Kurzfassung

Abstract:
Vanadate(V)-dependent bromoperoxidase I (Ascophyllum nodosum) was immobilized on magnetic micrometer-sized particles in quantitative yields, with up to 40% retention of initial bromoperoxidase (BPO) activity. The immobilized enzyme was stable with a half-life time of about 160 days. It served as reusable catalyst for bromide oxidation with H2O2 in up to 14 consecutive experiments. Reactivity that resulted from enzymatic bromide oxidation was applicable for methyl...Abstract:
Vanadate(V)-dependent bromoperoxidase I (Ascophyllum nodosum) was immobilized on magnetic micrometer-sized particles in quantitative yields, with up to 40% retention of initial bromoperoxidase (BPO) activity. The immobilized enzyme was stable with a half-life time of about 160 days. It served as reusable catalyst for bromide oxidation with H2O2 in up to 14 consecutive experiments. Reactivity that resulted from enzymatic bromide oxidation was applicable for methyl pyrrole-2-carboxylate conversion into derivatives of naturally occurring compounds (e.g. from Agelas oroides) with product selectivity of up to 75%.

Conclusion:
To sum up, immobilization of VBrPO(AnI) onto solid supports provides three distinctive advantages for future development of sustainable oxidative brominations.
(i) VBrPO(AnI) binding either to epoxide-functionalized or to glutardialdehyde-activated amino-substituted magnetic beads was feasible in quantitative yields, with almost 40% of the original catalyst activity being conserved.
(ii) Immobilized VBrPO(AnI) showed similar turnover characteristics for methyl pyrrole-2-carboxylate oxidative bromination as the free enzyme in homogeneous solutions. The unexpectedly high performance of immobilized enzyme was explained with substrate bromination that occurred in bulk solution and not in proximity to the active site. In this model, diffusion of bromide to the histidine-bound vanadate(V) co-factor would be rate determining and not migration of the organic stubstrate to a specific binding site.
(iii) Supported bromoperoxidase was applicable for 8–10 consecutive cycles without notable activity loss.
The most significant achievement compared to other techniques used for instance for immobilization of the iron-dependent chloroperoxidase from Caldariomyces fumago [FeClPO(CfI)] on mesoporous supports was the ease and the efficiency of magnetic separation of immobilized VBrPO(AnI) from reaction mixtures. Chemicals originating from a preceding transformation thus were removable from the catalyst by simply washing with the buffer needed for the subsequent run. This aspect has been noted previously for application of immobilized lipases in biofuel preparation but has not yet been applied to haloperoxidase chemistry. With this material in hand, application of VBrPO(AnI) in oxidative bromination has the potential to become an interesting alternative in instances where substitution of elemental bromine is desired for environmental reasons by the reagent combination H2O2, possibly generated in situ from aerobic D-Glc oxidation catalyzed by GO, NaBr and an adequate source of protons.

Leading References:
[1] Bromoperoxidase and Functional Enzyme Mimics for Oxidative Bromination – A Sustainable Synthetic Approach. D. Wischang, O. Brücher, J. Hartung, accepted for publication in Coord. Chem. Rev. angenommen.
[2] Vanadate(V)-dependent Bromoperoxidase immobilized on Paramagnetic Beads as Reusable Catalyst for Oxidative Brominations. D. Wischang, J. Hartung, T. Hahn, R. Ulber, T. Stumpf, C. Fecher-Trost, Green Chem. 2011, DOI:10.1039/c0gc00499e.
[3] On the Reactivity of Bromoperoxidase I (Ascophyllum nodosum) in Buffered Organic Media – Formation of Carbon Bromine Bonds. J. Hartung, Y. Dumont, M. Greb, D. Hach, F. Köhler, H. Schulz, M. Časný, D. Rehder, and H. Vilter, Pure and Applied Chemistry 2009, 81, 1251–1264.
[4] Bromoperoxidase Activity and Vanadium Level of the Brown Alga Ascophyllum nodosum. J. Hartung, O. Brücher, D. Hach, H. Schulz, H. Vilter, G. Ruick, Phytochemistry 2008, 69, 2826–2830 (DOI:10.1016j.phytochem.2008.09.004).

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