Preparative isolation of pseudolaric acids A and B,and their glucosides from the root bark of Pseudolarix kaempferi using high‐speed counter‐current chromatography

In order to provide the chemical markers for the quality control of herbal medicines, four diterpenoids, pseudolaric acids A and B (PAA and PAB), and their glucosides were isolated from the methanol extract of the Chinese herb Pseudolarix kaempferi using high‐speed counter‐current chromatography (HSCCC). The diphase solvent system was n‐hexane/EtOAc/MeOH/H₂O which was used at two ratios (5:5:5:5 and 1:9:4:6 by volume) in the separation of pseudolaric acids and their glycosides, respectively. As a result, PAA (14 mg), PAB (129 mg), PAA‐O‐β‐D ‐glucopyranoside (8 mg, PAAG), and PAB‐O‐β‐D ‐glucopyranoside (42 mg, PABG) were obtained from 0.5 g of the crude extract. Their purities were determined to be above 97% by HPLC analysis. Their chemical structures were confirmed by ¹H and ¹³C NMR analysis or HPLC comparison with the reference compounds.     

Palladium-Catalyzed Fluorinative Bifunctionalization of Aziridines and Azetidines with gem-Difluorocyclopropanes

An unprecedented Pd-catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C−C and C−F bond cleavage of gem-difluorocyclopropanes, leading to various β,β′-bisfluorinated amines and β,γ-bisfluorinated amines. This reaction was achieved by incorporating a 2-fluorinated allyl group and a fluorine atom scissored from gem-difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2-fluorinated allyl palladium complex to generate η²-coordinated N-allyl aziridine followed by fluoride ligand transfer affording the final β- and γ-fluorinated amines.     

The Inhibition of Gastric Cancer Cells’ Progression by 23,24-Dihydrocucurbitacin E through Disruption of the Ras/Raf/ERK/MMP9 Signaling Pathway

Gastric cancer is considered to be one of the most common causes of cancer death worldwide due to its high recurrence and metastasis rates. The molecule 23,24-Dihydrocucurbitacin E (DHCE) is a cucurbitacin-derived tetracyclic triterpenoid compound that has anti-tumor activity, but the exact mechanism remains to be elucidated. This research aimed to explore the effects of DHCE on human gastric cancer cells and the possible mechanisms. The results showed that DHCE suppressed proliferation, migration, and invasion of gastric cancer cells, as well as induced apoptosis and G2/M phase arrest. Mechanistically, the potential targets and pathways of DHCE were predicted using database screening and verified using a molecular docking study, fluorescence staining, and Western blot. The results indicated that DHCE obviously inhibited the kinase activity of ERK2 via targeting its ATP-binding domain, destroyed F-actin microfilament, and reduced the expression levels of Ras, p-c-Raf, ERK, p-ERK, and MMP9 proteins. Collectively, our study demonstrated that DHCE suppressed gastric cancer cells’ proliferation, migration, and invasion through targeting ERK2 and disrupting the Ras/Raf/ERK/MMP9 signaling pathway. These properties make DHCE a promising candidate drug for the further design and development of novel and effective Ras/Raf/ERK/MMP9 pathway inhibitors for treating gastric cancer.     

trans‐(dl‐Isoleucinato‐N,O)[tris(2‐aminoethyl)amine‐κ4N]cobalt(III) diperchlorate

The racemic title compound, trans‐[N,N‐bis(2‐amino­ethyl)‐1,2‐ethanediamine‐κ⁴N]­(dl ‐isoleucinato‐N,O)­cobalt(III) di­per­chlor­ate, [Co(C₆H₁₈N₄)(C₆H₁₂NO₂)](ClO₄)₂, crystallizes in the enantiomorphous space group P2₁2₁2₁ with Z = 12 (Z′ = 3). Each of the three cations in the asymmetric unit represents a different chirality of the isoleucine ligand; two of them are R (or d ) and the third is the S (or l ) enantiomer. The mixture crystallizes in a so‐called unbalanced crystallization, in which the cations adopt a chiral array of composition RRS or SSR, depending on the crystal selected for data collection.     

The Effect of Backbone Stereochemistry on the Folding of Acyclic β2, 3‐Aminoxy Peptides

As a new type of foldamer, β‐aminoxy peptides have the ability to adopt novel β N? O turns or β N? O helices in solution. Herein, we describe a new subclass of β‐aminoxy peptide, that is, peptides of acyclic β^{2, 3}‐aminoxy acids (NH₂OCHR₁CHR₂COOH), in which the presence of two chiral centers provides insight into the effect of backbone stereochemistry on the folding of β‐aminoxy peptides. Acyclic β^{2, 3}‐aminoxy peptides with syn and anti configurations have been synthesized and their conformations investigated by NMR, IR, and circular dichroism (CD) spectroscopic, and X‐ray crystallographic analysis. The β N? O turns or β N? O helices, which feature nine‐membered rings with intramolecular hydrogen bonds and have been identified previously in peptides of β³‐ and β^{2, 2}‐aminoxy acids, are also predominantly present in the acyclic β^{2, 3}‐aminoxy peptides with a syn configuration and N? O bonds gauche to the C_α? C_β bonds in both solution and the solid state. In the acyclic β^{2, 3}‐aminoxy peptides with an anti configuration, an extended strand (i.e., non‐hydrogen‐bonded state) is found in the solid state, and several conformations including non‐hydrogen‐bonded and intramolecular hydrogen‐bonded states are present simultaneously in nonpolar solvents. These results suggest that the backbone stereochemistry does affect the folding of the acyclic β^{2, 3}‐aminoxy peptides. Theoretical calculations on the conformations of model acyclic β^{2, 3}‐aminoxy peptides with different backbone stereochemistry were also conducted to elucidate structural characteristics. Our present work may provide useful guidelines for the design and construction of new foldamers with predicable structures.     

