Halogenation and oxidation of nitrogenated heterocycles by haloperoxidases

ROSARIO MÉDICI, JUAN I. GARAYCOECHEA, ELIZABETH LEWKOWICZ, ADOLFO M. IRIBARREN

Oviedo

Simposio; VIII Simposio Internacional de Biocatalisis y Biotransformaciones; 2007

Sociedad Europea de Biotecnología

The development of new, simple, versatile, efficient and environmentally friendly methods for the preparation of heterocycle analogues continues to be an intensive and interesting research topic. These compounds find applications in pharmaceutical and biological areas and as intermediates for chemical synthesis. In the present, the preparation of halogenated analogues of purine, benzimidazole or indole is carried out by traditional organic chemistry involving either aromatic displacement, using halogenated intermediates, or by diazotation reactions, which often involve difficult, inefficient and time-consuming multistage processes. The above mentioned halogenated derivatives could be prepared through biotechnological procedures. The number of so-far-known halogenating enzymes, is small. Among them, haloperoxidases catalyze the halogenation of organic compounds in the presence of halide ions and peroxides such as H2O2. Depending on the prosthetic group required, they can be subdivided into heme and vanadium-dependent. Some bacterial haloperoxidases have no prosthetic group and were further classified as perhydrolases. It has been shown that the haloperoxidase from Pseudomonas pyrrocinia carry out a regioselective chlorination of indole at carbon 7. Other sources of these enzymes are Streptomyces and Pseudomonas species. Haloperoxidases catalyze other oxidative reactions, such as sulfoxidation, oxidation and epoxidation. Current interest in industrial catalytic oxidative transformations is governed by two major issues. One is the replacement of oxidations, which use stoichiometric amounts of heavy metal salts, by catalytic processes using hydrogen peroxide or oxygen as the oxidant, and the other one is the need for high chemo-, regio- or enantioselectivies in order to improve chemical yields, to minimise waste streams and to avoid enantiomeric ballast. Haloperoxidases are potentially suitable biocatalysts for meeting these two goals. In particular, the use of C. fumago chloroperoxidase (CPO) is especially advantageous, due to its broad substrate acceptance and has been used in the oxidation of indole to indol-2-one. Compounds containing this structure exhibit important biological properties such as antitumor effect, and phosphodiesterase and tyrosine kinase inhibitory activities. In order to apply haloperoxidases to the halogenation and oxidation of indole, we have studied these biotransformations using different haloperoxidase containing whole cells, selected by screening our cell collection using the monochlorodimedone assay, and isolated CPO from C. fumago. We identified the reaction products derived from both halogenation and oxidation reactions and compared the enzymatic and microbial biotransformations. For example, using as biocatalyst whole cells of Pseudomona putida and Streptomyces cetonii 5-bromo-1H-indole and 5-bromo-1H-indol-2,3-dione were synthesized, while employing Serratia marcescens only oxidation products like 1,3-dihydroindol-2-one were formed. The experimental conditions to shift biotransformations to either halogenation or oxidition were also determined.