Application of pig liver esterase catalyzed transesterification in organic media to the kinetic resolution of glycerol derivatives

Article abstract of DOI:10.1016/S0957-4166(99)00380-8

The PLE/MPEG catalyzed transesterification of the glycerol ketals rac-1a and rac-1d-f with vinyl propionate in toluene proceeded with good selectivities (E=24-34) and gave the enantiomerically enriched S-alcohols 1a and 1d-f, and the S-esters 2a and 2d-f. High selectivities (E=99 and E≥200) were observed in the transesterification of the glycerol ether rac-3 and its desoxy analog rac-5, both having a secondary hydroxy group, with PLE/MPEG. In transesterifications in organic media PLE exhibited a much higher enantioselectivity than in hydrolysis in water.

Full text of DOI:10.1016/S0957-4166(99)00380-8

Pergamon
Tetrahedron: Asymmetry 10 (1999) 3747–3758
Application of pig liver esterase catalyzed transesterification in
organic media to the kinetic resolution of glycerol derivatives
Manfred Jungen and Hans-Joachim Gais ∗
Institut für Organische Chemie der Rheinisch-Westfälischen Technischen Hochschule Aachen, Professor-Pirlet-Straße 1,
D-52056 Aachen, Germany
Received 22 July 1999; accepted 27 August 1999
Abstract
The PLE/MPEG catalyzed transesterification of the glycerol ketals rac-1a and rac-1d–f with vinyl propionate
in toluene proceeded with good selectivities (E=24–34) and gave the enantiomerically enriched S-alcohols 1a and
1d–f, and the S-esters 2a and 2d–f. High selectivities (E=99 and E≥200) were observed in the transesterification
of the glycerol ether rac-3 and its desoxy analog rac-5, both having a secondary hydroxy group, with PLE/MPEG.
In transesterifications in organic media PLE exhibited a much higher enantioselectivity than in hydrolysis in water.
© 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Pig liver esterase (PLE) is one of the most valuable catalysts for the enantioselective hydrolysis of
esters in aqueous solution.1–4 However, unlike lipases PLE exhibits only very low activity in organic
media, which renders its application as such to the enantioselective acylation of alcohols practically
impossible. Initial attempts to convey activity to PLE in organic media by entrapment in water-filled
porous supports5,6 or by the covalent attachment of hydrated methoxypolyethylene glycol (MPEG)
residues7 were less successful. We have found recently that this problem can be overcome, at least
in part, by simply using a colyophilisate of PLE and MPEG (termed as PLE/MPEG) in toluene of a
low water content.8 We now describe the application of the PLE/MPEG catalyzed transesterification in
organic media to the kinetic resolution of glycerol ketals. Enantiomerically enriched glycerol ketals are
important starting materials for the synthesis of biologically active compounds.9–12 Resolution of 1,2-
ketals of glycerol is synthetically especially attractive because of the possibility of a complete conversion
of the racemate to a given enantiomer via an acid catalyzed racemization of the unwanted enantiomer.
∗
Corresponding author. E-mail: gais@rwth-aachen.de
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00380-8

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Previously, the kinetic resolution of glycerol ketals and esters of glycerol ketals had been accomplished
with various degrees of success when mainly lipases were used.13–38
2. Results and discussion
The racemic glycerol ketals rac-1a–f39–44 (Scheme 1) were selected for the present study because
of the possibility of a structure-based optimization of the enantioselectivity of the PLE/MPE catalyzed
transesterification.1–3 PLE/MPEG containing 0.8% water was prepared by colyophilization of desalted
PLE (30 mg, 160 U/mg) with MPEG (MW 5000, 1 g). The PLE/MPEG catalyzed acylations of rac-1a–f
were run on a 4–21 mmol scale by using 2900–6300 U of PLE, 3.6–5.0 equiv. of vinyl propionate as the
acyl donor and toluene as the solvent. The reaction mixtures consisted in most cases of two phases. The
progress of the reactions and the selectivities were determined by GC on achiral and chiral stationary
phases or by HPLC on a chiral stationary phase directly from samples of the reaction mixtures without
prior27 derivatization.
Scheme 1.
All ketals were substrates for PLE under the conditions employed (Table 1). Preparatively useful
enantioselectivities, as expressed in enantiomeric ratios (E),45,46 were observed in the case of the
dimethyl, diphenyl, cyclopentylidene and cyclohexylidene derivatives rac-1a, rac-1d, rac-1e and rac-1f,
respectively. In all the cases investigated the R-enantiomer of the racemic glycerol ketals reacted faster.47
The selectivities of the PLE/MPEG catalyzed transesterification of rac-1a and rac-1d–f are generally
higher than those recorded with lipases (cf. Table 1).
We had previously observed that in PLE/MPEG catalyzed transesterification of racemic alcohols in
toluene the activity of the enzyme and the enantioselectivity were crucially dependent on the water
content of the reaction mixture.8 While the maximum of the selectivity was reached with an initial
water content of 1%, the maximum of the activity was attained with an initial water content of 0.2%.
In the case of the transesterification of rac-1a–f the reaction mixtures initially contained 0.4% water. A
study of the resolution of rac-1f in toluene in the presence of varying amounts of water revealed similar
dependencies of the enantioselectivity and the activity on the initial water content (Table 2). The highest
E value was recorded with an initial water content of 1%. Changing the acyl donor from vinyl propionate
to isopropenyl propionate in the transesterification of rac-1f did not alter the selectivity but led to a
decrease of the activity of PLE.
Finally, the influence of the solvent upon the activity and the selectivity of PLE in the transesterification
of rac-1f was studied (Table 3). The results obtained show that the activity and selectivity of PLE in

