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天然药化2DNMR

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1、2D - NMR,Why Use 2D NMR,Just have a look at this 1D NMR spectrum of a protein:,1D protein spectra are far too complex for interpretation as most of the signals overlap heavily.,By the introduction of additional spectral dimensions these spectra are simplified and some extra information is obtained.,Introduction,The two dimensional (2D) NMR spectroscopy is based on the pulse variant briefly described in the previous section (1D-NMR). 2D NMR that there are two time variables, Generally the second

2、time that the variable sampling time t2, the first time variable t1 and t2 is independent of the independent variable is the pulse sequence changes in a certain time interval.,Anatomy of a 2D experiment,The construction of a 2D experiment is simple: In addition to preparation and detection which are already known from 1D，the 2D experiment has an indirect evolution time t1 and a mixing sequence.,Basic Pulse Scheme,Spectrum form,1. Accumulation map 2. Contour map 3. Projection,Classification,J-dec

3、omposition (2DJ) spectrum It separates the chemical shifts and coupling constants . Chemical shift correlation spectroscopy It shows the relevance of resonance signals ,including HOMO-COSY、HETCOR、NOESY Etc. Multi-quantum spectrum Determination of the NMR line usually single-quantum transition (m = 1). Pulse sequence used to detect when multiple quantum transitions, m integer greater than 1.,HOMO-COSY,Both axes correspond to the proton NMR spectra. The COSY spectra indicates which 1H atoms are co

4、upling with each other.,HETCOR,Proton NMR spectra on one axis and the 13C NMR spectra on the other. The HETCOR spectra matches the H to the appropriate C.,NOESY,A 2D NMR technique where the cross-peak appear between protons are within 6 of each other,the closer in space the two protons are to each other the more intense the cross peak. It is commonly used in protein analysis.,EXAMPLE,Polysciasoside A(1)是美国 Mississippi 大学 E.Bedir 等人从非洲中部山林里的一种药用植物Polysciasfulva 叶子里分离获得的一个新三萜糖苷化合物,结构如图：,根据1H NMR、 13CNMR、 TOCSY（总相关谱）和 HMQC（一种异核位移相关谱）的结果发现:含两个糖结构片段 ,根据其化学位移值、信号峰型和耦合常数即可确定两糖分别为吡喃鼠李糖和吡喃葡萄糖 ,并由 HMBC （一种异核位移相关谱,能反映跨越两三根化学键的13C 和1H 核之间的耦合关系）的结果得出两糖的连接顺序。再根据DEPT 信息 ,确定剩下的只能为四个环结构。,由TOCSY和 HMQC 推断出该配基含A、 B、 C、 D、 E五个自旋体系,再根据 HMBC一些关键的关叉峰将这五个结构片段和余下的几个季碳连成一体 ,即得到四环的三萜配基结构。这样便得出了整个糖苷的初步结构。,剩下的工作是确定立体化学,这主要由NOESY完成。一些关键的 NOESY交叉峰 , 等说明了哪些质子是共平面的 ,哪些质子占据了分子的面等等 ,从而证明该三萜配基具有 A/B 反 ,B/C反和 C/ D 反的环接方式。这样整个分子的立体化学便确定了下来。,(o)/,Thank you!,

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