2D INADEQUATE Experiment Research Articles

Long-Range 2D INADEQUATE in Structure Determination

It is demonstrated that the 2D INADEQUATE experiment utilizing long-range 13C-13C spin-spin couplings is feasible and that it can solve structural assignment problems when one-bond connectivities do not provide sufficient clue for structure determination. In such cases, the long-range 2D INADEQUATE can be used instead of the standard 2D INADEQUATE since it also yields the one-bond connectivities in addition to the connectivities over more bonds. The two types of connectivities are easily distinguished according to satellite separations. Because of similar magnitudes of various long-range 13C-13C couplings, the method of J-resolved INADEQUATE suggested earlier for such purpose is unlikely to provide unambiguous results. The proposed method is utilized for complete assignment of 13C and 1H NMR spectra of dicyclohexylphenylphosphine.

Two-dimensional 29Si MAS n.m.r. investigation of the three-dimensional structure of zeolite DD3R

The three-dimensional connectivities in the (solid-state) structure of zeolite DD3R have been investigated by two-dimensional 29Si MAS n.m.r. techniques. 2D COSY experiments on an 85% 29Si-enriched sample are in agreement with the expected connectivities using a partial assignment of the resonances based on their relative intensities. In addition, the results indicate that the structure is of lower symmetry than expected as there are two T 1 environments. 2D INADEQUATE experiments confirm these results, including the lower symmetry of the structure, and, in this case, all of the expected connectivities are observed. A high-temperature INADEQUATE experiment shows that the symmetry of the structure increases to that expected from the previous single crystal X-ray diffraction experiment on the as-synthesized material.

A structural reinvestigation of 4,6-dinitrobenzofuroxan by 1H, 13C, and 15N nuclear magnetic resonance

A detailed nuclear magnetic resonance study of 4,6-dinitro-2,1,3-benzoxadiazole N-oxide (DNBF), which includes a 2D INADEQUATE analysis and experiments with samples 15N-labelled at the NO2 groups, is described. The results lead to an unambiguous assignment of the carbon and proton chemical shifts in various solvents. Some 1H and 13C data pertaining to 4,6-dinitro-2,1,3-benzoxadiazole (DNBZ), the deoxygenated analog of DNBF, are also reported, allowing the influence of the N-oxide group on the proton and carbon chemical shifts to be discussed. It is shown that all of the 1H nmr evidence so far reported for the characterization of DNBF σ adducts as arising from nucleophilic addition to the 7-position, i.e., as structure 2a, has no significance. That complexation actually occurs at this position is, however, convincingly demonstrated by 15N data. These also allow us to establish that this process is both kinetically and thermodynamically favored. Keywords: nitrobenzofuroxans, Meisenheimer complexes, 13C nmr of benzofuroxans, 2,1,3-benzoxadiazole N-oxides, nitrobenzofuroxan σ-adducts.

13C NMR spectra of antiviral nucleosides' 3′‐azido‐3′‐deoxythymidine, 2′,3′‐dideoxyadenosine, 2′,3′‐dideoxycytidine and 2′,3′‐dideoxyinosine

Abstract13C NMR chemical shifts and one‐bond 13C1H couplings are reported for 3′azido‐3′‐deoxythymidine, 2′,3′‐dideoxyadeno‐ sine, 2′,3′‐dideoxycytidine and 2′, 3′‐dideoxyinosine. Unambiguous assignments were made on the basis of results from 2D INADEQUATE experiments to establish the carbon–carbon connectivities.

An alternative to the 2D INADEQUATE experiment for detecting scalar coupling correlations between protonated and unprotonated carbons

AbstractThe two‐dimensional INEPT‐INADEQUATE experiment gives correlation peaks for unprotonated carbons which show only half of the total available signal, because the enhanced 13C signal generated by polarization transfer is shared equally between protonated and unprotonated coupling partners by the double quantum filtration step. If precautions are taken to attenuate unwanted signals from protonated carbons, then the double quantum filtration step may be dispensed with, leaving a hydrogen‐carbon‐carbon relay sequence. This gives unidirectional coherence transfer, ensuring that the maximum possible signal is concentrated in a single cross‐peak identifying the correlation between protonated and unprotonated carbons. By extending the basic HCC relay sequence to include an evolution period an enhanced 13C‐13C COSY 2D spectrum may be produced, with the further advantage over the 2D INADEQUATE experiment that the range of 13C‐13C coupling constants detectable is limited only by the available resolution.

Studies on the biosynthesis of antibiotics.

In the framework of studies on the biosynthesis of several antibiotics, specifically asukamycin, acarbose, reductiomycin, actinorhodin, and granaticin, a variety of different approaches to biosynthetic problems are illustrated. These include multiple labeling with stable isotopes in conjunction with modern methods of nmr analysis, as illustrated by the development of a new triple-quantum 2D-INADEQUATE experiment for biosynthetic studies, the use of stereochemical probes, as illustrated by the synthesis and stereochemical analysis of chiral [13C, 2H]malonate, and combinations of genetic and chemical approaches, as illustrated by examples of the production of new hybrid antibiotics by genetic engineering.

Natural Abundance 13C—13C Coupling Constants Observed via ID and 2D INADEQUATE Experiments in Stigmasterol and 1,4-Androstadiene-3,11,17-trione

Abstract For two steroids, stigmasterol and 1,4-androstadiene-3,11,17-trione, natural abundance 13C -13C coupling constants are determ ined by 1D and 2D INADEQUATE experiments. Besides full assignment of the 13C resonances of these steroids is achieved