Stereoselective formation of bis(α-hydroxy ketones) via enzymatic carboligation

Article abstract of DOI:10.1021/jo0010274

The enzymatic approach to a novel class of chiral bis(α-hydroxy ketones) of type 5 and 8, which enable the synthesis of new multidentate ligands for asymmetric transition metal catalysis, is described. The key step is the second benzoylformate decarboxyla

Full text of DOI:10.1021/jo0010274

8608
J . Org. Chem. 2000, 65, 8608-8612
Ster eoselective F or m a tion of Bis(r-h yd r oxy k eton es) via
En zym a tic Ca r boliga tion
Thomas Du¨nnwald and Michael Mu¨ller*
Institut fu¨r Biotechnologie 2, Forschungszentrum J u¨lich GmbH, D-52425 J u¨lich, Germany
mi.mueller@fz-juelich.de
Received J uly 8, 2000
The enzymatic approach to a novel class of chiral bis(R-hydroxy ketones) of type 5 and 8, which
enable the synthesis of new multidentate ligands for asymmetric transition metal catalysis, is
described. The key step is the second benzoylformate decarboxylase catalyzed C-C-bond formation
between an aromatic dialdehyde and acetaldehyde, which proceeds with complete stereocontrol.
Transformation of enantiomerically enriched monoadduct (S)-4 (ee 88%) and (S)-7 (ee 79%) resulted
in optical pure (S,S)-5 and (S,S)-8 besides minor amounts of the corresponding diastereomeric meso-
forms.
Sch em e 1. Mech a n ism of BF D-Med ia ted
Ca r boliga tion of Ar om a tic Ald eh yd es a n d
Aceta ld eh yd e
In tr od u ction
In a former study we reported on the benzoylformate
decarboxylase (BFD) catalyzed formation of 2-hydroxy
ketones.1 BFD2,3 belongs to the class of thiamin diphos-
phate (ThDP) dependent enzymes which have been of
increasing interest during the past decade.4,5 Although
the main reaction catalyzed by BFD is the nonoxidative
decarboxylation of benzoyl formate,6 we could demon-
strate this biocatalyst to be suitable for the preparative
synthesis of (S)-2-hydroxypropanones7 and (R)-benzoins8
in high optical purity (Scheme 1) via C-C-coupling
reactions. Therefore, we want to extend this strategy by
subjecting bifunctionalized substrates to this benzoin
condensation type reaction with the aim to enable the
synthesis of new chiral transition metal complexes of type
1 and 2a for catalytic asymmetric processes9 and chiral
auxiliaries of type 2b. Due to its functional groups, 1
epoxides with TMS-N3. J acobsen and co-workers found
this reaction to be dependent on a second-order kinetics
with regard to the catalyst. It would be advantageous to
obtain covalently linked dimeric salen complexes which
can be synthesized by connecting the hydroxy moieties
of two molecules of 1 via, for example, polyether spacers.10
Especially compounds with C2 symmetry often exhibit a
higher capacity as stereochemical promotors compared
to those lacking totally in symmetry.11 Thus C2-sym-
metric chiral bis(oxazoline) copper(II) complexes such as
2a are effective promotors of enantioselective Diels-
Alder, aldol, ene, Michael, and amination reactions,12
whereas chiral bis(oxazolidinones)13 such as 2b may be
used as chiral auxiliaries.
(4) Sprenger, G. A.; Pohl, M. J . Mol. Catal. B: Enzymol. 1999, 6,
145.
(5) Scho¨rken, U.; Sprenger, G. A. Biochim. Biophys. Acta 1998, 1385,
229.
(6) Iding, H.; Siegert, P.; Mesch, K.; Pohl, M. Biochim. Biophys. Acta
1998, 1385, 307.
resembles a modified salen complex which might be used,
for example, for asymmetric ring opening of meso-
(7) Du¨nnwald, T.; Demir, A. S.; Siegert, P.; Pohl, M.; Mu¨ller, M. Eur.
J . Org. Chem. 2000, 2161.
(8) Demir, A. S.; Iding, H.; Pohl, M.; Du¨nnwald, T.; Mu¨ller, M.
Tetrahedron: Asymmetry 1999, 10, 4769.
(9) Type, H. J . Chem. Soc., Perkin Trans. 1 2000, 275.
(10) Konsler, R. G.; Karl, J .; J acobsen, E. N. J . Am. Chem. Soc. 1998,
120, 10780.
