Chemoenzymatic preparation of all the stereoisomers of 2-(1-hydroxyethyl)- and 2,6-bis(1-hydroxyethyl)pyridines and their acetates

Article abstract of DOI:10.1016/j.tetasy.2004.07.004

Several lipases were tested for the enantiomerically selective acetylation of racemic 1-[6-(1-hydroxyethyl)-pyridin-2-yl]ethanone rac-2 to yield alcohol (S)-2 and acetate (R)-3. Acetylation of a diastereomeric mixture of racemic and meso-2,6-bis(1-hydroxy-ethyl)pyridine, rac/meso-4, with the most selective Novozym 435 lipase in vinyl acetate resulted in a mixture of enantiopure diol (S,S)-4, monoacetate (R,S)-5 and diacetate (R,R)-6. Hydrolysis of the mixture of racemic and meso-2,6-bis(1-acetoxyethyl)pyridine rac/meso-6 by the same enzyme gave the pure enantiomers of diol (R,R)-4, monoacetate (S,R)-5 and diacetate (S,S)-6. Using further chemical and enzymatic steps alcohol (R)-2, acetate (S)-3, (S,S)- and (R,R)-monoacetates (S,S)-5 and (R,R)-5, meso-4 and its acetate meso-6 were also prepared and characterized.

Full text of DOI:10.1016/j.tetasy.2004.07.004

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 2483–2490
Chemoenzymatic preparation of all the stereoisomers of
2-(1-hydroxyethyl)- and 2,6-bis(1-hydroxyethyl)pyridines and
their acetates
*
´ ´ ´ ´ ´ ´ ´
Gabor Szatzker, Ildiko Moczar, Pal Kolonits, Lajos Novak, Peter Huszthy and
*
´ ´
Laszlo Poppe
Institute for Organic Chemistry and Research Group for Alkaloid Chemistry of the Hungarian Academy of Sciences,
´ ´
Budapest University of Technology and Economics, H-1111 Budapest, Gellert ter 4., Hungary
Received 22 May 2004; accepted 2 July 2004
´
Dedicated to Professor Karoly Lempert on the occasion of his 80th birthday
Abstract—Several lipases were tested for the enantiomerically selective acetylation of racemic 1-[6-(1-hydroxyethyl)-pyridin-2-
yl]ethanone rac-2 to yield alcohol (S)-2 and acetate (R)-3. Acetylation of a diastereomeric mixture of racemic and meso-2,6-
bis(1-hydroxy-ethyl)pyridine, rac/meso-4, with the most selective Novozym 435 lipase in vinyl acetate resulted in a mixture of enan-
tiopure diol (S,S)-4, monoacetate (R,S)-5 and diacetate (R,R)-6. Hydrolysis of the mixture of racemic and meso-2,6-bis(1-acetoxy-
ethyl)pyridine rac/meso-6 by the same enzyme gave the pure enantiomers of diol (R,R)-4, monoacetate (S,R)-5 and diacetate (S,S)-6.
Using further chemical and enzymatic steps alcohol (R)-2, acetate (S)-3, (S,S)- and (R,R)-monoacetates (S,S)-5 and (R,R)-5, meso-4
and its acetate meso-6 were also prepared and characterized.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
reagent10 or the (+)-DIP-Cl catalyst.12 Although these
methods resulted in one of the enantiomeric forms of diol
4 in various, usually high enantiomeric purity, none of
them were flexible enough for the production of all ster-
eoisomers of 4 in pure form (Figs. 1 and 2).
Optically active pyridyl alcohols are not only useful key
compounds for pharmaceutical intermediates,1,2 but
also for chiral ligands and auxiliaries in asymmetric syn-
thesis.3,4 Enantiopure 2,6-bis(1-hydroxy-ethyl)pyridines
(S,S)-4 and (R,R)-4 are useful chiral building blocks in
the syntheses of optically active crown ethers.5,6
By exploiting the stereoselectivity of hydrolases, the
acetylation of the isomeric mixture rac/meso-4 with ace-
tic anhydride catalyzed by lipoprotein lipase from Pseu-
domonas sp. (Amano P) was applied to produce a
mixture of optically active diol (S,S)-4, monoacetate
(S,R)-5 and diacetate (R,R)-6.13 From the diastereo-
meric mixture of rac/meso-4, highly enantiopure diacet-
ate (R,R)-6 was prepared by an elegant combination
of a highly selective lipase catalyzed acetylation and
ruthenium catalyzed in situ racemization.14
A number of methods have been published for the stereo-
selective production of 2,6-bis(1-hydroxyethyl)-pyri-
dines (S,S)-4 and (R,R)-4. Microbial reductions of the
2,6-diacetyl-pyridine 1 by bakerÕs yeast7,8 or Pseudomonas
putida UV4 strain9 have provided (S,S)-4 in high
enantiomeric purity. Asymmetric chemical reactions were
also successfully applied for producing the enan-
tiomers of diol 4. The (S,S)-enantiomer (S,S)-4 was
obtained by reduction with a chiral borane reagent10 or
by transfer hydrogenation using a chiral Ru catalyst,11
whereas (R,R)-4 was produced by using a chiral borane
Although many of these methods are applicable for
obtaining some of the stereoisomers of 4, 5 and 6 in opti-
cally active forms, they were either not flexible enough
or not selective enough for producing all stereoisomers
of diol 4 and its acetylated derivatives 5 and 6 in pure
form. Moreover, we have found inconsistencies between
*
Corresponding authors. Tel.: +36-1-463-1275; fax: +36-1-463-
3297; e-mail addresses: huszthy@mail.bme.hu; poppe@mail.bme.hu
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.07.004

