Cyclobutane Moiety Research Articles

1,3-Difunctionalization of [1.1.1]propellane through iron-hydride catalyzed hydropyridylation

Current methodologies for the functionalization of [1.1.1]propellane primarily focus on achieving 1, 3-difunctionalized bicyclo[1.1.1]pentane or ring-opened cyclobutane moiety. Herein, we report an innovative approach for the 1, 3-difunctionalization of [1.1.1]propellane, enabling access to a diverse range of highly functionalized cyclobutanes via nucleophilic attack followed by ring opening and iron-hydride hydrogen atom transfer. To enable this method, we developed an efficient iron-catalyzed hydropyridylation of various alkenes for C − H alkylation of pyridines at the C4 position, eliminating the need for stoichiometric quantities of oxidants or reductants. Mechanistic investigations reveal that the resulting N-centered radical serves as an effective oxidizing agent, facilitating single-electron transfer oxidation of the reduced iron catalyst. This process efficiently sustains the catalytic cycle, offering significant advantages for substrates with oxidatively sensitive functionalities that are generally incompatible with alternative approaches. The strategy presented herein is not only mechanistically compelling but also demonstrates broad versatility, highlighting its potential for late-stage functionalization.

Total Synthesis of the Euphorbia Diterpenoid Pepluacetal

AbstractThe first total synthesis of the Euphorbia diterpenoid pepluacetal is disclosed in both racemic and chiral fashions. The synthesis strategically relies on a photo‐induced Wolff rearrangement/lactonization cascade (WRLC) reaction to access the cyclobutane moiety, a ring‐closing metathesis/cyclopropanation sequence to rapidly forge the 7–3 bicyclic system, and a late‐stage Rh‐catalyzed transannular carbenoid insertion to C(sp3)−H bond followed by a Baeyer–Villiger oxidation and ring‐opening manipulations to install the side chain. The synthetic route demonstrates excellent stereochemical control on the non‐classical concave‐face bond formation, remote traceless stereochemical relay and high scalability to provide 20 mg of (+)‐pepluacetal.

Total Synthesis of the Euphorbia Diterpenoid Pepluacetal.

The first total synthesis of the Euphorbia diterpenoid pepluacetal is disclosed in both racemic and chiral fashions. The synthesis strategically relies on a photo-induced Wolff rearrangement/lactonization cascade (WRLC) reaction to access the cyclobutane moiety, a ring-closing metathesis/cyclopropanation sequence to rapidly forge the 7-3 bicyclic system, and a late-stage Rh-catalyzed transannular carbenoid insertion to C(sp3)-H bond followed by a Baeyer-Villiger oxidation and ring-opening manipulations to install the side chain. The synthetic route demonstrates excellent stereochemical control on the non-classical concave-face bond formation, remote traceless stereochemical relay and high scalability to provide 20 mg of (+)-pepluacetal.

Design, synthesis of (±)-millpuline A and biological evaluation for the lung cell protective effects through SRC.

In this paper, a visible-light-induced intermolecular [2+2] photocycloaddition reaction based on flavonoids was constructed to address the problems of low yield, poor physicochemical properties, and lack of target definition in total synthesis of(±)-millpuline A whose bioactivity remains unknown. As a result, 20 derivatives (B1-B20) were synthesized for bioactivity evaluation. Consequently, lung cell protective effects of (±)-millpuline A andB13awere revealed for the first time and the crucial role of stereoconfiguration of the cyclobutane moiety in their protective effects against NNK in normal lung cells was demonstrated. Moreover, through target prediction and experimental verification in MLE-12 cells, SRC was determined to be the target of (±)-millpuline A regarding its protective effect in NNK-induced lung cell injury. Results from RT-Q-PCR and HTRF experiments verified that (±)-millpuline A could repress SRC activity through a transcriptional mechanism but not acting as an inhibitor to directly bind to and thereby inhibit SRC protein. The results in this paper are informative for the further development of visible light-catalyzed cycloaddition of flavon-oids and lay a scientific foundation for understanding the bioactivity and underlying mechanism of (±)-millpuline A and other structurally similar natural skeletons.

