铜催化α-重氮酮对硼氢键的不对称插入反应

手性有机硼化合物在有机合成、医药、材料等诸多领域中有广泛的应用,发展该类化合物的高效合成方法一直广受关注.此前,我们发展了过渡金属催化卡宾对硼氢键(B—H)的插入反应,并实现了α-重氮酯对B—H键的不对称插入反应.本文以手性螺环双噁唑啉配体和铜的络合物作为催化剂,首次实现了α-重氮酮对膦-硼烷加合物的B—H键不对称插入反应,获得了较高的收率和高达83%ee的对映选择性.该研究成果是为数不多的以α-重氮酮作为卡宾前体的不对称杂原子氢键插入反应,为手性α-硼取代酮化合物这类新的有机硼化合物的合成提供了有效方法.     

3-Hydroxymethylglutaryl flavonol glycosides from a Mongolian and Tibetan medicine, Oxytropis racemosa

Three new flavonol 3-O-glycosides, rhamnetin 3-O-[(S)-3-hydroxy-3-methyl-glutaroyl(1→6)]-β-D-glucopyranoside (1), rhamnocitrin 3-O-[(S)-3-hydroxy-3-methylglutaroyl(1→6)]-β-D-glucopyranoside (2), and isorhamnetin 3-O-[(S)-3-hydroxy-3-methylglutaroyl(1→6)]-α-L-rhamnopyranosyl(1→2)-β-D-glucopyranoside (3), along with 13 known compounds, were isolated from Oxytropis racemosa TURCZ. Their structures were deduced by means of spectroscopic methods and chemical evidence. 2 and 6 showed cytotoxic activities against HCT-8 (IC?? 6.38 μM) and A549 (IC?? 5.20 μM), respectively.     

Theoretical Study of the Substituent Effects on the Nonlinear Optical Properties of a Room‐Temperature‐Stable Organic Electride

Excess‐electron compounds can be considered as novel candidates for nonlinear optical (NLO) materials because of their large static first hyperpolarizabilities (β₀). A room‐temperature‐stable, excess‐electron compound, that is, the organic electride Na@(TriPip222), was successfully synthesized by the Dye group (J. Am. Chem. Soc. 2005 , 127, 12416). In this work, the β₀ of this electride was first evaluated to be 1.13×10⁶ au, which revealed its potential as a high‐performance NLO material. In particular, the substituent effects of different substituents on the structure, electride character, and NLO response of this electride were systemically studied for the first time by density functional theory calculations. The results revealed that the β₀ of Na@(TriPip222) could be further increased to 8.30×10⁶ au by introducing a fluoro substituent, whereas its NLO response completely disappeared if one nitryl group was introduced because the nitro‐group substitution deprived the material of its electride identity. Moreover, herein the dependence of the NLO properties on the number of substituents and their relative positions was also detected in multifluoro‐substituted Na@(TriPip222) compounds.     

Efficient Regioselective Synthesis of the Crotonyl Polydatin Prodrug by <Emphasis Type="Italic">Thermomyces lanuginosus</Emphasis> Lipase: a Kinetics Study in Eco-friendly 2-Methyltetrahydrofuran

Bio-based solvents have recently been discussed as sustainable green and promising alternatives to conventional organic media for enzymatic processes. In this paper, highly regioselective synthesis of the 6″-O-crotonyl-polydatin catalyzed by Thermomyces lanuginosus lipase (TLL) in biomass-derived 2-methyltetrahydrofuran (2-MeTHF) was successfully performed for the first time. The results indicated that TLL lipase displayed significantly improved catalytic performance in 2-MeTHF than in other traditional solvents. Under the optimal conditions, the initial reaction rate, 6″-regioselectivity, and maximum substrate conversion were as high as 12.38 mM h^?1, 100 %, and 100 %, respectively. Moreover, further investigations on the operational stability, kinetic parameters like V _max, K _m, V _max/K _m, and E _a revealed that 2-MeTHF exhibited excellent biocompatibility and rendered the greener process of the enzymatic acylation.     

