Cyclobutane Ring Research Articles

Crystal structure of 2-ethyl-4-methyl-1-(2-oxido-3,4-dioxo-cyclo-but-1-en-1-yl)-1H-imidazol-3-ium.

In the title inner salt molecule, C10H10N2O3, the four-membered cyclobutene ring is twisted by 7.1 (2)° with respect to the five-membered imidazole ring. The crystal packing exhibits an R 2 (2)(9) hydrogen-bonding ring motif through N-H⋯O and C-H⋯O inter-actions. The potential non-linear optical properties were studied by a computational ab initio calculations performed at the DFT/B3LYP/6-31++G(d,p) level of theory.

Biginkgosides A-I, Unexpected Minor Dimeric Flavonol Diglycosidic Truxinate and Truxillate Esters from Ginkgo biloba Leaves and Their Antineuroinflammatory and Neuroprotective Activities.

Nine unexpected new flavonol glycoside cyclodimers in the truxinate (1-7, biginkgosides A-G, respectively) or truxillate [biginkgosides H (8) and I (9)] forms were isolated as minor components from the extract of Ginkgo biloba leaves. The new dimers possess an unusual cyclobutane ring formed by a [2+2]-cycloaddition between two symmetric (for compounds 1-5 and 7-9) or nonsymmetric (for 6) flavonol coumaroyl glucorhamnosides. A plausible biosynthetic pathway for these new compounds based on the frontier molecular orbital theory of cycloaddition reactions is briefly discussed. An antineuroinflammatory screening revealed that biginkgosides E (5) and H (8) inhibited nitric oxide production in lipopolysaccharide-activated BV-2 microglial cells, with IC50 values of 2.91 and 17.23 μM, respectively. Additionally, biginkgoside F (6) showed a significant neuroprotective effect (34.3% increase in cell viability at 1 μM) against Aβ25-35-induced cell viability decrease in SH-SY5Y neuroblastoma cells.

Investigation of Proposed Ladderane Biosynthetic Genes from Anammox Bacteria by Heterologous Expression in E. coli.

Ladderanes are hydrocarbon chains with three or five linearly concatenated cyclobutane rings that are uniquely produced as membrane lipid components by anammox (anaerobic ammonia-oxidizing) bacteria. By virtue of their angle and torsional strain, ladderanes are unusually energetic compounds, and if produced biochemically by engineered microbes, could serve as renewable, high-energy-density jet fuel components. The biochemistry and genetics underlying the ladderane biosynthetic pathway are unknown, however, previous studies have identified a pool of 34 candidate genes from the anammox bacterium, Kuenenia stuttgartiensis, some or all of which may be involved with ladderane fatty acid biosynthesis. The goal of the present study was to establish a systematic means of testing the candidate genes from K. stuttgartiensis for involvement in ladderane biosynthesis through heterologous expression in E. coli under anaerobic conditions. This study describes an efficient means of assembly of synthesized, codon-optimized candidate ladderane biosynthesis genes in synthetic operons that allows for changes to regulatory element sequences, as well as modular assembly of multiple operons for simultaneous heterologous expression in E. coli (or potentially other microbial hosts). We also describe in vivo functional tests of putative anammox homologs of the phytoene desaturase CrtI, which plays an important role in the hypothesized ladderane pathway, and a method for soluble purification of one of these enzymes. This study is, to our knowledge, the first experimental effort focusing on the role of specific anammox genes in the production of ladderanes, and lays the foundation for future efforts toward determination of the ladderane biosynthetic pathway. Our substantial, but far from comprehensive, efforts at elucidating the ladderane biosynthetic pathway were not successful. We invite the scientific community to take advantage of the considerable synthetic biology resources and experimental results developed in this study to elucidate the biosynthetic pathway that produces unique and intriguing ladderane lipids.

