Absolute configuration nuclear magnetic resonance

A variety of approaches has been employed including chemical correlation with compounds of known absolute configuration, nuclear magnetic resonance spectroscopy for obtaining relative stereochemistry, X-ray diffraction, optical rotatory dispersion and circular dichroism. The attention of the reader is directed to the specific examples in the Tables where stereochemistry is defined and particularly to the review of Nielsen 419),... 

Among the modem procedures utilized to estabUsh the chemical stmcture of a molecule, nuclear magnetic resonance (nmr) is the most widely used technique. Mass spectrometry is distinguished by its abiUty to determine molecular formulas on minute amounts, but provides no information on stereochemistry. The third most important technique is x-ray diffraction crystallography, used to estabUsh the relative and absolute configuration of any molecule that forms suitable crystals. Other physical techniques, although useful, provide less information on stmctural problems. 

The absolute configuration of the 9,10-dihydrodiol metabolite was established to be 9R,10R both by nuclear magnetic resonance spectroscopy and by the structures of the hydrolysis products formed from the svn and anti 9,10-dihydrodio 1-7,8-epoxides which were synthesized from the same 9,10-dihydrodiol enantiomer (13). The absolute configuration of a BaP trans-9.10-dihvdrodiol enantiomer, after conversion to a tetrahydro product, can also be determined by the exciton chirality method (Figure 2) (19.20). 

Fig. 9. Structures of homopumiliotoxins from dendrobatid frogs and bufonid toads. The structure of homopumiliotoxin 223G is based on nuclear magnetic resonance spectral analysis (77). The absolute configuration is unknown. Homopumiliotoxin 223G occurs in dendrobatids (77), ranids (73), and bufonids (8 ), while the other alkaloids have been detected only in the bufonid toads (Melanophryniscus) (81).

The isolation of indolizidine 207A in sufficient quantity for nuclear magnetic resonance spectroscopy (87) established a 5-(pent-4-enyl)-8-methylindolizidine structure as shown in IX. The (5R,8R,9S) absolute configuration shown is the same as that of 205A, which contains a terminal... 

Fig. 18. Alkaloids of the cyclopentaf/ilquinolizidine class from the dendrobatid frog, Minyobates bombetes. The structure of 251F was determined by nuclear magnetic resonance spectroscopy (/52), but the absolute configuration of 2S1F is unknown. The other structures are tentative and are based primarily on analogy and mass spectra.

Fig. 22. Structures of pseudophrynamines from myobatrachid frogs of the genus Pseu-dophryne. Structures of 2M, 286A, and 512 were determined by nuclear magnetic resonance spectroscopy (119). Structures of the other pseudophrynamines are tentative. The absolute configuration of 258 is uncertain but is presumably the same as /-physostigmine (119) as shown in structure XIV.

Corossolin was isolated by a French group in 1991, and the absolute configuration of its C-10 hydroxyl group remained unknown until its total synthesis was achieved by us in 1999 (Scheme 10-8). The first total synthesis of corossolin was achieved in 1996 by Makabe et al. in Japan. However, the specific rotations and nuclear magnetic resonances (NMRs) of their two synthetic C-10 epimers are... 

Seo S, Tomita Y, Tori K, Yoshimura Y (1978) Determination of the Absolute Configuration of a Secondary Hydroxy Group in a Chiral Secondary Alcohol Using Glycosidation Shifts in Carbon-13 Nuclear Magnetic Resonance Spectroscopy. J Amer Chem Soc 100 3331... 

The absolute configuration of (-)-swainsonine (1) was deduced on the basis of its biosynthesis and unambiguous nuclear magnetic resonance assignments.The relative stereochemistry of swainsonine was determined by X-ray crystallography. Noncarbohydrates have been used for the total synthesis of swainsonine and its isomers.The first total synthesis of 1 has established its absolute stereochemistry as (15, 2i ,8i ,8ai )-... 

The absolute configuration (43) for (—)-giaZa-quercitol was established by nuclear magnetic resonance and optical rotatory studies, and by correlation with (—)-inositol (93). ... 

Abscicic acid, 1027 Absolute configuration, 267—271, 292 Absorption of electromagnetic radiation, 489 in infrared spectroscopy, 518 in nuclear magnetic resonance spectroscopy, 490—493 in ultraviolet-visible spectroscopy, 524—525 Absorptivity. See Molar absorptivity Acetaldehyde, 655 bond angles, 657 enolization of, 706... 

Methods for determining the presence, kind, and amount of configurational base units can be classified as relative or absolute. Absolute methods do not require calibration with polymers of known tacticity. Relative methods, on the other hand, require comparison with standard substances. X-ray crystallography, nuclear magnetic resonance, infrared spectroscopy, and optical activity measurements are all absolute methods. Relative methods include crystallinity, solubility, glass transition temperature, and melting temperature measurements as well as chemical reactions (Table 3-2). 

Nuclear magnetic resonance (NMR) spectroscopy of polymers in solution is a very important method of studying polymer configuration since noncrystalline as well as crystalline compounds can be studied. The method depends on the fact that the chemical shift of the signals of bonded hydrogen atoms (protons), and atoms, etc., in fixed chemical environments depends on the configuration of the main chain. In theory, the technique represents an absolute method, but, on technical grounds, it can often only be used as a relative method. An example of this is the analysis of the spectra of poly(methyl methacrylates) of various tacticities. 

R. Kolodziejska, L. Jasinska, A. Karczmarska and M. Draminski, Determination of Absolute Configuration by Nuclear Magnetic Resonance , Wiadomosci Chemiczne, 2008, 62, 709. 

Rinaldi P 1982 The determination of absolute configuration using nuclear magnetic resonance techniques. Prog Nuc Magn Res Spec 15 291-352... 

Antillatoxin is a 15-membered cycHc Hpodepsipeptide isolated from the marine cyanobacterium Lynghya majuscula [135], A strong ichthyotoxicity and neurotoxicity agent, its structure 63b was determined by nuclear magnetic resonance (NMR) spectral studies, and the absolute configurations at of NMeVal and Ala were deduced... 

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