Copper catalyzed enantioselective [4＋2] annulations of D-A cyclobutanes and aldehydes have been developed. In the presence of a side arm modified chiral bisoxazoline （SaBOX） ligand, the [4＋2] annulations proceeded...Copper catalyzed enantioselective [4＋2] annulations of D-A cyclobutanes and aldehydes have been developed. In the presence of a side arm modified chiral bisoxazoline （SaBOX） ligand, the [4＋2] annulations proceeded smoothly with a broad substrate scope. 22 examples were studied, leading to the corresponding products with various functional groups in 41%-99% yields with 〉99/1 dr and 90%-96% ee. The resulting product with two ester groups was mono-reduced, giving the corresponding product in excellent diastereoselectivity without loss of the enantiopurity.展开更多
Transmetalation of carborane-fused zirconacycles to Cu（II） induces the C-C coupling reaction to form four-membered rings. This serves as a new efficient and general methodology for the generation of a series of carb...Transmetalation of carborane-fused zirconacycles to Cu（II） induces the C-C coupling reaction to form four-membered rings. This serves as a new efficient and general methodology for the generation of a series of carborane-fused cyclobutenes and cyclobutanes. A reaction mechanism involving transmetalation to Cu（II） and reductive elimination is proposed.展开更多
The field of polymer mechanochemistry has been revolutionized by implementing force-responsive functional groups—mechanophores.The rational design of mechanophores enables the controlled use of force to achieve const...The field of polymer mechanochemistry has been revolutionized by implementing force-responsive functional groups—mechanophores.The rational design of mechanophores enables the controlled use of force to achieve constructive molecular reactivity and material responses.While a variety of mechanophores have been developed,this Mini Review focuses on cyclobutane,which has brought valuable insights into molecular reactivity and dynamics as well as innovations in materials.We discuss its reactivity and mechanism,dynamics and stereoselectivity,as well as impacts on material properties.展开更多
[2+2]-Type cyclobutane derivatives comprise a large family of natural products with diverse molecular architectures.However,the structure elucidation of the cyclobutane ring,including its connection mode and stereoche...[2+2]-Type cyclobutane derivatives comprise a large family of natural products with diverse molecular architectures.However,the structure elucidation of the cyclobutane ring,including its connection mode and stereochemistry,presents a significant challenge.Plumerubradins A-C(1-3),three novel iridoid glycoside[2+2]dimers featuring a highly functionalized cyclobutane core and multiple stereogenic centers,were isolated from the flowers of Plumeria rubra.Through biomimetic semisynthesis and chemical degradation of compounds 1-3,synthesis of phenylpropanoid-derived[2+2]dimers 7-10,combined with extensive spectroscopic analysis,single-crystal X-ray crystallography,and microcrystal electron diffraction experiments,the structures with absolute configurations of 1-3 were unequivocally elucidated.Furthermore,quantum mechanics-based^(1)H NMR iterative full spin analysis successfully established the correlations between the signal patterns of cyclobutane protons and the structural information of the cyclobutane ring in phenylpropanoid-derived[2+2]dimers,providing a diagnostic tool for the rapid structural elucidation of[2+2]-type cyclobutane derivatives.展开更多
Five rice ( Oryza sativa L.) cultivars, widely planted in South China, were grown in greenhouse with or without supplemental UV_B radiation at level of 13.6 kJ·m -2 ·d -1 . After 15 day_UV_B treat...Five rice ( Oryza sativa L.) cultivars, widely planted in South China, were grown in greenhouse with or without supplemental UV_B radiation at level of 13.6 kJ·m -2 ·d -1 . After 15 day_UV_B treatment, significant intraspecific differences were observed in plant height, photosynthetic rate and total biomass. Based on the total biomass accumulation, cultivar “Tesanai” was found to be the most sensitive, and cultivar “Luhuangzhan” was the most tolerant species to UV_B radiation. UV_B induced cyclobutane pyrimidine dimer (CPD) in rice DNA were quantified by ELISA with specific monoclonal antibody. CPD accumulations in DNA extracted from 5 rice cultivars were remarkably increased by UV_B radiation, and it was confirmed that there was a strong positive correlation between CPD accumulation and the inhibition of total biomass. Photorepair was proved to be the predominant mode of CPD repair in UV_B irradiated rice. Light_dependent removal of CPD was very fast as compared with dark repair. Different levels of CPD accumulation among rice cultivars were related with different capacity of CPD photorepair. Capacity of light_dependent CPD removal may play an important role in UV_B resistance of rice.展开更多
The relationship between the yield of thymime-thymine dimer after laser irradiation and physical parameters, such as intensity and pulse number was studied to explore the function of laser irradiation to induce thym...The relationship between the yield of thymime-thymine dimer after laser irradiation and physical parameters, such as intensity and pulse number was studied to explore the function of laser irradiation to induce thymine-thymine dimer. A modified high-performance liquid chromatography (HPLC) method has been developed for the determination of thymine-thymine dimer in DNA for. The thymine-thymine dimer was prepared by a photochemical reaction to be used as the standard substance. The HPLC method we proposed is not interfered by other hydrolysate from DNA. The stability and reproducibility are good, and it can determine as little as 4.42×10 -5 μg·mL -1 thymime-thymine dimer. Three levels of laser intensity to irradiate DNA were selected from calf thymine to test the influence of the pulse number. The mechanism of DNA lesion and repair caused by laser irradiation was studied preliminarily.展开更多
