Isolation, X-ray Crystallography, and Computational Studies of Calydaphninone, a New Alkaloid from Daphniphyllum calycillum

Acid Gas Capture by Nitrogen Heterocycle Ring Expansion

Acid gases including CO2, OCS, CS2, and SO2 are emitted by industrial processes such as natural gas production or power plants, leading to the formation of acid rain and contributing to global warming as greenhouse gases. An important technological challenge is to capture acid gases and transform them into useful products. The capture of CO2, CS2, SO2, and OCS by ring expansion of saturated and unsaturated substituted nitrogen-strained ring heterocycles was computationally investigated at the G3(MP2) level. The effects of fluorine, methyl, and phenyl substituents on N and/or C were explored. The reactions for the capture CO2, CS2, SO2, and OCS by 3- and 4-membered N-heterocycles are exothermic, whereas ring expansion reactions with 5-membered rings are thermodynamically unfavorable. Incorporation of an OCS into the ring leads to the amide product being thermodynamically favored over the thioamide. CS2 and OCS capture reactions are more exothermic and exergonic than the corresponding CO2 and SO2 capture reactions due to bond dissociation enthalpy differences. Selected reaction energy barriers were calculated and correlated with the reaction thermodynamics for a given acid gas. The barriers are highest for CO2 and OCS and lowest for CS2 and SO2. The ability of a ring to participate in acid gas capture via ring expansion is correlated to ring strain energy but is not wholly dependent upon it. The expanded N-heterocycles produced by acid gas capture should be polymerizable, allowing for upcycling of these materials.

Biosyntheses of azetidine-containing natural products

Azetidine is a four-membered polar heterocycle including a basic secondary amine, and is characterized by its high ring-strain energy, strong molecular rigidity and satisfactory stability. As a result, azetidine exhibits great challenges in its chemical synthesis and biosynthesis, which may explain the limited number of azetidine-containing natural products uncovered to date. In particular, the biosynthetic mechanisms of naturally occurring azetidines are poorly understood. Only some of them have been intensively investigated and few reviews have been published for the summarization of azetidine biosynthesis. In this review, we provide a comprehensive description of the biosyntheses of all the azetidine-containing natural products, especially the biosyntheses of azetidine moieties. We hope that this review will draw much attention to the biosynthetic research of the largely unexplored azetidine moieties as well as the discovery of novel azetidine-containing natural products in the near future.

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.

Computational studies of biologically active alkaloids of plant origin: an overview

Computational studies nowadays constitute a crucial source of information for drug development, because they provide information on many molecular properties and also enable predictions of the properties of not-yet-synthesized compounds. Alkaloids are a vast group of natural products exhibiting a variety of biological activities, many of which are interesting for drug development. On the other hand, computational studies of biologically active alkaloids have so far mostly focused on few particularly relevant or “popular” molecules, such as quinine, caffeine, or cocaine, with only few works on the other molecules. The present work offers an overview of existing computational studies on alkaloid molecules, from the earliest ones to the most recent, and considering all the theoretical approaches with which studies have been performed (both quantum mechanics and molecular dynamics). The considered studies are grouped according to their objectives and outcomes, such as conformational analysis of alkaloid molecules, effects of selected solvents on their properties, docking studies aimed at better understanding of the interactions between alkaloid molecules and biological targets, studies focusing on structure activity relationships, and computational studies performed to confirm experimental results. It is concluded that it would be important that computational studies on many other alkaloid molecules are performed and their results made available, covering their different classes as well as the variety of their biological activities, to attain better understanding of the properties not only of individual molecules, but also of groups of related molecules and of the overall alkaloids family.

Natural product sciences: an integrative approach to the innovations of plant natural products

The study on plant natural products not only helps us understand that their structural diversity is the inevitable result of plant species diversity, but also helps us understand certain rules and unity of the inevitable connection between the two. The diversity and complexity of chemical structures of many natural products are beyond imagination before we elucidated their structures. The question that follows is what is the biological significance of these natural products. Intrigued by the relationship between plant resources, natural products and biological functions, the Hao laboratory has taken an integrative approach that employs tools and knowledge from multi-disciplines, including natural product chemistry, chemical ecology and chemical biology, to unveil the effects of plant natural products on plant resistance to diseases, and environmental acclimations. Collaborating with cell biologists, the research has resulted in discovery of new mechanisms of cellular signaling and lead compounds.

