ORGANIC
LETTERS
2006
Vol. 8, No. 19
4227-4229
Sequential Kinetic Resolution Catalyzed
by Halohydrin Dehalogenase
Maja Majeric´ Elenkov,† Lixia Tang,† Bernhard Hauer,‡ and Dick B. Janssen*,†
Biochemical Laboratory, Groningen Biomolecular Sciences and Biotechnology
Institute, UniVersity of Groningen, Nijenborgh 4, 9747 AG, Groningen,
The Netherlands, and BASF AG, Fine Chemicals & Biocatalysis Research,
Ludwigshafen, Germany
Received June 5, 2006
ABSTRACT
A sequential kinetic resolution catalyzed by halohydrin dehalogenase was employed for the synthesis of two valuable enantiopure building
blocks. Resolution of methyl 4-chloro-3-hydroxybutanoate methylester ((R,S)-2) with use of a Trp249Phe mutant of halohydrin dehalogenase
yielded methyl 4-cyano-3-hydroxybutanoate methylester ((S)-4) with 96.8% ee (40% yield) and (S)-2 with 95.2% ee (41% yield). This reaction is
carried out in aqueous solution under mild conditions and provides access to a useful statin side-chain building block.
Halohydrin dehalogenases are bacterial enzymes that catalyze
the conversion of vicinal halohydrins into their corresponding
epoxides. Alternatively, they can catalyze the kinetic resolu-
tion of racemic epoxides by enantioselective ring opening,
which provides a new biocatalytic strategy for the preparation
of optically active compounds. In this nonnatural reaction,
various nucleophiles are accepted, such as cyanide,1,2 azide,3
and nitrite,4 making it possible to obtain different enantiopure
â-substituted alcohols. The enzyme from Agrobacterium
radiobacter AD1 (HheC) is the best studied halohydrin
dehalogenase. Its crystal structure and catalytic mechanism
have been determined. Earlier, we showed that HheC is an
efficient biocatalyst for the enantioselective and regioselec-
tive formation of â-azido alcohols3 and â-hydroxynitriles.2
In this paper we explore the potential of halohydrin deha-
logenase to catalyze the synthesis of optically pure methyl
4-cyano-3-hydroxybutanoate (4). This is a versatile building
block containing three functional groups. The R-enantiomer
can be applied as an intermediate in the production of
cholesterol-lowering drugs of the statin type. Various
chemoenzymatic strategies have been developed for the
synthesis of statin side-chain building blocks.5 Biocatalysts
that are used include alcohol dehydrogenase,6 R-chymo-
trypsin,7 nitrilase,8 and aldolase.9
The route to cyanohydrin 4 that we report here is based
on a sequential kinetic resolution of racemic 4-chloro-3-
hydroxybutyric acid methylester ((R,S)-2).
Initially, the racemic epoxide (R,S)-3 was tested as a
substrate for a reaction with cyanide in the presence of wild-
type halohydrin dehalogenase. The starting compound (R,S)-3
was prepared from commercially available methyl 4-chlo-
roacetoacetate (1). Reduction of 1 to (R,S)-2 was followed
by ring closure to the epoxide (Scheme 1). When (R,S)-3
was converted by cyanide-mediated ring opening catalyzed
by wild-type HheC, a moderate E value of 15 was found
and the enantiopurity of the product was low (Table 1).
† University of Groningen.
‡ BASF AG, Fine Chemicals & Biocatalysis Research.
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10.1021/ol061369h CCC: $33.50
© 2006 American Chemical Society
Published on Web 08/25/2006