China
Africa
Explore chapters and articles related to this topic
Halogenases with Potential Applications for the Synthesis of Halogenated Pharmaceuticals
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Georgette Rebollar-Pérez, Cynthia Romero-Guido, Antonino Baez, Eduardo Torres
Vanadium haloperoxidases are halogenating enzymes that can be found in bacteria, fungi and macroalgae where they catalyze the oxidative halogenation of electron-rich organic substrates (Kaysser et al., 2012). They were first found in the brown alga Ascophyllum nodosum (van Pée, 1996). Since the discovery of this first halogenase in marine kelp, vanadium bromoperoxidases (V-BPO) and vanadium CPOs have also been isolated (Butler and Sandy, 2009). These halogenases are enzymes that contain a vanadate (VO43−) moiety as prosthetic group and that catalyze the two-electron oxidation of halides (Cl–, Br–, I–). Unlike the heme-dependent haloperoxidases, these enzymes do not suffer from oxidative inactivation, which makes them more attractive from an operational point of view. Initially, hydrogen peroxide reacts at the distal position of the vanadate complex, producing a peroxo-vanadate intermediate. Then, halide ion is oxidized, which leads to the production of hypohalous acid as halogenating agent (Fig. 16.1b). Like the heme-dependent haloperoxidases, the vanadium-dependent enzymes catalyze the halogenation of a variety of substrates in a nonselective manner, resulting in several monohalogenated, dihalogenated and trihalogenated metabolites that are susceptible to electrophilic attack (Gkotsi et al., 2018).
Iodination of vanillin and subsequent Suzuki-Miyaura coupling: two-step synthetic sequence teaching green chemistry principles
Published in Green Chemistry Letters and Reviews, 2019
James J. Palesch, Beau C. Gilles, Jared Chycota, Moriana K. Haj, Grant W. Fahnhorst, Jane E. Wissinger
Our aim was to design a guided-inquiry experiment exemplifying similar learning outcomes to the nitration experiment through a greener, safer transformation. The ideal substrate would have multiple possible substitution positions so that EAS selectivity could be studied and would afford a crystalline product with instructive 1H NMR spectral features. Recently, we developed an oxidation of borneol to camphor using Oxone® and catalytic sodium chloride (3). This experiment has been a highly successful green addition to our organic chemistry laboratory curriculum. Oxone® is a stable triple salt consisting of 2KHSO5•KHSO4•K2SO4 which has found wide spread application in synthetic chemistry (4). One such application is the halogenation of aromatic rings using a combination of Oxone® and a halide salt in various solvents (5–7). This reaction works most efficiently with aromatic substrates containing one or more electron-donating substituents (8). The active oxidizing agent in Oxone® is potassium peroxymonosulfate (KHSO5) which is thought to react with halide salts (M + X-) to produce a source of the electrophilic X+ in the form of a hypohalous acid, HOX (4). After workup, the by-products of the reaction are environmentally-benign potassium sulfate salts.