相转移催化氧化合成苯甲酸

苯甲酸一般由甲苯氧化而成 ,工业上采用液相空气氧化生产苯甲酸[1 ] 。ＫＭｎＯ4氧化甲苯制备苯甲酸的方法是在实验室中最常见的一种方法[2 ] ,该法的优点是反应条件温和 ,操作简便 ;其缺点是反应时间长 ,产率低 (低于 40 % ) [3] 。为了提高ＫＭｎＯ4氧化法的产率 ,本文采用十六烷基三丁基溴化磷 (ＨＤＴＢＰ)和苄基三乙基氯化铵(ＢＴＥＡ)作相转移催化剂氧化甲苯制备苯甲酸 ,具有时间短 ,收率高等优点。同时又考虑到ＨＤＴＢＰ的催化效果虽然好 ,但价格昂贵 ,因此本文采用价廉易得的苄基三乙基氯化铵 (ＢＴＥＡ)作相转移催化剂氧化甲苯制…     

Bioorthogonal SERS Nanoprobes for Mulitplex Spectroscopic Detection,Tumor Cell Targeting,and Tissue Imaging

A surface‐enhanced Raman scattering (SERS) technique shows extraordinary features for a range of biological and biomedical applications. Herein, a series of novel bioorthogonal SERS nanoprobes were constructed with Gold nanoflower (AuNF) and Raman reporters, the signals of which were located in a Raman‐silent region of biological samples. AS1411 aptamer was also co‐conjugated with AuNF through a self‐assembled monolayer coverage strategy. Multiplex SERS imaging using these nanoprobes with three different bioorthogonal small‐molecule Raman reporters is successfully achieved with high multiplexing capacity in a biologically Raman‐silent region. These Raman nanoprobes co‐conjugated with AS1411 showed high affinity for tumor cells with overexpressed nucleolin and can be used for selective tumor cell screening and tissue imaging.     

Quantitative analysis of thymine with surface-enhanced Raman spectroscopy and partial least squares (PLS) regression

Silver sol surface-enhanced Raman spectroscopy (SERS) was considered as a technique in the quantitative analysis of low-concentration thymine. Because of the poor stability and reproducibility of SERS signal, a polymer of polyacrylic acid sodium was selected as a stable medium to add into silver sol in order to obtain a surface-enhanced Raman spectroscopy signal. Assignments of Raman shift for solid thymine, SERS of thymine, and SERS of thymine containing stable medium were given. The comparison of Raman peaks between them showed that the addition of stable medium had a little influence on the SERS of thymine and is suitable for the quantitative analysis of low-concentration thymine.     

Comparative performance study of ICP mass spectrometers by means of U “isotopic measurements”

The performance of four commercially available ICPMS instruments of three different types was compared by means of uranium “isotopic measurements”. Examined were two quadrupole sector (different generation, different manufacturer), one single detector double focusing magnetic sector and one multiple collector double focusing magnetic sector instruments. The same samples of the IRMM-072 series were used under routine conditions to measure the ²³³U/²³⁵U and the ²³³U/²³⁸U ratios which, in these samples, vary over almost three orders of magnitude from ～ 1 to ～ 2 · 10^–3. Within expanded (k = 2) uncertainties, good agreement was observed between the certified values and the data internally corrected for mass-discrimination effects. The magnitude of the evaluated uncertainties was different for each type of instrument. With the multiple collector instrument, expanded uncertainties varied from ± 0.04% to± 0.24% for the ²³³U/²³⁵U ratio, and from ± 0.08% to ± 0.27% for the ²³³U/²³⁸U ratio. They were ～ 1 to 5 times larger with the single detector magnetic sector instrument, and ～ 10 to 25 times larger with both quadrupole sector instruments. With the multiple collector instrument, repeatability of the measurements seemed to be limited by the difficulty of correcting properly for instrumental background, whereas with the single detector magnetic sector instrument the counting statistics was the only limitation (on smallest ratios). Apparent mass-discrimination was clearly found to be larger but more reproducible (and hence easier to correct for) in the case of magnetic sector instruments than for both quadrupole sector instruments. If space charge effects were the main source of mass-discrimination for all instruments, these results are in contradiction with the hypothesis of the size of mass-discrimination decreasing with the acceleration voltage. With the single detector magnetic sector instrument in particular (when operated by changing the ion energy only), our results pointed at more than only one major source of mass-discrimination, with variable size depending on the ratios measured.