DNA damage in the form of cyclobutane pyrimidine dimers(CPDs) and (6-4) photoproducts(6-4PPs) induced by UV-B radiation in Arabidopsis thaliana at different temperatures was investigated using ELISA with specific mono...DNA damage in the form of cyclobutane pyrimidine dimers(CPDs) and (6-4) photoproducts(6-4PPs) induced by UV-B radiation in Arabidopsis thaliana at different temperatures was investigated using ELISA with specific monoclonal antibodies. CPDs and 6-4PPs increased during 3 h UV-B exposure, but further exposure led to decreases. Contrary to the commonly accepted view that DNA damage induced by UV-B radiation is temperature-independent because of its photochemical nature, we found UV-B-induction of CPDs and 6-4PPs in Arabidopsis to be slower at a low than at a high temperature. Photorepair of CPDs at 24℃ was much faster than that at 0℃ and 12℃, with 50% CPDs removal during 1 h exposure to white light. Photorepair of 6-4PPs at 12℃ was very slow as compared with that at 24℃, and almost no removal of 6-4PPs was detected after 4 h exposure to white light at 0℃. There was evidence to suggest that temperature-dependent DNA damage and photorepair could have important ecological implications.展开更多
The title compound (C28H21ClN2O, Mr = 436.92) was synthesized by the cross- photodimerization of (E)-2-(2-phenylethenyl)benzoxazole and (E)-4-[2-(4-chlorophenyl)ethenyl]- pyridine in sulfuric acid solution. Its molecu...The title compound (C28H21ClN2O, Mr = 436.92) was synthesized by the cross- photodimerization of (E)-2-(2-phenylethenyl)benzoxazole and (E)-4-[2-(4-chlorophenyl)ethenyl]- pyridine in sulfuric acid solution. Its molecular structure has been unequivocally determined by X-ray crystallography. The title compound belongs to triclinic system, space group P?with cell parameters: a = 9.648(3), b = 10.458(4), c = 12.106(4) , a = 89.089(7), b = 75.644(6), g = 68.441(7)? V = 1096.7(7) 3, Z = 2, Dc = 1.323 g/cm3, F(000) = 456 and m(MoKa) = 0.198 mm-1. The final R and wR are 0.0627 and 0.1285, respectively for 1737 observed reflections with I > 2s(I). S = 0.921 and (/s)max = 0.001. The cyclobutane ring has a puckered conformation with four different aryl groups substituted on each carbon atom. The dihedral angles of the cyclobutane ring are 20.2 and 20.6? The bond distances of the cyclobutane ring are 1.541, 1.555, 1.560 and 1.563 ? respectively, which are slightly longer than that of the normal CC single bond. The title compound is the only cross-dimer and its two heteroaryl groups are situated at the trans-1,3 position of the cyclobutane ring, revealing that the cross-photodimerization proceeds in a head-to-tail pattern with high stereo-selectivity.展开更多
As a highly strained small molecule,[1.1.1]propellane has been widely used in various synthetic transformations owing to the exceptional reactivity of the central bond between the two bridgehead carbons.Utilizing stra...As a highly strained small molecule,[1.1.1]propellane has been widely used in various synthetic transformations owing to the exceptional reactivity of the central bond between the two bridgehead carbons.Utilizing strain-release approaches,the rapid development of strategies for the construction of bicyclo[1.1.1]pentane(BCP)and cyclobutane derivatives using[1.1.1]propellane as the starting material has been witnessed in the past few years.In this review,we highlight the most recent advances in this field.Accordingly,the reactivity of[1.1.1]p ropellane can be divided into three pathways,including radical,anionic and transition metal-catalyzed pathways under appropriate conditions.展开更多
Excess electrons are not only an important source of radiation damage,but also participate in the repair process of radiation damage such as cyclobutane pyrimidine dimer(CPD).Using ab initio molecular dynamics(AIMD)si...Excess electrons are not only an important source of radiation damage,but also participate in the repair process of radiation damage such as cyclobutane pyrimidine dimer(CPD).Using ab initio molecular dynamics(AIMD)simulations,we reproduce the single excess electron stepwise catalytic CPD dissociation process in detail with an emphasis on the energy levels and molecular structure details associated with excess electrons.On the basis of the AIMD simulations on the CPD aqueous solution with two vertically added excess electrons,we exclude the early-proposed[2+2]-like concerted synchronous dissociation mechanism,and analyze the difference between the symmetry of the actual reaction and the symmetry of the frontier molecular orbitals which deeply impact the mechanism.Importantly,we propose a new model of the stepwise electron-catalyzed dissociation mechanism that conforms to the reality.This work not only provides dynamics insights into the excess electron catalyzed dissociation mechanism,but also reveals different roles of two excess electrons in two bond-cleavage steps(promoting versus inhibiting).展开更多
The Cu（Ⅱ） and Co（Ⅱ） supramolecular coordination polymers, [CuCl2（DPO）- （CH3CN）0.5（CH2Cl2）0.5]n （CuDPO, DPO = rctt-1,3-diphenyl-2,4-bis[2-（5-phenyl）oxazolyl]cyclo- butane） and [CoCl2（DPO）]n （CoDPO）,...The Cu（Ⅱ） and Co（Ⅱ） supramolecular coordination polymers, [CuCl2（DPO）- （CH3CN）0.5（CH2Cl2）0.5]n （CuDPO, DPO = rctt-1,3-diphenyl-2,4-bis[2-（5-phenyl）oxazolyl]cyclo- butane） and [CoCl2（DPO）]n （CoDPO）, were synthesized and characterized by single-crystal X-ray diffraction method. CuDPO crystallizes in monoclinic, space group P21/n, with a = 11.243（5）, b = 16.070（8）, c = 19.872（9） A, β = 95.678（10）°, Z = 4, V= 3573（3） A3, C35.50H28.50Cl3CuN2.50O2, Mr = 692.00, Dc = 1.287 g/cm3, p = 0.868 mm^-1, F（000） = 1420, S = 1.089, （△/σ）max = 0.069, the final R = 0.0682 and wR = 0.1749. CoDPO is of monoclinie, space group P21/n, with a = 11.396（4）, b = 15.151（5）, c = 17.673（6） A, β = 90.528（6）°, Z = 4, V = 3051.4（17） A3, C34H26Cl2CoN2O2, Mr = 624.40, Dc = 1.359 g/cm3, μ = 0.770 mm^-1, F（000） = 1284, S = 0.981, （△/σ）max = 0.001, the final R = 0.0471 and wR = 0.0961. In each case, the metal cation is coordinated by two C1 anions and two N atoms from oxazole ring of the ligands, which leads to the formation of a one-dimensional polymeric structure. It is found that the cyclobutane ring of coordinated DPO adopts a distorted conformation in the crystal, which is attributed to the increased steric effect between adjacent aryl substituents for the coordination of oxazole ring to metal cation. Thermal gravimetric analysis of the two complexes was also observed.展开更多
