Heterocycloaddition of thermally generated 1,2-diaza-1,3-butadienes to [60]fullerene

Stable C₆₀-fused tetrahydropyridazine derivatives were synthesized through the hetero-Diels-Alder cycloaddition of C₆₀ with 1,2-diaza-1,3-butadienes, which were generated in situ by the thermal extrusion of sulfur dioxide from 2,5-dihydro-1,2,3-thiadiazole-1,1-dioxides.     

Construction of diverse peptide structural architectures via chemoselective peptide ligation

Herein, we report the development of a facile synthetic strategy for constructing diverse peptide structural architectures via chemoselective peptide ligation. The key advancement involved is to utilize the benzofuran moiety as the peptide salicylaldehyde ester surrogate, and Dap–Ser/Lys–Ser dipeptide as the hydroxyl amino functionality, which could be successfully introduced at the side chain of peptides enabling peptide ligation. With this method, the side chain-to-side chain cyclic peptide, branched/bridged peptides, tailed cyclic peptides and multi-cyclic peptides have been designed and successfully synthesized with native peptidic linkages at the ligation sites. This strategy has provided an alternative strategic opportunity for synthetic peptide development. It also serves as an inspiration for the structural design of PPI inhibitors with new modalities.

Methods of introducing peptide salicylaldehyde esters and hydroxyl amine functionality into the peptide side chain have been developed. Diverse peptide structural motifs were constructed via ligation with native amide linkages at the ligation sites.     

Complexation of silver and co-recovered metals with novel aza-crown ether macrocycles by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is used to evaluate the metal binding selectivities of an array of novel caged macrocycles for silver, gold, copper, nickel, zinc, iron, lead, manganese and alkali metal ions. It is found that five of the new compounds display silver selectivity, and their relative affinities for various metals depend on the type, number, and arrangement of heteroatoms (N, O), the cavity size, and the presence of aromatic substituents. Alkali metal cation binding studies are used to evaluate the size-selectivities of the cavities of the macrocycles. Electronic structure calculation by B3LYP density function theory methods were used to model the metal complexes. The presence of nitrogen atoms in the macrocyclic ring is essential for silver selectivity over other transition metals and alkali metal ions, and the presence of aromatic groups also enhances silver avidity. Macrocycle 3, a triaza-18-crown-6 analog modified with two phenyl groups and a cage group, is capable of selective extraction of Ag+ from aqueous solutions in the presence of other transition metal ions and the most common alkali and alkaline earth metal ions.     

Hyperoxygenation enhances the tumor cell killing of photofrin-mediated photodynamic therapy

Tumor hypoxia, either preexisting or as a result of oxygen depletion during photodynamic therapy (PDT) light irradiation, can significantly reduce the effectiveness of PDT-induced cell killing. To overcome tumor hypoxia and improve tumor cell killing, we propose using supplemental hyperoxygenation during Photofrin-PDT. The mechanism for the tumor cure enhancement of the hyperoxygenation-PDT combination is investigated using an in vivo-in vitro technique. A hypoxic tumor model was established by implanting mammary adenocarcinoma in the hind legs of mice. Light irradiation (200 J/cm2 at either 75 or 150 mW/cm2), under various oxygen supplemental conditions (room air, carbogen, 100% normobaric or hyperbaric oxygen), was delivered to animals that received 12.5 mg/kg Photofrin 24 h before light irradiation. Tumors were harvested at various time points after PDT and grown in vitro for colony formation analysis. Treated tumors were also analyzed histologically. The results show that when PDT is combined with hyperoxygenation, the hypoxic condition could be improved and the cell killing rate at various time points after PDT could be significantly enhanced over that without hyperoxygenation, suggesting an enhanced direct and indirect cell killing associated with high-concentration oxygen breathing. This study further confirms our earlier observation that when a PDT treatment is combined with hyperoxygenation it can be more effective in controlling hypoxic tumors.     

Synthesis of the JKLM-ring fragment of ciguatoxin

A stereoselective synthesis of the LM-ring fragment has been achieved starting from a sugar derivative. A stereoselective synthesis of the JKLM-ring fragment has been achieved through a coupling between two segments via heteroconjugate addition, seven-membered ether ring formation mediated by an acetylene cobalt complex, and spiroketalization reaction.     