(11) Whitesell, J . K. Chem. Rev. 1989, 89, 1581.
(12) J ohnson, J . S.; Evans, D. A. Acc. Chem. Res. 2000, 33, 325.
(13) Lee, S.; Lim, C. W.; Kim, D. C.; Lee, J . K. Tetrahedron:
Asymmetry 2000, 11, 1455.
* To whom correspondence should be addressed. Phone:
+49(0)2461/613374. Fax: +49(0)2461/613870.
(1) Iding, H.; Du¨nnwald, T.; Greiner, L.; Liese, A.; Mu¨ller, M.;
Siegert, P.; Gro¨tzinger, J .; Demir, A. S.; Pohl, M. Chem. Eur. J . 2000,
6, 1483.
(2) Ward, O. P.; Wilcocks, R.; Prosen, E.; Collins, S.; Dewdney, N.
J .; Hong, Y. In Microbial Reagents in Organic Synthesis; Servi, A.; Ed.,
NATO ASI Ser., Kluwer Acad. Publ.: New York, 1992; Vol. 67.
(3) Wilcocks, R.; Ward, O. P.; Collins, S.; Dewdney, N. J .; Hong, Y.;
Prosen, E. Appl. Environ. Microbiol. 1992, 58, 1699.
10.1021/jo0010274 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/21/2000

Stereoselective Formation of Bis(R-hydroxy ketones)
J . Org. Chem., Vol. 65, No. 25, 2000 8609
Sch em e 2. BF D-Med ia ted Ca r boliga tion of
Isop h th a la ld eh yd e a n d Aceta ld eh yd e Yield in g
(S)-4 a n d (S,S)-5
F igu r e 1. Progress of BFD-mediated carboligation of iso-
phthalaldehyde (3) and acetaldehyde yielding (S)-4 and (S,S)-
5; concentration of 3 (b), (S)-4 (9), (S,S)-5 (2), and ee of (S)-4
(1) are shown.
performed in situ without a requirement for isolation of
intermediate 4. To evaluate the stereoselectivity of both
enzymatic reaction steps, we had to synthesize racemic
standard samples. These were available by reaction of 3
with trimethylsilyl cyanide (“Umpolung”),14 deprotona-
tion with LDA, and subsequent quenching15 with acet-
aldehyde (Scheme 3). The separation of all stereoisomers
of both 4 and 5 was performed by chiral phase HPLC
using a Chiralpak AD column. Due to symmetry reasons,
bis(R-hydroxy ketone) 5 consists of two enantiomers,
(S,S)- and (R,R)-isomer, and one diastereomeric meso-
form. When comparing the chromatograms of both, the
enzymatically and chemically (racemic) prepared 4 and
5 (Scheme 3), we observed that enzymatically synthesized
monoadduct 4 exhibited an enantiomeric excess of about
88-90% at the maximum of product formed (Figure 1).
The absolute configuration of (S) was assigned by mecha-
nistical studies1 and comparison of HPLC data with
already known 2-hydroxy ketones.7 It is noteworthy that
the ee of (S)-4 increases with a progressive in situ
formation of bisadduct 5 (Figure 1). For that reason it
can be concluded that BFD accepts both enantiomers of
4 as substrate. Therefore, in that case it is not possible
to use BFD for kinetic racemate resolution, if the first
stereocenter is generated chemically in racemic form.
However, the second reaction step proceeds within detec-
tion limits completely stereospecific. Monoadduct (S)-4
is converted to (S,S)-5 in optical pure form (ee >99%),
whereas the minor enantiomer (R)-4 leads to (meso)-5
which is the diastereomeric form of the former one. No
formation of (R,R)-5 could be detected by chiral phase
HPLC. Separation of (S,S)-5 and meso-5 using several
different methods resulted only in slight partition of the
two diastereomeric forms on silica HPLC phases, and no
baseline separation has been achieved so far.
Resu lts a n d Discu ssion
In former work we observed that meta-substituted
aromatic aldehydes provide the highest ee values in good
to excellent conversion rates in the BFD-catalyzed cou-
pling reaction with acetaldehyde. Para-substituted benz-
aldehyde derivatives afforded 2-hydroxy ketones with
lower ee values and simultaneous lower conversion rates,
in general. Ortho-substituted aromatic aldehydes, except
2-fluorobenzaldehyde, are not accepted as substrates at
all.7 With this knowledge we subjected isophthalaldehyde
(3), which comprises a 1,3-substitution pattern, to this
biotransformation. Due to the presence of two carbalde-
hyde functionalities, we expected the formation of bis-
(R-hydroxy ketones) as products for this kind of substrate.
