Executive Summary : | Haloperoxidase enzymes are well known for their catalytic properties in various organic transformation reactions. They occur widely in nature and are found in most marine algae, seaweed, bacetria and in a class of fungi called dematiceous hyphomycetes. There are two types haloperoxidases viz., heme-containing haloperoxidases and non-heme haloperoxidases. The non-heme haloperoxidases include vanadium-containing enzymes, wherein vanadium oxides (vanadates) are found to be present in the active sites. Over 5000 halogenated natural products are known to exhibit a wide variety of chemical functions and applications. The efficacy of these natural products in bio-systems is sustained because of the halogen atoms present therein. In this regard, VHPOs are thought to be involved in in the production of a large quantity of halogenated products in vivo. These enzymes have been classified according to the most electronegative halide they can oxidize catalytically. Thus, chloroperoxidases (V-ClPO) can catalyze the oxidation of chloride, bromide and iodide, while bromoperoxidases (V-BrPO) catalyzes bromide and iodide only. These haloperoxidases utilize H2O2 for electrophilic halogenation via the oxidation of halides. Here, the ‘X-’ ion undergoes two electron oxidation giving rise to a ‘X+’ intermediate in HOX, which can halogenate the substrate. Due to the efficient catalytic properties exhibited by the these naturally occurring VHPOs, researchers are trying to reproduce the activity and investigate the mechanisms by fabricating some homogeneous robust vanadium(v)-oxo complexes. We intend to prepare functional models for vanadium haloperoxidases (VHPOs) using some tripodal tertiary amine ligands having pyrazole and pyridne based N-donor atoms. |