INADEQUATE heteronuclear

DQ coherence between C (,-) and C m and then let the DQ coherence evolve under the influence of the heteronuclear I3C-15N dipole-dipole interaction [181, 182]. The virtue of this design is that it can be easily combined with other resolution enhancement technique such as INADEQUATE [183]. Alternatively, the magnetization of C (,) dephased under the 13C-15N dipolar coupling can be transferred to C (j) for another period of 13C-15N dipolar dephasing [183]. This idea can be combined with the NCOCA experiment so that the superior resolution provided by the C (,-)-N(j+i) correlation could be exploited. The overall efficiency, however, is relatively low due to the use of two polarization-transfer steps, viz. 15N —> 13C and 13C —> 13C [183]. In comparison with the techniques, the advan-... 

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. 

Fig. 1. Pulse sequences modified for multiple selective excitation. I ID TOCSY, II het-eronuclear ID NOE, III ID INADEQUATE, IVa heteronuclear ID COSY (optimized to detect Jch), IVb heteronuclear ID COSY (optimized to detect "Jch), V 2D TOCSY-COSY, Via 2D HMBC (designed to detect heteronuclear long-range couplings "Jch only), VIh 2D HMBC (extended pulse sequence to detect both heteronuclear long-range "Jch and...

DEPT to enhance the signal of some other experiment in the sections devoted to those experiments (e.g. heteronuclear correlations, INADEQUATE, DQF COSY, 7-resolved spectra). Similarly, an INEPT experiment can be made selective in a number of ways some are discussed in Section VI.C.l on selective experiments. 

Another ID experiment that can be and has been utilized for 29Si line assignment in even more difficult situations [with /(29Si—13C) 1-2 Hz] is selective heteronuclear INADEQUATE253,254. ID heteronuclear INADEQUATE with 13C detection is a simple two-step pulse sequence in which the pulses are applied simultaneously to both nuclei ... 

FIGURE 39. The 29Si satellites in the 13C NMR spectra of 2 at 90.6 MHz measured with the selective heteronuclear INADEQUATE (the 29Si line selectively irradiated is indicated on the left for each trace, 13C assignment is given on the top). Total experimental time 15 min. Reproduced by permission of John Wiley Sons, Ltd from Reference 253... 

Later in 1997, Ondeyka et a/.83 reported the isolation and identification of the structure of nodulisporic acid (27) using micro-NMR probe technology. Nod-ulisporic acid is a novel insecticide from Nodulisporium sp. and was the first representative of a new class of indole terpenes to be identified. The authors used a combination of -detected homo- and heteronuclear 2D-NMR experiments to assemble the structure in conjunction with a series of three INADEQUATE, each 5 days long, optimized from 40 to 60 Hz that employed a 26 mg sample of 27. The INADEQUATE data were subjected to computer analysis,84 86 which identified 32 of 47 possible 13C-13C connectivities. 

Two dimensional sequences are commonly used in solution state NMR spectroscopy to elucidate connectivity of atoms within molecular structures. Sequences are available for heteronuclear shift correlation, homonuclear correlation (COSY and INADEQUATE) and other sequences for longer-range connectivities. In general the basis of these... 

INADEQUATE Homo/heteronuclear connectivity when coupling is weak Benn et al. (1988)... 

In the early days of heteronuclear correlation spectroscopy, a gradient free version of the double low-pass filter was proposed [5.212, 5.213], but the necessity to suppress unwanted coherences, particularly in INADEQUATE experiments, has forced the design of a gradient version [5.214]. The application of this filter is not just restricted to INADEQUATE experiments it has also become the element of choice in ACCORD-HMBC and ACCORD-CIGAR-HMBC experiments to reduce residual one-bond correlations. These experiments are very sensitive to the suppression of one-bond... 

NMR is the tool most widely used to identify the structure of triterpenes. Different one-dimension and two-dimension techniques are usually used to study the structures of new compounds. Correlation via H-H coupling with square symmetry ( H- H COSY), homonuclear Hartmann-Hahn spectroscopy (HOHAHA), heteronuclear multiple quantum coherence (HMQC), heteronuclear multiple bond correlation (HMBC), distortionless enhancement by polarisation transfer (DEPT), incredible natural abundance double quantum transfer experiment (INADEQUATE) and nuclear Overhauser effect spectroscopy (NOESY) allow us to examine the proton and carbon chemical shift, carbon types, coupling constants, carbon-carbon and proton-carbon connectivities, and establish the relative stereochemistry of the chiral centres. 

HMBC. Heteronuclear multiple bond correlation. HMQC. Heteronuclear multiple quantum correlation. HSQC. Heteronuclear single quantum correlation. INADEQUATE. Incredible natural abundance double quantum transfer. 

FIGURE 13. Top. Chemical structure-2D NMR connectivity diagrams (a) skeletal chemical structure of androstane corresponds to connectivities revealed in its 2D INADEQUATE spectrum (b) 5a,14a-androstane with H-C connectivity revealed by its heteronuclear shift-correlated,... 

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