Gold(I)‐Catalyzed Cascade Cyclization of Nitrogen or Oxygen Containing Nucleophile Tethered‐Vinylidenecyclopropanes to Pyrrole, Furan, Pyrrolidine and Piperidine Skeletons

AbstractIn this paper, we report a gold(I)‐catalyzed cascade cyclization of N‐ or O‐nucleophile tethered‐vinylidenecyclopropanes (VDCPs), resulting in the synthesis of pyrrole, furan, pyrrolidine, and piperidine skeletons in 30%‐98% yields. Depending on the carbon chain length connecting the nucleophile and VDCPs, two reaction pathways are available, leading to different products. Both α‐amino VDCPs and α‐hydroxyl VDCPs, where nucleophiles and VDCPs are connected by a methylene group, undergo intramolecular nucleophilic addition and aromatization, followed by ring‐opening of the cyclopropane unit to produce substituted pyrroles and furans. By extending the chain length to three or four carbons, it becomes possible to form pyrrolidines and piperidines with a cyclobutene moiety via ring expansion of the cyclopropane unit, accompanied by gold carbene induced vinylogous nucleophilic addition.

Raman Spectroscopic and DFT Study of COA-Cl and Its Analogues.

COA-Cl is a newly synthesized adenosine analogue that exhibits various physiological activities. Its angiogenic, neurotropic, and neuroprotective potencies make it promising for the development of medicines. In this study, we show Raman spectroscopic study of COA-Cl to elucidate molecular vibrations and related chemical properties. Density functional theory calculations were combined with the Raman spectroscopic data to understand the details of each vibrational mode. Comparative analysis with adenine, adenosine, and other nucleic acid analogues enabled identification of unique Raman peaks originating from the cyclobutane moiety and chloro group of COA-Cl. This study provides fundamental knowledge and crucial insights for further development of COA-Cl and related chemical species.

Two Pairs of 7,7'-Cyclolignan Enantiomers with Anti-Inflammatory Activities from Perilla frutescens.

Perilla frutescens (L.) Britt. (Labiatae), a medicinal plant, has been widely used for the therapy of multiple diseases since about 1800 years ago. It has been demonstrated that the extracts of P. frutescens exert significant anti-inflammatory effects. In this research, two pairs of 7,7′-cyclolignan enantiomers, possessing a cyclobutane moiety, (+)/(−)-perfrancin [(+)/(−)-1] and (+)/(−)-magnosalin [(+)/(−)-2], were separated from P. frutescens leaves. The present study achieved the chiral separation and determined the absolute configuration of (±)-1 and (±)-2. Compounds (+)-1 and (−)-1 have notable anti-inflammatory effects by reducing the secretion of pro-inflammatory factors (NO, TNF-α and IL-6) and the expression of pro-inflammatory mediators (iNOS and COX-2). These findings indicate that cyclolignans are effective substances of P. frutescens with anti-inflammatory activity. The present study partially elucidates the mechanisms underlying the effects of P. frutescens.

Antibacterial Gilvocarcin-Type Aryl-C-Glycosides from a Soil-Derived Streptomyces Species

Seven new gilvocarcin-type aryl-C-glycosides (1-7) and six known analogues (8-13) were isolated from the soil-derived Streptomyces sp. OUCMDZ-945. Their structures including absolute configurations were determined based on detailed spectroscopic analysis, chemical methods, ECD curves, and quantum chemical calculations. Compound 1, which we named digilvocarcin A, is the first reported bis-gilvocarcin derivative possessing a novel cyclobutane moiety. This dimeric skeleton was confirmed to be formed from gilvocarcin V (8) through a light-induced [2 + 2] cycloaddition. Compounds 1, 2, 5-8, and 11 showed antibacterial activity against Staphylococcus aureus ATCC 6538 and methicillin-resistant Staphylococcus aureus subsp. aureus ATCC 43300 (MIC values: 0.25-64 μg/mL).