Three new ent-kaurane diterpenoids,silvaticusins A-C(1-3),along with a new ent-kaurane dimer silvaticusin D(4)were isolated from the aerial parts of Isodon silvaticus.The structures of these new compounds were establi...Three new ent-kaurane diterpenoids,silvaticusins A-C(1-3),along with a new ent-kaurane dimer silvaticusin D(4)were isolated from the aerial parts of Isodon silvaticus.The structures of these new compounds were established mainly by comprehensive analysis of their NMR and MS data.The absolute configuration of compounds 1 and 4 were determined using a single-crystal X-ray diffraction and computational methods,respectively.Compounds 2 and 3 were found to exhibit remarkable cytotoxic effects against five human tumor cell lines(HL-60,A-549,SMMC-7721,MDA-MB-231,and SW-480),with IC_(50) values spanning from 1.27±0.08 to 7.52±0.33μM.展开更多
Cyclobutanes are distributed widely in a large class of natural products featuring diverse pharmaceutical activities and intricate structural frameworks.The[2+2]cycloaddition is unequivocally the primary and most comm...Cyclobutanes are distributed widely in a large class of natural products featuring diverse pharmaceutical activities and intricate structural frameworks.The[2+2]cycloaddition is unequivocally the primary and most commonly used method for synthesizing cyclobutanes.In this review,we have summarized the application of the[2+2]cycloaddition with different reaction mechanisms in the chemical synthesis of selected cyclobutane-containing natural products over the past decade.展开更多
AIM: To establish whether d-limonene can protect against induction of cyclobutane pyrimidine dimers(CPDs) and sunburn in ultraviolet irradiation(UVR) irradiated mouse skin. METHODS: The d-limonene was given in 4 daily...AIM: To establish whether d-limonene can protect against induction of cyclobutane pyrimidine dimers(CPDs) and sunburn in ultraviolet irradiation(UVR) irradiated mouse skin. METHODS: The d-limonene was given in 4 daily oral 20 μL aliquots at different concentrations as follows: 100%, 10% or 1% in liponate and 100% liponate as control. One day after the final d-limonene treatment, the mice were anesthetized with i.p. sodium pentobarbital and placed in boxes to allow a rectangular(2 cm × 4 cm) region of dorsal skin to be irradiated with a single, ultraviolet radiation dose of 1.5 kJ /m2. Skin samples from UVR irradiated area were obtained at 5 min after UVR exposure for CPD detection, at 6 d after UVR exposure, skin samples were obtained for in situ analysis for N-myc downstream regulating gene 1(NDRG1)(a stress response gene), proliferating cell nuclear antigen(PCNA)(an S-phase marker) and filaggrin(a barrier integrity gene). Based on immunohistochemistry staining, the number of CPD, NDRG1 and PCNA positive cells, as well as unstained cells was counted in 3 different individually selected areas and percentage of positive cells was established. RESULTS: CPD reduction occurred as follows: liponate only-none; 1% d-limonene-54.3% reduction of CPDs; 10% d-limonene-73.4% reduction of CPDs; 100% d-limonene-86.1% reduction of CPDs, the latter equivalent to a UV dose of only 0.21 k J/m2. Sunburn was also dose-dependently reduced by d-limonene. The NDRG1 protein was strongly induced by UVR(70.0% ± 10.4% positive cells), but 1% d-limonene reduced the response to 64.6% ± 9.2%, 10% d-limonene reduced the response to 16.2% ± 3.4% and 100% d-limonene reduced the response to 6.3% ± 1.7%. Similarly, PCNA was 52.4% ± 9.9% positive in UVR exposed skin, and 1% d-limonene reduced it to 42.9% ± 8.1%, 10% d-limonene reduced it to 36.2% ± 6.7% and 100% d-limonene reduce it to 13.8% ± 3.4%. NDRG1 and PCNA were increased by d-limonene or UVR separately, but combined they produced less than either agent separately owing to the protective effect of pre-exposure to d-limonene. CONCLUSION: Overall d-limonene acted to protect against ultraviolet B-induced DNA photodamage and sunburn in UVR exposed skin.展开更多
CONSPECTUS:The concept of photoresponsive coordination polymer(CP)single crystal platforms(CPSCPs)is based on photoresponsive olefin CP single crystals,which can undergo photocycloaddition reactions under light irradi...CONSPECTUS:The concept of photoresponsive coordination polymer(CP)single crystal platforms(CPSCPs)is based on photoresponsive olefin CP single crystals,which can undergo photocycloaddition reactions under light irradiation through a single-crystal-to-single-crystal(SCSC)transformation.Taking advantage of the coordination of olefin ligands to metal ions of Zn^(2+),Cd^(2+),etc.,a pair of C=C double bonds is positioned adjacent to each other in space at a suitable distance and orientation to allow[2+2]photocycloaddition triggered by UV−vis irradiation,affording cyclobutanes in the CPs.The single crystal nature of CPs allows their structures to be determined by X-ray diffraction,providing details of the arrangements in space of the C=C double bonds.These CPs are promising platforms for the synthesis of organic molecules,such as cyclobutanes and derivatives,with high regioselectivity and stereoselectivity without any catalyst.The[2+2]photocycloaddition reactions may induce structural modifications like expansion or shrinking of unit cells,resulting in macroscopic changes(e.g.,cracking,bending,etc.)of the whole CP single crystals and leading to changes in chemical and physical properties.Applications take advantage of their optical properties,including luminescence and absorption,and allow the detection of vip molecules and photomechanical motions.Although much effort has been devoted to such studies,it remains challenging to develop systematic investigations aiming at increasing the diversity of CPs and properties to meet practical needs.Moreover,more efficient methods are desirable to investigate the reaction mechanisms in the solid state and monitor the structural changes occurring during the process.In this Account,we introduce our research on the design and applications of photoresponsive CPSCPs.It is divided into three parts.First,the design and construction of various CPs with different olefin ligands are discussed.Through a suitable and sometimes sophisticated choice of metal ions and auxiliary carboxylate ligands,these olefin ligands meet the requirements to undergo[2+2]photocycloaddition reactions in CP structures,allowing for the precise synthesis of cyclobutanes and their derivatives.These compounds could be subsequently extracted from the CPs to give pure organic products.Second,we introduce new strategies,such as a combination of single crystal X-ray diffraction(SCXRD)with thermal/phototreatments of CPs and in situ fluorescence spectroscopy,to monitor the structural changes occurring on the olefin ligands during the reaction.Furthermore,the fast stepwise photoreaction could also be visualized with high resolution.These data significantly strengthen our understanding of solid-state[2+2]photocycloaddition reactions in CPs.Third,applications of photoresponsive CPs are described,which focus on optical and photoinduced mechanical properties.Considering the optical properties,the conjugated structures of the olefin ligands change during the reactions,and circular dichroism(CD)and fluorescence were used for their detection and imaging.Furthermore,the photoinduced mechanical properties of CPs could be significantly expanded through the combination of CP crystals with polymers.Lastly,we point out the challenges and directions for future research in the field.We hope this Account will provide an overview of research on photoresponsive CPSCPs,attract more attention from the community,and inspire future research.展开更多
Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis.We report here a practical and facile approach to synthesizing all-trans 2,3,4...Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis.We report here a practical and facile approach to synthesizing all-trans 2,3,4-trisubstituted cyclobutanones from readily available dichlorocyclobutanones.The substitution reaction proceeds smoothly via oxyallyl cation intermediates under mild basic conditions.Further transformation to the synthesis of 1,2,3,4-tetrasubstituted cyclobutanes was also explored.展开更多
Photo[2+2]cycloaddition of olefins is a sought-after tool for making cyclobutanes,which are the building blocks for a wide range of biologically active molecules and natural products.However,the formation of cyclobuta...Photo[2+2]cycloaddition of olefins is a sought-after tool for making cyclobutanes,which are the building blocks for a wide range of biologically active molecules and natural products.However,the formation of cyclobutane derivatives from aryl terminal olefins is problematic due to their high redox potential,and high energy in the excited state,making visible-light-absorbing photocatalyst difficult to realize either electron or energy transfer to olefins during the photocyclic addition process.Herein,we report,for the first time,the aggregationinduced photo[2+2]cycloaddition of two olefins by visible-light catalysis in homogeneous solution.An array of control experiments and spectroscopic analyses reveal that the terminal olefins tend to aggregate to form excimers/exciplexes,which possess much lower energy than their monomeric forms,and enables triplet energy transfer from excited Ir(ppy)3*to supramolecular self-assembly feasible,leading to homo and cross[2+2]photodimerization of the olefins to fabricate cyclobutanes at ambient conditions in good to excellent yields.展开更多
The evolution of synthetic design toward the efficient synthesis of cyclobutane natural product(±)-piperarborenine B is demonstrated.Taking the advantages of good functional group compatibility of contractive syn...The evolution of synthetic design toward the efficient synthesis of cyclobutane natural product(±)-piperarborenine B is demonstrated.Taking the advantages of good functional group compatibility of contractive synthesis of cyclobutanes from pyrrolidines,stereoselective synthesis of unsymmetric highly functionalized cyclobutanes core of(±)-piperarborenine B was realized in one step.Also,an unprecedented carboxylic acid assisted-diastereoselective Kracho decarboxylation/transmethylation features a new strategy for a non-symmetrical cyclobutane core.The synthesis of(±)-piperarborenine B illustrates the advancement of methodology resulting in the improvement in synthetic efficiency.展开更多
Utilizing a pulse radiolysis equipment with time-resolved optical detector, kinetic processes of electron-induced splitting of cis-syn 1,3-dimethyluracil cyclobutane dimer (DMUD) in aqueous solution were investigated ...Utilizing a pulse radiolysis equipment with time-resolved optical detector, kinetic processes of electron-induced splitting of cis-syn 1,3-dimethyluracil cyclobutane dimer (DMUD) in aqueous solution were investigated in the presence or absence of riboflavin (RF) or flavin adenine dinucleotide (FAD). It has been observed that the cyclobutane pyrimidine dimer reacting with hydrated electron splits spontaneously to give a monomer and a monomer radical anion, and the anion transfers one electron to RF or FAD. From the buildup kinetics of radical species, the rate constants of electron transfer from the monomer radical anion to RF and FAD have been determined. On the basis of comparison of the interactions between DMUD and hydrated electron in the presence and absence of RF or FAD, a chain reaction process in the absence of RF or FAD has been demonstrated.展开更多
The oxidative splitting process of cis-syn 1,3-dimethyluracil cyclobutane dimer (DMUD) in aqueous solution was investigated using pulse radiolysis technique. The results indicated that DMUD can be splitted into 1,3-...The oxidative splitting process of cis-syn 1,3-dimethyluracil cyclobutane dimer (DMUD) in aqueous solution was investigated using pulse radiolysis technique. The results indicated that DMUD can be splitted into 1,3-dimethyluracil (DMU) by OH radicals (OH ·) and Br_2 radical anions (Br ·-_2), but not by azide radicals (N ·_3). The oxidative mechanisms that an H-abstracted from DMUD for OH · oxidative splitting and an electron transfer from DMUD to Br ·-_2, were suggested. Related kinetic parameters were determined.展开更多
基金We thank for the financial support from the National Natural Science Foundation of China （Nos. 21421091 and 21432011）, the National Basic Research Program of China （973 Program） （2015CB856600）, the Natural Science Foundation of Shanghai （17ZR1436900）, the Strategic Priority Research Program of the Chinese Academy of Sciences （Grant No. XDB20000000） and the Youth Innovation Promotion Association CAS （2017301）. We thank Dr. Xue-Bing Leng for X-ray crystal analysis
文摘Copper catalyzed enantioselective [4＋2] annulations of D-A cyclobutanes and aldehydes have been developed. In the presence of a side arm modified chiral bisoxazoline （SaBOX） ligand, the [4＋2] annulations proceeded smoothly with a broad substrate scope. 22 examples were studied, leading to the corresponding products with various functional groups in 41%-99% yields with 〉99/1 dr and 90%-96% ee. The resulting product with two ester groups was mono-reduced, giving the corresponding product in excellent diastereoselectivity without loss of the enantiopurity.
