dr. Frank Hollmann

T: +31 15 27 81957
E: F.Hollmann@remove-this.tudelft.nl
Room C2.
Van der Maasweg 9
2629 HZ Delft
The Netherlands

 

 

 

Read more about Frank here.

Enzymes as Catalysts for industrial Biotechnology

General research topic description about Enzymes as Catalysts for industrial Biotechnology will be added here soon.

Chemo-enzymatic cascade reactions

Chemo-enzymatic cascade reactions are one of the mainstays of the section Biocatalysis. By combining several steps in one pot a significant step economy can be realised and the potential for environmentally benign synthesis is improved. Thus several work up steps can be avoided and pure products are ideally isolated after a series of reactions in one single vessel after just one straightforward purification step. Immobilisation of homogenous catalysts and then combining them with enzymes (Scheme 1 & 2) were developed, many of them in collaboration with other research groups. 

Scheme 1: Enantioselective reductions combined with enantioselective hydrolyses to obtain highly pure chiral intermediates (Adv. Synth. Catal. 2006, 348, 471-475 and Top. Catal. 2006, 40, 35-44.).

Scheme 2: Immobilised TEMPO as organo-catalyst in the oxidation of a sensitive alcohol to aldehyde and subsequent enantioselective cyanide addition catalysed by a Hydroxynitrile lyase (Eur. J. Org. Chem. 2006, 1672–1677).

 

Today the focus is shifting to redox enzymes in combination with heterogeneous catalysts, such as Pd nanoparticles (Scheme 3). For this international collaborations as well as in house production of enzymes and chemo catalysts is utilised. In this manner a wide variety of compounds is assembled enantioselectively via concise routes in high purity.

 

Scheme 3: 3 step sequence for the synthesis of amino alcohol via alcohol dehydrogenase and Pd nanoparticle catalysed reactions (Green Chem. DOI: 10.1039/c3gc41666f).

 

For other sequences and synthesis routes please contact:  u.hanefeld@remove-this.tudelft.nl or f.hollmann@remove-this.tudelft.nl

Application of enzymes in Organic Chemistry

Since the very beginning enzymes are an essential tool in organic chemistry. Although occasionally not at centre stage of chemistry their application dates back to Liebigs and Wöhlers application of Hydroxynitrile lyases 180 years ago, Emil Fischers application of enzymes in sugar chemistry, when he formulated the lock and key hypothesis and to the first enantioselective synthesis ever described (L. Rosenthaler, Biochem. Z., 1908, 14, 238-253; Scheme 1). Here again Hydroxynitrile lyases are the enzymes of choice. Indeed these enzymes are still in use in our group. Both, the immobilisation (Chem. Soc. Rev., 2013, 42, 6308 - 6321) and application in organic solvents (Chem. Eur. J. 2010, 16, 7596 – 7604), as well as new Hydroxynitrile lyases (FEBS Journal 2013, 280, 5815–5828) or their genetic modification are studied. In this way these versatile tools are modernised continuously; often in collaboration with other groups.

Scheme 1: First enantioselective reaction in chemistry. The topic is still under investigation in Delft and countless variations and additions are done.

The range of enzymes was extended since 1908 and today we study other C-C bond forming enzymes and many hydrolytic and redox enzymes.

  • Trans ketolase (Top. Catal. 2013, 56, 750–764) for the environmentally benign C-C bond synthesis starting from sugars.
  • Alcohol dehydrogenases for the enantioselective synthesis of alcohols and for ketone synthesis (see also redox enzymes)
  • Enoate reductases for the synthesis of enantiopure building blocks (see also redox enzymes)
  • Hydratases for the enantioselective addition of water to C=C bonds. Chemically this reaction is extremely difficult due to the poor nucleophilicity of water (Scheme 2)
  • Nitrile reductase, an enzyme that can reduce nitriles under mild condition (Scheme 3)

Scheme 2: Chemically the addition of water to isolated C=C and in Michael fashion is a question almost unanswered. By applying enzymes these conversions can be performed under mild conditions with high selectivity (Chem. Commun. 2011, 47, 2502–2510. and Eur. J. Org. Chem. DOI: 10.1002/ejoc.201301230).

