Palladium-Catalyzed Enantioselective Directed C(sp3)-H Functionalization Using C5-Substituted 8-Aminoquinoline Auxiliaries.

8-Aminoquinoline (AQ) has proven to be a highly effective bidentate directing group for palladium-catalyzed C-H functionalization reactions. However, enantiocontrol of AQ-directed C(sp3)-H functionalization reactions has been challenging. Herein, a new protocol is presented for the Pd-catalyzed enantioselective arylation of unactivated ß C(sp3)-H bonds of alkyl carboxamides with aryl iodides using a C5-iodinated 8-aminoquinolines (IQ) auxiliary in conjugation with a BINOL ligand. Additionally, a C5-aryl substituted 8-aminoquinoline auxiliary can facilitate enantioselective alkenylation and alkynylation of benzylic C(sp3)-H bonds of 3-arylpropanamides with the corresponding bromide reagents under similar conditions.

Analysis of taste characteristics and identification of key chemical components of fifteen Chinese yellow tea samples.

In order to explore the taste characteristics and molecular sensory basis of Chinese yellow tea, in this study, quantitative descriptive analysis (QDA) and partial least squares regression (PLSR) were used to analyze the sensory characteristics and chemical components of 15 yellow tea samples from different regions of China. The results showed that: 11 sensory descriptors and their definitions were obtained by QDA, namely, sweet, umami, bitter, sour, astringent, sweet after taste, mellow, neutral, after-taste, thick and tainted taste. The results of variance indicated that there were significant variation in taste sub-attributes of different samples (p <0.05). Principal component analysis indicated that there was a positive correlation between bitter and astringent, between sweet, umami and sour, and between mellow, thick, after-taste and neutral. All yellow tea samples were divided into four categories according to cluster analysis. The results of PLSR showed that there were 22 chemical components that had an important contribution to the taste characteristics of yellow tea, and the chemical components that had an important influence on each taste component were obtained. The identification of key contribution components of taste characteristics in yellow teas will provide a theoretical basis for further research on the directional adjustment and control of tea taste quality.

Monitoring the authenticity of pu'er tea via chemometric analysis of multielements and stable isotopes.

Mineral elements and stable isotopes combined with stoichiometric methods were used as a potential tool for first authenticating Chinese tea according to it's production year. A total of 86 mineral elements and stable isotope compositions were determined from the Xiangzhujing Pu'er tea in five different production years using ICP-MS and ICP-OES. On the basis of 78 statistically significant mineral elements and stable isotopes, HCA, PCA, PLS-DA, BP-ANN, and LDA were employed to build authentication models for predicting the Pu'er tea with different production years. The clustering results of the HCA and PCA were worse than that of PLS-DA, BP-ANN, and LDA. The PLS-DA model displayed a perfect model performance (R2X = 0.86, R2Y = 0.974, and Q2 = 0.922). The authentication performance of LDA and BP-ANN revealed their 100% recognition sensitivity and prediction ability and was thus better than that of PLS-DA. Mn, 68Zn, and 203Tl were the markers for enabling the successful authentication of Pu'er tea with different production years. This study contributes toward generalizing the use of mineral element and stable isotope fingerprinting combined with LDA and BP-ANN as a promising tool for authentication of tea worldwide.

Improved geographical origin discrimination for tea using ICP-MS and ICP-OES techniques in combination with chemometric approach.

