Heteronuclear COSY

The H- and 13C-NMR spectra of gelsemine (1) have been reinvestigated with 2D homonuclear NOESY and heteronuclear COSY techniques (31). As a result some of the original assignments (4,32) have been revised. Thus the <5H of values of H-14a, H-14e, H-15, and H-16 are revised from 2.37, 2.0,2.83, and 2.30 to 2.83, 2.01, 2.30, and 2.43 ppm, respectively, while the most significant corrections of <5C values involve that of C-6 from 40.2 to 50.47 ppm and 1V-CH3 from 50.4 to 40.40 ppm. These adjustments will be helpful in future studies of alkaloids in this series. 

Figure 3.22 Pulse sequence used to produce 1H-I3C heteronuclear COSY spectrum. (Adapted with permission of Nelson Thornes Ltd. from Figure 8.9 of Akitt, J. W. NMR and Chemistry, 3rd ed., 1992.)...

The heteronuclear COSY experiment investigates the connectivities imparted by coupling paths between two different nuclei, most commonly those between and The experiment is facilitated by the fact that one-bond CH coupling constants are much larger than the two or three bond (CCH or CCCH) coupling constants. Decoupling of protons from is accomplished... 

Figure 3.16 Pulse sequence used to produce a heteronuclear COSY spectrum.

Stored data sets a, b, c and d are obtained. If for the basic inverse ID heteronuclear COSY experiment NS scans are acquired, then NS/4 scans must be used in this case for each of the subexperiments to compare the results of the two experiments on the basis of equal total measuring time. The four data sets a-d are linearly combined in three ditferent ways as outlined in the processing scheme above (processing steps 1-3) and allow to calculate the corresponding suhspectra A, B and C. These schemes may easily be expanded accordingly, if more target spins to be selectively perturbed have been selected. 

For an effective measurement of "/(SiH) (1 < n < 4) values in silylated silyl enol ethers, a selective population transfer experiment was modified so that selective decoupling was applied during acquisition. 1H-29Si heteronuclear COSY confirmed the presence of silylated groups in the molecule6. 

Figure 3. H-NMR (400 MHz) of compound X isolated from a K329A reaction mixture by chromatography on MonoQ. The chemical shifts and proton-proton coupling assignments, based on selective decoupling and 2D experiments (not shown), are consistent with the structure of 2-carboxytetritol 1,4-bisphosphate (inset). Two phosphorous resonances were observed by 3 P-NMR proton-phosphorous couplings, assigned by broad-band decoupling and 2D heteronuclear COSY experiments (not shown), are also consistent with the proposed structure.

Haliclamines A (43) and B (44). Isolated from Haliclona sp., the structures of these reduced analogs were deduced by homonuclear and heteronuclear COSY and HMBC spectra. 43 and 44 showed a 1,3-disubstituted-3,4-dehydropiperidine moiety that is also present in saraines and isosaraines. Both compoimds not only inhibit cell division of fertilized sea urchin eggs, but also growth of L1210 (IC50 1-5 and 0.9 jug/ml, respectively) and P388 leukemia cell lines (0.75 and 0.39) [40]. 

Abstract— Hemiaria fcmUoKsU Gay (caiyophyllaceae) is widespread in the Mediterranean area. In the traditional pharmacopoda of Morocco, the aerial parts of this plant are used for the treatment of lithiasis. We have studied the title plant and now we report the isolation and identification of tree flavonoids and four oleanane saponins. The mixture of glycosides was isolated from the methanol extract of the aerial parts of H.fontanesii and separated by multiple chromatographic steps. The structure of the pure glycosids was elucidated by means of mass spectrometry (FAB-MS), NMR technics ( H, C, 2D homo and heteronuclear COSY) and chemical analysis (methanolysis, methylation, alkaline hydrolysis). The flavonoids isolated are (-) catechine 1 3-0-robinobioside Isorhamnetine 2 and a new one 3 feniloyl-3-O-robinobioside Isorhamnetine 3. 

Fig. 2.43 a. Contour plot of the homonuclear COSY spectrum (HOMCOR) of rhizobactin (42) revealing the coupling connectivities of the four separate units that compose the molecule plus an impurity b contour plot of the heteronuclear COSY (HECTOR) showing carbon and proton assign-... 

Recently two-dimensional solid-state heteronuclear chemical shift correlation experiments involving magic angle sample spinning (MASS) have been described. This technique results in an increase in the resolution of solid-state proton spectra by a factor of 5-10. Solid-state NMR spectroscopy has hitherto been confined to C-NMR spectra since the residual line widths in the spectra of solid samples are around 2 ppm, so that only four or five nonequivalent protons can be distinguished in the normal proton spectral region of 10-15 ppm. The increase in resolution attained by the 2D solid-state heteronuclear COSY experiment should promote further studies of the H-NMR spectra of solid samples. 

Figure 5.54. (A) Pulse sequence for 2D DEPT heteronuclear COSY experiment. (B) couplings between weakly coupled protons can be removed by inserting the...

Alternatively, we may consider a heteronuclear COSY experiment (HETCOR) shown in Fig. 2c. It begins in the same way as the homonuclear COSY sequence shown in Fig. 2a, except the read pulse followed by acquisition is usually applied to the X-nuclei. Of course, on a multi-receiver system we may choose to detect signals from both the A and X nuclei (see Fig. 2c). With a proper phase cycle in place and with A = and X = C, both H- H and correlation spectra can be... 

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