M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
3749
Table 1
PLE/MPEG catalyzed acylation of the glycerol derivatives rac-1a–f with vinyl propionate in toluene
(initial water content: 0.4%)[a]
Table 2
PLE/MPEG catalyzed transesterification of rac-1f in toluene in the presence of varying amounts of
water and additives
transesterification in organic solvents are generally the highest in solvents of low polarity8 as judged by
their ET values48 or log P values.49
Acetaldehyde and acetone are formed as by-products in the above PLE/MPEG catalyzed transesteri-
fications with vinyl propionate and isopropenyl propionate, respectively. It has recently been demonstra-
ted that in lipase catalyzed transesterifications with vinyl acetate the acetaldehyde liberated can lead to
a deactivation of the enzyme.50 Thus, the influence of acetaldehyde and acetone upon the activity and
enantioselectivity of PLE in the transesterification of rac-1f with vinyl propionate in toluene was studied.
While the addition of 9 equiv. of acetaldehyde resulted in a complete loss of the activity of PLE, that of
8 equiv. of acetone decreased the activity of the enzyme but left the selectivity practically unchanged.
In addition to the ketals rac-1a–f the carbonate rac-1g22,41 was investigated because of its different
structure (Scheme 2). The PLE/MPEG catalyzed acylation of rac-1g51 with vinyl propionate in chloro-
form (0.4% water), which had to be used as solvent because of the low solubility of rac-1g in toluene,
proceeded rather slowly with a similar selectivity (E=14) to that of the diethyl ketal rac-1b in toluene.
Finally, we studied the PLE/MPEG catalyzed transesterification of the glycerol ether rac-319 which
carries a secondary hydroxy group (Scheme 3). Although the activity of PLE/MPEG towards rac-3 was

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M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
Table 3
PLE/MPEG catalyzed transesterification of rac-1f in different solvents
Scheme 2.
relatively low under the conditions employed, the selectivity of the transesterification (E=99) was much
higher than in the case of rac-1a–f. At 28% conversion (10 d) the S-alcohol 318,52 was obtained with 42%
ee in 56% yield and the R-ester 4 with 97% ee in 27% yield. Similar selectivities had been reported for
the transesterification of other racemic secondary alcohols of type 3 by using lipases.38a,c,d
Scheme 3.
Having obtained these results, we were wondering whether the high enantioselectivity would be
retained in the case of the secondary alcohol rac-553 which carries, at the stereogenic center, a benzyl
group instead of a phenoxymethyl group. The PLE/MPEG catalyzed transesterification of rac-5 with
vinyl propionate in toluene (0.4% water) proceeded with high selectivity (E≥200) and led after 47%
conversion (5 days) to the isolation of the R-alcohol 554,55 with 90% ee in 41% yield and of the S-ester 6
with 97% ee in 39% yield. Thus, it seems as if the PLE/MPEG catalyzed transesterification is especially
appropriate for the resolution of secondary alcohols, carrying a phenoxymethyl or a benzyl group at the
stereogenic center, as exemplified by rac-3, rac-5 and racemic 1-phenyl-2-propanol.8
In all of the above described transesterifications with MPEG/PLE the enzyme was discharged during
work-up. However, we have shown previously that PLE can conveniently be immobilized in transes-
terifications simply by the placement of a polyaramide ultrafiltration membrane in the flask, containing

M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
3751
PLE/MPEG, the substrate and the acyl donor in toluene.8 Within a short time a spontaneous and complete
adsorption of PLE together with MPEG and water occurs on the membrane. Thus, after the completion of
the transesterification the liquid phase is removed and the immobilized PLE can be reused several times
without significant loss of activity.56
For comparison we studied the hydrolysis of the propionates rac-2f and rac-4 with PLE in aqueous
solution (Scheme 4). Most surprisingly, the hydrolysis of rac-2f proceeded only with a low enantioselec-
tivity (E=2) and that of rac-4 was almost unselective. A similar low enantioselectivity (E=2–5) had been
reported previously for the PLE catalyzed hydrolysis of the butyrate of rac-1a in aqueous solution.34 In
contrast, the lipase catalyzed hydrolyses of esters of rac-1a–f proceed with somewhat higher selectivities
(E values up to 13).18,33,57
Scheme 4.
3. Conclusion
The PLE/MPEG catalyzed transesterification in organic media allows for the attainment of enantiome-
rically enriched glycerol ketals and their esters on a g-scale. In the case of solketal (rac-1a) PLE/MPEG
should permit a larger scale resolution. Interestingly, the PLE/MPEG catalyzed transesterification of
rac-1a and rac-5 in organic media proceeded with much higher enantioselectivities than the PLE
catalyzed hydrolysis of the corresponding esters rac-2f and rac-4 in water. The activity of PLE/MPEG
in transesterification with vinyl acetate in toluene is lower than that of most lipases in organic media.
However, the activity of PLE under these conditions can perhaps be significantly increased by the removal
of the acetaldehyde liberated during the transesterification.
4. Experimental
4.1. General remarks
Chemical shifts are given in ppm relative to Me4Si: δ 0.00 as internal standard. J values are reported in
hertz. Peaks in the 13C NMR spectra are denoted as ‘u’ for carbons with zero or two attached protons or
‘d’ for carbons with one or three attached protons, as determined from the ATP pulse sequence. Specific
rotations are given in grad mL/dm g (c in g/100 mL). The enzymatic transesterifications, which were
run at ca. 22°C, were monitored by GC analysis on a CP-Sil-8 column. PLE (EC 3.1.1.1, 150 U/mg)
was purchased from Boehringer Mannheim as a suspension in 3.2 M NH4SO4. The activity of PLE
was determined by hydrolysis of ethyl butyrate in aqueous buffer solution (pH 8.0, 25°C). PLE/MPEG
was prepared as previously described from MPEG and PLE which was first desalted by ultrafiltration
(cut-off 30 kDa) under ice cooling.8 Enantiomeric ratios were determined by GC analysis on an octakis-
(2,3-O-dipentyl-6-O-methyl)-γ-cyclodextrin column (25 m×0.25 mm) (Lipodex γ-6-Me) (Macherey