GCMS analysis proved the formation of two products
generated by the reaction of 3 and acetaldehyde. These
products were assigned to the structures 4 and 5 (Scheme
2) by evaluation of mass data. Determination of conver-
sion rates depending on reaction time (Figure 1) indicated
the feasibility of the 2-fold reaction for such substrates
in general. It should be possible to isolate either the
mono- or the diadduct of isophthalaldehyde and acet-
aldehyde in high yield by variation of the reaction time
or substrate feed strategies. The yield of 4 passes through
a maximum of 75% after 7 h, whereas compound 5 is
formed in 10% yield. Prolonged reaction time led to an
increase of 5 to 65% yield with concomitant decrease of
monoadduct 4. Transferring this strategy to preparative
scale synthesis the biotransformation was performed in
a simple batch reactor by dissolving isophthalaldehyde
and acetaldehyde in aqueous buffer solution containing
ThDP with subsequent addition of BFD. Depending on
the reaction time, we could isolate both 4 (0.4 g scale)
and 5 (1 g scale), in 58% and 82% yield, respectively. The
second enzymatic coupling reaction affording 5 was
Encouraged by this results, we swapped the 1,3-
substitution pattern of the substrate for the BFD-
catalyzed C-C-bond forming reaction for an 1,4-aromatic
dicarboxaldehyde (terephthalaldehyde). In fact, first
experiments on an analytical scale indicated the general
applicability of terephthalaldehyde as substrate in con-
(14) Cf. Deuchert, K.; Hertenstein, U.; Hu¨nig, S.; Wehner, G. Chem.
Ber. 1979, 112, 2045.
(15) Cf. Hu¨nig, S.; Wehner, G. Chem. Ber. 1979, 112, 2062.

8610 J . Org. Chem., Vol. 65, No. 25, 2000
Du¨nnwald and Mu¨ller
Sch em e 3. Ch em ica l Syn th esis of All Ster eoisom er s of 4 a n d 5. HP LC Ch r om a togr a m s of r a c-4 (bottom ),
r a c/m eso-5 (m id d le) a n d En zym a tica lly P r ep a r ed 4 a n d 5 (top ) Ar e Sh ow n
junction with acetaldehyde, although the reaction time,
especially for the second coupling step, had to be in-
creased significantly. Preparative enzymatic conversion
of terephthalaldehyde and acetaldehyde yielded 7 and 8
in moderate yield (23% and 14%, respectively). Even
elongation of reaction time to three weeks did not result
in increased product formation. Nevertheless, the bis-
adduct (S,S)-8 was obtained, besides diastereomeric
meso-8, in optically pure form from (S)-7 (ee ) 79%)
(Figure 2). For determination of stereoisomers by chiral
phase HPLC (Chiralcel OB), racemic 8 was synthesized
using the same protocol as for rac-5.
In summary we have developed a new enzymatic
strategy to a novel class of C2-symmetric chiral bis(R-
hydroxy ketones) comprising two stereogenic centers. The
enzymatic approach functioned well with aromatic di-
aldehydes in an effective manner, particularly when
applying 1,3-disubstituted substrates. This method en-
ables the synthesis of novel multidentate complex ligands
and chiral auxiliaries of type 1 and 2 by diastereoselective
reductive amination of (S,S)-5 and (S,S)-8, respectively.
Exp er im en ta l Section
Gen er a l Met h od s. All reagents were used in analytical
grade. Isophthalaldehyde (3) and terephthalaldehyde were
purchased from Aldrich. Solvents were dried and distilled by
standard methods if necessary. BFD was used as a recombi-
nant enzyme elongated with a hexahistidine tail (BFD-His)
expressed in E. coli.1 Purification of the enzyme is described
in the supplement. BFD activity is related to the catalytic
decarboxylase activity which was determined in a coupled
photometric assay. One unit is defined as the amount of
enzyme that decarboxylates 1 µmol of benzoyl formate per
minute at 30 °C in potassium phosphate buffer (50 mmol‚L-1
,
pH 6.0). Enzymatic syntheses were performed in standard
buffer consisting of potassium phosphate (50 mmol‚L-1, pH
7.0) containing MgSO4 (0.5 mmol‚L-1) and ThDP (0.5 mmol‚L-1).
