Up to 2024Due to the widespread distribution of protoberberine alkaloids (PBs) and tetrahydroberberine alkaloids (THPBs) in nature, coupled with their myriad unique physiological activities, they have garnered considerable attention from medical practitioners. Over the past few decades, synthetic chemists have devised various total synthesis methods to attain these structures, continually expanding reaction pathways to achieve more efficient synthetic strategies. Simultaneously, the chiral construction of THPBs has become a focal point. In this comprehensive review, we categorically summarized the developmental trajectory of the total synthesis of these alkaloids based on the core closure strategies of protoberberine and tetrahydroberberine.

Palladium-Catalyzed Arylation of Endocyclic 1-Azaallyl Anions: Concise Synthesis of Unprotected Enantioenriched cis-2,3-Diarylpiperidines

Unprotected cis-2,3-diarylpiperidines are synthesized through an unprecedented palladium-catalyzed cross-coupling reaction between aryl halides and elusive endocyclic 1-azaallyl anions. These intermediates are generated in situ by the deprotonation of 2-aryl-1-piperideines, precursors that are readily prepared in two operations from simple piperidines. An asymmetric version of this reaction with (2R, 3R)-iPr-BI-DIME as the ligand provides products in moderate to good yields and enantioselectivities. This study significantly expands the synthetic utility of endocyclic 1-azaallyl anions.

Collective Syntheses of 8-Oxoprotoberberines via Sequential In(OTf)3-Catalyzed Cyclization and Pd(OAc)2-Catalyzed Heck Coupling

Six 8-oxoprotoberberines were synthesized collectively in four steps with acceptable yields (14-19%), of which the products 8-oxopalmatine, 8-oxopseudopalmatine, 8-oxoberberine, and 8-oxopseudoberberine come from nature. The synthetic route was featured with the In(OTf)₃-catalyzed cyclization and Heck coupling. Moreover, the syntheses of the natural products berberine, canadine, and iambertine were achieved via various reductions from 8-oxoberberine, which provided a concise approach to the syntheses of this kind of alkaloids.

Dimeric oxyberberine CT4-1 targets LINC02331 to induce cytotoxicity and inhibit chemoresistance via suppressing Wnt/β-catenin signaling in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a type of cancer characterized by high recurrence rates. Overcoming chemoresistance can reduce HCC recurrence and improve patients' prognosis. This work aimed to identify HCC chemoresistance-associated long non-coding RNA (lncRNA) and find an effective drug targeting the identified lncRNA for ameliorating the chemoresistance. In this investigation, bioinformatics analysis based on The Cancer Genome Atlas revealed a new chemoresistance index and suggested LINC02331 as an HCC chemoresistance and patients' prognosis-associated lncRNA that served as an independent prognostic indicator. Moreover, LINC02331 promoted DNA damage repair, DNA replication, and epithelial-mesenchymal transition as well as attenuated cell cycle arrest and apoptosis through regulating Wnt/β-catenin signaling, thus stimulating HCC resistance to cisplatin cytotoxicity, proliferation, and metastasis. Interestingly, we developed a novel oxidative coupling approach to synthesize a dimeric oxyberberine CT4-1, which exerted superior anti-HCC activities without obvious side effects measured by in vivo mice model and could downregulate LINC02331 mice model and could downregulate LINC02331 to mitigate LINC02331-induced HCC progression by suppressing Wnt/β-catenin signaling. RNA sequencing analyses verified the involvement of CT4-1-affected differential expression genes in dysregulated pathways and processes, including Wnt, DNA damage repair, cell cycle, DNA replication, apoptosis, and cell adhesion molecules. Furthermore, CT4-1 was demonstrated to be an effective cytotoxic drug in ameliorating HCC patients' prognosis with a prediction model constructed based on RNA-sequencing data from CT4-1-treated cancer cells and public cancer database. In summary, HCC chemoresistance-associated LINC02331 independently predicted poor patients' prognosis and enhanced HCC progression by promoting resistance to cisplatin cytotoxicity, proliferation, and metastasis. Targeting LINC02331 by the dimeric oxyberberine CT4-1 that exhibited synergistic cytotoxicity with cisplatin could alleviate HCC progression and improve patients' prognosis. Our study identified LINC02331 as an alternative target and suggested CT4-1 as an effective cytotoxic drug in HCC treatment.

Synthesis of Hydroxylated Polycyclic Pyrrolo/Indolo[1,2-a]quinoxaline-Fused Lactam Derivatives via PhI(OAc)2-Promoted 1,2-Bond Migration and Solvent Insertion

PhI(OAc)₂-mediated ring expansion via 1,2-bond migration and concurrent solvent insertion generate hydroxylated polycyclic pyrrolo/indolo[1,2-a]quinoxaline-fused lactam derivatives in a highly diastereoselective fashion from spiro-fused quinoxalines in good-to-excellent yield. X-ray crystal structure analysis reveals that the polycyclic lactams are nonplanar molecules devoid of any symmetry as they possess one or two axially chiral biaryl or N-arylindolyl bridges along with one chiral center at the bridgehead carbon.