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M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
Nagel), a permethylated β-cyclodextrin column (25 m×0.25 mm) (CP-Chirasil-Dex-CB) (Chrompack),
and on an octakis-(2,6-di-O-pentyl-3-O-butyl)-γ-cyclodextrin column (25 m×0.25 mm) (Lipodex E)
(Macherey–Nagel). Hydrogen was used as the carrier gas at 100 kPa. Column chromatography was
done on a Merck silica gel 60 (230–400 mesh). MPEG5000 was purchased from Sigma. The water
content of PLE/MPEG was determined by Karl–Fischer titration with Karl–Fischer solutions from Merck
and Riedel–de Haën. Correct C,H analyses were obtained for all enantiomerically enriched compounds
described.
4.2. Determination of enantiomeric ratios
GC: rac-1a and rac-2a: Lipodex γ-6-Me, split 1:40, 50°C (15 min)→80°C (10°C/min) (5 min)→140°C
(10°C/min) (5 min): tR (1a)=17.6 min, tR (ent-1a)=18.2 min, tR (2a)=22.4 min, tR (ent-2a)=21.9 min.
rac-1b and rac-2b: CP-Chirasil-Dex-CB, split 1:40, 50°C (10 min)→100°C (10°C/min), (2 min)→150°C
(10°C/min) (2 min): tR (1b)=20.9 min, tR (ent-1b)=21.0 min, tR (2b)=22.3 min, tR (ent-2b)=22.6 min.
rac-1c and rac-2c: CP-Chirasil-Dex-CB, split 1:40, 100°C (5 min)→130°C (10°C/min) (5 min)→160°C
(10°C/min) (5 min): tR (1c)=11.6 min, tR (ent-1c)=12.0 min, tR (2c)=14.6 min, tR (ent-2c)=14.8 min.
rac-1e and rac-2e: CP-Chirasil-Dex-CB, split 1:40, 80°C (5 min)→120°C (10°C/min) (5 min)→160°C
(10°C/min) (5 min): tR (1e)=15.0 min, tR (ent-1e)=14.7 min, tR (2e)=17.7 min, tR (ent-2e)=18.1 min.
rac-1f and rac-2f: CP-Chirasil-Dex-CB, split 1:40, 60°C (5 min)→100°C (10°C/min) (5 min)→140°C
(10°C/min) (5 min): tR (1f)=19.4 min, tR (ent-1f)=19.3 min, tR (2f)=23.5 min, tR (ent-2f)=23.8 min.
rac-1g: Lipodex E, split 1: 40, 50°C (10 min)→80°C (10°C/min) (5 min)→120°C (10°C/min) (5 min):
tR (1g)=31.0 min, tR (ent-1g)=31.1 min. rac-2g: CP-Chirasil-Dex-CB, split 1:40, 50°C (60 min)→80°C
(10°C/min) (5 min)→140°C (10°C/min) (5 min): tR (2g)=81.1 min, tR (ent-2g)=81.3 min. rac-3 and rac-
4: CP-Chirasil-Dex-CB, split 1:40, 120°C (10 min)→140°C (10°C/min) (5 min)→160°C (10°C/min) (5
min): tR (3)=14.3 min, tR (ent-3)=14.5 min, tR (4)=18.9 min, tR (ent-4)=18.8 min. rac-6: CP-Chirasil-
Dex-CB, split 1:40, 80°C (5 min)→120°C (10°C/min) (5 min)→160°C (10°C/min) (5 min): tR (6)=17.5
min, tR (ent-4)=17.4 min.
HPLC: rac-1d and rac-2d: Baker–Daicel Chiralcel OD/OD-H column, n-hexane:iPrOH, 9:1, flow
rate: 0.5 mL/min: tR (1d)=19.2 min, tR (ent-1d)=18.6 min, tR (2d)=13.6 min, tR (ent-2d)=14.6 min. rac-
5: Baker–Daicel Chiralcel OD/OD-H column, n-hexane:iPrOH, 18:1, flow rate: 0.5 mL/min: tR (5)=22.0
min, tR (ent-5)=23.4 min.
4.3. Transesterification of rac-1a
Vinyl propionate (5.0 g, 50 mmol) and alcohol rac-1a (1.4 g, 10 mmol) were dissolved in toluene (60
mL, saturated with water) and water (0.5 mL) was added to the solution. After stirring the mixture for 30
min at room temperature, PLE/MPEG (0.80 g, 4900 U) and toluene (60 mL, water saturated) were added.
The reaction mixture was stirred at room temperature for 5 days (58% conversion). Subsequently, MgSO4
(10 g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through
Celite. The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.4
mbar, 100°C). Chromatography (cyclohexane:iPrOH, 8:1) gave alcohol 1a43,58 (0.43 g, 31%) with 92%
25
25
ee, [α]D +9.1 (c 1.48, MeOH) and ester 2a (0.89 g, 45%) with 77% ee, [α]D +1.1 (c 1.48, MeOH),
as colorless oils.
1
Compound 1a: H NMR (300 MHz, CDCl3) δ 4.24 (m, 1H), 4.04 (dd, J=6.7, J=8.4, 1H), 3.78 (dd,
J=6.3, J=8.0, 1H), 3.72 (m, 1H), 3.60 (m, 1H), 2.27 (s, 1H), 1.44 (s, 3H), 1.37 (s, 3H); 13C NMR (75
MHz, CDCl3) δ 25.3 (d), 26.7 (d), 63.0 (u), 65.8 (u), 76.2 (d), 109.4 (u).

