C NMR Spectra of Natural Products

Figure 2 C NMR spectra of amination products, a. DEPT 135 spectra following an amination reaction using natural abundance, b. DEPT 45 spectra following an amination using [l- C]-ethanol.

A review of the occurrence in nature and production of solasodine is available [632]. The completely assigned and l C NMR spectra of 281 have been reported [633]. 

Comparing the results of EC-NMR and IR investigations, we find that the potential dependence of C NMR shift and the vibrational frequency of adsorbed CO are primarily electronic in nature, and originate from changes in the f-LDOS. C NMR results show that CO adsorbed on Pt, either directly from CO gas or from methanol oxidation, have the same electronic properties. That is, the chemisorbed product (surface CO) from CO solutions and from methanol decomposition is the same. The electrode potential dependence of the C NMR spectra of CO adsorbed on Pt and Pd nanoparticles provide direct evidence for electric field induced alterations in the E/ -LDOS. In relation to fuel cell catalysis, EC-NMR investigations of Pt nanoparticles decorated with Ru show that there exist two different kinds of CO populations having markedly different electronic properties. COs... 

On the basis of the NMR spectroscopic considerations and molecular modeling studies, the correct structure of lyngbyaloside B was deduced as that represented by 87 (Scheme 15). Thus, we undertook the total synthesis of 87 basically in accordance with that of 1. Much to our delight, the H and C NMR spectra of our synthetic 87 were identical with those of the natural product. Moreover, the specific rotation value of our synthetic material closely matched that of the authentic one. Therefore, the complete stereostructure of lyngbyaloside B was established to be that shown by 87. ... 

The 50.31 MHz 13C NMR spectra of the chlorinated alkanes were recorded on a Varian XL-200 NMR spectrometer. The temperature for all measurements was 50 ° C. It was necessary to record 10 scans at each sampling point as the reduction proceeded. A delay of 30 s was employed between each scan. In order to verify the quantitative nature of the NMR data, carbon-13 Tj data were recorded for all materials using the standard 1800 - r -90 ° inversion-recovery sequence. Relaxation data were obtained on (n-Bu)3SnH, (n-Bu)3SnCl, DCP, TCH, pentane, and heptane under the same solvent and temperature conditions used in the reduction experiments. In addition, relaxation measurements were carried out on partially reduced (70%) samples of DCP and TCH in order to obtain T data on 2-chloropentane, 2,4-dichloroheptane, 2,6-dichloroheptane, 4-chloroheptane, and 2-chloroheptane. The results of these measurements are presented in Table II. In the NMR analysis of the chloroalkane reductions, we measured the intensity of carbon nuclei with T values such that a delay time of 30 s represents at least 3 Tj. The only exception to this is heptane where the shortest T[ is 12.3 s (delay = 2.5 ). However, the error generated would be less than 10%, and, in addition, heptane concentration can also be obtained by product difference measurements in the TCH reduction. Measurements of the nuclear Overhauser enhancement (NOE) for carbon nuclei in the model compounds indicate uniform and full enhancements for those nuclei used in the quantitative measurements. Table II also contains the chemical... 

In contrast to X -phosphorins, X -phosphorins can be protonated. The basicity is very much influenced by the nature of the substituents R and R at the phosphorus. 1.1-Dialkyl or 1.1-diaryl-X -phosphorins are even protonated by aqueous HCl the salts are deprotonated by aqueous NaOH. Strong acids in organic solvents, e. g. trifluoroacetic acid in hexane or benzene, (see p. 106), are required to proto-nate 1.1-dialkoxy-X -phosphorins. Addition of tert-butoxide deprotonates the salt. By studying the NMR spectra of 1. l-dimethoxy-2.4.6-tris-pentadeuterophenyl-X -phosphorin 185 in benzene solutions containing H and D-trifluoroacetic acid Stade could show that two different protonation products are formed in a ratio of 3 1. One product is the result of C—2 protonation 186 the other of C-4 protonation 187 (Fig. 38). Similar results were observed in the case of 1.1-bis-dimethylamino-2.4.6-triphenyl-X -phosphorin... 

We would probably have invested more effort in perfecting the synthesis of 1 by either path A or C, but when we first isolated 1, we discovered that our natural product was not the natural product The NMR spectra of 1 differed significantly from those reported for saca-... 

Biosynthetic pathways can be conveniently elucidated by employing specifically enriched C precursors. The sites and extents of incorporation into metabolites are simply determined from their C NMR spectra without recourse to tedious degradations required with radioactive C tracers. C Sources are readily available [21]. The C spectrum of the purified metabolite is compared with the same product having C in natural abundance (1.1%). Broad-band proton noise decoupling is used and five times the longest T, (or at least three times) should be allowed between pulses so that the FT spectra are unaffected by relaxation effects. 

ACD/Structure Elucidator has matured over the past 6 years to become the most capable commercial CASE system available today. The expert system has been described in detail in previous works." " The first generation system was developed for the elucidation of molecular structures of intermediate-sized organic molecules with 20-25 skeletal atoms using simple ID C NMR spectra. The second pubhcation" " reported on developments allowing the elucidation of structures of large molecules, typical of those found in the world of natural products, and utilizing mainly 2D NMR data as the source datasets. The application and success of the system as a powerful and versatile tool for the structure elucidation of complex chemical structures has been demonstrated in numerous works and will not be discussed in more detail in this review. " " ... 

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