Dimeric styrylpyrones with stimulating GLP-1 secretion activities from Alpinia kwangsiensis

Stimulating glucagon-like peptide-1 (GLP-1) secretion is an important approach for the treatment of type 2 diabetes. Chemical investigation of Alpinia kwangsiensis rhizomes produced six dimeric styrylpyrones (1–6), including two new degraded ones (1 and 2). Compounds 1–4 were identified as four pairs of enantiomers and successfully prepared by chiral HPLC separation. These compounds incorporate the distinctive cyclobutane moiety via [2 + 2] cycloaddition, a key step in the biosynthetic pathway. The bioactivities of isolates in stimulating GLP-1 secretion in STC-1 cells were evaluated. Results showed that compounds (+)-1, (+)-2, (−)-2, (−)-4, 5 and 6 significantly increased GLP-1 secretion, and compound (+)-1 exhibited the strongest activity with EC50 value of 6.51 μM. In addition, compounds (+)-2, (−)-4 and 5 promoted GLP-1 secretion by increasing intracellular calcium concentration dependent on the PKA pathway, which could provide a chemical basis for the development of diabetes drugs especially that directly promote GLP-1 secretion.

Puckering the Planar Landscape of Fragments: Design and Synthesis of a 3D Cyclobutane Fragment Library.

Fragment‐based drug discovery (FBDD) has a growing need for unique screening libraries. The cyclobutane moiety was identified as an underrepresented yet attractive three‐dimensional (3D) scaffold. Synthetic strategies were developed via a key 3‐azido‐cyclobutanone intermediate, giving potential access to a range of functional groups with accessible growth vectors. A focused set of 33 novel 3D cyclobutane fragments was synthesised, comprising three functionalities: secondary amines, amides, and sulfonamides. This library was designed using Principal Component Analysis (PCA) and an expanded version of the rule of three (RO3), followed by Principal Moment of Inertia (PMI) analysis to achieve both chemical diversity and high 3D character. Cis and trans ring isomers of library members were generated to maximise the shape diversity obtained, while limiting molecular complexity through avoiding enantiomers. Property analyses of the cyclobutane library indicated that it fares favourably against existing synthetic 3D fragment libraries in terms of shape and physicochemical properties.

Molecular docking, spectroscopic, and quantum chemical studies on aromatic heterocycle tetrakis(4-pyridyl)cyclobutane regioisomers: potential membrane-permeable inhibitors.

Aromatic heterocyclic compounds are commonly used in pharmaceutical and agrochemical products. The usage has been also extended in the production of corrosion inhibitors and electronic, opto-electronic, and NLO devices. The four regioisomers of the aromatic heterocyclic molecule, tetrakis(4-pyridyl)cyclobutane (tpcb), were optimized, and their chemical, electronic, and biological properties were examined. The rctt and rtct isomers were isolated and further characterized by the infrared and Raman spectroscopic techniques, and their vibrational modes with attention on important functional groups were discussed. The theoretical vibrational data obtained by DFT/B3LYP/6-311++G(d,p) were in very good agreement with the experimental ones. The occupancy, bond polarization, hybridization of the N-C bond, bonding characteristics between the pyridyl carbon and cyclobutane moiety, and distribution of electron density for the four tpcb isomers have been explored through NBO analysis. The inversion barrier of the cyclobutane moiety was obtained based on the optimized structures of the planar and puckered configurations of the isomers. The rccc isomer exhibited the least electrophilic character compared to the other tpcb isomers. The chemical significance of tpcb has been further explained by the wave function analyses. Molecular docking results revealed that the tpcb ligand would possess a potential anti-viral and anti-bacterial activity via a membrane-permeable mechanism.