M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
3753
1
Compound 2a: H NMR (300 MHz, CDCl3) δ 4.31 (m, 1H), 4.04–4.21 (m, 3H), 3.74 (dd, J=6.0,
J=8.0, 1H), 2.39 (q, J=7.6, 2H), 1.43 (s, 3H), 1.37 (s, 3H), 1.15 (t, J=7.6, 3H); 13C NMR (75 MHz,
CDCl3) δ 9.1 (d), 25.4 (d), 26.7 (d), 27.4 (u), 64.6 (u), 66.4 (u), 73.7 (d), 109.8 (u), 174.2 (u).
4.4. Transesterification of rac-1b
Vinyl propionate (7.8 g, 78 mmol) and alcohol rac-1b (3.25 g, 20 mmol) were dissolved in toluene
(100 mL, saturated with water) and water (0.8 mL) was added to the solution. After stirring the mixture
for 30 min at room temperature, PLE/MPEG (1.39 g, 5700 U) and toluene (100 mL, water saturated)
were added. The reaction mixture was stirred at room temperature (25°C) for 6 days (35% conversion).
Subsequently, MgSO4 (20 g) and NaHCO3 (10 g) were added. After stirring the suspension for 5 min,
it was filtered through Celite. The filtrate was concentrated in vacuo, and the residue was purified by
kugelrohr distillation (0.4 mbar, 110°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 1b18
25
(1.61 g, 50%) with 41% ee, [α]D25 +5.8 (c 1.89, MeOH) and ester 2b (1.34 g, 31%) with 75% ee, [α]D
−3.4 (c 1.34, MeOH), as colorless oils.
1
Compound 1b: H NMR (300 MHz, CDCl3) δ 4.23 (m, 1H), 4.04 (dd, J=6.4, J=8.1, 1H), 3.75 (dd,
J=7.0, J=7.7, 1H), 3.72 (m, 1H), 3.60 (m, 1H), 2.17 (t, J=6.0, 1H), 1.65 (m, 4H), 0.91 (m, 6H); 13C NMR
(75 MHz, CDCl3) δ 8.0 (d), 8.3 (d), 29.2 (u), 29.6 (u), 63.1 (u), 66.2 (u), 76.4 (d), 113.3 (u).
1
Compound 2b: H NMR (400 MHz, CDCl3) δ 4.32 (m, 1H), 4.07–4.22 (m, 3H), 3.70 (dd, J=7.1,
J=8.3, 1H), 2.37 (q, J=7.3, 2H), 1.65 (m, 4H), 1.43 (s, 3H), 1.37 (s, 3H), 1.15 (t, J=7.5, 3H), 0.91 (m,
6H); 13C NMR (100 MHz, CDCl3) δ 7.9 (d), 8.2 (d), 9.1 (d), 27.4 (u), 29.4 (u), 29.6 (u), 64.4 (u), 66.9
(u), 73.9 (d), 113.7 (u), 174.3 (u).
4.5. Transesterification of rac-1c
Vinyl propionate (4.0 g, 40 mmol) and alcohol rac-1c (2.04 g, 11 mmol) were dissolved in toluene
(50 mL, saturated with water) and water (0.4 mL) was added. After stirring the mixture for 30 min at
room temperature, PLE/MPEG (0.69 g, 2900 U) and toluene (50 mL, water saturated) were added. The
reaction mixture was stirred at room temperature for 5 days (7% conversion). Subsequently, MgSO4
(10 g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through
Celite. The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.4
mbar, 110°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 1c24–27 (1.64 g, 80%) with 3%
20
ee, [α]D +0.4 (c 1.50, MeOH) and ester 2c (0.18 g, 7%) with 30% ee, [α]D20 −5.2 (c 1.75, MeOH).
Compound 1c: 1H NMR (400 MHz, CDCl3) δ 4.33 (m, 1H), 4.12 (t, J=7.4, 1H), 3.70 (m, 2H), 3.63
dd, J=7.4, J=8.8, 1H), 2.16 (m, 2H), 2.08 (m, 1H), 0.94 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 17.4
(d), 17.5 (d), 17.5 (d), 17.5 (d), 33.6 (d), 34.7 (d), 63.5 (u), 68.5 (u), 78.2 (d), 117.0 (u).
1
Compound 2c: H NMR (400 MHz, CDCl3) δ 4.40 (m, 1H), 4.13–4.21 (m, 3H), 3.64 (dd, J=7.7,
J=8.7, 1H), 2.36 (q, J=7.5, 2H), 2.09 (sept, J=6.9, 1H), 1.15 (t, J=7.5, 3H), 0.93 (m, 12H); 13C NMR
(100 MHz, CDCl3) δ 9.0 (d), 17.3 (d), 17.4 (d), 17.4 (d), 17.5 (d), 27.4 (u), 33.7 (d), 34.7 (d), 64.3 (u),
69.1 (u), 75.4 (d), 117.4 (u), 174.3 (u).
4.6. Transesterification of rac-1d
Vinyl propionate (1.9 g, 19 mmol) and alcohol rac-1d (1.1 g, 4 mmol) were dissolved in toluene
(50 mL, saturated with water) and water (0.4 mL) was added. After stirring the mixture for 30 min at
room temperature, PLE/MPEG (0.73 g, 3600 U) and toluene (50 mL, water saturated) were added. The

