Total Synthesis of Fawcettimine-Type Alkaloid, Lycojaponicumin A

In Silico Design, Synthesis, and Evaluation of Novel Enantiopure Isoxazolidines as Promising Dual Inhibitors of α-Amylase and α-Glucosidase

Isoxazolidine derivatives were designed, synthesized, and characterized using different spectroscopic techniques and elemental analysis and then evaluated for their ability to inhibit both α-amylase and α-glucosidase enzymes to treat diabetes. All synthesized derivatives demonstrated a varying range of activity, with IC50 values ranging from 53.03 ± 0.106 to 232.8 ± 0.517 μM (α-amylase) and from 94.33 ± 0.282 to 258.7 ± 0.521 μM (α-glucosidase), revealing their high potency compared to the reference drug, acarbose (IC50 = 296.6 ± 0.825 µM and 780.4 ± 0.346 µM), respectively. Specifically, in vitro results revealed that compound 5d achieved the most inhibitory activity with IC50 values of 5.59-fold and 8.27-fold, respectively, toward both enzymes, followed by 5b. Kinetic studies revealed that compound 5d inhibits both enzymes in a competitive mode. Based on the structure-activity relationship (SAR) study, it was concluded that various substitution patterns of the substituent(s) influenced the inhibitory activities of both enzymes. The server pkCSM was used to predict the pharmacokinetics and drug-likeness properties for 5d, which afforded good oral bioavailability. Additionally, compound 5d was subjected to molecular docking to gain insights into its binding mode interactions with the target enzymes. Moreover, via molecular dynamics (MD) simulation analysis, it maintained stability throughout 100 ns. This suggests that 5d possesses the potential to simultaneously target both enzymes effectively, making it advantageous for the development of antidiabetic medications.

Synthesis of Bridged Cycloisoxazoline Scaffolds via Rhodium-Catalyzed Coupling of Nitrones with Cyclic Carbonate

Bridged isoxazolidines were synthesized via Rh(III)-catalyzed C-H allylation of α-aryl nitrones with 5-methylene-1,3-dioxan-2-one. The nitrone group serves as a directing group and 1,3-dipole in the C-H activation/[3 + 2] cycloaddition cascade, exhibiting excellent chemo- and stereoselectivity along with good functional group compatibility. The resulting skeletal structure was conveniently modified to produce a range of important chemical frameworks, and the protocol was applied to biologically active molecules.

Axially chiral styrene-based organocatalysts and their application in asymmetric cascade Michael/cyclization reaction

An axially chiral styrene-based organocatalyst, featuring a combination of axially chiral styrene-based structure and a pyrrole ring, has been designed and synthesized. This catalyst demonstrates remarkable capabilities in producing a wide range of densely substituted spirooxindoles that feature an alkyne-substituted quaternary stereogenic center. These spirooxindoles are generated through mild cascade Michael/cyclization reactions, resulting in high conversion rates and exceptional enantioselectivity. Our catalytic model, based on experiments, X-ray structure analysis and DFT calculations suggests that chiral matched π-π interactions and multiple H-bonds between the organocatalyst and substrates play significant roles in controlling the stereoselectivity of the reaction.

Discovery and Biomimetic Semisynthesis of Spirophyllines A-D from Uncaria rhynchophylla

Spirophyllines A-D (1-4), four new spirooxindole alkaloids all characterized by the spiro[pyrrolidin-3,3'-oxindole] core and a rare isoxazolidine ring, were isolated from Uncaria rhynchophylla. Their structures were determined by spectroscopic methods and confirmed by X-ray crystallography. Based on the biomimetic semisynthesis strategy, compounds 1-8 were synthesized in three steps via the key reactions of 1,3-dipolar cycloaddition and Krapcho decarboxylation from corynoxeine. Interestingly, compound 3 showed moderate inhibitory activity against the Kv1.5 potassium channel (IC50 = 9.1 μM).

Two Green Protocols for Halogenative Semipinacol Rearrangement

Semipinacol rearrangement is a special type of Wagner-Meerwein rearrangement that involves carbocation 1,2-rearrangement to provide carbonyl compounds with an α-quaternary carbon center. It has been strategically used for natural product synthesis and construction of highly congested quaternary carbons. Herein, we report a safe and green protocol that uses oxone/halide and Fenton bromide to achieve halogenative semipinacol rearrangement. The key feature of this method is the green in situ generation of reactive halogenating species from oxidation of halide with oxone or H₂O₂, which produces a nontoxic byproduct (potassium sulfate or water). Easy operation (insensitive to air and moisture) at room temperature without using special equipment adds additional advantage over previous methods.