Synthesis, structural characterization, and DFT calculations of 3-buthyl-4-(3-methyl-3-mesitylcyclobut-1-yl)-1,3-thiazole-2(3H)-thione

The title compound, C21H29NS2, has been synthesized and its crystal structure has been determined from single crystal X-ray diffraction data. Crystals are monoclinic, a = 11.4923(8), b = 13.1842(7), c = 14.6583(8) A, β = 109.983(6)°, sp. gr. P21/c, Z = 4. Mesityl and thiazole groups are in cis positions with respect to the cyclobutane ring. The cyclobutane ring is puckered, with a dihedral angle of 26.6(2)° between the two three-atom planes. The crystal structure involves one weak intermolecular C–H···S hydrogen-bond. The molecular geometry was also optimized using density functional theory (DFT/B3LYP) method with the 6-311G(d, p) basis set in ground state. Geometric parameters (bond lengths, bond angles and torsion angles) and vibrational assignments have been calculated theoretically and compared with the experimental data.

Cis,trans,cis-1,2,3,4-Tetrakis[2-(ethylsulfanyl)phenyl]cyclobutane

The title cyclobutane derivative, C36H40S4, formed serendipitously through a photochemically initiated [2 + 2] cycloaddition. The asymmetric unit contains half a molecule with the 2-(ethylsulfanyl)phenyl substituents in acisconfiguration, the other half of the molecule being generated by the application of a twofold rotation operation. The substituents in both halves of the molecules are in atransarrangement relative to each other. The cyclobutane ring shows angular and torsional strains, with C—C—C bond angles of 89.80 (8) and 88.40 (8)°, and an average absolute torsion angle of 14.28 (10)°. The angle of pucker in the ring is 20.27 (12)°. The Ccb—Ccb—Cbangles between the cyclobutane (cb) ring atoms and the attached benzene (b) ring atoms are widened and range from 115.19 (10) to 121.66 (10)°. A weak intramolecular C—H...S hydrogen-bonding interaction between one of the cyclobutane ring H atoms and the S atom may help to establish the molecular conformation. No specific intermolecular interactions are found.

Lecanicillones A–C, three dimeric isomers of spiciferone A with a cyclobutane ring from an entomopathogenic fungus Lecanicillium sp. PR-M-3

Lecanicillones A–C (1–3), three unusual dimeric spiciferones with a cyclobutane ringvia[2 + 2] cycloaddition, were isolated from an entomopathogenic fungusLecanicilliumsp. PR-M-3.

A metal-free one-pot synthesis of benzo[c]chromen-6-ones from 3,4-dichlorocoumarins and butadienes using tandem photo-thermal-photo reactions.

An efficient, simple and versatile synthesis of biologically valuable benzo[c]chromen-6-ones is achieved using a tandem photo-thermal-photo reaction sequence starting from 3,4-dichlorocoumarins and a 1,3-butadiene. In this concise one-pot protocol, neither metal catalyst nor peroxide promoter is needed and the products can be purified through simple recrystallization in most cases. The synthesis consists of a reaction sequence of photo-induced [4 + 2] and [2 + 2] cycloadditions, silica gel promoted elimination of HCl and electrocyclic cyclobutene ring opening followed by a photo-induced 6π electrocyclization. The reactions proceed well with a range of dichlorocoumarins and some typical butadienes to provide the corresponding annulated products in 70-80% yield.

STRUCTURAL FEATURES OF 2-(4,5-DIPHENYL-4H-1,2,4-TRIAZOL-3-YL)THIO)-1-(3-METHYL-3-PHENYLCYCLOBUTYL) ETHANONE: X-RAY DIFFRACTION AND DFT CALCULATIONS