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M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
reaction mixture was stirred at room temperature for 4 days (20% conversion). Subsequently, MgSO4
(10 g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through
Celite. The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation
(0.001 mbar, 110°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 1d18 (0.78 g, 71%) with
22
22
35% ee, [α]D +8.1 (c 1.10, MeOH), mp 53°C, and ester 2d (0.24 g, 18%) with 91% ee, [α]D −14.0
(c 1.86, MeOH), mp 44°C.
1
Compound 1d: H NMR (400 MHz, CDCl3) δ 7.51 (m, 4H), 7.30 (m, 6H), 4.32 (m, 1H), 4.00 (m,
2H), 3.78 (m, 1H), 3.64 (m, 1H), 1.87 (t, J=6.3, 1H); 13C NMR (100 MHz, CDCl3) δ 63.1 (u), 66.2 (u),
76.9 (d), 110.0 (u), 126.0 (d), 126.2 (d), 128.2 (d), 128.2 (d), 128.2 (d), 128.3 (d), 141.9 (u), 142.0 (u).
1
Compound 2d: H NMR (400 MHz, CDCl3) δ 7.50 (m, 4H), 7.30 (m, 6H), 4.41 (m, 1H), 4.22 (m,
2H), 4.10 (dd, J=6.9, J=8.2, 1H), 3.91 (dd, J=6.9, J=8.2, 1H), 2.31 (q, J=7.4, 2H), 1.11 (t, J=7.5, 3H);
13C NMR (100 MHz, CDCl3) δ 9.0 (d), 27.4 (u), 64.2 (u), 67.0 (u), 74.3 (d), 110.2 (u), 126.3 (d), 126.3
(d), 128.1 (d), 128.2 (d), 128.2 (d), 128.3 (d), 141.8 (u), 141.9 (u), 174.2 (u).
4.7. Transesterification of rac-1e
Vinyl propionate (8.1 g, 81 mmol) and alcohol rac-1e (3.1 g, 20 mmol) were dissolved in toluene
(100 mL, saturated with water) and water (0.8 mL) was added. After stirring the mixture 30 min at
room temperature, PLE/MPEG (1.72 g, 6300 U) and toluene (100 mL, water saturated) were added. The
reaction mixture was stirred at room temperature for 12 days (39% conversion). Subsequently, MgSO4
(15 g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through
Celite. The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.4
mbar, 110°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 1e24–27,59 (1.60 g, 52%) with
22
22
43% ee, [α]D +4.1 (c 1.35, MeOH) and ester 2e (1.29 g, 31%) with 88% ee, [α]D +0.2 (c 1.64,
MeOH).
1
Compound 1e: H NMR (400 MHz, CDCl3) δ 4.18 (m, 1H), 3.98 (dd, J=6.7, J=8.4, 1H), 3.74 (dd,
J=6.0, J=8.1, 1H), 3.70 (m, 1H), 3.60 (m, 1H), 2.38 (s, 1H), 1.64–1.90 (m, 8H); 13C NMR (100 MHz,
CDCl3) δ 23.3 (u), 23.7 (u), 36.0 (u), 36.5 (u), 63.2 (u), 65.7 (u), 75.9 (d), 119.4 (u).
1
Compound 2e: H NMR (400 MHz, CDCl3) δ 4.26 (m, 1H), 4.16 (m, 1H), 4.10 (m, 1H), 4.01 (dd,
J=6.6, J=8.5, 1H), 3.73 (dd, J=5.8, J=8.5, 1H), 2.37 (q, J=7.7, 2H), 1.65–1.88 (m, 8H), 1.15 (t, J=7.3,
3H); 13C NMR (100 MHz, CDCl3) δ 9.1 (d), 23.4 (u), 23.7 (u), 27.4 (u), 36.2 (u), 36.6 (u), 64.6 (u), 66.3
(u), 73.4 (d), 119.7 (u), 174.3 (u).
4.8. Transesterification of rac-1f
Vinyl propionate (7.9 g, 79 mmol) and alcohol rac-1f (3.6 g, 21 mmol) were dissolved in toluene
(100 mL, saturated with water) and water (0.8 mL) was added. After stirring the mixture for 30 min at
room temperature, PLE/MPEG (1.38 g, 5900 U) and toluene (100 mL, water saturated) were added. The
reaction mixture was stirred at room temperature for 5 days (36% conversion). Subsequently, MgSO4 (10
g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through Celite.
The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.0004
mbar, 100°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 1f18,59 (1.88 g, 53%) with 51%
20
20
ee, [α]D +3.9 (c 2.10, MeOH) and ester 2f (1.40 g, 30%) with 89% ee, [α]D +1.2 (c 1.30, MeOH).
Alcohol 1f (0.75 g, 4 mmol, 51% ee) and vinyl propionate (1.74 g, 17 mmol) were dissolved in toluene
(37.5 mL, saturated with water) and water (0.3 mL) was added. After stirring the mixture for 30 min at
room temperature, PLE/MPEG (0.55 g, 2300 U) and toluene (37.5 mL, water saturated) were added. The

M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
3755
reaction mixture was stirred at room temperature for 12 days (28% conversion). Subsequently, MgSO4 (5
g) and NaHCO3 (2 g) were added. After stirring the suspension for 5 min, it was filtered through Celite.
The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.4 mbar,
23
130°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 1f (0.49 g, 65%) with 91% ee, [α]D
+6.0 (c 1.08, MeOH) and ester 2f (0.24 g, 24%) with 45% ee, [α]D23 +0.7 (c 1.35, MeOH).
1
Compound 1f: H NMR (300 MHz, CDCl3) δ 4.23 (m, 1H), 4.03 (dd, J=6.4, J=8.1, 1H), 3.78 (dd,
J=6.4, J=8.1, 1H), 3.70 (m, 1H), 3.59 (m, 1H), 2.33 (t, J=6.4, 1H), 1.35–1.66 (m, 8H); 13C NMR (75
MHz, CDCl3) δ 23.8 (u), 24.0 (u), 25.1 (u), 35.0 (u), 36.4 (u), 63.1 (u), 65.4 (u), 75.8 (d), 110.0 (u).
Compound 2f: 1H NMR (300 MHz, CDCl3) δ 4.31 (m, 1H), 4.13 (m, 1H), 4.11 (m, 1H), 4.06 (m, 1H),
3.77 (dd, J=6.0, J=8.4, 1H), 2.37 (q, J=7.4, 2H), 1.30–1.66 (m, 8H), 1.15 (t, J=7.4, 3H); 13C NMR (75
MHz, CDCl3) δ 9.1 (d), 23.8 (u), 24.0 (u), 25.1 (u), 27.4 (u), 35.0 (u), 36.4 (u), 64.7 (u), 66.1 (u), 73.3
(d), 110.4 (u), 174.2 (u).
4.9. Transesterification of rac-1f under variation of the initial water content
Vinyl propionate or isopropenyl propionate (4 mmol) and alcohol rac-1f (1 mmol) were dissolved in
toluene (5 mL, saturated with water). After the addition of the calculated amount of water, the mixture
was stirred for 30 min at room temperature. Subsequently, PLE/MPEG (75 mg, 300–400 U) and toluene
(5 mL, water saturated) were added. The reaction mixture was stirred at room temperature. Alternatively,
dry acetone (8 equiv.) or freshly distilled acetaldehyde (9 equiv.) was added following the addition of
PLE/MPEG.
4.10. Transesterification of rac-1f under variation of the solvent
Vinyl propionate (4 mmol, except when used as solvent) and alcohol rac-1f (1 mmol) were dissolved
in dry toluene, benzene, n-decane, chloroform, methylene chloride, dimethoxyethane, vinyl propionate
or methyl tert-butyl ether (5 mL). After the addition of water (43 µL), the mixture was stirred for 30 min
at room temperature. Subsequently, PLE/MPEG (65 mg, 350 U) and an additional amount of solvent (5
mL) were added. The reaction mixture was stirred at room temperature.
4.11. Transesterification of rac-1g
Vinyl propionate (483 mg, 4.8 mmol) and alcohol rac-1g (170 mg, 1.4 mmol) were dissolved in
chloroform (5 mL) (the alcohol was not completely dissolved) and water (0.43 µL) was added. After
stirring the mixture for 30 min at room temperature, PLE/MPEG (74.8 mg, 300 U) and chloroform (5
mL) were added. The reaction mixture was stirred at room temperature for 5 days (61% conversion).
Subsequently, MgSO4 (1 g) was added. After stirring the suspension for 5 min, the mixture was filtered
through Celite.
4.12. Transesterification of rac-3
Vinyl propionate (3.9 g, 39 mmol) and alcohol rac-3 (1.8 g, 10 mmol) were dissolved in toluene
(75 mL, saturated with water) and water (0.6 mL) was added. After stirring the mixture for 30 min at
room temperature, PLE/MPEG (1.07 g, 6300 U) and toluene (75 mL, water saturated) were added. The
reaction mixture was stirred at room temperature for 10 days (28% conversion). Subsequently, MgSO4
(10 g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through

