4th EucheMs chemistry congress

Monday, 27-Aug 2012
s706
chem. Listy 106, s587–s1425 (2012)
life sciences
Biocatalysis session – ii
o - 0 5 6
MiChAeL Addition of wAter: An enzyMAtiC
enAntioSeLeCtive APProACh
u. hAnefeLd 1
1 Delft University of Technology, Biotechnology, Delft,
Netherlands
The addition of water to carbon-carbon double bonds at first
glance seems straightforward. However, both chemically and
enzymatically this reaction is very difficult to perform. Indeed the
Michael addition of water is virtually unknown. [1] However,
recently a Michael hydrates was identified. Interestingly, the
hydration product is further oxidized to a 1,3-diketone by the same
enzyme which was therefore named Michael hydratase ÷ alcohol
dehydrogenase MhyADH. [2] Fascinatingly, this bifunctional
enzyme can also be used to catalyze only one of the two steps.
The hydroxylation of alpha beta unsaturated ketones can be
uncoupled because in the absence of electron acceptors MhyADH
functions only as a hydratase, considerably extending the scope
of the enzyme. To efficiently work with MhyADH, it was purified
from A. denitrificans and the gene was cloned. The sequence of
MhyADH revealed that this enzyme belongs to the molybdenumcontaining
hydroxylases which contain two Fe -S clusters, one
2 2
FAD and two molybdopterins which coordinate a molybdate. [3]
We will report on the purification, characterization and application
of MhyADH. The focus will be on the enantioselective addition
of water to the unsaturated conjugated carbonyl compounds.
Enantioselectivity and substrate scope of the enzyme will be
discussed and first mechanistic studies will be presented. Another
problem of this reaction, the position of the equilibrium, will be
addressed. Although one might assume that the reaction will
always give quantitative yields since the reaction is performed in
water and a powerful driving force is therefore present, this is not
the case.
references:
1. Jianfeng Jin and Ulf Hanefeld, Chem. Commun. 2011, 47,
2502–2510.
2. Jianfeng Jin, Philip C. Oskam, Sanjib K. Karmee, Adrie J.
J. Straathof and Ulf Hanefeld, Chem. Commun. 2010, 46,
8588–8590.
3. Jianfeng Jin, Adrie J. J. Straathof, Martijn W. H. Pinkse,
and Ulf Hanefeld, Appl. Microbiol. Biotechnol. 2011, 89,
1831–1840.
Keywords: Michael Addition; enzyme catalysis;
Enantioselectivity; Metalloenzymes;
Biocatalysis session – iii
4 th EucheMs chemistry congress
o - 0 5 7
the queSt for MiLd And effiCient oxidAtive
AGentS: SynthetiC exPLoitAtion of LACCASeS
S. rivA 1
1 Istituto di Chimica del Riconoscimento Molecolare, C.N.R.,
Milano, Italy
Laccases are oxidoreductases belonging to the multinuclear
copper-containing oxidases. The overall outcome of their catalytic
cycle is the reduction of one molecule of oxygen to two molecules
of water and the concomitant oxidation of four substrate
molecules to give four radicals. [1, 2]
Typical substrates of laccases are phenols and aliphatic or
aromatic amines, the reaction products being mixtures of dimers
or oligomers derived by the coupling of the reactive radical
intermediates. For instance, we have exploited these
biotransformations to isolate new dimeric derivatives of natural
phenolic derivatives (resveratrol and its analogues, β-estradiol,
totarol, sylibin). In these studies we have also observed a
significant influence of the solvent on the reaction outcomes.
More recently, we have described the use of laccasecatalyzed
reactions for the selective hydroxylation of ergot
alkaloids and for the synthesis of the bisindole alkaloid
anhydrovinblastine.
Additionally, laccases oxidation of non-phenolic groups,
particularly benzyl and – more generally – primary alcohols, is
also possible thanks to the ancillary action of the so-called
“mediators” (i.e., TEMPO, HBT, ABTS): the oxidation step is
performed by the oxidized form of a suitable mediator, generated
by its interaction with the laccase. Accordingly, we have oxidized
a series of sugar derivatives and of natural glycosides.
references:
1. D. Monti, G. Ottolina, G. Carrea, S. Riva Chem. Rev.
2011, 111, 4111-4140.
2. S. Riva, Trends Biotechnol. 2006, 24, 219-226.
Keywords: biocatalysis; oxidoreductases; oxidation; natural
products;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc