Huperserratines A and B, Two Macrocyclic Lycopodium Alkaloids with an Unusual Skeleton from Huperzia serrata

The Chemistry and Biology of Lycopodium Alkaloids

Lycopodiales, an order comprising 388 distinct species, is the source of Lycopodium alkaloids (LAs), a group of naturally occurring alkaloids that share a common biosynthesis and structural attributes. These remarkable organisms are considered vestiges of ancient ferns, with fossil evidence dating their existence back to an impressive 300 million years. LAs usually are tricyclic or tetracyclic compounds with C16N or C16N2 skeleton. But then there are also have a few C11N, C15N, C15N2, C22N2, and C27N3 skeleton. LAs have attracted much scientific attention because of their important biological activities related to acetylcholinesterase and unique structural characteristics. From 1881 to December 2023, there are 593 LAs from 49 species of Lycopodiales have been reported. Because the total amount of LAs is nearly five times that of 1994, the classification and group allocation of some newly isolated LAs is often challenging and not unambiguous by Ayer's simple classification. This review makes a more systematic and detailed classification for it and provides extensive coverage of naturally occurring LAs discovered from 1881 to December 2023. Until now, there is no comprehensively summary of biological activity of the LAs. This review is the first time covered the biological activity of the all LAs.

Casuattimines A-N, fourteen new Lycopodium alkaloids from Lycopodiastrum casuarinoides with Cav3.1 channel inhibitory activity

Two new dimeric Lycopodium alkaloids, casuattimines A and B (1 and 2), along with twelve previously undescribed Lycopodium alkaloids, casuattimines C-N (3-14), and eight known Lycopodium alkaloids, were isolated from Lycopodiastrum casuarinoides. Casuattimines A and B (1 and 2) are the first two ether-linked Lycopodium alkaloid dimers. Casuattimines C and D (3 and 4) are unique Lycopodium alkaloids characterized by a long fatty acid chain. Structural elucidation was achieved through HRESIMS, NMR, and electronic circular dichroism (ECD) calculations. In addition, the absolute configurations of compounds 7, 13, and 14 were determined by single crystal X-ray diffraction. Compounds 1, 2, and 4 demonstrated notable Cav3.1 channel inhibitory activities presenting IC50 values of 10.75 ± 1.02 μM, 9.33 ± 0.79 μM, and 7.14 ± 0.86 μM, respectively. The dynamics of compound 4 against the Cav3.1 channel and preliminary structure-activity relationships of these active Lycopodium alkaloids were also discussed.

Natural products as potential lead compounds to develop new antiviral drugs over the past decade

Virus infection has been one of the main causes of human death since the ancient times. Even though more and more antiviral drugs have been approved in clinic, long-term use can easily lead to the emergence of drug resistance and side effects. Fortunately, there are many kinds of metabolites which were produced by plants, marine organisms and microorganisms in nature with rich structural skeletons, and they are natural treasure house for people to find antiviral active substances. Aiming at many types of viruses that had caused serious harm to human health in recent years, this review summarizes the natural products with antiviral activity that had been reported for the first time in the past ten years, we also sort out the source, chemical structure and safety indicators in order to provide potential lead compounds for the research and development of new antiviral drugs.

Lycopodium Alkaloids from Huperzia serrata and Their Anti-acetylcholinesterase Activities

One new fawcettimine-type alkaloid (1), one new miscellaneous-type alkaloid (2), four new lycodine-type alkaloids (3-6), and eight known ones (7-14) were isolated from the whole plants of Huperzia serrata. Their structures and absolute configurations were elucidated based on spectroscopic data, X-ray diffraction, ECD calculation and Mosher's method. Compound 1 was a rare C18 N2 -type Lycopodium alkaloid, possessing serratinine skeleton with an amide side chain in C-5. The absolute configuration of the 18-OH of compounds 4-6 were first determined by Mosher's method. Moreover, compounds 1-14 were assayed anti-acetylcholinesterase effect in vitro, and compound 7 showed significant anti-acetylcholinesterase activity with an IC50 value of 16.18±1.64 μM.

Synthesis of Isomeric 3-Benzazecines Decorated with Endocyclic Allene Moiety and Exocyclic Conjugated Double Bond and Evaluation of Their Anticholinesterase Activity

Transformations of 1-methoxymethylethynyl substituted isoquinolines triggered by terminal alkynes in alcohols were studied and new 3-benzazecine-containing compounds synthesized, such as 6-methoxymethyl-3-benzazecines incorporating an endocyclic C6–C8 allene fragment and the -ylidene derivatives 6-methoxymethylene-3-benzazecines. The reaction mechanisms were investigated and a preliminary in vitro screening of their potential inhibitory activities against human acetyl- and butyrylcholinesterases (AChE and BChE) and monoamine oxidases A and B (MAO-A and MAO-B) showed that the allene compounds were more potent than the corresponding -ylidene ones as selective AChE inhibitors. Among the allenes, 3e (R³ = CH₂OMe) was found to be a competitive AChE inhibitor with a low micromolar inhibition constant value (K_i = 4.9 μM), equipotent with the corresponding 6-phenyl derivative 3n (R³ = Ph, K_i = 4.5 μM), but 90-fold more water-soluble.

Hupertimines A-E, Fawcettimine-Type Lycopodium Alkaloids from Huperzia serrata

Five new fawcettimine-type Lycopodium alkaloids, hupertimines A-E (1-5), were discovered from the whole plant of Huperzia serrata, along with two known alkaloids, 8α-hydroxyphlegmariurine B (6) and 8β-hydroxyphlegmariurine B (7). The structures of 1-7 were identified through HR-MS, IR, ¹ H, ¹³ C, and 2D NMR, and single-crystal X-ray diffraction analysis. Structurally, compound 1 was the fourth example of Lycopodium alkaloid with an ether linkage between C-5 and C-13 and 2 was the third example of Lycopodium alkaloid with a 5/5/5/5/6 pentacyclic ring system and featuring a 1-aza-7-oxabicyclo[2.2.1]heptane unit. Compounds 1-7 were tested for their BACE1 inhibitory activity. In addition, the correct ¹ H- and ¹³ C-NMR data for 7 were reported in current study.