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M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
Celite. The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.4
mbar, 110°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 318,52 (1.02 g, 56%) with 42%
25
20
ee, [α]D −1.7 (c 1.02, EtOH) and ester 4 (0.63 g, 96%) with 97% ee, [α]D +27.0 (c 2.14, MeOH).
Compound 3: 1H NMR (400 MHz, CDCl3) δ 7.28 (m, 2H), 6.94 (m, 3H), 4.17 (m, 1H), 4.02 (m, 2H),
3.56 (m, 2H), 3.41 (s, 3H), 2.72 (d, J=5.2, 1H); 13C NMR (100 MHz, CDCl3) δ 59.3 (d), 68.9 (u), 69.0
(d), 73.5 (u), 114.5 (d), 121.1 (d), 129.5 (d), 158.5 (u).
Compound 4: 1H NMR (400 MHz, CDCl3) δ 7.25 (m, 2H), 6.93 (m, 3H), 5.32 (m, 1H), 4.13 (m, 2H),
3.65 (m, 2H), 3.38 (s, 3H), 2.37 (q, J=7.7, 2H), 1.14 (t, J=7.4, 3H); 13C NMR (100 MHz, CDCl3) δ 9.0
(d), 27.6 (u), 59.3 (d), 66.2 (u), 70.7 (d), 71.0 (u), 114.6 (d), 121.1 (d), 129.5 (d), 158.5 (u), 174.0 (u).
4.13. Transesterification of rac-5
Vinyl propionate (9.2 g, 92 mmol) and alcohol rac-5 (3.4 g, 21 mmol) were dissolved in toluene
(100 mL, saturated with water) and water (0.8 mL) was added. After stirring the mixture for 30 min at
room temperature, PLE/MPEG (1.32 g, 5800 U) and toluene (100 mL, water saturated) were added. The
reaction mixture was stirred at room temperature for 5 days (49% conversion). Subsequently, MgSO4
(10 g) and NaHCO3 (5 g) were added. After stirring the suspension for 5 min, it was filtered through
Celite. The filtrate was concentrated in vacuo, and the residue was purified by kugelrohr distillation (0.8
mbar, 100°C). Chromatography (cyclohexane:EtOAc, 1:1) gave alcohol 558,59 (1.41 g, 41%) with 90%
22
22
22
ee, [α]D +9.3 (c 1.20, EtOH), [α]D +7.6 (c 1.10, MeOH), [α]D −0.7 (c 1.21, CHCl3), and ester 6
(1.79 g, 39%) with 97% ee, [α]D22 −4.1 (c 1.71, MeOH).
Compound 5: 1H NMR (300 MHz CDCl3) δ 7.29 (m, 2H), 7.22 (m, 3H), 4.00 (m, 1H), 3.40 (m, 1H),
3.38 (s, 3H), 3.30 (m, 1H), 2.79 (m, 2H), 2.48 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 39.9 (u), 59.1 (d),
71.3 (d), 76.0 (u), 126.5 (d), 128.5 (d), 129.4 (d), 138.0 (u).
Compound 6: 1H NMR (300 MHz CDCl3) δ 7.28 (m, 2H), 7.22 (m, 3H), 5.20 (m, 1H), 3.43 (m, 2H),
3.37 (s, 3H), 2.93 (m, 2H), 2.31 (q, J=7.7, 2H), 1.09 (t, J=7.4, 3H); 13C NMR (75 MHz, CDCl3) δ 9.1
(d), 27.7 (u), 37.0 (u), 59.1 (d), 72.6 (u), 73.1 (d), 126.6 (d), 128.4 (d), 129.5 (d), 137.2 (u), 174.0 (u).
4.14. Hydrolysis of rac-2f
Ester rac-2f (0.55 g, 2 mmol) was dissolved in aqueous phosphate buffer solution (36 mL, pH 8) and
acetone (4 mL). After stirring the mixture for 5 min at room temperature, PLE (1 mg, 180 U) (NH4Cl
suspension) was added and a pH value of 8.0 was maintained by the addition of 1N NaOH via pH-
STAT-autotitration. The hydrolysis was terminated after 50 min (45% conversion) by the extraction of
the aqueous solution with CH2Cl2 in a perforator overnight. The organic phase was dried (MgSO4) and
concentrated in vacuo to give a 45:55 mixture (0.46 g) of alcohol ent-1f with 31% ee and of ester ent-2f
with 12% ee.
4.15. Hydrolysis of rac-4
Ester rac-4 (0.40 g, 1.7 mmol) was added to an aqueous phosphate buffer solution (60 mL, pH 7.2).
After stirring the mixture for 5 min at room temperature, PLE (1 mg, 180 U) (NH4Cl suspension) was
added and a pH value of 7.2 was maintained by the addition of 0.1N NaOH via pH-STAT-autotitration.
The hydrolysis was terminated after 30 min (95% conversion) by the extraction of the aqueous solution
with ether. The organic phase was dried (MgSO4) and concentrated in vacuo to give a 96:4 mixture (0.34
g) of alcohol ent-3 with 2% ee and ester ent-4 with 5% ee.

