Assignment of oxime and hydrazone configuration using H- N and C- N coupling measurements at natural abundance.

Measurement of H- N and C- N coupling constants at natural abundance is demonstrated to be a reliable and generic method to determine the configuration of oximes, hydrazines, and related systems. Data on H- N and C- N coupling constants on a variety of systems obtained at natural abundance confirm the geometric dependence of the measured H- N and C- N coupling constants. In addition, we summarize a simple "decision-tree" for determining configuration based on practical considerations of sample quantity, solubility, and complexity.

Exploiting natural abundance 13C-15N coupling as a method for identification of nitrogen heterocycles: practical use of the HCNMBC sequence.

In this paper, we detail the results of (1)H-(15)N correlation data obtained via (13)C-(15)N coupling at natural abundance on a number of classes of azoles including pyrazoles, imidazoles and triazoles. The experiment produces data that is highly complementary to direct (1)H-(15)N HMBC type correlations in that it can provide (15)N chemical shift data for nitrogen that may not show up in the HMBC. This is particularly advantageous in the triazoles where (15)N chemical shift can be diagnostic of regiochemistry.

HCNMBC--a pulse sequence for H-(C)-N Multiple Bond Correlations at natural isotopic abundance.

We propose a pulse sequence, HCNMBC for multiple-bond H-(C)-N correlation experiments via one-bond (1)J(C,H) and one- or multiple bond (n)J(N,C) coupling constants (typically n=1-3) at the natural isotopic abundance. A new adiabatic refocussing sequence is introduced to provide accurate and robust refocussing of both chemical shift and J-evolution over wide ranges of C-13 and N-15 frequencies. It is demonstrated that the proposed pulse sequence provides high quality spectra even for sub-milligram samples.

Comparative metabolism of 1,2,3,3,3-pentafluoropropene in male and female mouse, rat, dog, and human liver microsomes and cytosol and male rat hepatocytes via oxidative dehalogenation and glutathione S-conjugation pathways.

In vitro metabolism of 1,2,3,3,3-pentafluoropropene (PFP) was investigated in the present study. PFP was metabolized via cytochrome P450-catalyzed oxidative dehalogenation in liver microsomes and glutathione transferase (GST)-catalyzed conjugation in liver microsomes and cytosol. Two oxidation products, 2,3,3,3-tetrafluoropropionaldehyde (TPA) and 3,3,3-trifluoropyruvaldehyde (TFPA), and two GSH conjugates, S-(2,3,3,3-tetrafluoropropenyl)-GSH (TFPG) and S-(1,2,3,3,3-pentafluoropropyl)-GSH (PFPG) were identified.

Enhanced automated structure elucidation by inclusion of two-bond specific data.

The availability of cryogenically cooled probes permits routine acquisition of data from low sensitivity pulse sequences such as inadequate and 1,1-adequate. We demonstrate that the use of cryo-probe generated 1,1-adequate data in conjunction with HMBC dramatically improves computer-assisted structure elucidation (CASE) both in terms of speed and accuracy of structure generation. In this study data were obtained on two dissimilar natural products and subjected to CASE analysis with and without the incorporation of two-bond specific data.

Two-dimensional spectroscopy with parallel acquisition of 1H-X and 19F-X correlations.

Two-dimensional NMR spectra correlating both (1)H and (19)F nuclei with either (13)C or (15)N, are recorded at the same time, using a 600-MHz broadband radio frequency probe feeding independent (1)H and (19)F receiver channels. This technique, known as parallel acquisition NMR spectroscopy (PANSY), speeds up multidimensional NMR and is compatible with other fast-acquisition schemes. The method is illustrated with single-bond (HSQC) and multiple-bond (HMBC) experiments on 2-bromophenyl-3-trifluoromethyl-5-methylpyrazole, giving simultaneous (1)H-X and (19)F-X correlation spectra (X = (13) C or (15)N).

Unambiguous assignment of trifluoromethylpyrazole regioisomers by 19F-15N correlation spectroscopy.

Analysis of the 19F chemical shifts of trifluoromethylpyrazole regioisomers has shown that while chemical shift is in general a reliable predictor of regiochemistry in this series, there is a narrow chemical shift range in which the two isomers overlap and the regiochemistry cannot be assigned with certainty. We have examined the usage of 19F--15N correlation spectroscopy as a method to provide a second unambiguous confirmation of regiochemistry of 3- and 5-trifluoromethylpyrazole regioisomers. In the case of 3-trifluoromethyl analogs, one expects a three-bond coupling to the pyridine type nitrogen (N-2).