基金supported by the Research Grants Council of the Hong Kong Special Administration Region (404011)the National Natural Science Foundation of China (21372245 to QIU ZaoZao)
文摘Transmetalation of carborane-fused zirconacycles to Cu（II） induces the C-C coupling reaction to form four-membered rings. This serves as a new efficient and general methodology for the generation of a series of carborane-fused cyclobutenes and cyclobutanes. A reaction mechanism involving transmetalation to Cu（II） and reductive elimination is proposed.
基金supported by the National Science Foundation(CHE-2204079)supported by the National Science Foundation(DGE-2152210)+1 种基金Foundation for a Sloan Research Fellowship(FG-2023-20341)the Camille and Henry Dreyfus Foundation for a Camille Dreyfus Teacher-Scholar Award(TC-24-087)。
文摘The field of polymer mechanochemistry has been revolutionized by implementing force-responsive functional groups—mechanophores.The rational design of mechanophores enables the controlled use of force to achieve constructive molecular reactivity and material responses.While a variety of mechanophores have been developed,this Mini Review focuses on cyclobutane,which has brought valuable insights into molecular reactivity and dynamics as well as innovations in materials.We discuss its reactivity and mechanism,dynamics and stereoselectivity,as well as impacts on material properties.
基金supported by the National Key R&D Program of China(No.2023YFC3503902)the National Natural Science Foundation of China(Nos.82293681(82293680)and 82321004)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(Nos.2022B1515120015 and 2021A1515111021)the Guangdong Major Project of Basic and Applied Basic Research(No.2023B0303000026)the Science and Technology Projects in Guangzhou(No.202102070001).
文摘[2+2]-Type cyclobutane derivatives comprise a large family of natural products with diverse molecular architectures.However,the structure elucidation of the cyclobutane ring,including its connection mode and stereochemistry,presents a significant challenge.Plumerubradins A-C(1-3),three novel iridoid glycoside[2+2]dimers featuring a highly functionalized cyclobutane core and multiple stereogenic centers,were isolated from the flowers of Plumeria rubra.Through biomimetic semisynthesis and chemical degradation of compounds 1-3,synthesis of phenylpropanoid-derived[2+2]dimers 7-10,combined with extensive spectroscopic analysis,single-crystal X-ray crystallography,and microcrystal electron diffraction experiments,the structures with absolute configurations of 1-3 were unequivocally elucidated.Furthermore,quantum mechanics-based^(1)H NMR iterative full spin analysis successfully established the correlations between the signal patterns of cyclobutane protons and the structural information of the cyclobutane ring in phenylpropanoid-derived[2+2]dimers,providing a diagnostic tool for the rapid structural elucidation of[2+2]-type cyclobutane derivatives.
文摘Five rice ( Oryza sativa L.) cultivars, widely planted in South China, were grown in greenhouse with or without supplemental UV_B radiation at level of 13.6 kJ·m -2 ·d -1 . After 15 day_UV_B treatment, significant intraspecific differences were observed in plant height, photosynthetic rate and total biomass. Based on the total biomass accumulation, cultivar “Tesanai” was found to be the most sensitive, and cultivar “Luhuangzhan” was the most tolerant species to UV_B radiation. UV_B induced cyclobutane pyrimidine dimer (CPD) in rice DNA were quantified by ELISA with specific monoclonal antibody. CPD accumulations in DNA extracted from 5 rice cultivars were remarkably increased by UV_B radiation, and it was confirmed that there was a strong positive correlation between CPD accumulation and the inhibition of total biomass. Photorepair was proved to be the predominant mode of CPD repair in UV_B irradiated rice. Light_dependent removal of CPD was very fast as compared with dark repair. Different levels of CPD accumulation among rice cultivars were related with different capacity of CPD photorepair. Capacity of light_dependent CPD removal may play an important role in UV_B resistance of rice.
文摘The relationship between the yield of thymime-thymine dimer after laser irradiation and physical parameters, such as intensity and pulse number was studied to explore the function of laser irradiation to induce thymine-thymine dimer. A modified high-performance liquid chromatography (HPLC) method has been developed for the determination of thymine-thymine dimer in DNA for. The thymine-thymine dimer was prepared by a photochemical reaction to be used as the standard substance. The HPLC method we proposed is not interfered by other hydrolysate from DNA. The stability and reproducibility are good, and it can determine as little as 4.42×10 -5 μg·mL -1 thymime-thymine dimer. Three levels of laser intensity to irradiate DNA were selected from calf thymine to test the influence of the pulse number. The mechanism of DNA lesion and repair caused by laser irradiation was studied preliminarily.
