COSY technique

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. 

In order to assign the chemical shifts of the carbon atoms of the conjugated diene system of each CLA isomer, it was necessary to conduct INADEQUATE, HMBC (heteronuclear multiple bond correlation) and two-dimensional 1H-13C correlation spectroscopy (COSY) techniques on the carbon signals of the diene system of the ,Z-isomers. The results of these experiments for the CLA isomers are summarized in Table 13. 

The 300 MHz XH NMR spectra of the all- isomers of 67-72 were measured in CDCI3. The signals were assigned using the COSY technique. The chemical shift values and the values of the coupling constants are completely in agreement with their all-trans structures and are summarized in Tables 19 and 20, respectively, together with the values for 66 which are included for comparison. 

NMR spectroscopy on nuclei in 2-aminopyrans, in many cases, fail to report shifts with a reference, or are assigned inaccurately (86H(24)935). Some examples of chemical shifts and references are given below the data for pyran 19 have been proven by the COSY technique (02X953). One paper (85MI2) was devoted to a comparative analysis of the spectra of pyrans 16, 17, as well as of those of a 2,6-dimethyl-4H-pyran analog. 

Since there is a waste of time in the phase cycling (and some extra loss of signal due to the overall length of the sequence), there is no advantage in using these or other COSY techniques in the place of the simple COSY experiment described in Fig. 8.2C. However, the relaxation of the ZQ transitions may be little affected by the presence of unpaired electrons and under certain conditions may also have some advantages as far as resolution is concerned [21]. 

The CH COSY technique with carbon-13 detection and proton decoupling, and more sen-sitive and thus time saving methods with H detection and 13C decoupling denoted as inverse CH COSY, correlate l3C shifts in one dimension with the lH shifts in the other via one-bond CH coupling JCH-... 

In particular, the H NMR spectra of the dichelated proto-hemin cyanide complexes reported by Traylor and Berzinis in 1980, which show eight methyl resonances ranging from 20.4 to 4.8 ppm at 35 °C in DMSO- 4, or from 30.2 to 3.7 ppm at 57 °C in DMF- /7, have been assigned by NOES Y/EXS Y, COSY, ROESY and DQF-COSY techniques and the nodal planes of the single imidazole ligand in the two isomers have been shown to lie at 100° and 170° counterclockwise of the x-axis of the hemes shown in Figure 14, bottom. Isomer... 

R163 R. C. R. Grace and N. Syryaprakash, Application of Z-Cosy Technique for the Analyses of NMR Spectra of Oriented Molecules , p. Pl/441... 

This example (Fig. 2.10) also shows the limitations of the HH COSY technique first. 

Despite these limitations, structural fragments may almost always be derived by means of the HH COSY technique, so that with complementary information from other two-dimensional NMR experiments it is possible to deduce the complete structure. Thus the HH COSY technique is especially useful in finding a solution to problems 10, 28, 29, 45, 49 and 50. 

The CH COSY technique correlates the C shifts in one dimension with the... 

The conclusive assignment of the H and benzene ring at 80 and 20 MHz, respectively, encounters difficulties. However, the frequency dispersion is so good at 400 and 100 MHz, respectively, that the HH COSY in combination with the CH COSY technique allows a conclusive assignment to be made. Proton connectivities are derived from the HH COSY the CH correlations assign each of the four CH units. Both techniques converge to establish the CH skeleton of the ortho-disubstituted benzene ring. 

The HH COSY technique - jj, photon magnetic resonance is a quick alterna-... 

The E.COSY experiment uses extensive phase cycling and in an effort to reduce the long acquisition times the P.E.COSY and P.COSY techniques have been developed. However these techniques require excessive post-processing of the data and consequently only the E.COSY experiment will be illustrated in Check it 5.4.1.6. For a comprehensive review of the other techniques the reader is referred to the literature [5.34,5.35]. 

Navelbine . The most recent application of inverse-detected 2D NMR methods to a bis-indole was the reported assignment of the proton and carbon NMR spectra of Navelbine (24) reported by the authors (Spitzer et al. 1992). Direct proton-carbon shift correlations were established using an HMQC spectrum. The authors also reported the comparative evaluation of the recently reported GEM-COSY technique (Domke et al. 1991), which affords a heteronuclear correlation spectrum of only the methylenes of a molecule, with the HMQC spectrum. Based on their assessment, GEM-COSY, while useful, did not offer any advantage over the HMQC experiment. In addition, the nature of the experiment required high levels of... 

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