Two novel alkaloids with a unique fused hexacyclic skeleton from Daphniphyllum subverticillatum

The chemistry of Daphniphyllum alkaloids

The triterpenoids Daphniphyllum alkaloids share the unique fused hexacyclic ring framework are isolated from the genus Daphniphyllum. These natural products possess comprehensive biological activities and exhibit excellent potential medicinal appliment. This review covers the reported isolation studies and biological activities of Daphniphyllum alkaloids spanning the period from 1966 to the beginning of 2020, In the meantime, the total synthesis of Daphniphyllum alkaloids will be emphatically summarized for supplement over this review series.

Daphnillonins A and B: Alkaloids Representing Two Unknown Carbon Skeletons from Daphniphyllum longeracemosum

Two highly rearranged daphniphyllum alkaloids, daphnillonins A (1) and B (2), were isolated from Daphniphyllum longeracemosum and structurally characterized by a combination of diverse methods, including the calculation of electronic circular dichroism. Compound 1 possesses an unprecedented carbon architecture with a very unique 8-methyl-6-azabicyclo[3.2.1]octane moiety, and compound 2 represents a new carbon skeleton with an uncommon 7/6/5/7/5/5-fused ring system. The biosynthetic pathways for the two alkaloids were proposed with the concurrent major alkaloids as the precursors.

Calyciphylline B-Type Alkaloids: Total Syntheses of (-)-Daphlongamine H and (-)-Isodaphlongamine H

The first total synthesis of the complex hexacylic Daphniphyllum alkaloid (-)-daphlongamine H has been accomplished. Key to the success of the strategy are a complexity-building Mannich reaction, efficient cyclizations, and a highly diastereoselective hydrogenation to assemble multigram quantities of the tricyclic core bearing four contiguous stereocenters. Following construction of the hydro-indene substructure by means of a Pauson-Khand reaction, endgame redox manipulations delivered the natural product. Importantly, the synthetic studies have also given access to (-)-isodaphlongamine H and led to a revision of the reported structure of deoxyisocalyciphylline B.

Oxazaborinines from Vinylogous N-Allylic Amides: Reactivities of Underexplored Heterocyclic Building Blocks

Access to a new class of oxazaborinines using an efficient transition-metal-catalyzed rearrangement is demonstrated. The method overcomes the synthetic challenge of achieving an aza-Claisen rearrangement of vinylogous N-allylic amide substrates, giving rise to a variety of highly modifiable oxazaborinine products. An investigation of the unique reactivity of these boron-based heterocycles has unveiled their underexplored potential as valuable building blocks and intermediates for organic synthesis.

Recent Progress in the Chemistry of Daphniphyllum Alkaloids †

Daphniphyllum is an evergreen species known since 1826. After initial systematic investigations, more than 320 members of this family have been isolated, which comprise complex and fascinating structures. Unique azapolycyclic architectures containing one or more quaternary stereocenters render these alkaloids synthetically challenging. This review covers efforts toward the synthesis of Daphniphyllum alkaloids spanning the period from 2005 to the beginning of 2016, including reported biological activities as well as the isolation of new members of this genus.

Strategies toward the Total Synthesis of Calyciphylline B-type Alkaloids: A Computational Perspective Aided by DFT Analysis

Herein we describe synthetic efforts toward the total synthesis of calyciphylline B-type alkaloids. In the process, we disclose a detailed DFT study of equilibrium geometries and transition states that explains the stereochemical outcome during the formation of critical intermediates. X-ray crystallographic analysis reveals interesting conformational features in the naturally occurring deoxycalyciphylline B and its synthetic congeners.

Synthesis of a Model Tetracyclic Core Structure of Calyciphylline B-Type Alkaloids

Herein, we report the enantioselective synthesis of a functionalized aza-octahydropentalene and its elaboration to a model tetracyclic core structure of calyciphylline B-type alkaloids.

New alkaloids from Daphniphyllum himalense

A series ofDaphniphyllumalkaloids with selective kinase inhibitory activity were isolated and structurally characterized fromDaphniphyllum himalense.

Five new alkaloids from the stem bark of Daphniphyllum macropodum

Five new alkaloids, daphnicyclidins M and N (compounds 1 and 2) and calyciphyllines Q-S (compounds 3-5), along with four known ones, paxiphylline C (6), macropodumine B (7), macropodumine C (8) and daphnicyclidin A (9) were isolated from the stem bark of Daphniphyllum macropodum. Calyciphylline Q (3) is the first calyciphylline A derivative possessing a double bond between C-18 and C-19. Their structures and relative configurations were elucidated on the basis of spectroscopic methods, especially 2D NMR techniques. Compounds 1, 2, 8 and 9 exhibited cytotoxic activity against P-388 cells with IC₅₀ values of 5.7, 6.5, 10.3 and 13.8 µM, respectively. Compounds 1 and 2 also showed cytotoxic activity against SGC-7901 cells with IC₅₀ values of 22.4 and 25.6 µM.

A one-pot multicomponent strategy for stereospecific construction of tricyclic pyrrolo[1,2-a]quinolines

A novel multicomponent strategy for the efficient synthesis of tricyclic pyrrolo[1,2-a]quinolines has been described. The bond-forming efficiency, accessibility and generality of this synthesis make it highly attractive to assemble tri-heterocyclic scaffolds.

