Trifunović Snezana, Milosavljević Slobodan, Vajs Vlatka, Macura Slobodan, Todorović Nina
Faculty of Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia.
Magn Reson Chem. 2008 May;46(5):427-31. doi: 10.1002/mrc.2193.
From detailed study of 1D and 2D NMR spectra of ten natural 1,2-epoxyguaianolides (bis-1,2:3,4-epoxyguaianolides and guaianolide-1,2-epoxychlorohydrins), we identified general spectral traits helpful for stereochemical assignment of such sesquiterpene lactones. We found that the chemical shifts of certain (1)H and (13)C nuclei are consistently dependent on the configuration of 1,2-epoxy-ring which could be used as a simple rule for establishing this configuration. Then, from 1D and 2D (COSY, NOESY, HMQC, HMBC) NMR data, applying the observed rule, the structure and stereochemistry of two new, diastereomeric guaianolide-1,2-epoxychlorohydrins, isolated from Achillea serbica, are determined. The NMR data, namely, nuclear overhauser enhancement (NOE) correlations, pointed out two conformations of guaianolide's cycloheptane ring. The semiempirical calculations (AM1 and PM3 methods), performed in order to gain additional information regarding conformations, resulted in three geometries of investigated lactones. Even so, the conformations derived from the NMR data agreed well with those calculated by semiempirical methods.
通过对十种天然1,2-环氧愈创木内酯（双-1,2:3,4-环氧愈创木内酯和愈创木内酯-1,2-环氧氯醇）的一维和二维核磁共振谱进行详细研究，我们确定了有助于对此类倍半萜内酯进行立体化学归属的一般光谱特征。我们发现某些氢（1H）和碳（13C）原子核的化学位移始终取决于1,2-环氧环的构型，这可作为确定该构型的一条简单规则。然后，根据一维和二维（COSY、NOESY、HMQC、HMBC）核磁共振数据，应用观察到的规则，确定了从塞尔维亚蓍草中分离出的两种新的非对映体愈创木内酯-1,2-环氧氯醇的结构和立体化学。核磁共振数据，即核Overhauser增强（NOE）相关性，指出了愈创木内酯环庚烷环的两种构象。为了获得有关构象的更多信息而进行的半经验计算（AM1和PM3方法）得出了所研究内酯的三种几何形状。即便如此，从核磁共振数据得出的构象与通过半经验方法计算得出的构象非常吻合。