Chiral Phosphoric Acid Catalyzed Asymmetric Addition of 2-(Vinyloxy)ethanol to Imines and Applications of the Products

Chiral nitrogen-containing molecules such as chiral amines, azetidines, and 2-substituted tetrahydroquinolines are important privileged scaffolds in medicinal chemistry. In this paper, an efficient and highly enantioselective chiral phosphoric acid catalyzed asymmetric addition of 2-(vinyloxy)ethanol to imines has been developed for the first time, providing the corresponding chiral amines containing dioxolane acetals that can transform into useful chiral N-heterocycles including azetidines and 2-substituted tetrahydroquinolines with excellent optical purity.

Class I Methyltransferase VioH Catalyzes Unusual S-Adenosyl-l-methionine Cyclization Leading to 4-Methylazetidinecarboxylic Acid Formation during Vioprolide Biosynthesis

S-Adenosyl-l-methionine (SAM)-dependent methyltransferases are intensely studied because they play important roles in the methylation of biomolecules in all domains of life. In this study, we describe that the methyltransferase VioH from Cysotobacter violaceus catalyzes a so far unknown cyclization of SAM to azetidine-2-carboxylic acid (AZE), which is proposed to be the precursor of the unusual 4-methylazetidinecarboxylic acid (MAZ) moiety of vioprolides. In vitro biochemical investigations reveal that SAM is converted to AZE in the presence of VioH while MAZ is generated by coexpression of VioH and the radical SAM enzyme VioG in Myxococcus xanthus or by combination of VioH and the cell lysate of M. xanthus expressing VioG. Thus, our findings unveil a novel function of SAM-dependent methyltransferases and shed light on the biosynthetic mechanism of MAZ formation.

An Explorer of Chemical Biology of Plant Natural Products in Southwest China, Xiaojiang Hao

Xiaojiang Hao, who obtained Master Degree from Kunming Institute of Botany (KIB), Chinese Academy of Sciences (CAS) in 1985, and Doctor in Pharmacy degree in Pharmacy from Institute for Chemical Research, Kyoto University, in 1990, was born in Chongqing in July, 1951. In 1991, he returned to KIB, CAS, as an Associate professor and served as the chair of the Department of Phytochemistry. In 1994, he was promoted to a full professor at the current institute. He served as the Deputy Director of KIB and the Director of Open Laboratory of Phytochemistry from 1995 to 1997, and the Director of KIB from 1997 to 2005. Professor Hao has published more than 450 peer-reviewed SCI papers, which have been cited over 6000 times. He has obtained one PCT patent and 23 patents in China. Due to his tremendous efforts, one candidate drug, phenchlobenpyrrone, has entered the Phase II clinical trail for the treatment of Alzheimer's disease. Moreover, he won the First Prize of Natural Sciences in Yunnan Province for three times, and Ho Leung Ho Lee Fund Science and Technology Innovation Award in 2017.

Facile Synthesis of Azetidine Nitrones and Diastereoselective Conversion into Densely Substituted Azetidines

An electrocyclization route to azetidine nitrones from N-alkenylnitrones was discovered that provides facile access to these unsaturated strained heterocycles. Reactivity studies showed that these compounds undergo a variety of reduction, cycloaddition, and nucleophilic addition reactions to form highly substituted azetidines with excellent diastereoselectivity. Taken together, these transformations provide a fundamentally different approach to azetidine synthesis than traditional cyclization by nucleophilic displacement and provide novel access to a variety of underexplored strained heterocyclic compounds.