Scheme 3: Nitrile reductase is a new class of enzymes only described recently. The scope of the E. coli enzyme is currently studied in Delft (Enz. Microb. Tech. 2013, 52, 129– 133).

For further details please contact:  u.hanefeld@remove-this.tudelft.nl or f.hollmann@remove-this.tudelft.nl

 

Biocatalytic pathways for redox transformations

Redox enzymes (Oxidoreductases) potentially are very useful tools for organic synthesis as they allow highly selective reduction, oxidation and oxyfunctionalisation reactions (Scheme 1). [1]

Scheme 1. Selection of products obtainable via oxidoreductase catalysis.

One major challenge of oxidoreductases catalysis still is the issue of supplying the enzymes with the redox equivalents (electrons) needed for catalysis. Naturally, oxidoreductases obtain these via the reduced nicotinamide cofactor (NAD(P)H). Due to the prohibitively high price of NAD(P)H, they have to be used in catalytic amounts together with an in situ regeneration system resulting in sometimes very complicated multi enzyme cascades that are difficult to optimize and maintain robust for a long time.

One approach followed in BOC is to use cheap, synthetic analogues of the natural cofactors (Scheme 2). [2] With this concept even ‘better than naturally designed’ reaction schemes can be obtained.

Scheme 2. Enantioselective reduction of conjugated C=C-double bonds using simple NAD(P)H mimetics as stoichiometric reductants.

The most elegant source of reducing equivalents would be water. However, oxidation of water is a very difficult task due to the high thermodynamic and kinetic stability of the water molecule. Recently, we have succeeded in using visible light to promote water oxidation (catalyzed by a TiO2-catalyst) and transfer the electrons to an oxidoreductases to catalyze enantioselective reduction of conjugated C=C-double bonds (Scheme 3).[3] Thus, a highly interesting reaction concept for green and catalytic redox chemistry was established.

Scheme 3. A Photobiocatalytic reduction system. TiO2-based photocatalysts mediate the light-driven oxidation of water yielding O2 as sole by-product. The reducing equivalents liberated are transferred via flavin mediation to the active site of the oxidoreductase (here: the old yellow enzyme homologue from Thermus scotoductus SA-01).

 

Next to the above-mentioned reduction reactions also oxyfunctionalisation reactions are highly interesting for organic chemistry – especially because the current chemical catalysts are not capable of performing the introduction of oxygen into non-activated C-H-bonds with the selectivity of oxygenases. Peroxygenases represent one relatively new class of oxygenases catalyzing the selective hydroxylation of a broad range of compounds. For catalytic activity, these enzymes need H2O2, which-due to its high reactivity – has to be supplied continuously in small amounts. Recently, we have developed a photochemical system for the in situ generation of H2O2 to promote peroxygenase-catalyzed hydroxylations (Scheme 4). [4]

Scheme 4. Specific oxyfunctionalization reactions catalyzed by peroxygenases and driven by photochemical in situ generation of H2O2.

  1. a) F. Hollmann, I. W. C. E. Arends, D. Holtmann, Green Chem. 2011, 13, 2285–2313;
          b) F. Hollmann, I. W. C. E. Arends, K. Buehler, A. Schallmey, B. Buhler, Green Chem. 2011, 13, 226-265.
  2. a) C. E. Paul, I. W. C. E. Arends, F. Hollmann, ACS Catalysis 2014, 4, 788−797;
         b) C. E. Paul, S. Gargiulo, D. J. Opperman, I. Lavandera, V. Gotor-Fernández, V. Gotor, A. Taglieber, I. W. C. E. Arends, F. Hollmann, Org. Lett. 2012, 15, 180-183.
  3.      M. Mifsud, S. Gargiulo, S. Iborra, I. W. C. E. Arends, F. Hollmann, A. Corma, Nat Commun 2014
  4. a) E. Churakova, I. W. C. E. Arends, F. Hollmann, ChemCatChem 2013, 5, 565-568;
         b) E. Churakova, M. Kluge, R. Ullrich, I. Arends, M. Hofrichter, F. Hollmann, Angew. Chem. Int. Ed. 2011, 50, 10716-10719;
         c) D. I. Perez, M. Mifsud Grau, I. W. C. E. Arends, F. Hollmann, Chem. Comm. 2009, 6848 - 6850.

 

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