Prior to product workup reaction mixtures containing enzyme
were filtered using an ultrafiltration membrane (Amicon
YM10, cut off 10000 Da) in order to remove proteins. TLC was
carried out on aluminum sheets precoated with silica gel 60F254
(Merck), and the spots were visualized with UV light (λ ) 254
nm). Preparative column chromatography was carried out on
silica gel 60 (mesh size 40-63 µm). NMR spectra were recorded
as CDCl3 solutions at 300 MHz (1H) and 75.5 MHz (13C,
DEPT135), respectively. Chemical shifts (δ) are reported in
ppm relative to CHCl3 (1H, δ ) 7.26) and CDCl3 (13C, δ ) 77.0)
F igu r e 2. All stereoisomers of 2-hydroxy ketone 7 and bis-
(2-hydroxy ketone) 8 resulting from chemical (racemic) syn-
thesis. Product ratio and ee of products prepared enzymatically
from terephthalaldehyde and acetaldehyde are given.

Stereoselective Formation of Bis(R-hydroxy ketones)
J . Org. Chem., Vol. 65, No. 25, 2000 8611
as internal standard. GCMS spectra were determined on a HP-
5MS capillary column (5% phenyl methyl siloxane, 30 m ×
250 µm; TGC(injector) ) 250 °C, TMS(ion source) ) 200 °C, time
program (oven): T0 min ) 60 °C, T3 min ) 60 °C, T14 min ) 280 °C
mol‚L-1), and BFD (2000 U) in standard buffer (200 mL). After
14 d the reaction was stopped and the resulting crude product
purified by column chromatography (i-hexane/ethyl acetate
2:1) to yield (S)-7 (81 mg, 23%; Rf ) 0.35) and (S,S)-8 (60 mg,
14%; Rf ) 0.13). The second fraction consisting of (S,S)-8 as
main product contained 7.5% of meso-8. Unreacted substrate
was recovered.
(heating rate 20 °C‚min-1), T19
) 280 °C, MS: EI, 70 eV).
min
HPLC was performed on a chiral phase column Chiralpak AD
(Daicel Ltd., 250 × 4 mm, equipped with a precolumn, 80 × 4
mm; i-hexane:2-propanol ) 85:15, flow 0.75 mL‚min-1, 10 °C)
or Chiralcel OB (Daicel Ltd., 250 ×4 mm, equipped with a
precolumn, 80 ×4 mm; i-hexane:2-propanol ) 80:20, flow 0.75
mL‚min-1, 20 °C). Preparative HPLC was carried out using a
Kromasil Si-10 column (CS, Germany, 250 × 10 mm; gradient
(S)-7: ee ) 79%. [R]20 ) -37° (c ) 0.3, CHCl3). HPLC
D
1
(Chiralcel OB): tR(S) ) 25.1 min; tR(R) ) 41.3 min. H NMR:
δ ) 1.43 (d, J ) 7.2 Hz, 3H), 3.85 (br, 1H), 5.18 (q, J ) 7.1 Hz,
1H), 7.98 (d, J ) 7.8 Hz, 2H), 8.06 (d, J ) 7.8, 2H),), 10.08 (s,
1H). 13C NMR: δ ) 22.2 (CH3), 70.2 (CHOH), 129.6, 130.4
(CH), 138.2, 139.9 (Cq), 191.9 (CHO), 202.4 (CO). GCMS: tR
) 10.1 min; m/z (%) ) 178 (M+, 0.5), 133 (M+ - C2H5O, 100),
105 [M+ - C2H5O - CO, 57). HRMS [M+ - C2H5O]; m/z calcd
for C8H5O2 133.0290; found 133.0289.
i-hexane:2-propanol T0
) 99:1, T50
) 94:6, T80
) 94:
min
min
min
6, flow 4 mL‚min-1, 4 °C). HRMS (EI) and microanalyses were
carried out at the Analytical Department, Chemische Institute
der Universita¨t Bonn.