文摘DNA damage in the form of cyclobutane pyrimidine dimers(CPDs) and (6-4) photoproducts(6-4PPs) induced by UV-B radiation in Arabidopsis thaliana at different temperatures was investigated using ELISA with specific monoclonal antibodies. CPDs and 6-4PPs increased during 3 h UV-B exposure, but further exposure led to decreases. Contrary to the commonly accepted view that DNA damage induced by UV-B radiation is temperature-independent because of its photochemical nature, we found UV-B-induction of CPDs and 6-4PPs in Arabidopsis to be slower at a low than at a high temperature. Photorepair of CPDs at 24℃ was much faster than that at 0℃ and 12℃, with 50% CPDs removal during 1 h exposure to white light. Photorepair of 6-4PPs at 12℃ was very slow as compared with that at 24℃, and almost no removal of 6-4PPs was detected after 4 h exposure to white light at 0℃. There was evidence to suggest that temperature-dependent DNA damage and photorepair could have important ecological implications.
基金the foundation for University Key Teacher by the Ministry of Education
文摘The title compound (C28H21ClN2O, Mr = 436.92) was synthesized by the cross- photodimerization of (E)-2-(2-phenylethenyl)benzoxazole and (E)-4-[2-(4-chlorophenyl)ethenyl]- pyridine in sulfuric acid solution. Its molecular structure has been unequivocally determined by X-ray crystallography. The title compound belongs to triclinic system, space group P?with cell parameters: a = 9.648(3), b = 10.458(4), c = 12.106(4) , a = 89.089(7), b = 75.644(6), g = 68.441(7)? V = 1096.7(7) 3, Z = 2, Dc = 1.323 g/cm3, F(000) = 456 and m(MoKa) = 0.198 mm-1. The final R and wR are 0.0627 and 0.1285, respectively for 1737 observed reflections with I > 2s(I). S = 0.921 and (/s)max = 0.001. The cyclobutane ring has a puckered conformation with four different aryl groups substituted on each carbon atom. The dihedral angles of the cyclobutane ring are 20.2 and 20.6? The bond distances of the cyclobutane ring are 1.541, 1.555, 1.560 and 1.563 ? respectively, which are slightly longer than that of the normal CC single bond. The title compound is the only cross-dimer and its two heteroaryl groups are situated at the trans-1,3 position of the cyclobutane ring, revealing that the cross-photodimerization proceeds in a head-to-tail pattern with high stereo-selectivity.
基金the National Natural Science Foundation of China(Nos.21672037 and 21532001)the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang(No.2019R01005)。
文摘As a highly strained small molecule,[1.1.1]propellane has been widely used in various synthetic transformations owing to the exceptional reactivity of the central bond between the two bridgehead carbons.Utilizing strain-release approaches,the rapid development of strategies for the construction of bicyclo[1.1.1]pentane(BCP)and cyclobutane derivatives using[1.1.1]propellane as the starting material has been witnessed in the past few years.In this review,we highlight the most recent advances in this field.Accordingly,the reactivity of[1.1.1]p ropellane can be divided into three pathways,including radical,anionic and transition metal-catalyzed pathways under appropriate conditions.
基金supported by the National Natural Science Foundation of China(No.21873056,No.21773137,and No.21573128)。
文摘Excess electrons are not only an important source of radiation damage,but also participate in the repair process of radiation damage such as cyclobutane pyrimidine dimer(CPD).Using ab initio molecular dynamics(AIMD)simulations,we reproduce the single excess electron stepwise catalytic CPD dissociation process in detail with an emphasis on the energy levels and molecular structure details associated with excess electrons.On the basis of the AIMD simulations on the CPD aqueous solution with two vertically added excess electrons,we exclude the early-proposed[2+2]-like concerted synchronous dissociation mechanism,and analyze the difference between the symmetry of the actual reaction and the symmetry of the frontier molecular orbitals which deeply impact the mechanism.Importantly,we propose a new model of the stepwise electron-catalyzed dissociation mechanism that conforms to the reality.This work not only provides dynamics insights into the excess electron catalyzed dissociation mechanism,but also reveals different roles of two excess electrons in two bond-cleavage steps(promoting versus inhibiting).
文摘The Cu（Ⅱ） and Co（Ⅱ） supramolecular coordination polymers, [CuCl2（DPO）- （CH3CN）0.5（CH2Cl2）0.5]n （CuDPO, DPO = rctt-1,3-diphenyl-2,4-bis[2-（5-phenyl）oxazolyl]cyclo- butane） and [CoCl2（DPO）]n （CoDPO）, were synthesized and characterized by single-crystal X-ray diffraction method. CuDPO crystallizes in monoclinic, space group P21/n, with a = 11.243（5）, b = 16.070（8）, c = 19.872（9） A, β = 95.678（10）°, Z = 4, V= 3573（3） A3, C35.50H28.50Cl3CuN2.50O2, Mr = 692.00, Dc = 1.287 g/cm3, p = 0.868 mm^-1, F（000） = 1420, S = 1.089, （△/σ）max = 0.069, the final R = 0.0682 and wR = 0.1749. CoDPO is of monoclinie, space group P21/n, with a = 11.396（4）, b = 15.151（5）, c = 17.673（6） A, β = 90.528（6）°, Z = 4, V = 3051.4（17） A3, C34H26Cl2CoN2O2, Mr = 624.40, Dc = 1.359 g/cm3, μ = 0.770 mm^-1, F（000） = 1284, S = 0.981, （△/σ）max = 0.001, the final R = 0.0471 and wR = 0.0961. In each case, the metal cation is coordinated by two C1 anions and two N atoms from oxazole ring of the ligands, which leads to the formation of a one-dimensional polymeric structure. It is found that the cyclobutane ring of coordinated DPO adopts a distorted conformation in the crystal, which is attributed to the increased steric effect between adjacent aryl substituents for the coordination of oxazole ring to metal cation. Thermal gravimetric analysis of the two complexes was also observed.
基金supported by the National Science Fund for Distinguished Young Scholars(82325047)Second Tibetan Plateau Scientific Expedition and Research(STEP)program(2019QZKK0502)+1 种基金NSFC-Joint Foundation of Yunnan Province(U2002221)Youth Innovation Promotion Association CAS(2023409).