Bioactive Compounds and Their Derivatives: An Insight into Prospective Phytotherapeutic Approach against Alzheimer’s Disease

Alzheimer's disease (AD) is a common neurodegenerative brain disorder that causes cellular response alterations, such as impaired cholinergic mechanism, amyloid-beta (Aβ) AD aggregation, neuroinflammation, and several other pathways. AD is still the most prevalent form of dementia and affects many individuals across the globe. The exact cause of the disorder is obscure. There are yet no effective medications for halting, preventing, or curing AD's progress. Plenty of natural products are isolated from several sources and analyzed in preclinical and clinical settings for neuroprotective effects in preventing and treating AD. In addition, natural products and their derivatives have been promising in treating and preventing AD. Natural bioactive compounds play an active modulatory role in the pathological molecular mechanisms of AD development. This review focuses on natural products from plant sources and their derivatives that have demonstrated neuroprotective activities and maybe promising to treat and prevent AD. In addition, this article summarizes the literature pertaining to natural products as agents in the treatment of AD. Rapid metabolism, nonspecific targeting, low solubility, lack of BBB permeability, and limited bioavailability are shortcomings of most bioactive molecules in treating AD. We can use nanotechnology and nanocarriers based on different types of approaches.

Asymmetric Total Synthesis and Structure Elucidation of Huperzine H

A first asymmetric total synthesis of huperzine H has been achieved in a 12% overall yield from commercially available (+)-pulegone. The key steps of this synthesis include a highly diastereoselective Mukaiyama-Michael addition reaction of a pyrrole bearing a silyl enol ether and an intramolecular S_N2 cyclization reaction with iodinated pyrrole acting as an effective nucleophile for the formation of the nine-membered ring. As a result, the relative and absolute stereochemistry of huperzine H is established.

Total Synthesis of Huperserratines A and B

Huperserratines A (1) and B (2), two novel macrocyclic Lycopodium alkaloids, possess an aza-12-membered ring. Here, we describe the first total synthesis of these two natural products in 12 steps....

Survey of natural products reported by Asian research groups in 2020

The new natural products reported in 2020 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2020 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Application of HPLC-DAD for In Vitro Investigation of Acetylcholinesterase Inhibition Activity of Selected Isoquinoline Alkaloids from Sanguinaria canadensis Extracts

Isoquinoline alkaloids may have a wide range of pharmacological activities. Some of them have acetylcholinesterase activity inhibition. Nowadays, neurodegenerative disorders such as Alzheimer’s disease have become a serious public health problem. Searching for new effective compounds with inhibited acetylcholinesterase activity is one of the most significant challenges of modern scientific research. The aim of this study was the in vitro investigation of acetylcholinesterase activity inhibition of extracts obtained from Sanguinaria canadensis collected before, during and after flowering. The acetylcholinesterase activity inhibition of these extracts has not been previously tested. The aim was also to quantify selected alkaloids in the investigated extracts by high performance liquid chromatography (HPLC). The analyses of alkaloid content were performed using HPLC in reversed phase (RP) mode using Polar RP column and mobile phase containing acetonitrile, water and ionic liquid (IL). The acetylcholinesterase activity inhibition of the tested plant extracts and respective alkaloid standards were examined using high performance liquid chromatography with diode-array detector (HPLC-DAD) for the quantification of 5-thio-2-nitro-benzoic acid, which is the product of the reaction between the thiocholine (product of the hydrolysis of acetylthiocholine reaction) with Ellman reagent. The application of the HPLC method allowed for elimination of absorption of interfering components, for example, alkaloids such as sanguinarine and berberine. It is revealed that the HPLC method can be successfully used for the evaluation of the acetylcholinesterase inhibitory activity in samples such as plant extracts, especially those containing colored components adsorbing at wavelength in the range 405–412 nm. The acetylcholinesterase inhibition activity synergy of pairs of alkaloid standards and mixture of all investigated alkaloids was also determined. Most investigated alkaloids and all Sanguinaria canadensis extracts exhibited very high acetylcholinesterase activity inhibition. IC₅₀ values obtained for alkaloid standards were from 0.36 for berberine to 23.13 µg/mL for protopine and from 61.24 to 89.14 µg/mL for Sanguinaria canadensis extracts. Our investigations demonstrated that these plant extracts can be recommended for further in vivo experiments to confirm their acetylcholinesterase activity inhibition.

Cunlanceloic acids A–D: unprecedented labdane diterpenoid dimers with AChE inhibitory and cytotoxic activities from Cunninghamia lanceolata

Four unprecedented labdane diterpenoid dimers with new carbon skeletons, cunlanceloic acids A–D (1–4), were isolated from the cones of Cunninghamia lanceolata.

Deciphering the Biosynthetic Mechanism of Pelletierine in Lycopodium Alkaloid Biosynthesis

Pelletierine, a proposed building block of Lycopodium alkaloids (LAs), was demonstrated to be synthesized via the non-enzymatic Mannich-like condensation of Δ¹-piperideine and 3-oxoglutaric acid produced by two new type III PKSs (HsPKS4 and PcPKS1) characterized from Huperzia serrata and Phlegmariurus cryptomerianus, respectively. The findings provide new insights for further understanding the biosynthesis of LAs such as huperzine A.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as baphicacanthcusine A from Baphicacanthus cusia.