ABSTRACT This paper reported that the combined X-ray diffraction and DFT computational study on molecular structure of the title compound, [C 27 H 25 N 3 O 2 S]. The com -pound contains a cyclobutane, a triazole and three phenyl rings. The molecular geometry of the compound was brought to light by X-ray single crystal structure de -termination. X-ray study shows that the title compound has a weak intermolecular C—O ···π interaction as well as many D—H ···A and D—H ···π hydrogen bonds. The initial guess on the compound was first obtained from the X-ray coordinates which were optimized by Density Functional Theory (DFT)/B3LYP method with 6-31G(d, p) and 6-31G+(d, p) as basis sets. DFT electronic structures were compared to the experimentally determined molecular structure in the solid state.e-mail: fatihsen55@gmail.com ) INTRODUCTION In recent years, the synthesis and structural investigation 1,2,4-triazole derivatives have attracted considerable attention because of their pharmacological and biological properties such as antibacterial [1-3], antidepressant [4], antitubercular [5], analgesic [6], antiviral [7], etc. Cyclobutane itself is of no commercial or biological significance, but more complex derivatives are important in biology and biotechnology [8]. It is well known that 3-substituted cyclobutane carboxylic acid derivatives exhibit anti-inflammatory and anti-depressant activity [9], and also liquid crystal properties [10]. When these effects are taken into account, compounds containing 1,2,4-triazole and cyclobutane rings has become more remarkable. In this study, a novel compound named as 2-((4,5-diphenyl-4H-1,2,4-triazol-3-yl)thio)-1-(3-methyl-3-phenylcyclobutyl)ethanone is firstly synthesized in our laboratories by us. Previously, we have reported the cyclobutane derivatives compound [11-12]. The difference of this study from the other studies, the molecular structure of the compound is supported by theoretical studies. Because it is given good results in the calculation of the molecular geometry, density functional theory (DFT) method was used in the theoretical calculations.Our work makes up of the synthesis, X-ray molecular structure analysis and Density Functional Theory (DFT) studies of the title compound.The molecular structure of the title compound brought to light by X-ray diffraction. The initial guess of the compound was first obtained from the X-ray coordinates was optimized by DFT/B3LYP method with 6-31G(d, p) and 6-31G+(d, p) as basis sets. The calculated geometric parameters (bond lengths, bond angles and torsion angles) of theoretical structures were compared with their experimental data.

Structural rearrangement cascade initiated by irradiation of but-3-enyl orotates

Abstract Upon irradiation at λ = 254 nm in acetonitrile solution, the title compounds formed 8-(2-formyloxyethyl)-substituted 2,4-diazabicyclo[4.2.0]oct-1(8)-en-3,5-diones, which underwent thermal cyclobutene ring opening to 6-substituted pyrimidine-2,4-diones. The reaction cascade results in an unprecedented formal 1,5-shift of the substituent at the pyrimidine-2,4-dione core. It was shown that the reaction is likely to proceed via the [2 + 2] photocycloaddition products of the orotates, which could be intercepted in good yields (85% and 98%) upon irradiation at λ = 300 nm. At shorter wavelength a cleavage of the bond between the lactone carbonyl carbon atom and the α-carbon atom is induced, which leads – as shown by deuterium labelling experiments – by intramolecular hydrogen abstraction to the above-mentioned cyclobutenes.

Intrinsic Folding Proclivities in Cyclic β-Peptide Building Blocks: Configuration and Heteroatom Effects Analyzed by Conformer-Selective Spectroscopy and Quantum Chemistry.

This work describes the use of conformer-selective laser spectroscopy following supersonic expansion to probe the local folding proclivities of four-membered ring cyclic β-amino acid building blocks. Emphasis is placed on stereochemical effects as well as on the structural changes induced by the replacement of a carbon atom of the cycle by a nitrogen atom. The amide A IR spectra are obtained and interpreted with the help of quantum chemistry structure calculations. Results provide evidence that the building block with a trans-substituted cyclobutane ring has a predilection to form strong C8 hydrogen bonds. Nitrogen-atom substitution in the ring induces the formation of the hydrazino turn, with a related but distinct hydrogen-bonding network: the structure is best viewed as a bifurcated C8/C5 bond with the N heteroatom lone electron pair playing a significant acceptor role, which supports recent observations on the hydrazino turn structure in solution. Surprisingly, this study shows that the cis-substituted cyclobutane ring derivative also gives rise predominantly to a C8 hydrogen bond, although weaker than in the two former cases, a feature that is not often encountered for this building block.

Mono-, Di-, and Trifluoroalkyl Substituent Effects on the Torquoselectivities of Cyclobutene and Oxetene Electrocyclic Ring Openings.