(S)-3-(2-Hyd r oxyp r op ion yl)ben za ld eh yd e ((S)-4). Iso-
phthalaldehyde (3) (512 mg, 3.8 mmol, 10 mmol‚L-1) was
dissolved in standard buffer (380 mL). After addition of
acetaldehyde (10.7 mL, 0.19 mol, 0.5 mol‚L-1), the reaction
was started by adding BFD (600 U), and the reaction mixture
was allowed to stand at rt for 16 h. Conversion was monitored
by HPLC by extracting analytical samples (150 µL) with
trichloromethane (150 µL) followed by phase separation by
centrifugation (13000 rpm). The reaction mixture was filtered
using an ultrafiltration membrane, the filtrate was extracted
with ethyl acetate (3 × 60 mL), and the organic layer was dried
with Na2SO4. Evaporation of the solvent and purification of
the crude product by column chromatography (i-hexane/ethyl
acetate 2:1; Rf ) 0.27) afforded (S)-4 as a viscous yellowish oil
(396 mg, 58%). ee ) 88%. [R]20D ) -78° (c ) 1.2, CHCl3). HPLC
(Chiralpak AD): tR(S) ) 21.5 min; tR(R) ) 25.3 min. 1H NMR:
δ ) 1.49 (d, J ) 7.1 Hz, 3H), 3.75 (br, 1H), 5.23 (q, J ) 7.1 Hz,
1H), 7.72 (‘t’, J ) 7.7 Hz, 1H), 8.16 (d‘t’, J ) 7.7, 1.4 Hz, 1H),
8.21 (d‘t’, J ) 7.7, 1.4 Hz, 1H), 8.42 (‘t’, J ) 1.4 Hz, 1H), 10.12
(s, 1H). 13C NMR: δ ) 22.5 (CH3), 70.0 (CHOH), 130.1, 130.3,
134.5 (CH), 134.6 (Cq), 134.8 (CH), 137.2 (Cq), 191.5 (CHO),
201.9 (CO). GCMS: tR ) 9.7 min; m/z (%) ) 178 (M+, 1.6), 133
(M+ - C2H5O, 100), 105 (M+ - C2H5O - CO, 46). HRMS [M+];
m/z calcd for C10H10O3 178.0630; found 178.0622.
(S,S)-2-Hyd r oxy-1-[3-(2-h yd r oxyp r op ion yl)p h en yl]p r o-
p a n -1-on e ((S,S)-5). Isophthalaldehyde (3) (670 mg, 5.0 mmol,
10 mmol‚L-1) was dissolved in standard buffer (500 mL). After
addition of acetaldehyde (14.1 mL, 0.25 mol, 0.5 mol‚L-1), the
reaction was started by adding BFD (1200 U), and the reaction
mixture was allowed to stand at rt. Conversion was monitored
by HPLC by extracting analytical samples (150 µL) with
trichloromethane (150 µL) followed by phase separation by
centrifugation (13000 rpm). If conversion stagnated, one more
portion of BFD (400 U) was added. After 4 d the reaction
mixture was filtered using an ultrafiltration membrane, the
filtrate was extracted with ethyl acetate (3 × 60 mL), and the
organic layer was dried with Na2SO4. Evaporation of the
solvent gave a mixture (1.04 g) consisting of (S)-4 (18%), (S,S)-5
(75%), and meso-5 (7%). Purification of the crude product by
either column chromatography (CH2Cl2/ethyl acetate 3:1; Rf
) 0.19) or preparative HPLC on Kromasil Si-10 afforded a
mixture of (S,S)-5 (94%, ee >99%) and meso-5 (6%) as a viscous
yellowish oil. [R]20D ) -90° (c ) 1.4, CHCl3). HPLC (Chiralpak
AD): tR(S,S) ) 31.1 min; tR(meso) ) 38.4 min. Preparative
HPLC (Kromasil Si-10): tR((S,S)-5) ) 49.6 min; tR(meso-5) )
51.9 min. 1H NMR: δ ) 1.50 (d, J ) 7.0 Hz, 6H), 3.71 (br,
2H), 5.22 (q, J ) 7.0 Hz, 2H), 7.69 (t, J ) 7.6 Hz, 1H), 8.17
(dt, J ) 7.6, 1.7 Hz, 2H),), 8.48 (t, J ) 1.7 Hz, 1H). 13C NMR:
δ ) 22.50, 22.52 (meso) (CH3) 70.0 (CHOH), 129.0, 129.1
(meso), 130.1, 133.9, 134.0 (meso) (CH), 134.5 (Cq), 201.88
(meso), 201.93 (CO). GCMS: tR ) 11.1 min; m/z (%) ) 177 (M+
- C2H5O, 82), 162 (M+ - C2H5O-CH3, 46), 133 (M+ - C4H9O2,
100), 105 (M+ - C4H9O2 - CO, 96). HRMS [M+ - C2H5O]; m/z
calcd for C10H9O3 177.0552; found 177.0550.