M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
3757
Acknowledgements
Financial support from the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 380 and
Transferbereich 11) for this work is gratefully acknowledged.
References
1. Ohno, M.; Otsuka, M. Org. React. 1989, 37, 1.
2. Zhu, L.-M.; Tedford, M. C. Tetrahedron 1990, 46, 6587.
3. Gais, H.-J. In Enzyme Catalysis in Organic Synthesis; Drauz, K.; Waldmann, H., Eds.; VCH: Weinheim, 1995; Vol. I, p.
165.
4. Gais, H.-J.; Lukas, K. L. In Preparative Biotransformations; Roberts, S. M.; Wiggins, K.; Casy, G., Eds.; Wiley: New
York, 1992–1997; Part 1.
5. Cambou, B.; Klibanov, A. M. J. Am. Chem. Soc. 1984, 106, 2687.
6. Kirchner, G.; Scollar, M. P.; Klibanov, A. M. J. Am. Chem. Soc. 1985, 107, 7072.
7. Heiss, L.; Gais, H.-J. Tetrahedron Lett. 1995, 36, 3833.
8. Ruppert, S.; Gais, H.-J. Tetrahedron: Asymmetry 1997, 8, 3657.
9. Jurczak, J.; Pikul, S.; Bauer, T. Tetrahedron 1986, 42, 447.
10. Lemaire, M.; Jeminet, G.; Gourcy, J.-G.; Dauphin, G. Tetrahedron: Asymmetry 1993, 4, 2101.
11. Zhang, D.; Poulter, C. D. J. Am. Chem. Soc. 1993, 115, 1270.
12. Golding, B. T.; Griffin, A. L.; Robinson, D. H. Tetrahedron Lett. 1993, 34, 6459.
13. Ladner, W. E.; Whitesides, G. M. J. Am. Chem. Soc. 1984, 106, 7250.
14. Sonnet, P. E. J. Org. Chem. 1987, 52, 3477.
15. Fuganti, C.; Grasselli, P.; Servi, S.; Lazzarini, A.; Casati, P. J. Chem. Soc., Chem. Commun. 1987, 538.
16. Terao, Y.; Tsuji, K.; Murata, M.; Achiwa, K.; Nishio, T.; Watanabe, N.; Seto, K. Chem. Pharm. Bull. 1989, 37, 1653.
17. Parmar, V. S.; Prasad, A. K.; Singh, P. K.; Gupta, S. Tetrahedron: Asymmetry 1992, 3, 1395.
18. Partali, V.; Melbye, A. G.; Alvik, T.; Anthonsen, T. Tetrahedron: Asymmetry 1992, 3, 65.
19. Waagen, V.; Hollingsaeter, I.; Partali, V.; Thorstad, O.; Anthonsen, T. Tetrahedron: Asymmetry 1993, 4, 2265.
20. Bosetti, A.; Bianchi, D.; Cesti, P.; Golini, P. Biocatalysis 1994, 9, 71.
21. Yi, L; Ward, O. P. J. Ind. Microbiol. 1994, 13, 49.
22. Pallavicini, M.; Valoti, E.; Villa, L.; Piccolo, O. J. Org. Chem. 1994, 59, 1751.
23. Phung, A. N.; Braun, J.; Le Goffic, F. Synth. Commun. 1995, 25, 1783.
24. Hess, R.; Bornscheuer, U.; Capewell, A.; Scheper, T. Enzyme Microbiol. Chem. 1995, 17, 725.
25. Bornscheuer, U.; Yamane, T. J. Am. Oil Chem. Soc. 1995, 72, 193.
26. Bornscheuer, U.; Gaziola, L.; Schmid, R. D. Ann. N.Y. Acad. Sci. 1996, 799, 757.
27. Gaziola, L.; Bornscheuer, U.; Schmid, R. D. Enantiomer 1996, 1, 49.
28. Krebsfänger, N.; Schierholz, K.; Bornscheuer, U. Biotechnol. 1998, 60, 105.
29. Molinari, F.; Brenna, O.; Valenti, M.; Aragozzini, F. Enzyme Microbiol. Technol. 1996, 19, 551.
30. Matsumoto, K.; Fuwa, S.; Shimojo, M.; Kitajima, H. Bull. Chem. Soc. Jpn. 1996, 69, 2977.
31. Vänttinen, E.; Kanerva, L. T. J. Chem. Soc., Perkin Trans. 1 1994, 3459.
32. Vänttinen, E.; Kanerva, L. T. Tetrahedron: Asymmetry 1996, 7, 3037.
33. Vänttinen, E.; Kanerva, L. T. Tetrahedron: Asymmetry 1997, 8, 923.
34. Janes, L. E.; Löwendahl, A. C.; Kazlauskas, R. J. Chem. Eur. J. 1998, 4, 2324.
35. Takashi, S.; Tetsuo, K.; Yukie, T.; Tadasi, E.; Masanori, U. Tetrahedron Lett. 1998, 39, 7881.
36. For a resolution using alcohol dehydrogenases, see: Geerlof, A.; van Tol, J. B. A.; Jongejan, J. A.; Duine, J. A. Biosci.
Biotech. Biochem. 1994, 58, 1028.
37. For the lipase catalyzed enantioselective synthesis of glycerol ethers, see: (a) Breitgoff, D.; Laumen, K.; Schneider, M. P.
J. Chem. Soc., Chem. Commun. 1986, 1523. (b) Kerscher, V.; Kreiser, W. Tetrahedron Lett. 1987, 28, 531. (c) Wang, Y.-F.;
Lalonde, J. J.; Momongan, M.; Bergbreiter, D. E.; Wong, C.-H. J. Am. Chem. Soc. 1988, 110, 7200.
38. For the lipase catalyzed resolution of glycerol ethers, see: (a) Herradon, B.; Cueto, S.; Morcuende, Valverde, S.
Tetrahedron: Asymmetry 1993, 4, 845. (b) Theil, F.; Weidner, J.; Ballschuh, S.; Kunath, A.; Schick, H. J. Org. Chem.
1994, 59, 388. (c) Theil, F.; Lemke, K.; Ballschuh, S.; Kunath, A.; Schick, H. Tetrahedron: Asymmetry 1995, 6, 1323. (d)
Theil, F. Catalysis Today 1994, 22, 517.