Discovery of structurally diverse and bioactive compounds from plant resources in China

This review describes the major discoveries of structurally diverse and/or biologically significant compounds from plant resources in China, mainly from the traditional Chinese medicines (TCMs) since the establishment of our research group in 1999. In the past decade, a large array of biologically significant and novel structures has been identified from plant resources (or TCM) in our laboratory. The structural modification of several biologically important compounds led to more than 400 derivatives, some of which exhibited significantly improved activities and provided opportunities to elucidate the structure-activity relationship of the related compound class. These findings are important for drug discovery and help us understand the biological basis for the traditional applications of these plants in TCM.

Deoxycalyciphylline B, a hepatotoxic alkaloid from Daphniphyllum calycinum

Daphniphyllum calycinum (DC), a main component of Chinese patent drug Fengliao-Changweikang, is effectively used to cure bowel disease in the clinic. It was recorded that DC possessed slight toxicity, which was caused by the alkaloids existing in its extract. Unfortunately, to date the toxicity level and toxic constituents are still unclear. The present study is designed to illustrate the acute toxicity and induced organ damages of the total alkaloids as well as to determine the toxic constituents. Based on the above studies, not only was the acute toxicity determined but also hepatic toxicity was characterized by increased plasma biomarkers of ALT and AST and liver cell inflammatory infiltrate as well necrosis that was firstly observed. Significantly, deoxycalyciphylline B exhibited exactly the same hepatic toxicity so it was identified as the main toxic constituent in DC. An obvious dose-effect relationship between the toxic compound and induced hepatic injuries was also observed. Moreover, the Chinese patent drug Fengliao-Changweikang contained low levels of the toxic compound, compared with the total alkaloids. Therefore, this Chinese patent drug could be regarded to be safe in this point of view.

Alkaloids from the leaves of Daphniphyllum subverticillatum

Four new alkaloids, 17-hydroxydaphnigraciline (1), subdaphnidine A (2), daphnezomine L methyl ester (3), and 11-hydroxycodaphniphylline (4), along with 24 known analogues, were isolated from the leaves of Daphniphyllum subverticillatum. The structures of 1-4 were elucidated on the basis of spectroscopic methods and from chemical evidence. Daphnilongeridine (5) showed cytotoxicity against several tumor cell lines at IC(50) values in the range 2.4-9.7 microM and against the HMEC human microvascular endothelial cell line with an IC(50) of 2.7 microM.

Dapholdhamines A-D, alkaloids from Daphniphyllum oldhami

Four new Daphniphyllum alkaloids, dapholdhamines A-D (1-4), were isolated from the leaves of Daphniphyllum oldhami. The structures and relative configurations of 1-4 were elucidated on the basis of spectroscopic data.

Alkaloids from the twigs of Daphniphyllum calycinum

Twelve new alkaloids, caldaphnidines G-R (1-12), along with 24 known ones, were isolated from the twigs of Daphniphyllum calycinum. Their structures were elucidated by spectroscopic methods, especially two-dimensional NMR techniques.

Alkaloids from Daphniphyllum oldhami

Four new Daphniphyllum alkaloids, daphnioldhanines H-K ( 1- 4), along with 34 known alkaloids, were isolated from Daphniphyllum oldhami. The known alkaloid dehydrodaphnigraciline ( 5) is now reported as a natural product. Their structures were elucidated by spectroscopic methods, especially 2D NMR techniques. The effects against platelet aggregation of compounds 1, 3, and 5 were evaluated, and 3 showed stronger activity against platelet aggregation induced by PAF. This is the first report of quinolizidine alkaloids from the genus Daphniphyllum.

Secophnane-type alkaloids from Daphniphyllum oldhami

Four new alkaloids, daphnioldhanins D-G (1-4, resp.), together with five known alkaloids, daphmacropodine (5), secodaphniphylline (6), deoxycalyciphylline B (7), deoxyisocalyciphylline B (8), and daphmanidin A (9), were isolated from the roots of Daphniphyllum oldhami. Their structures were elucidated on the basis of spectroscopic data and chemical methods. Compound 1 at 2.0 microM showed potent antioxidant activity against H(2)O(2)-induced impairment in PC12 cells.

Small-molecule natural products: new structures, new activities

A wide variety of novel small-molecule natural products has recently been reported. These compounds were isolated from marine and terrestrial sources, and from a variety of animals, plants and microorganisms. With the breadth of diversity represented in these bioactive small molecules, the future of natural product drug discovery looks bright.

Oldhamiphylline A: a Novel Hexacyclic Alkaloid fromDaphniphyllum oldhami

A novel Daphniphyllum alkaloid, oldhamiphylline A (1), together with five known alkaloids, deoxycalyciphylline B, deoxyisocalyciphylline B, calyciphylline, secodaphniphylline, and calycicine A, was isolated from the leaves of Daphniphyllum oldhami. The structure of 1 was established by spectroscopic methods, especially 2D NMR techniques (1H,1H-COSY, HMQC, HMBC, and NOESY).