文摘Three new ent-kaurane diterpenoids,silvaticusins A-C(1-3),along with a new ent-kaurane dimer silvaticusin D(4)were isolated from the aerial parts of Isodon silvaticus.The structures of these new compounds were established mainly by comprehensive analysis of their NMR and MS data.The absolute configuration of compounds 1 and 4 were determined using a single-crystal X-ray diffraction and computational methods,respectively.Compounds 2 and 3 were found to exhibit remarkable cytotoxic effects against five human tumor cell lines(HL-60,A-549,SMMC-7721,MDA-MB-231,and SW-480),with IC_(50) values spanning from 1.27±0.08 to 7.52±0.33μM.
基金financially supported by the National Science Fund for Distinguished Young Scholars(82325047)Second Tibetan Plateau Scientific Expedition and Research(STEP)program(2019QZKK0502)NSFC-Joint Foundation of Yunnan Province(U2002221).
文摘Cyclobutanes are distributed widely in a large class of natural products featuring diverse pharmaceutical activities and intricate structural frameworks.The[2+2]cycloaddition is unequivocally the primary and most commonly used method for synthesizing cyclobutanes.In this review,we have summarized the application of the[2+2]cycloaddition with different reaction mechanisms in the chemical synthesis of selected cyclobutane-containing natural products over the past decade.
基金Supported by NCI Center Grant CA16087(NYU Kaplan Cancer)NIEHS Center Grant(Nelson Institute of the NYU Schoolof Medicine)Biokeys for Flavors,LLC,No.ES00260
文摘AIM: To establish whether d-limonene can protect against induction of cyclobutane pyrimidine dimers(CPDs) and sunburn in ultraviolet irradiation(UVR) irradiated mouse skin. METHODS: The d-limonene was given in 4 daily oral 20 μL aliquots at different concentrations as follows: 100%, 10% or 1% in liponate and 100% liponate as control. One day after the final d-limonene treatment, the mice were anesthetized with i.p. sodium pentobarbital and placed in boxes to allow a rectangular(2 cm × 4 cm) region of dorsal skin to be irradiated with a single, ultraviolet radiation dose of 1.5 kJ /m2. Skin samples from UVR irradiated area were obtained at 5 min after UVR exposure for CPD detection, at 6 d after UVR exposure, skin samples were obtained for in situ analysis for N-myc downstream regulating gene 1(NDRG1)(a stress response gene), proliferating cell nuclear antigen(PCNA)(an S-phase marker) and filaggrin(a barrier integrity gene). Based on immunohistochemistry staining, the number of CPD, NDRG1 and PCNA positive cells, as well as unstained cells was counted in 3 different individually selected areas and percentage of positive cells was established. RESULTS: CPD reduction occurred as follows: liponate only-none; 1% d-limonene-54.3% reduction of CPDs; 10% d-limonene-73.4% reduction of CPDs; 100% d-limonene-86.1% reduction of CPDs, the latter equivalent to a UV dose of only 0.21 k J/m2. Sunburn was also dose-dependently reduced by d-limonene. The NDRG1 protein was strongly induced by UVR(70.0% ± 10.4% positive cells), but 1% d-limonene reduced the response to 64.6% ± 9.2%, 10% d-limonene reduced the response to 16.2% ± 3.4% and 100% d-limonene reduced the response to 6.3% ± 1.7%. Similarly, PCNA was 52.4% ± 9.9% positive in UVR exposed skin, and 1% d-limonene reduced it to 42.9% ± 8.1%, 10% d-limonene reduced it to 36.2% ± 6.7% and 100% d-limonene reduce it to 13.8% ± 3.4%. NDRG1 and PCNA were increased by d-limonene or UVR separately, but combined they produced less than either agent separately owing to the protective effect of pre-exposure to d-limonene. CONCLUSION: Overall d-limonene acted to protect against ultraviolet B-induced DNA photodamage and sunburn in UVR exposed skin.
基金supported by the National Natural Science Foundation of China(Grant Nos.U24A20507,22271203,and 22301204)the State Key Laboratory of Organometallic Chemistry,Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences(Grant No.2024KF005)+1 种基金Open Research Fund of State Key Laboratory of Coordination Chemistry,School of Chemistry and Chemical Engineering,Nanjing University,the Collaborative Innovation Centre of Suzhou Nano Science and Technology,the Priority Academic Program Development of Jiangsu Higher Education Institutions,the Project of Scientific and Technologic Infrastructure of Suzhou(Grant No.SZS201905)Soochow University Starting Grant(No.NH10902124 to Q.L.).
