Hahn route

Because of the complexity of the polyether antibiotics tittle progress has been made in stmcture determination by the chemical degradation route. X-ray methods were the techniques most successfully applied for the early stmcture elucidations. Monensin, X206, lasalocid, lysocellin, and salinomycin were included in nineteen distinct polyether x-ray analyses reported in 1983 (190). Use of mass spectrometry (191), and H (192) and nmr (141) are also reviewed. More recently, innovative developments in these latter techniques have resulted in increased applications for stmcture determinations. Eor example, heteronuclear multiple bond connectivity (hmbc) and homonuclear Hartmann-Hahn spectroscopy were used to solve the stmcture of portimicin (14) (193). East atom bombardment mass spectrometry was used in solving the stmctures of maduramicin alpha and co-factors (58). 

Lichtenthaler, W. F. Hahn, S. Flath, F. J. Pyranoid exo- and enrfo-D-fructals and L-sorbals practical routes for their acquisition and ensuing reactions, Liebigs Ann. Chem., 1995, 2081-2088. 

Although arguably the most popular route to NHC is via the azolium salt, there are many other options for their synthesis. An excellent and comprehensive overview of the synthesis of NHC and some of their complexes can be found in Hahn [34]. An interesting route to tri- and tetracarbenes is provided by the template controlled cyclisation of isocyanides, a method pionered by Lappert and coworkers [35,36] (see Fignre 1.2). 

No evidence linking oral exposure to uranium to human cancer has been found. Although natural, depleted, or enriched uranium and uranium compounds have not been evaluated in rodent cancer bioassays by any route by the NTP (BEIR 1980, 1988, 1990 Hahn 1989 Sanders 1986 UNSCEAR 1982,1986,1988), there is potential for the carcinogenicity of uranium, since it emits primarily alpha radiation. Nevertheless, no evidence has been found to associate human exposure to uranium compounds and carcinogenesis. The National Academy of Sciences has determined that bone sarcoma is the most likely cancer from oral exposure to uranium however, their report noted that this cancer has not been observed in exposed humans and concluded that exposure to natural uranium may have no measurable effect (BEIR IV). 

J.-P. Andre, S.-K. Hahn, S.-H. Kwon, and W. Min, An Economical Route to High Quality Lubricants, Paper AM-96-38, presented at the National Petroleum Refiners Association annual meeting, San Antonio, Texas, March 17-19, 1996. 

Several convenient routes for signal enhancement in quadrupolar SSNMR experiments involve manipulation of the ST populations [46], which results in an enhanced CT population difierence, thereby boosting experimental S/N and reducing experimental times. The apphcation of double-frequency sweeps (DFS) before a Hahn-echo or QCPMG experiment results in the DFS-echo [61,62] and DFS—QCPMG [50,63] pulse sequences, respectively, which Rossini et al. showed are very usefijl for the acquisition of challenging SSNMR spectra [64]. Utilization of... 

Lee, C. C., and B.-S. Hahn Rearrangement Studies with Carbon-14. XXXIV. The 71 Route to the Norbornyl Cation from Solvolyses of 2-(A -Cyclopentenyl)-2- C-/7-Nitrobenzenesulfonate. J. Amer. Chem. Soc. 91, 6420 (1969). 

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