A new taxane composed of two N-formyl rotamers from Taxus canadensis

A taxane with an amino-side chain on C-5 was identified for the first time from rooted cuttings of the Canadian yew, Taxus canadensis. The structure was characterized as 7β,9α,10β,13α-tetraacetoxy-5α-[3′-(N-formyl-N-methylamino)-3′-phenylpropanoyl]oxytaxa-4(20),12-diene (1) on the basis of 1D-, 2D-NMR data, and HR-FABMS analyses. The spectra revealed that in CDCl₃ solution 1 was composed of two rotamers (1a and 1b) in a ratio of approximately 2:1.     

Oplopanphesides A-C, three new phenolic glycosides from the root barks of Oplopanax horridus

Three new phenolic glycosides, named oplopanphesides A-C (1-3), have been isolated from the root barks of Oplopanax horridus. Their structures were elucidated by a combination of spectroscopic analyses, including 1D- and 2D-NMR techniques. These phenolic glycosides possess a novel feature in their sugar moieties that a 3-hydroxy-3-methylglutaryl moiety was connected with C-6 of the β-D-glucopyranosyl group. Those compounds showed no cytotoxic effects against human cancer cell lines (MDA-231 and MCF-7) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method.     

Efficient iron(III)-catalyzed three-component coupling reaction of alkynes, CH2Cl2 and amines to propargylamines

An iron(III)-catalyzed three-component coupling reaction of alkynes, CH(2)Cl(2) and amines was developed for facile synthesis of propargylamines. Preliminary mechanism investigation using in situ FT-IR reveals that the crucial Fe-acetylide intermediate could be formed through C-H bond activation of alkynes thanks to cooperative effect of FeCl(3) and 1,1,3,3-tetramethylguanidine.     

Enantioseparation and absolute configuration determination of angular-type pyranocoumarins from peucedani radix using enzymatic hydrolysis and chiral HPLC-MS/MS analysis

Angular-type pyranocoumarins from Peucedani Radix (Chinese name: Qian-hu) have exhibited potential for use on treatment of cancer and pulmonary hypertension. Due to the existence of C-3' and C-4' chiral centers, compounds belonging to this chemical type commonly exist in enantiomers and/or diastereoisomers, which may elicit distinct activities during their interactions with the human body. In the present study, a new method, which combines enzymatic hydrolysis with chiral LC-MS/MS analysis, has been developed to determine the absolute configurations of these angular-type pyranocoumarins. Pyranocoumarins isolated from Qian-hu, their enantiomers, or metabolites were individually incubated with rat liver microsomes. As the common end product from enzymatic hydrolysis of all tested pyranocoumarins, cis-khellactone was collected and its absolute configuration was determined by comparison with (+)-cis-khellactone and (-)-cis-khellactone using chiral LC-MS/MS. The absolute configurations of all tested parent pyranocoumarins were determined by combination of LC-MS/MS, NMR and polarimetric analysis. The results revealed that the metabolite cis-khellactone retained the same absolute configurations of the stereogenic carbons as the respective parent compound. This method was proven to be rapid and sensitive and also has advantages in discriminating single enantiomers and mixtures of optical isomers with different ratios.     

Fabrication and characterization of 4H—SiC bipolar junction transistor with double base epilayer

In this paper we report on a novel structure of a 4H-SiC bipolar junction transistor with a double base epilayer that is continuously grown.The measured dc common-emitter current gain is 16.8 at IC = 28.6 mA(J C = 183.4 A/cm2),and it increases with the collector current density increasing.The specific on-state resistance(Rsp-on) is32.3mΩ·cm 2 and the open-base breakdown voltage reaches 410 V.The emitter N-type specific contact resistance and N + emitter layer sheet resistance are 1.7×10-3 Ω·cm2 and 150 /,respectively.     

5,6-Didehydroginsenosides from the roots of Panax notoginseng

Two minor novel dammarane-type saponins - 5,6-didehydroginsenoside Rd (1) and 5,6-didehydroginsenoside Rb1 (2) - were isolated from the dried roots of Panax notoginseng along with sixteen known saponins. The structures of the new compounds were elucidated on the basis of spectroscopic and chemical methods.     

Four new epoxy taxanes from needles of Taxus cuspidata (Taxaceae)

Four new epoxy taxoids were isolated from the needles of Taxus cuspidata. Their structures were established as 2a,9a-diacetoxy-5a-cinnamoyloxy-11,12-epoxy-10ss-hydroxytax-4(20)-en-13-one (1), 2a,10ss-diacetoxy-5a-cinnamoyloxy-11,12-epoxy-9a-hydroxytax-4(20)-en-13-one (2), 2a,9a-diacetoxy-11,12-epoxy-10ss,20-dihydroxytax-4-en-13-one (3) and 2a,10ss-diacetoxy-11,12-epoxy-9a,20-dihydroxytax-4-en-13-one (4) on the basis of spectral analysis including 1H-NMR, 13C-NMR, 1H-1H-COSY, HSQC, HMBC and HRFABMS. Compounds 3 and 4 are the first example of 11,12-epoxy taxoids with C-4 double bond found in T. cuspidata.     

琼脂糖凝胶电泳法分离金属性和半导体性单壁碳纳米管

琼脂糖凝胶电泳(AGE)是实现金属性单壁碳纳米管(m-SWCNTs)和半导体性单壁碳纳米管(s-SWCNTs)低成本、规模化分离的有效技术之一。本研究利用琼脂糖凝胶电泳分离单壁碳纳米管。通过紫外-可见-近红外吸收光谱和拉曼光谱对色谱带进行分段表征,发现电泳中迁移的最快的部分m-SWCNTs含量最高。考察了琼脂糖的浓度对SWCNTs中m-SWCNTs分离的影响。结果表明:高的琼脂糖浓度有利于m-SWC-NTs的富集,可以通过扩大电荷密度带来的迁移速率的差异来使SWCNTs中的m-SWCNTs得到更有效的分离。     

面向地壳形变观测的超高分辨率光纤应变传感系统

高分辨率光纤应变传感系统是地球物理学中地壳微弱形变观测的有力工具.相比于传统的地壳应变观测技术,光纤应变传感器具有测量分辨率高、抗干扰能力强、尺寸小、可复用、易于安装布设等特性,在建立新型地壳形变监测网络中具有很大的应用潜力.本文围绕面向地壳形变观测的纳应变级分辨率光纤应变传感器技术,阐述了应变传感原理与实现超高测量分辨率的机理,并详细介绍了扫频探测、Pound-Drever-Hall解调技术、边带探测、双回路锁定传感、传感器时分复用等技术及相应的传感器系统实现方案,最后,给出了超高分辨率光纤传感器在现场观测的实验结果与分析.