Four‐ and Five‐Coordinate Gallium Complexes Stabilized by Bidentate 2‐(Dimethylaminomethyl)Pyrrole Ligand: Molecular Structures of Ga[NC4H3(CH2NMe2)‐2]3 and GaMe2[NC4H3(CH2NMe2)‐2]

Treatment of GaCl₃ with one equiv of Li[NC₄H₃(CH₂NMe₂)‐2] (n = 1, 2, 3) in diethyl ether at ?78 °C yields GaCl_3‐n[NC₄H₃(CH₂NMe₂)‐2]_n (n = 1, 1 ; n = 2, 2 ; n = 3, 3 ). Compound 1 reacts with two equiv of RLi to afford GaR₂[NC₄H₃(CH₂NMe₂)‐2] ( 4a, R=Me; 4b, R=Bu ) via transmetallation. Reacting 2 with one equiv of RLi in diethyl ether, 3 and 4 are formed via ligand redistribution. Variable temperature ¹H NMR spectroscopic experiments reveal that the five‐coordinate gallium compound 3 is fluxional and results in a coalescence temperature at 5 °C, at which ΔG^≠ is calculated at ca. 10.4 Kcal/mole. All the new compounds have been characterized by ¹H and ¹³C NMR spectroscopy and the structures of compounds 3 and 4a have also been determined by X‐ray crystallography.     

“双一流”背景下高等农业院校有机化学基础课程教学新模式的构建及实践

The crop science of Sichuan Agricultural University is an authorized first-class discipline. As the strategic supporting department for innovative talent cultivation in agriculture and forestry major, we are facing a long-term challenge in reforming the teaching mode for basic course-organic chemistry and cultivating talented students with solid basic knowledge and strong sense of innovation. Herein a thorough survey was performing to establish the executable teaching programs for this course during the "Double-First Class Universities Plan" period. A multidimensional teaching resource library for organic chemistry course was also constructed. The new classroom teaching mode "Interest cultivation-Creative thought development-Autonomous and Cooperative learning", along with a stepwise practice teaching mode "Foundation skills-Integrated application-Innovative trial" was proposed and practiced among thirty-five majors including agriculture, forestry and veterinary, to improve the quality for innovative talent cultivation and support our first-class discipline construction. This research could probably serve as a reference for congeneric agricultural university.     

Organotitanium chemistry 12. Synthesis of some new chiral cyclopentadienyl titanium and zirconium complex. The crystal structure of (S-cyclo-C4H7OCH2Cp)2TiCl2

Summary New chiral cyclopentadienyl-titanium and-zirconium complexes Cp₂TiCl₂, CpCpTiCl₂ and Cp₂ZrCl₂ (Cp=⁵ -cyclopentadienyl and Cp=substituted cyclopentadienyl), have been synthesized. The (S,S)-3 complex, which forms red plate crystals, has been studied by x-ray analysis. It belongs to the monoclinic space groupC2, witha 23.963(3),b 6.6470(6),c 12.6618(9) Å, 103.089(7)°, V=1964.4(3) ų and Z=4. The structure was relined to an R factor of 0.048 for 868 observed reflections.     

CrO3在γ-Al2O3和SiO2载体表面的分散状态

用X光衍射(XRD)方法研究了CrO_3/SiO_2和CrO_3/γ-Al_2O_3体系。用相定量外推法测定活性组份在载体表面的最大分散量。在干燥气氛中将CrO_3与载体混合, 并在低于CrO_3熔点的温度下烘烤制备样品, 实验得到CrO_3在SiO_2或者γ-Al_2O_3表面的最大分散量都随温度的升高而增大。CrO_3在SiO_2表面的最大分散量由101 ℃的0.27gCrO_3/g SiO_2到170 ℃的0.38g CrO_3/g SiO_2; CrO_3在γ-Al_2O_3表面的最大分散量由120 ℃的0.22g CrO_3/g γ-Al_2O_3到171 ℃的0.42g CrO_3/g γ-Al_2O_3。CrO_3在SiO_2或γ-Al_2O_3表面的最大分散量超过密置单层量, 可由易聚合形成同多酸根来解释。     

Pseudo-MS3 in a MALDI orthogonal quadrupole-time of flight mass spectrometer

Both the matrix selected and the laser fluence play important roles in MALDI-quadrupole/time of flight (QqTOF) fragmentation processes. "Hot" matrices, such as alpha-cyano4-hydroxycinnamic acid (HCCA), can increase fragmentation in MS spectra. Higher laser fluence also increases fragmentation. Typical peptide fragment ions observed in the QqTOF are a, b, and y ion series, which resemble low-energy CID product ions. This fragmentation may occur in the high-pressure region before the first mass-analyzing quadrupole. Fragment ions can be selected by the first quadrupole (Q1), and further sequenced by conventional MS/MS. This allows pseudo-MS3 experiments to be performed. For peptides of higher molecular weight, pseudo-MS3 can extend the mass range beyond what is usually accessible for sequencing, by allowing one to sequence a fragment ion of lower molecular weight instead of the full-length peptide. Peptides that predominantly show a single product ion after MS/MS yield improved sequence information when this technique is applied. This method was applied to the analysis of an in vitro phosphorylated peptide, where the intact enzymatically-generated peptide showed poor dissociation via MS/MS. Sequencing a fragment ion from the phosphopeptide enabled the phosphorylation site to be unambiguously determined.