Enantioselective Total Synthesis of (+)-Sieboldine A and Analogues Thereof

An 11-step enantioselective total synthesis of (+)-sieboldine A (1) has been accomplished from (5R)-methylcyclohex-2-en-1-one (16), in which an intramolecular ketone/ester reductive coupling followed by one-pot acidic treatment to quickly construct the unique oxa-spiroacetal and a TsOH-catalyzed displacement to directly form the characteristic N-hydroxyazacyclononane ring successfully served as the key methodologies. Moreover, several full-skeleton analogues of 1 were also synthesized on the basis of the advanced intermediates, and their inhibitory effects on electric eel acetylcholinesterase were examined.

Unified Total Synthesis of Tetracyclic Diquinane Lycopodium Alkaloids (+)-Paniculatine, (-)-Magellanine, and (+)-Magellaninone

A unified route for the total synthesis of three tetracyclic diquinane Lycopodium alkaloids (+)-paniculatine, (-)-magellanine, and (+)-magellaninone has been accomplished in 13-14 overall steps based on late-stage diverse transformations from an advanced tetracyclic common intermediate. In the established synthesis, quick formation of the two five-membered rings was efficiently achieved by an intramolecular reductive coupling of ketone-carbonyl and ester-carbonyl and an organocatalytic intramolecular Michael addition of aldehyde-derived enamine to an internal enone functionality with satisfactory redox and step economies and excellent stereoselectivities, providing the requisite tricyclic carbo-framework possessing multiple dense stereogenic centers, and an intramolecular reductive amination finally furnished the essential piperidine ring.

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....

Recent development and applications of semipinacol rearrangement reactions

As has been well-recognized, semipinacol rearrangement functions as an exceptionally useful methodology in the synthesis of β-functionalized ketones, creation of quaternary carbon centers, and construction of challenging carbocycles. Due to their versatile utilities in organic synthesis, development of novel rearrangement reactions has been a vibrant topic that continues to shape the research field. Recent breakthroughs in novel electrophiles, tandem processes, and enantioselective catalytic transformations further enrich the toolbox of this chemistry and spur the strategic applications of this methodology in natural product synthesis. These achievements will be discussed in this minireview.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.

Bioinspired Diversification Approach Toward the Total Synthesis of Lycodine-Type Alkaloids

Nitrogen heterocycles (azacycles) are common structural motifs in numerous pharmaceuticals, agrochemicals, and natural products. Many powerful methods have been developed and continue to be advanced for the selective installation and modification of nitrogen heterocycles through C-H functionalization and C-C cleavage approaches, revealing new strategies for the synthesis of targets containing these structural entities. Here, we report the first total syntheses of the lycodine-type Lycopodium alkaloids casuarinine H, lycoplatyrine B, lycoplatyrine A, and lycopladine F as well as the total synthesis of 8,15-dihydrohuperzine A through bioinspired late-stage diversification of a readily accessible common precursor, N-desmethyl-β-obscurine. Key steps in the syntheses include oxidative C-C bond cleavage of a piperidine ring in the core structure of the obscurine intermediate and site-selective C-H borylation of a pyridine nucleus to enable cross-coupling reactions.

The Total Synthesis of Diquinane-Containing Natural Products

Diquinane or bicyclo[3.3.0]octane is a conspicuous structural unit existing in the carbo-frameworks of a wide range of natural products such as alkaloids and terpenoids. These diquinane-containing molecules not merely exhibit intriguing architectures, but also showcase a broad spectrum of significant bioactivities, which draw widespread attention from the global synthetic community. During the past decade, with an aim to accomplish the total syntheses of such specified cornucopias of natural products, a variety of elegant strategies for construction of the diquinane ring system have been disclosed. In this Minireview, the achievements on this subject in the timeline from 2010 to June 2020 are demonstrated and it is discussed how the diquinane unit is strategically forged in the context of the specific target structure. In addition, impacts of the selected works to the field of natural product total synthesis is highlighted and the particular outlook of diquinane-containing natural product synthesis is provided.

Total Synthesis of Lyconesidine B, a Lycopodium Alkaloid with an Oxygenated, Amine-Type Fawcettimine Core

This report describes the total synthesis of the complex, oxygenated tetracyclic alkaloid, lyconesidine B. The key synthetic challenge involves diastereoselective generation of a decahydroquinoline ring with a quaternary carbon at the angular position via domino cyclopropanation, ring-opening, and reduction. Another crucial step is the domino ene-yne metathesis involving a quaternary ammonium ion, leading to the construction of a decahydroazaazulen framework.

Total Synthesis of Sieboldine A

Previously, we have finished the total synthesis of lycojaponicumin A (2) via development of an efficient synthetic strategy using semipinacol rearrangement as a key step. In order to further demonstrate the generality of this synthetic route, herein, we report the total synthesis of another fawcettimine-type alkaloid sieboldine A (1) from the same intermediate, which possesses an A/B/D tricyclic ring system and vicinal quaternary centers of 1. The synthesis features late-stage site-selective redox reactions, Schmidt glycosylation cyclization, and highly selective transformations.