(S,S)-8: ee >99%. [R]20 ) -29° (c ) 0.4, CHCl3). HPLC
D
1
(Chiralpak OB): tR(S,S) ) 23.0 min; tR(meso) ) 32.7 min. H
NMR: δ ) 1.40 (d, J ) 7.1 Hz, 6H), 3.79 (br, 2H), 5.18 (q, J )
7.1 Hz, 2H), 8.04 (s, 4H). 13C NMR: δ ) 22.2 (CH3) 70.2
(CHOH), 129.4 (CH), 137.7 (Cq), 202.2 (CO). GCMS: tR ) 11.9
min; m/z (%) ) 177 (M+ - C2H5O, 100), 133 (M+ - C4H9O2,
18), 105 (M+ - C4H9O2 - CO, 30). HRMS [M+ - C2H5O]; m/z
calcd for C10H9O3 177.0552; found 177.0543.
[3-(Cya n otr im eth ylsila n yloxym eth yl)p h en yl]tr im eth -
ylsila n yloxya ceton itr ile (6).14 Isophthalaldehyde (3) (1.88
g, 14 mmol) was added slowly to a mixture of trimethylsilyl
cyanide (2.98 g, 30 mmol) and anhydrous ZnI2 (catalytic
amount). The reaction mixture was heated to 95 °C for 2 h.
The resulting crude product was fractionated in vacuo, yielding
pure 6 (3.95 g, 85%) as a colorless liquid. Bp0.02 mbar 108 °C. 1H
NMR: δ ) 0.27 (s, 18H), 5.55 (s, 2H), 7.51 (m, 3H), 7.58 (s,
1H). 13C NMR: δ ) 0.2 (Si(CH3)3), 63.7 (CHCN), 119.3 (CN),
124.5, 127.6, 130.1 (CH), 137.7 (Cq). GCMS: tR ) 12.3 min;
m/z (%) ) 332 (M+, 0.1), 317 (M+ - CH3, 47), 218 (M+ - C4H8-
NOSi, 100).
r a c-3-(2-Hyd r oxyp r op ion yl)ben za ld eh yd e (r a c-4). A
solution of LDA (3 mmol) in dry THF (10 mL) was added
dropwise to 6 (1 g, 3 mmol) dissolved in dry THF (5 mL) at
-55 °C. The resulting red-colored solution was stirred for 30
min at -55 °C, whereupon dry acetaldehyde (0.4 mL, 7 mmol)
was added at this temperature. The reaction mixture was
warmed to rt within 4 h and subsequently quenched with
saturated NH4Cl-solution (20 mL). After an additional 5 min
of stirring at rt, the mixture was extracted with diethyl ether
(3 × 10 mL) and the organic layer dried with Na2SO4 and
evaporated to dryness. The resulting crude TMS-ether of rac-4
was stirred in a mixture of hydrochloric acid (2 N, 10 mL) and
methanol (5 mL) for 15 h. After addition of water (10 mL),
the crude product was extracted with ethyl acetate (3 × 10
mL), the organic layer washed with aqueous NaOH (1 N, 10
mL) and dried with Na2SO4. Purification by column chroma-
tography (i-hexane/ethyl acetate 2:1; Rf ) 0.27) afforded rac-4
as a viscous yellowish oil (270 mg, 51%). HPLC (Chiralpak
AD): tR(S) ) 21.5 min; tR(R) ) 25.3 min. All analytical data
are in accordance with enzymatically prepared (S)-4.
