Daphnezomines A and B, Novel Alkaloids with an Aza-adamantane Core from Daphniphyllum humile

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.

Total Synthesis of Daphniphyllum Alkaloids: From Bicycles to Diversified Caged Structures

Native to the Asia-Pacific region and widely applied in traditional Chinese medicine, the genus Daphniphyllum has produced over 330 known Daphniphyllum alkaloids. Investigations into these alkaloids have shown an exceptional range of interesting bioactivities. Challenging and caged polycyclic architectures and the promising biological profiles make Daphniphyllum alkaloids intriguing synthetic targets. Based on their backbones, these alkaloids can be categorized into 13-35 structurally distinct subfamilies. In addition to our work, almost 30 impressive total syntheses of Daphniphyllum alkaloids from seven subfamilies, namely, daphniphylline-type, secodaphniphylline-type, daphnilactone A-type, bukittinggine-type, daphmanidin A-type, calyciphylline A-type, and calyciphylline B-type alkaloids, have been reported by 11 research groups. However, many Daphniphyllum alkaloid subfamilies remain inaccessible by chemical synthesis.In this Account, we summarize our recent endeavors in the total synthesis of Daphniphyllum alkaloids commencing from simple chiral bicyclic synthons. Daphniphyllum alkaloids with diversified skeletons from four different subfamilies, namely, calyciphylline A-type, daphnezomine A-type, bukittinggine-type, and yuzurimine-type alkaloids, have been achieved. Furthermore, the tricyclic core structure of daphniglaucin C-type alkaloids daphnimacropodines was also synthesized. First, we describe a 14-step synthesis of calyciphylline A-type alkaloid (-)-himalensine A, which features a mild Cu-mediated nitrile hydration, an intramolecular Heck reaction to assemble the pivotal 2-azabicyclo[3.3.1]nonane moiety, and a Meinwald rearrangement to introduce the critical oxidative state into the skeleton. We then introduce the synthesis of daphnezomine A-type alkaloid dapholdhamine B, which possesses a unique aza-adamantane core. This target molecule was fabricated using key reactions including Huang's amide-activation-annulation. An unexpected radical detosylation during the synthesis of dapholdhamine B further inspired an ambitious radical cyclization cascade strategy, which eventually led to an efficient total synthesis of bukittinggine-type alkaloid (-)-caldaphnidine O. This highly chemo-, regio-, and stereoselective radical reaction cascade also shed light on the synthetic strategy of other alkaloids with caged structures. We next describe the first total synthesis of yuzurimine-type alkaloid (+)-caldaphnidine J. The key steps in our approach include a Pd-catalyzed regioselective hydroformylation and a novel Swern oxidation/ketene dithioacetal Prins reaction cascade. The work has achieved the first synthesis of a member of the largest subfamily of Daphniphyllum alkaloids. Finally, we show our efforts toward the total synthesis of daphniglaucin C-type alkaloids. Overall, we hope that the interesting strategies and synthetic methods demonstrated in our efforts could inspire a wide variety of additional applications to natural product synthesis.

Total Synthesis of (-)-Daphnezomines A and B

Daphnezomines A and B are structurally unusual Daphniphyllum alkaloids that contain a unique aza-adamantane core skeleton. Herein, a modular approach to these alkaloids is presented that exploits a diverse array of reaction strategies. Commencing from a chiral pool terpene-(S)-carvone, the azabicyclo[3.3.1]nonane backbone, which occurs widely in Daphniphyllum alkaloids, was easily accessed through a Sharpless allylic amination and a palladium-catalyzed oxidative cyclization. A protecting group enabled a stereoselective B-alkyl Suzuki-Miyaura coupling sequence and an Fe-mediated hydrogen atom transfer (HAT)-based radical cyclization were then applied to construct C6 and C8 stereocenters. A final epimer locking strategy enabled the assembly of the highly congested aza-adamantane core, thereby achieving the first total synthesis of (-)-daphnezomines A and B in 14 steps.

Pharmacological profile of natural and synthetic compounds with rigid adamantane-based scaffolds as potential agents for the treatment of neurodegenerative diseases

This review is dedicated to the comparative analysis of structure-activity relationships for more than 75 natural and synthetic derivatives of adamantane. Some of these compounds, such as amantadine and memantine, are currently used to treat dementia, Alzheimer's and Parkinson's diseases and other neurodegenerative diseases. The data presented show that the pharmacological potential of 1-fluoro- and 1-phosphonic acid adamantane derivatives against Alzheimer's and Parkinson's diseases and other neurodegenerative diseases exceeds those of well-known amantadine and memantine. The information presented in this review highlights the promising directions of studies for biochemists, pharmacologists, medicinal chemists, physiologists, and neurologists, as well as to the pharmaceutical industry.

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.

A piperidine alkaloid and limonoids from Arisaema decipiens, a traditional antitumor herb used by the Dong people

A new piperidine alkaloid and three known tetranortriterpenoids were isolated from the methanol extracts of the rhizomes of Arisaema decipiens Schott (Araceae) and their chemical structures were identified as (-)-(2R*,3S*,6S*)-N,2-dimethyl-3-hydroxy-6-(9-phenylnonyl) piperidine (1), 6-deacetylnimbin (2), 28-deoxonimbolide (3) and nimbin (4). The N-methylated derivative (1a) of 1 was synthesized. Compound 1 exhibited weak inhibitory activity against the MCF-7 cell line, while compound 1a showed potential inhibitory activity against the MCF-7 cell line with an IC₅₀ value of 4.6 μM and weak inhibitory activity against K562 and SK-OV-3 cells. This plant in genus Arisaema is firstly reported as the source of limonoids that are considered a natural antitumor herbal medicine.

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.

Pordamacrines A and B, alkaloids from Daphniphyllum macropodum

The new Daphniphyllum alkaloids, pordamacrines A (1) and B (2), have been isolated from the leaves of Daphniphyllum macropodum, and their structures were elucidated on the basis of interpretation of spectroscopic data and by the single-crystal X-ray diffraction analysis of 2. Pordamacrines A (1) and B (2) exhibited moderate vasorelaxant effects on the rat aorta.

Daphmanidins C and D, Novel Pentacyclic Alkaloids fromDaphniphyllumteijsmanii

[structure: see text] Two novel alkaloids with an unprecedented fused-pentacyclic skeleton, daphmanidins C (1) and D (2), have been isolated from the leaves of Daphniphyllum teijsmanii, and the structures were elucidated on the basis of spectroscopic data. The relative stereochemistry of 1 and 2 was assigned by combination of NOESY correlations and a simulation analysis. Daphmanidin C (1) elevated activity of NGF biosynthesis.