Antibacterial Activity of Synthesized Derivatives of Purpurin Containing Cyсlopropane and Cyclobutane Fragment

The present study is a continuation of the scientific research works for the synthesis of anthraquinonе-containing derivatives with cyclic ring systems by the interaction of 1,2,4-trihydroxyanthraquinone (purpurin) with cyclopropanecarboxylic acid chloride and cyclobutanecarboxylic acid chloride by using the ultrasonic treatment. Esters of purpurin, studied for antibacterial activity in museum test strains of microorganisms (Staphylococcus aureus ATCC 6538-P, Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25922, Pseudomonas aeruginosa АТСС 27853, Сandida albicans АТСС 10231) in vitro with the determination of the minimum inhibitory concentration (MIC) value. The study revealed that the cyclopropane substituent exhibits moderate antibacterial activity against Bacillus subtilis ATCC 6633. While with the cyclobutane moiety it had a weak effect with respect to Pseudomonas aeruginosa ATCC strain. It has been found that the compounds with the cyclopropane and cyclobutane fragment have possessed antimicrobial activity in relation to strains of microorganisms Staphylococcus aureus АТСС 6538 for which the MIC value was 62.5 μg/ml.

Angustifolinoid B, a flavonoid glycoside dimer with cyclobutane from Elaeagnus angustifolia flowers

A novel flavonoid glycoside dimer with an unprecedented cyclobutane moiety, named angustifolinoid B (1), was isolated from Elaeagnus angustifolia flowers. Its structure was determined by extensive spectroscopic analysis (HRMS, NMR) and chemical hydrolysis. The new dimer was formed via a [2 + 2] cycloaddition between two symmetric tiliroside. Bioassay revealed that compound 1 showed significant α-glucosidase inhibitory activity with IC50 value at 4.40 μM.

DFT supported structural elucidations of seiridiasteriscane A, unique 15-nor-asteriscane and novel pestalotiopsin Congeners from Seiridium sp. KT3957

Seiridiasteriscane A (1), pestalotiopsins L-N (2–4), and 2-O-deacetylpestalotiopsin A (5) were isolated along with known pestalotiopsins A (7), B (6), and fuscoatrol A (8) from Seiridium sp. KT3957. Their relative structures were elucidated by extensive NMR analysis and verified using DFT (density functional theory) chemical shift calculations. The absolute configurations were determined by reproducing their experimental ECD spectra based on DFT calculations. Although 3 and 4 existed as conformational mixtures in CDCl3, DFT-based 13C chemical shift calculations were useful for evaluating each conformer. Simultaneous isolation of seiridiasteriscane A (1) and pestalotiopsins 2–8 suggested a plausible route for the biosynthesis of 1 involving the expansion of the cyclobutane moiety into a cyclopentane ring.

Synthesis, biological evaluation, and modeling studies of 1,3-disubstituted cyclobutane-containing analogs of combretastatin A4

With the aim of circumventing the adverse cis/trans-isomerization of combretastatin A4 (CA4), a naturally occurring tumor-vascular disrupting agent, we designed novel CA4 analogs bearing 1,3-disubstituted cyclobutane moiety instead of the cis-stilbene unit of the parent compound. The corresponding cis and trans cyclobutane-containing derivatives were prepared as pure diastereomers. The structure of the target compounds was confirmed by X-ray diffraction study. The title compounds were evaluated for their cytotoxic properties in human cancer cell lines HepG2 (hepatocarcinoma) and SK-N-DZ (neuroblastoma), and the overall activity was found in micromolar range. Molecular docking studies and molecular dynamics simulation within the colchicine binding site of tubulin were in good agreement with the obtained cytotoxicity data.

Orthoscuticellines A-E, β-Carboline Alkaloids from the Bryozoan Orthoscuticella ventricosa Collected in Australia.

Antiplasmodial high-throughput screening of extracts derived from marine invertebrates collected from northern NSW, Australia, resulted in the methanol extract of the bryozoan Orthoscuticella ventricosa being identified as inhibitory toward the 3D7 strain of Plasmodium falciparum. Purification of this extract resulted in two new bis-β-carbolines that possess a cyclobutane moiety, orthoscuticellines A and B (1 and 2), three new β-carboline alkaloids, orthoscuticellines C-E (3-5), and six known compounds, 1-ethyl-4-methylsulfone-β-carboline (6), 1-ethyl-β-carboline (7), 1-acetyl-β-carboline (8) 1-(1'-hydroxyethyl)-β-carboline (9), 1-methoxycarbonyl-β-carboline (10), and 1-vinyl-β-carboline (11). The structures of all compounds were determined from analysis of MS and 1D and 2D NMR data. The compounds showed modest antiplasmodial activity against P. falciparum in the range of 12-21 μM.