r a c/m eso-2-Hyd r oxy-1-[3-(2-h yd r oxyp r op ion yl)p h en yl]-
p r op a n -1-on e (r a c/m eso-5). A solution of 6 (1 g, 3 mmol) in
dry THF (5 mL) was added dropwise to a solution of LDA (6.2
mmol) in dry THF (20 mL) at -55 °C. The resulting dark red-
colored solution was stirred for 30 min at -55 °C, whereupon
dry acetaldehyde (1.0 mL, 17.5 mmol) was added at this
temperature. The reaction mixture was warmed to rt within
4 h and subsequently quenched with saturated NH4Cl solution
(20 mL). After an additional 5 min of stirring at rt, the mixture
was extracted with diethyl ether (3 × 10 mL), the organic layer
dried with Na2SO4 and evaporated to dryness. The resulting
crude TMS-ether of rac/meso-5 was stirred in a mixture of
hydrochloric acid (2 N, 20 mL) and methanol (10 mL) for 15
h. After addition of water (30 mL), the crude product was
extracted with ethyl acetate (3 × 20 mL), the organic layer
washed with aqueous NaOH (1 N, 15 mL) and dried with
Na2SO4. Purification by column chromatography (CH2Cl2/ethyl
acetate 3:1; Rf ) 0.19) afforded rac/meso-5 as a viscous
yellowish oil (354 mg, 53%). HPLC (Chiralpak AD): tR(S,S) )
(S)-4-(2-Hyd r oxyp r op ion yl)ben za ld eh yd e ((S)-7) a n d
(S,S)-2-Hydr oxy-1-[4-(2-h ydr oxypr opion yl)ph en yl]pr opan -
1-on e ((S,S)-8). (S)-7 and (S,S)-8 were prepared according to
the procedure for (S,S)-5 dissolving terephthalaldehyde (268
mg, 2 mmol, 10 mmol‚L-1), acetaldehyde (5.6 mL, 0.1 mol, 0.5

8612 J . Org. Chem., Vol. 65, No. 25, 2000
Du¨nnwald and Mu¨ller
31.1 min; tR(R,R) ) 34.5 min; tR(meso) ) 38.4 min. All
analytical data are in accordance with enzymatically prepared
(S,S)-5 and meso-5.
23.0 min; tR(meso) ) 32.7 min; tR(R,R) ) 39.5 min. All
analytical data are in accordance with enzymatically prepared
(S,S)-8 and meso-8.
[4-(Cya n otr im eth ylsila n yloxym eth yl)p h en yl]tr im eth -
ylsila n yloxya ceton itr ile (9). 9 was prepared according to
the procedure for 6 using terephthalaldehyde (1.88 g, 14
mmol), trimethylsilyl cyanide (2.98 g, 30 mmol), and anhy-
drous ZnI2 (catalytic amount). The crude product was fraction-
ated in vacuo yielding pure 9 (3.83 g, 82%) as a colorless liquid.
Ack n ow led gm en t. This work has been supported
by the Deutsche Forschungsgemeinschaft in the scope
of SFB 380. The skillful technical assistance of Ms.
Lydia Walter is gratefully acknowledged. We thank Dr.
Martina Pohl and Dipl.-Chem. Petra Siegert (Institut
fu¨r Enzymtechnologie, Heinrich-Heine-Universita¨t Du¨s-
seldorf, Germany) for providing the biocatalyst.
Bp0.03
128 °C. 1H NMR: δ ) 0.28 (s, 18H), 5.53 (s, 2H),
mbar
7.54 (s, 4H). 13C NMR: δ ) 0.2 (Si(CH3)3), 63.6 (CHCN), 119.3
(CN), 127.3 (CH), 137.9 (Cq). GCMS: tR ) 11.9 min; m/z (%) )
332 (M+, 1.6), 317 (M+ - CH3, 100), 218 (M+ - C4H8NOSi,
65).
Su p p or t in g In for m a t ion Ava ila b le: 1H NMR and 13C
NMR spectra of compounds (S)-4, (S,S)-5, (S)-7, and (rac/
meso)-8 as well as the method for the preparation of the
enzyme. This material is available free of charge via the
Internet at http://pubs.acs.org.
r a c/m eso-2-Hyd r oxy-1-[4-(2-h yd r oxyp r op ion yl)p h en yl]-
p r op a n -1-on e (r a c/m eso-8). rac/meso-8 was prepared accord-
ing to the procedure for rac/meso-5 using 9 (1 g, 3 mmol), LDA
(6.2 mmol), and dry acetaldehyde (1 mL, 17.5 mmol). Purifica-
tion of the crude product by column chromatography (i-hexane/
ethyl acetate 1:1; Rf ) 0.27) afforded rac/meso-8 as a viscous
yellowish oil (208 mg, 31%). HPLC (Chiralpak OB): tR(S,S) )
J O0010274