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M. Jungen, H.-J. Gais / Tetrahedron: Asymmetry 10 (1999) 3747–3758
39. Boekelheide, V.; Liberman, L.; Figueras, J.; Krespan, C.; Pennington, F. C.; Tarbell, D. S. J. Am. Chem. Soc. 1949, 71,
3303.
40. Blicke, F. F.; Schumann, E. L. J. Am. Chem. Soc. 1952, 74, 2613.
41. Pfaendler, H. R.; Müller, F. X. Synthesis 1992, 350.
42. Henry, P. M. J. Am. Chem. Soc. 1972, 94, 7316.
43. Baer, E.; Fischer, H. O. L. J. Biol. Chem. 1939, 128, 463.
44. Gelas, J. Bull. Soc. Chim. Fr. 1970, 2341.
45. Chen, C. S.; Sih, C. J. Angew. Chem., Int. Ed. Engl. 1989, 28, 695.
46. The E values were calculated according to Ref. 45 by using the equations for irreversible reactions although reversibility
of the transesterifications under the conditions employed cannot be rigorously excluded. However, we observed only a
minor dependency of the calculated E values on the extent of conversion of the substrate.
47. Note that acylation of the R-alcohol gives the S-ester due to a change in the priority sequence of the substituents.
48. Laane, C.; Boeren, S.; Hilhorst, R.; Veeger, C. In Biocatalysis in Organic Media; Laane, C.; Tramper, J.; Lilly, M. D.,
Eds.; Elsevier: Amsterdam, 1987; p. 65.
49. Reichardt, C. Solvents and Solvent Effects in Organic Chemistry; VCH: Weinheim, 1988.
50. Weber, H. K.; Zuegg, J.; Faber, K.; Pleiss, J. J. Mol. Catal. B: Enzymatic 1997, 3, 131.
51. The transesterification was carried out on a 1 mmol scale, and the alcohol and the ester have not been isolated.
52. Waagen, V.; Hollingsaeter, I.; Huang, M. S. S.; Anthonsen, T. Acta Chem. Scand. 1994, 48, 506.
53. Biggs, J.; Chapman, N. B.; Wray, V. J. Chem. Soc. (B) 1971, 66.
54. Ferraboschi, P.; Grisenti, P.; Manzocchi, A.; Santaniello, E. Tetrahedron 1994, 50, 10539.
55. Determination of the absolute configuration of 5 was accomplished by chemical correlation with L-phenylalanine
according to the scheme below:
23
23
Thus, treatment of 5 (90% ee) with NaH and MeI afforded 7 (Ref. 54) ([α]D −9.1 (c 1.76, CHCl3); [α]D −4.1 (c 1.37,
23
EtOH); [α]546 −7.2 (c 1.37, EtOH)). L-Phenylalanine was converted via diazotization, hydrolysis and esterification to
the S-ester 8 [Cohen, S. G.; Weinstein, S. Y. J. Am. Chem. Soc. 1964, 86, 5326 and McKenzie, A.; Barrow, F. J. Chem.
Soc. 1911, 99, 1910] ([α]D +4.2 (c 1.27, EtOH)) which, upon reduction with LiAlH4, delivered the S-diol 9 [Bergstein,
W.; Kleemann, A.; Martens, J. Synthesis 1981, 76] ([α]D −24.7 (c 1.37, EtOH)). Treatment of 9 with NaH and MeI
furnished the S-dimethyl ether ent-7 (Ref. 54). [α]D +7.1 (c 1.50, CHCl3); [α]D +3.5 (c 1.25, EtOH); [α]546 +5.8 (c
1.25, EtOH) with 81% ee (GC: Lipodex E, split 1:40, 70°C (5 min)→100°C (10°C/min) (5 min)→140°C (10°C/min) (5
min): tR (ent-7)=9.2 min, tR (7)=9.3 min).
23
23
25
25
25
56. Following this procedure PLE has been used repeatedly in the batch-wise resolution of rac-1a without a decrease of the E
value: Gais, H.-J.; Jadhav, V., unpublished results.
57. However, recently the isolation and purification of a carboxylesterase from Bacillus coagulans has been described, which
exhibited a high selectivity (E=55) in the hydrolysis of the caprylate of rac-1a, see: Ref. 29.
58. Hirth, G.; Saroka, H.; Bannwarth, W.; Barner, R. Helv. Chim. Acta 1983, 66, 1210.
59. Toda, F.; Matsuda, S.; Tanaka, K. Tetrahedron: Asymmetry 1991, 2, 983.