Constituents of the Edible Leaves of Melicope pteleifolia with Potential Analgesic Activity.

Melicope pteleifolia has long been consumed as a popular vegetable and tea in Southeast Asian countries, including Malaysia and southern mainland China, and is effective in the treatment of colds and inflammation. In the search for active metabolites that can explain its traditional use as an antipyretic, six new phloroacetophenone derivatives (3-8) along with seven known compounds (1, 2, and 9-13) were isolated from the leaves of M. pteleifolia. Their chemical structures were confirmed by extensive spectroscopic analysis including NMR, IR, ECD, and HRMS. All compounds isolated from the leaves of M. pteleifolia (1-13) have a phloroacetophenone skeleton. Notably, the new compound 8 contains an additional cyclobutane moiety in its structure. The bioactivities of the isolated compounds were evaluated, and compounds 1, 6, and 7 inhibited tumor necrosis factor-α-induced prostaglandin E2. Moreover, the major constituent, 3,5-di-C-β-d-glucopyranosyl phloroacetophenone (1), was found to be responsible for the antipyretic activity of M. pteleifolia based on in vivo experiments.

Synthesis of the Sex Pheromone of the Oleander Scale ( Aspidiotus nerii).

A total synthesis of the oleander scale [ Aspidiotus nerii (Bouche)] sex pheromone, the unique sesquiterpenoid containing a cyclobutane moiety of this class of compounds, has been developed. In order to implement this sex pheromone as a new environmentally friendly tool to manage this pest, a more cost-effective, multigram synthesis was required. This new synthetic route, having a Blaise reaction, iron-catalyzed carbon-carbon coupling, and [2 + 2] photocycloaddition reactions as key steps, provides a general access to 4-alkyl lactones as well as a robust access to the target sex pheromone. Starting from readily available compounds as 3-hydroxypropanenitrile, ethyl bromoacetate, and 2-acetyl butyrolactone, the synthetic sequence afforded the A. nerii sex pheromone with minimum intermediate purification and good overall yield in nine linear steps.

Construction of 4-substituted 2-(pyrrolidine-3-yl)acetic acid derivatives as cyclic γ-aminobutyric acid analogues employing intermolecular [2+2]-photocycloaddition as key steps

The synthesis of new 2-(pyrrolidine-3-yl)acetic acid derivatives as cyclic γ-aminobutyric acid analogues, which are additionally substituted at the 4-position, is reported. A de Mayo reaction, i.e. a combination of an intermolecular [2+2]-photocycloaddition of 1,3-dioxinones with N-protected 3-pyrroline and a fragmentation reaction of the resulting cyclobutane moiety, represent the key steps.

Enantioselective Rhodium-Catalyzed Cycloisomerization of 1,6-Allenynes to access 5/6-Fused Bicycle[4.3.0]nonadienes

Transition-metal-catalyzed cycloisomerization of 1,n-allenynes represents a powerful synthetic tool to rapidly assemble complex polycyclic skeletons from simple linear substrates. Nevertheless, there are no reports of the asymmetric version of these reactions. Moreover, most of these reactions proceed through a 6-endo-dig cyclization pathway, which preferentially delivers the distal product (via 5/5 rhodacyclic intermediate) rather than the proximal one (via 6/5 rhodacyclic intermediate). Herein, we report an enantioselective rhodium(I)-catalyzed cycloisomerization of 1,6-allenynes to provide the proximal product 5/6-fused bicycle[4.3.0]nonadienes in good yields and with excellent enantioselectivities. Remarkably, this chemistry works perfectly for 1,6-allenynes having a cyclic substituent within the allene component, thereby affording synthetically formidable tricyclic products with excellent enantioselectivities. Moreover, extensive DFT calculations suggest an uncommon pathway involving 5-exo-dig cycloisomerization, ring-expansion, rate-determining alkene isomerization involving Csp3-H activation, C-C activation of the cyclobutene moiety and finally reductive elimination. Deuterium labeling experiments support the rate-determining step involving the C–H bond activation in this transformation.