The reactivities and torquoselectivities of electrocyclic ring opening reactions of fluoromethyl-substituted cyclobutenes and oxetenes were studied with M06-2X density functional theory. The torquoselectivities of a series of mono-, di-, and trifluoromethylcyclobutenes and oxetenes result from the interplay of favorable orbital interactions and closed-shell repulsions. When the substituent rotates inward, there can be a favorable interaction between the breaking σ(CO) bond and the σ(CF)* orbital (σ(CO) → σ(CF)*) of the fluoromethyl group in fluoromethyloxetenes. The preference for rotation of a fluoromethyl group is decreased in trifluoromethyloxetenes because closed-shell repulsions between the breaking σ(CO) bond and trifluoromethyl substituent orbitals compete with the σ(CO) → σ(CF)* interaction.

Stereoselective synthesis of highly branched chiral cyclobutane-cored triamines and their conjugation to Gd-DOTA

Several chiral cyclobutane-containing chemical platforms were synthesized in a stereoselective manner starting from (−)-verbenone as a suitable precursor. These compounds bear three orthogonally protected amine functions, two of them on side-chain and the other directly linked to the cyclobutane ring. Selective deprotection of the latter amine and subsequent coupling with the DOTA macrocycle followed by complexation with Gd(III) allowed the preparation of new GdDO3A monoamides whose potential ability as contrast agents (CAs) in magnetic resonance imaging (MRI) preliminary experiments was tested. Image contrast enhancement was shown to be dependent on the amine substitution and protecting groups (–NH–Cbz, –NH–CO–C6H4–p-NO2, –NH–Ac, and –NMe–Cbz), and in the case of acetamide the corresponding Gd complex manifested a better contrast enhancement than DOTAREM, a Gd-based commercial CA which was used as a reference. Computational studies suggest that water exchange rate in these complexes is associated to the ability of the amido-carbonyl groups in the cyclobutane side-chains to coordinate to Gd.

Cyclophanes, Part 73: diastereoselective dimerization of an α,β-unsaturated ketone. Structure of all-trans-1,3-dibenzoyl-2,4-di([2.2]paracyclophan-4-yl)cyclobutane

Abstract The dimerization of an α,β-unsaturated ketone led to a product that consists of a single diastereomer with all-trans configuration, as shown by an X-ray structure investigation. We postulate that the steric bulk of the 4-[2.2]paracyclophanyl substituent is responsible for the diastereoselectivity. The central cyclobutane ring is puckered, with a fold angle of 27.9(1)°. The cyclophane units show the usual distortions associated with the bridge strain.

Shear induced carboplatin binding within the cavity of a phospholipid mimic for increased anticancer efficacy.

Vesicles 107 ± 19 nm in diameter, based on the self-assembly of tetra-para-phosphonomethyl calix[4]- arene bearing n-hexyl moieties attached to the phenolic oxygen centres, are effective in binding carboplatin within the cavity of the macrocycle under shear induced within a dynamic thin film in a continuous flow vortex fluidic device. Post shearing the vesicles maintain similar diameters and retain carboplatin within the cavity of the calixarene in a hierarchical structure, with their size and morphology investigated using DLS, TEM, SEM and AFM. Location of the carboplatin was confirmed using NMR, FTIR, ESI-MS and EFTEM, with molecular modelling favouring the polar groups of carboplatin hydrogen bonded to phosphonic acid moieties and the four member cyclobutane ring directed into the cavity of the calixarene. The loading efficiency and release profile of carboplatin was investigated using LC-TOF/MS, with the high loading of the drug achieved under shear and preferential released at pH 5.5, offering scope for anti-cancer drug delivery. The hierarchical structured vesicles increase the efficacy of carboplatin by 4.5 fold on ovarian cancer cells, lowered the IC50 concentration by 10 fold, and markedly increased the percent of cells in the S-phase (DNA replication) of the cell cycle.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo-Polymerization Reaction.

Getting suitable crystals for single-crystal X-ray crystallographic analysis still remains an art. Obtaining single crystals of metal-organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single-crystal-to-single-crystal manner. The spacer ligands with trans,trans,trans-conformation in the pillared-layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans-conformation prior to [2+2] photo-cycloaddition reaction and yield single crystals of MOF containing two-dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.