Oligomers of a 5-carboxy-methanopyrrolidine β-amino acid. A search for order

CD spectra for homooligomers (n = 4, 6, 8) of (1S,4R,5R)-5-syn-carboxy-2-azabicyclo[2.1.1]hexane (MPCA), a methano-bridged pyrrolidine β-carboxylic acid, suggest an ordered secondary structure. Even in the absence of internal hydrogen bonding, solution NMR, X-ray, and in silico analyses of the tetramer are indicative of conformations with trans-amides and C(5)-amide-carbonyls oriented toward the C(4) bridgehead. This highly constrained β-amino acid could prove useful in the ongoing development of well-defined foldamers.     

Tryptophan-based peptides to synthesize gold and silver nanoparticles: a mechanistic and kinetic study

Synthetic oligopeptides with a tryptophan residue at the C-terminus have been used for the synthesis of gold and silver nanoparticles at pH 11. The tryptophan residue in the peptides is responsible for the reduction of metal ions to the respective metals, possibly through electron transfer. A mechanistic pathway has been proposed to explain the reductive properties of the tryptophan moiety of the peptide based on some spectroscopic techniques, such as UV-visible and fluorescence spectroscopy. This study reveals that some of the peptide molecules are converted to its corresponding ditryptophan, kynurenine form and some cross-linked products, all of which are highly fluorescent species. The resultant peptide-functionalized metal nanoparticles have also been characterized by UV-visible spectroscopy, transmission electron microscopy, and Fourier transform IR spectroscopy and thermogravimatric analysis.     

Insight into 6π Electrocyclic Reactions of 1,8‐Dioxatetraene

A variety of benzofuranone‐based spiroisochromenes were originally designed and synthesized to gain insight into the oxa‐6π electrocyclic reaction of cis,cis‐1,8‐dioxatetraene for the first time. The stability of the 1,8‐dioxatetraene intermediate is governed by its steric congestion and can be fine‐tuned through modification of the backbone structure, leading to the reactivity differences in the 6π electrocyclic reaction and the emergence of photochromic properties.     

Location of Si vacancies and [Ti(OSi)4] and [Ti(OSi)3OH] sites in the MFI framework: a large cluster and full ab initio study

Titanium silicalite-1 (TS-1) is an important catalyst for selective oxidation reactions. However, the nature and structure of the active sites and the mechanistic details of the catalytic reactions over TS-1 have not been well-understood, leaving a continuous debate on the genesis of active sites on the TS-1 surface in the literature. In this work, the location of Si vacancies and [Ti(OSi)(4)] and [Ti(OSi)(3)OH] sites in the MFI (Framework Type Code of ZSM-5 (Zeolite Socony Mobile-Five)) framework has been studied using a full ab initio method with 40T clusters with a Si:Ti molar ratio of 39:1. It was shown that the former four energetically favorable sites for Si vacancies are T6, T12, T4, and T8 and for Ti centers of [Ti(OSi)(4)] are T10, T4, T8 and T11, being partially the same sites. Whether by replacing Si vacancies or substituting the fully coordinated Si sites, the most preferential site for Ti is T10, which indicates that the insertion mechanism does not affect the favorable sites of Ti in the MFI lattice. For the defective [Ti(OSi)(3)OH] sites, it was found that the Si vacancy at T6 with a Ti at its neighboring T9 site (T6-def-T9-Ti pair) is the most energetically favorable one, followed by a T6-def-T5-Ti pair with a small energy gap. These findings are significant to elucidate the nature of the active sites and the mechanism of reactions catalyzed by TS-1 and to design the TS-1 catalyst.     

溶胶-凝胶法制备壳聚糖/SiO2杂化材料

以正丁酐（Butyric anhydride)、壳聚糖(Chitosan）、甲基丙烯酰氧基丙基三甲氧基硅烷（MPTMS）、正硅酸乙酯（TEOS）为原料,采用迈克尔加成反应合成了丁酰壳聚糖-MPTMS,配合酸催化sol-gel过程,制备了透明的壳聚糖/SiO2杂化材料,FTIR表征了杂化材料的结构。TGA,SEM以及力学性能测试结果表明,杂化材料的成型工艺对材料的表面形貌、热分解温度以及力学性能的影响显著。