Communications
solution from the nonsoluble solid, thus resulting in the enzyme
respectively, see e.g.: K. Faber, Biotransformations in Organic
Chemistry, 4th ed., Springer, Berlin, 2000, chap. 2.1.1, pp. 28 – 52.
[10] The workup was analogous to that described for the reaction in
the two-phase solvent system, see Ref. [7]. The development of a
workup protocol specifically for reactions in miniemulsions is
the subject of future work.
[11] Further examples for biocatalytic reactions at high substrate
concentrations are described, e.g., in: a) A. Liese, K. Seelbach,
C. Wandrey, Industrial Biotransformations, Wiley-VCH, Wein-
heim 2000; b) D. R. Yazbeck, C. A. Martinez, S. Hu, J. Tao,
Tetrahedron: Asymmetry 2004, 15, 2757 – 2763; c) M. Kataoka,
K. Kita, M. Wada, Y. Yasohara, J. Hasegawa, S. Shimizu, Appl.
Microbiol. Biotechnol. 2003, 62, 437 – 445; d) M. Schmidt, H.
Griengl, Top. Curr. Chem. 1999, 200, 193 – 226.
concentrate. In parallel, a miniemulsion consisting of rac-1 (65.2 g),
hexadecane (1.37 g), and 96 mL of a 1% surfactant solution (Lutensol
AT 50, BASFAG) was prepared by stirring these components with an
ultrasound tip (4 min at 200 W). Subsequently, the enzyme concen-
trate and the miniemulsion were mixed. In addition, the pH was
adjusted to pH 8.2 and maintained at this value by automated
titration with a 1m aqueous solution of sodium hydroxide. The
reaction temperature was 208C, and the reaction time was 17 h.
During the reaction, a white precipitate consisting of the desired
product (S)-2 forms. After the reaction, 160 mL of acetone were
added in order to complete the precipitation, and the resulting
mixture was stirred for a further 45 min. The solid material was
filtered and washed with a small amount of acetone and 100 mL of
MTBE. At a reaction time of 17 h, a conversion of ca. 45% was
achieved. The product (S)-2 was isolated after work-up in a yield of
37% and with an enantiomeric excess of > 99.4% ee.
[12] J.-Y. Houng, M.-L. Wu, S.-T. Chen, Chirality 1996, 8, 418 – 422.
[13] The n-propyl ester of rac-phenylalanine, rac-3, is considerably
more stable than the corresponding methyl ester, which under-
goes a nonenzymatic hydrolysis to a significant extent.
Received: August 11, 2005
Published online: February 7, 2006
Keywords: biphasic catalysis · emulsions · enantioselectivity ·
.
enzyme catalysis · hydrolysis
[1] Enzyme Catalysis in Organic Synthesis, Vol. 1–3, 2nd ed. (Eds.:
K. Drauz, H. Waldmann), Wiley-VCH, Weinheim 2002.
[2] For a review, see: P. S. J. Cheetham, J. Biotechnol. 1998, 66, 3 –
10.
[3] For selected examples of commercial biotransformations in two-
phase solvent systems, see: a) M. Kataoka, K. Kita, M. Wada, Y.
Yasohara, J. Hasegawa, S. Shimizu, Appl. Microbiol. Biotechnol.
2003, 62, 437 – 445; b) N. M. Shaw, K. T. Robins, A. Kiener in
Asymmetric Catalysis on Industrial Scale (Eds.: H. U. Blaser, E.
Schmidt), Wiley-VCH, Weinheim, 2004, pp. 105 – 115; c) P.
Poechlauer, W. Skranc, M. Wubbolts in Asymmetric Catalysis
on Industrial Scale (Eds.: H. U. Blaser, E. Schmidt), Wiley-VCH,
Weinheim, 2004, pp. 151 – 164; d) Ref. [7].
[4] A further interesting concept is the use of water-in-oil micro-
emulsions; for selected contributions, see: a) B. Orlich, H.
Berger, M. Lade, R. Schomäcker, Biotechnol. Bioeng. 2000, 70,
638 – 646; b) H. Stamatis, A. Xenakis, F. N. Kolisis, Biotechnol.
Adv. 1999, 17, 293 – 318; c) K. Holmberg, Adv. Colloid Interface
Sci. 1994, 51, 137 – 174.
[5] a) K. Landfester, M. Antonietti in Colloids and Colloid Assem-
blies (Ed.: F. Caruso), Wiley-VCH, Weinheim, 2004, chap. 6,
pp. 175 – 215; b) The expression “nanoreactors” describes stable
droplets on the nanometer scale in miniemulsions, in which or at
which the desired reaction occurs; for this concept of “nano-
reactors” also see: K. Landfester, Abstracts of Papers, 224th ACS
National Meetings, Boston, MA, USA, August 18 – 22, 2002 and
Ref. [5a].
[6] A. Taden, M. Antonietti, K. Landfester, Macromol. Rapid
Commun. 2003, 24, 512 – 516.
[7] H. Grꢀger, H. Werner (Degussa AG), US Patent 6869781, 2005.
[8] For previous, selected contributions to the hydrolase-catalyzed
resolution of rac-b-amino acid esters and corresponding N-
acylated derivatives, see: a) S. G. Cohen, S. Y. Weinstein, J. Am.
Chem. Soc. 1964, 86, 725 – 728; b) M. Prashad, D. Har, O. Repic,
T. J. Blacklock, P. Giannousis, Tetrahedron: Asymmetry 1998, 9,
2133 – 2136; c) S. Katayama, N. Ae, R. Nagata, Tetrahedron:
Asymmetry 1998, 9, 4295 – 4299; d) S. J. Faulconbridge, K. E.
Holt, L. G. Sevillano, C. J. Lock, P. D. Tiffin, N. Tremayne, S.
Winter, Tetrahedron Lett. 2000, 41, 2679 – 2681.
[9] For the definition of the terms “E value” and “ee value ” for the
quantification of the enantioselectivity and enantiomeric excess,
1648
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 1645 –1648