文摘CONSPECTUS:The concept of photoresponsive coordination polymer(CP)single crystal platforms(CPSCPs)is based on photoresponsive olefin CP single crystals,which can undergo photocycloaddition reactions under light irradiation through a single-crystal-to-single-crystal(SCSC)transformation.Taking advantage of the coordination of olefin ligands to metal ions of Zn^(2+),Cd^(2+),etc.,a pair of C=C double bonds is positioned adjacent to each other in space at a suitable distance and orientation to allow[2+2]photocycloaddition triggered by UV−vis irradiation,affording cyclobutanes in the CPs.The single crystal nature of CPs allows their structures to be determined by X-ray diffraction,providing details of the arrangements in space of the C=C double bonds.These CPs are promising platforms for the synthesis of organic molecules,such as cyclobutanes and derivatives,with high regioselectivity and stereoselectivity without any catalyst.The[2+2]photocycloaddition reactions may induce structural modifications like expansion or shrinking of unit cells,resulting in macroscopic changes(e.g.,cracking,bending,etc.)of the whole CP single crystals and leading to changes in chemical and physical properties.Applications take advantage of their optical properties,including luminescence and absorption,and allow the detection of vip molecules and photomechanical motions.Although much effort has been devoted to such studies,it remains challenging to develop systematic investigations aiming at increasing the diversity of CPs and properties to meet practical needs.Moreover,more efficient methods are desirable to investigate the reaction mechanisms in the solid state and monitor the structural changes occurring during the process.In this Account,we introduce our research on the design and applications of photoresponsive CPSCPs.It is divided into three parts.First,the design and construction of various CPs with different olefin ligands are discussed.Through a suitable and sometimes sophisticated choice of metal ions and auxiliary carboxylate ligands,these olefin ligands meet the requirements to undergo[2+2]photocycloaddition reactions in CP structures,allowing for the precise synthesis of cyclobutanes and their derivatives.These compounds could be subsequently extracted from the CPs to give pure organic products.Second,we introduce new strategies,such as a combination of single crystal X-ray diffraction(SCXRD)with thermal/phototreatments of CPs and in situ fluorescence spectroscopy,to monitor the structural changes occurring on the olefin ligands during the reaction.Furthermore,the fast stepwise photoreaction could also be visualized with high resolution.These data significantly strengthen our understanding of solid-state[2+2]photocycloaddition reactions in CPs.Third,applications of photoresponsive CPs are described,which focus on optical and photoinduced mechanical properties.Considering the optical properties,the conjugated structures of the olefin ligands change during the reactions,and circular dichroism(CD)and fluorescence were used for their detection and imaging.Furthermore,the photoinduced mechanical properties of CPs could be significantly expanded through the combination of CP crystals with polymers.Lastly,we point out the challenges and directions for future research in the field.We hope this Account will provide an overview of research on photoresponsive CPSCPs,attract more attention from the community,and inspire future research.
基金supported by the National Natural Science Foundation of China(22071028,21921003).
文摘Stereoselective synthesis of multi-substituted cyclobutanes with different substituents is still a daunting challenge in organic synthesis.We report here a practical and facile approach to synthesizing all-trans 2,3,4-trisubstituted cyclobutanones from readily available dichlorocyclobutanones.The substitution reaction proceeds smoothly via oxyallyl cation intermediates under mild basic conditions.Further transformation to the synthesis of 1,2,3,4-tetrasubstituted cyclobutanes was also explored.
基金This work was supported financially by the Ministry of Science and Technology of China(2017YFA0206903)the National Natural Science Foundation of China(21861132004)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17000000)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(QYZDY-SSW-JSC029),and K.C.Wong Education Foundation.
文摘Photo[2+2]cycloaddition of olefins is a sought-after tool for making cyclobutanes,which are the building blocks for a wide range of biologically active molecules and natural products.However,the formation of cyclobutane derivatives from aryl terminal olefins is problematic due to their high redox potential,and high energy in the excited state,making visible-light-absorbing photocatalyst difficult to realize either electron or energy transfer to olefins during the photocyclic addition process.Herein,we report,for the first time,the aggregationinduced photo[2+2]cycloaddition of two olefins by visible-light catalysis in homogeneous solution.An array of control experiments and spectroscopic analyses reveal that the terminal olefins tend to aggregate to form excimers/exciplexes,which possess much lower energy than their monomeric forms,and enables triplet energy transfer from excited Ir(ppy)3*to supramolecular self-assembly feasible,leading to homo and cross[2+2]photodimerization of the olefins to fabricate cyclobutanes at ambient conditions in good to excellent yields.
基金A.P.A.thanks for the support of the DFG(No.AN 1064/4–1)and the Boehringer Ingelheim Foundation(Plus 3).C.H.thanks the International Max Planck Research School for Living Matter(Dortmund,Germany).
文摘The evolution of synthetic design toward the efficient synthesis of cyclobutane natural product(±)-piperarborenine B is demonstrated.Taking the advantages of good functional group compatibility of contractive synthesis of cyclobutanes from pyrrolidines,stereoselective synthesis of unsymmetric highly functionalized cyclobutanes core of(±)-piperarborenine B was realized in one step.Also,an unprecedented carboxylic acid assisted-diastereoselective Kracho decarboxylation/transmethylation features a new strategy for a non-symmetrical cyclobutane core.The synthesis of(±)-piperarborenine B illustrates the advancement of methodology resulting in the improvement in synthetic efficiency.
基金This work was supported by the National Natural Science Foundation of China(Grant No.30000036)Special Fund for Doctoral Program fromthe Ministry of Education of China and Foundation of University of Science and Technology of China.
文摘Utilizing a pulse radiolysis equipment with time-resolved optical detector, kinetic processes of electron-induced splitting of cis-syn 1,3-dimethyluracil cyclobutane dimer (DMUD) in aqueous solution were investigated in the presence or absence of riboflavin (RF) or flavin adenine dinucleotide (FAD). It has been observed that the cyclobutane pyrimidine dimer reacting with hydrated electron splits spontaneously to give a monomer and a monomer radical anion, and the anion transfers one electron to RF or FAD. From the buildup kinetics of radical species, the rate constants of electron transfer from the monomer radical anion to RF and FAD have been determined. On the basis of comparison of the interactions between DMUD and hydrated electron in the presence and absence of RF or FAD, a chain reaction process in the absence of RF or FAD has been demonstrated.
基金ProjectsupportedbytheNationalNaturalScienceFoundationofChina (No .30 0 0 0 0 36)andDoctoralProgrammefromtheStateEducationCom missionofChina .
文摘The oxidative splitting process of cis-syn 1,3-dimethyluracil cyclobutane dimer (DMUD) in aqueous solution was investigated using pulse radiolysis technique. The results indicated that DMUD can be splitted into 1,3-dimethyluracil (DMU) by OH radicals (OH ·) and Br_2 radical anions (Br ·-_2), but not by azide radicals (N ·_3). The oxidative mechanisms that an H-abstracted from DMUD for OH · oxidative splitting and an electron transfer from DMUD to Br ·-_2, were suggested. Related kinetic parameters were determined.
