An acceleration of the transesterification of arylboronates by a factor of about 109 can be achieved by introduction of nitrogen‐containing substituents or moieties into phenylboronic acid esters. Examples are aryl o‐(dimethylaminomethyl)phenyl, o‐(dimethylamino)phenyl, 8‐quinolyl. Arylboronic acids thus become available which are suitable, after immobilization, for a very rapid chromatographic separation of diols.
1969with an OLIS 3820 Data System for data collection, storage, and analysis. and, after stabilization at -20 'C, their "P spectra.Methods. The 3'P('H) NMR spectra were recorded at 121.5 MHz on a Bruker WM 300 spectrometer with appropriate temperature control for spectra recorded below ambient temperature. Splitting patterns were NT-300 spectrometer. The latter instrument was also used for routine 'H spectra. UV-vis spectra and the kinetics measurements in the slower reactions were measured on a Cary Model 219 spectrophotometer. Kinetic data were fit to suitable equations by standard least-squares programs. More rapid reactions were monitored at suitable wavelengths on a Canterbury Model SF-3A stopped-flow spectrophotometer interfaced
Acknowledgment.Abstract: Pyridoxamine has been attached to the primary side and to the secondary side of P-cyclodextrin; the resulting compounds convert a-keto acids to amino acids with substrate selectivity and some stereoselectivity. Pyridoxamine has also been attached to a synthetic macrocycle; the attached binding group showed substrate selectivity. Chains carrying catalytic basic groups have been attached to pyridoxamine; appropriate systems catalyze the prototropic rearrangement characteristic of transamination. A catalyzed HCI elimination involving chloropyruvic acid was also observed. A tetrahydrcquinoline system related to pyridoxamine was synthesized to permit the stereochemically defined placement of a basic catalytic group. This converted keto acids to amino acids with good stereoselectivity for the formation of optically active products.( I ) NIH postdoctoral fellow, 1981-1983.
Communications to the Editor 421 Preliminary studies on trimethylamine reactions with the halogenated c/cwo-carboranes 5,6-Cl2-2,4-C2B5Hs and 2-C1-1,6-C2B4H5 definitely implicate pyramidal nido adducts, although the subsequent removal of halide ion appears more complicated than in the case of the 5-chloro-2,4-dicarbaheptaborane adduct.
Zur spateren Verwendung als Haftgruppen in Polymeren wurden ortho-substituierte Phenylboronsauren untersucht. Die Einfiihrung verschiedener Aminomethyl-Gruppierungen ergab eine starke Beschleunigung fur die Gleichgewichtseinstellung der Veresterung rnit Diolen sowie der Umesterung solcher Ester. Die Geschwindigkeit der Umesterung wurde an geeigneten Systemen mit Hilfe der dynamischen NMR-Spektroskopie abgeschatzt und war gegeniiber der unsubstituierten Verbindung bis 108fach beschleunigt. Die meisten Verbindungen zeigten eine starke B -N-Koordination, wie im "B-NMR-Spektrum erkennbar war. Jedoch konnte ein einfacher Zusammenhang zwischen B -N-Koordination und katalytischer Wirksamkeit der Nachbargruppe nicht festgestellt werden. Nachbargruppen mit Sauerstoff, Schwefel oder Fluor zeigten weder eine Beschleunigung der Veresterung oder Umesterung noch eine Koordination mit dem Bor.
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