Optimization of and Mechanistic Considerations for the Enantioselective Dihydroxylation of Styrene Catalyzed by Osmate‐Laccase‐Poly(2‐Methyloxazoline) in Organic Solvents

Abstract

The Sharpless dihydroxylation of styrene with the artificial metalloenzyme osmate‐laccase‐poly(2‐methyloxazoline) was investigated to find reaction conditions that allow this unique catalyst to reveal its full potential. After changing the co‐oxidizing agent to tert‐butyl hydroperoxide and optimizing the osmate/enzyme ratio, the turnover frequency and the turnover number could be increased by an order of magnitude, showing that the catalyst can compete with classical organometallic catalysts. Varying the metal in the active center showed that osmate is by far the most active catalytic center, but the reaction can also be realized with permanganate and iron(II) salts.

Multicore Artificial Metalloenzymes Derived from Acylated Proteins as Catalysts for the Enantioselective Dihydroxylation and Epoxidation of Styrene Derivatives

“…The resulting acylated LYS′s are not soluble in organic solvents in contrast to the respective formerly reported poly(2‐oxazoline) (POx)‐conjugates, but form stable suspensions in various organic solvents such as toluene and chloroform (Figure ).…”

“…The reaction was carried out with 0.03 μmol mL −1 protein conjugate, 0.03 μmol mL −1 K 2 OsO 2 (OH) 4 , 110 μmol mL −1 t BuOOH and 100 μmol mL −1 styrene. The reaction times were adjusted to previously determined surviving times of a respective Os‐laccase‐PMOx under the used conditions and temperatures, being 7 d at 0 °C, 72 h at 20 °C, and 24 h at 40 °C . The TOF is defined as μmol product per μmol protein per hour.…”

“…As shown previously, the solvent plays an important role in the selectivity of enzymes . This was addressed by carrying out the experiments above at 0 °C with acylated LYS′s in toluene (results provided in Table S2 in the supplements).…”

“…However, no significant conversion occurs after 24 h. The yield is again increased to 47 % with a drop of enantioselectivity to 50 % ee ( R ). This indicates that the generated active site for epoxidation in the protein is somehow altered during the course of the reaction like it has been found for dihydroxylation of styrene with Os‐laccase‐PMOx in a previous study . It is worth noting that the enantioselectivity does not significantly change during the course of the reaction (see Table S3 in the supplements).…”

Poly(2‐ethyloxazoline) as matrix for highly active electrospun enzymes in organic solvents

“…Goal of the present study was to explore the potential of poly(2‐ethyloxazoline) (PEtOx) as matrix material for the activation of enzymes in electrospun nanofibers in organic solvents. We choose this polymer, because it was found enzyme friendly in solution, in amphiphilic polymer conetworks based on PEtOx, and even as enzyme–polymer conjugates to make the proteins organosoluble (Konieczny et al, ), reactive (Konieczny et al, ), and even applicable as ligands for organo‐metal catalysis (Konieczny et al, ; Leurs et al, ). Al‐Shehri et al () have reported that enzymes can be electrospun from an aqueous solution of commercial PEtOx ( M w = 500,000 g/mol).…”