Formation of a Syndiotactic Organic Polymer Inside a MOF by a [2+2] Photo‐Polymerization Reaction

AbstractGetting suitable crystals for single‐crystal X‐ray crystallographic analysis still remains an art. Obtaining single crystals of metal–organic frameworks (MOFs) containing organic polymers poses even greater challenges. Here we demonstrate the formation of a syndiotactic organic polymer ligand inside a MOF by quantitative [2+2] photopolymerization reaction in a single‐crystal‐to‐single‐crystal manner. The spacer ligands with trans,trans,trans‐conformation in the pillared‐layer MOF with guest water molecules in the channels, undergo pedal motion to trans,cis,trans‐conformation prior to [2+2] photo‐cycloaddition reaction and yield single crystals of MOF containing two‐dimensional coordination polymers fused with the organic polymer ligands. We also show that the organic polymer in the single crystals can be depolymerized reversibly by cleaving the cyclobutane rings upon heating. These MOFs also show interesting photoluminescent properties and sensing of small organic molecules.

Synthesis, spatial structure and spectral properties of pyrylo-4 (thio) squaraines variously substituted in cyclobutene moiety

Synthetic routes have been developed to a number of (thio) squaraine dyes containing the residues of CH-acids at the central cyclobutene ring. The electronic and spatial structure as well as the chemical conversions and optical behaviour of the compounds obtained have been studied both theoretically and by X-ray diffraction analysis, 1H NMR and electronic spectroscopy. As shown, the electronic nature and sterical characteristics of the central ring substituents give rise to some general conformational features and crystal packing regularities and also govern the spectral position of the first π–π* absorption band. The structure–property relationships established in the study provide guidance for the purposeful design of deeply coloured (thio) squaraines. Copyright © 2015 John Wiley & Sons, Ltd.

Unexpected dimerization of 1,3‐dimethyl‐5‐methylenebarbituric acid revealed by a combined experimental and computational study

A comparison of experimental and calculated 13C‐nuclear magnetic resonance chemical shifts reveals the molecular structure of a dimer that was obtained by an unexpected dimerization of 1,3‐dimethyl‐5‐methylenebarbituric acid. Furthermore, the puckering angle of the cyclobutane unit linking the six‐membered rings is discussed in detail. The influence of substituents on 1,3‐position of the cyclobutane ring on the puckering angle is demonstrated based on 1,1,3,3‐tetramethylcyclobutane. Copyright © 2015 John Wiley & Sons, Ltd.

New Insights into the Hexaphenylethane Riddle: Formation of an α,o‐Dimer

AbstractUpon reduction of a 1H‐cyclobuta[de]naphthalene‐4,5‐diylbis(diarylmethylium) species, a new CC bond is formed between the Cα and Cortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the Cα carbon atoms was elongated beyond the limit of σ‐bond formation through “scissor effects”. The suppression of CαCα bond formation, which would lead to hexaphenylethane‐type compounds, is key to the first successful isolation of the α,o‐adducts. The 5‐diarylmethylene‐6‐triarylmethyl‐1,3‐cyclohexadiene unit in the α,o‐adducts is stable, and isomerization of the cyclohexadiene unit into an aromatic system was not observed. The newly formed CαCortho bond was cleaved upon two‐electron oxidation to regenerate the dicationic dye.

New insights into the hexaphenylethane riddle: formation of an α,o-dimer.

Upon reduction of a 1H-cyclobuta[de]naphthalene-4,5-diylbis(diarylmethylium) species, a new CC bond is formed between the Cα and Cortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the Cα carbon atoms was elongated beyond the limit of σ-bond formation through "scissor effects". The suppression of Cα Cα bond formation, which would lead to hexaphenylethane-type compounds, is key to the first successful isolation of the α,o-adducts. The 5-diarylmethylene-6-triarylmethyl-1,3-cyclohexadiene unit in the α,o-adducts is stable, and isomerization of the cyclohexadiene unit into an aromatic system was not observed. The newly formed Cα Cortho bond was cleaved upon two-electron oxidation to regenerate the dicationic dye.