Parameters for bromination of pyrroles in bromoperoxidase-catalyzed oxidations
作者:Diana Wischang、Jens Hartung
DOI:10.1016/j.tet.2011.04.010
日期:2011.6
Ester-, cyano-, and carboxamide-substituted 1H-pyrroles undergo electrophilic aromatic bromination, if treated with hydrogen peroxide and sodium bromide at pH 6.2 and 20 degrees C. Oxidation of bromide under such conditions is catalyzed by a vanadate(V)-dependent bromoperoxidase, in a substrate/enzyme ratio of 32-63 mu mol %. To obtain maximum yields of bromopyrroles (up to 91%) by spending least amount of substrates and catalyst, hydrogen peroxide and sodium bromide have to be added continuously to the enzyme and the 2-acceptor-substituted pyrrole (1.5 mmol) in a solution of morpholine-4-ethanesulfonic acid buffer. This technique was applied to prepare two marine natural products under biomimetic conditions, that is, methyl 4,5-dibromopyrrole-2-carboxylate (from Agelas oroides) and 4,5-dibromopyrrole-2-carboxamide (from Acanthella carteri). (C) 2011 Elsevier Ltd. All rights reserved.
Vanadate-dependent bromoperoxidases from Ascophyllum nodosum in the synthesis of brominated phenols and pyrroles
作者:Diana Wischang、Madlen Radlow、Jens Hartung
DOI:10.1039/c3dt51582f
日期:——
aqueous tert-butanol (pH 6.2) molecular bromine as reagent for electrophilic hydrocarbon bromination. Alternative compounds, such as tribromide and hypobromous acid are not sufficiently electrophilic for being directly involved in carbon–bromine bond formation. A decrease in electrophilicity from bromine via hypobromous acid to tribromide correlates in a frontier molecular orbital (FMO) analysis with