16-nor Limonoids from Harrisonia perforata as promising selective 11β-HSD1 inhibitors

Two new 16-nor limonoids, harperspinoids A and B (1 and 2), with a unique 7/5/5/6/5 ring system, have been isolated from the plant Harrisonia perforate together with a known one, Harperforin G (3). Their structures were elucidated by NMR spectroscopy, X-ray diffraction analysis and computational modelling. Compound 1 exists as polymorphic crystals. Conformations of 1 in solution were further discussed based on the computational results. These compounds exhibited notable inhibitory activity against the 11β-HSD1 enzyme. Compound 3 had potencies for the inhibition of human 11β-HSD1 with high selectivity against 11β-HSD2 (IC₅₀ 0.58 μM, SI > 174). Molecular docking and quantitative structure-activity relationship studies revealed a mixed regulatory mechanism.

Diastereoselective synthesis of 3,3-dimethylazetidines via an intramolecular iodine-mediated cyclization reaction

An iodine-mediated intramolecular cyclization reaction of γ-prenylated amines has been developed to provide a convenient route to 3,3-dimethylazetidines.

Myriberine A, a new alkaloid with an unprecedented heteropentacyclic skeleton from Myrioneuron faberi

Myriberine A (1) possessing an unprecedented carbon skeleton was isolated from Myrioneuron faberi. The structure and absolute configuration of 1 were elucidated by a combination of spectroscopic data, X-ray crystallographic, and computational methods. Myriberine A (1) demonstrated inhibition against the hepatitis C virus (HCV) life cycle in vitro.

Daphhimalenine A, a new alkaloid with an unprecedented skeleton, from Daphniphyllum himalense

Daphhimalenine A (1), a novel alkaloid with a rearrangement C-21 skeleton, containing a unique 1-azabicyclo[5.2.1]decane ring system, was isolated from the leaves of Daphniphyllum himalense, along with biogenetically related alkaloids daphhimalenine B (2) and daphnezomine T. Their structures were established on the basis of spectroscopic data, and the absolute configuration of 1 was assigned by computational methods. A plausible biosynthetic pathway of 1 was also proposed.

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.

Two new Daphniphyllum alkaloids from Daphniphyllum macropodum Miq

Two new Daphniphyllum alkaloids, 4,21-deacetyl-deoxyyuzurimine (1) and macropodumine L (2), together with the two known related alkaloids, have been isolated from the bark of Daphniphyllum macropodum Miq. The structures of the new compounds were elucidated on the basis of the detailed analysis of spectroscopic data, chemical method, and by comparison of the spectroscopic data with those of known compounds. Compounds 2 and 4 exhibited weak cytotoxicity against human carcinoma cell lines SMMC-7721 and HO-8910.

Daphniphyllum and diterpenoid alkaloids from Daphniphyllum longeracemosum

Four new Daphniphyllum alkaloids, daphlongamines A-D (1-4), were isolated from the fruits of Daphniphyllum longeracemosum. Their structures were characterized by spectroscopic methods, especially 2D NMR techniques. A single-crystal X-ray diffraction analysis was used to confirm the stereochemistry of 3. Remarkably, this is the first report of aconitine- and veatchine-type diterpenoid alkaloids from the genus Daphniphyllum.

A Novel Alkaloid from the Seeds of Daphniphyllum calycinum

One novel alkaloid, named as caldaphnidine G (1), and two known alkaloid calycicine A (2), daphnezomine L (3) were isolated from the seeds of Daphniphyllum calycinum. The structure of 1 was established by spectral methods, especially 2D NMR techniques.

Daphnipaxianines A-D, alkaloids from Daphniphyllum paxianum

Four new Daphniphyllum alkaloids, daphnipaxianines A-D ( 1- 4), along with six known ones, have been isolated from the leaves and fruits of Daphniphyllum paxianum. Daphnipaxianines A and B ( 1, 2), a pair of epimers differing at C-10, are the first caliciphylline A type Daphniphyllum alkaloids with a Delta (9(15))-unsaturated cyclic ketone unit, and daphnipaxianine D ( 4) is the first yuzurine-type Daphniphyllum alkaloid containing a hexacyclic ring system. The structures of these alkaloids were characterized by spectroscopic methods, especially 2D NMR techniques. A single-crystal X-ray diffraction analysis was used to confirm the structure of 1.