BACKGROUND: There is an urgent need to strengthen the testing and certification of geographically iconic foods, as well as to use discriminatory science and technology for their regulation and verification. Multi-element and stable isotope analyses were combined to provide a new chemometric approach for improving the discrimination tea samples from different geographical origins. Different stoichiometric methods [principal component analysis (PCA), hierarchical cluster analysis (HCA), partial least squares-discriminant analysis (PLS-DA), back propagation based artificial neural network (BP-ANN) and linear discriminant analysis (LDA)] were used to demonstrate this discrimination approach using Yongchuanxiuya tea samples in an experimental test. RESULTS: Multi-element and stable isotope analyses of tea samples using inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectrometry easily distinguished the geographical origins. However, the clustering ability of the two unsupervised learning methods (PCA and HCA) were worse compared to that of the three supervised learning methods (PLS-DA, BP-ANN and LDA). BP-ANN and LDA, with 100% recognition and prediction abilities, were found to be better than PLS-DA. 86 Sr and 112 Cd were the markers enabling the successful classification of tea samples according to their geographical origins. Under the validation by 'blind' dataset, the prediction accuracies of the BP-ANN and LDA methods were all greater than 90%. The LDA method showed the best performance, with an accuracy of 100%. CONCLUSION: In summary, determination of mineral elements and stable isotopes using inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectrometry techniques coupled with chemometric methods, especially the LDA method, is a good approach for improving the authentication of a diverse range of tea. The present study contributes toward generalizing the use of fingerprinting mineral elements and stable isotopes as a promising tool for testing the geographic roots of tea and food worldwide. © 2020 Society of Chemical Industry.

The Effect of Different Treatments of (-)-Epigallocatechin-3-Gallate on Colorectal Carcinoma Cell Lines.

Backgroud: (-)-Epigallocatechin-3-gallate (EGCG), the major component of green tea, is well documented to induce apoptosis and cell cycle arrest in cancer by targeting multiple signal transduction pathways. However, EGCG is extremely unstable in general culture conditions and rapidly degraded. So, to what extent EGCG or which degradation products of EGCG play a role in anti-tumor is still unknown. In this study, we evaluated the effect of different treatments of EGCG on HCT116 cells. DESIGN: MTT assay was applied to evaluated the inhibitory effect of different treatments of EGCG on HCT116 cells. Cell cycle and apoptosis were performed by flow cytometry. Finally, western blot analysis was used to elucidate the molecular mechanism associated with cell cycle arrest and apoptosis. RESULTS: Compared with control, both EGCG and O-EGCG (i.e., EGCG being pre-incubated at 37°C for 3 h) significantly inhibited HCT116 cells growth. Surprisingly, we found that the inhibitory effect of O-EGCG was stronger than that of EGCG. The IC50 values of EGCG and O-EGCG were 8.75 and 5.40 µM, respectively. Cell cycle analysis showed that 20 µM of EGCG simultaneously caused cell cycle arrest at G1 and G2 phase in HCT116 cells, differing from O-EGCG which exclusively caused cell cycle arrest at G2. This result suggested that parent EGCG at the early treatment might cause cell cycle arrest at G1. As time went on, EGCG disappeared and degraded products of EGCG were formed which might cause cell cycle arrest at G2. Further studies revealed that EGCG induced cell cycle arrest at G1 by downregulation of cyclin E and cyclin D1 and upregulation of p21. On the other hand, O-EGCG induced HCT116 cells apoptosis mainly by increasing the expression of p53 and cleaved caspase-3, which might be the underlying reason why O-EGCG had stronger inhibitory effect on HCT116 cells line than EGCG. CONCLUSIONS: The pretreatment of EGCG may be an effective way to enhance its antitumor effect.

[Progress in catechins oxidation products and their formation mechanism].

Catechins are the key components of tea and have a great impact on its quality. Catechins can be oxidized to form a new black tea polyphenols, some of which have better pharmacological effect. However, the formation mechanism of these new polyphenols is still unclear. In this paper, oxidation products coming from catechins and the formation mechanism of the new compounds are reviewed.It is the base of further study on theaflavins, thearubigins and theabrownines.

An Enantioselective Bidentate Auxiliary Directed Palladium-Catalyzed Benzylic C-H Arylation of Amines Using a BINOL Phosphate Ligand.

A new enantioselective palladium(II)-catalyzed benzylic C-H arylation reaction of amines is enabled by the bidentate picolinamide (PA) directing group. This reaction provides the first example of enantioselective benzylic γ-C-H arylations of alkyl amines, and proceeds with up to 97 % ee. The 2,2'-dihydroxy-1,1'-binaphthyl (BINOL) phosphoric acid ligand, Cs2 CO3 , and solvent-free conditions are essential for high enantioselectivity. Mechanistic studies suggest that multiple BINOL ligands are involved in the stereodetermining C-H palladation step.