2484
G. Szatzker et al. / Tetrahedron: Asymmetry 15 (2004) 2483–2490
Novozym 435
+
N
N
N
H2O
O
OAc
O
OH
O
OAc
OAc
OAc
rac-3
(R)-2
(S)-3
Ac2O, Et3N
0.25 eq.
NaBH4
lipase
+
N
N
N
N
vinyl
O
OH
acetate
O
OH
O
O
O
1
rac-2
(S)-2
(R)-3
0.5 eq.
NaBH4
Novozym 435
S
R
+
+
N
N
N
N
vinyl
OH
OH
acetate
OH
OH
OH
OAc
OAc
rac/meso-4
(S,S)-4
(R,S)-5
(R,R)-6
Ac2O, Et3N
Novozym 435
H2O
R
S
+
+
N
N
N
N
OAc
OAc
OH
OH
OH
OAc
OAc
OAc
rac/meso-6
(R,R)-4
(S,R)-5
(S,S)-6
Figure 1. Preparation of enantiopure stereoisomers of 2-(1-hydroxyethyl)- and 2,6-bis(1-hydroxyethyl)pyridines 2 and 4 and their acetylic esters 3, 5
and 6.
the reported enantiomeric compositions and the corre-
sponding specific rotation values.
We thought therefore that it was important to enhance
the selectivity of the most flexible enzymatic acetylation
method13 by searching for a highly selective and efficient
enzyme and extend the use of this method for the prep-
aration of all pure stereoisomers of diol 4 and their acet-
ylated derivatives 5 and 6.
N
OH
OAc
(R,S)-5
NaOH,
H2O
Ac2O,
Et3N
2. Results and discussion
N
N
OH
OH
OH
OAc
OAc
OAc
OAc
OAc
Due to the stereoselective acetylation of the isomeric
mixture of diol rac/meso-4 being rather complex and
that the intrinsic selectivity of the process cannot be
detected directly, the enzyme catalyzed enantiomeric
selective acetylation (i.e., simple kinetic resolution) of
meso-4
meso-6
CAL A
N
N
racemic
1-[6-(1-hydroxy-ethyl)pyridin-2-yl]ethanone
vinyl
acetate
OH
OH
rac-2 was chosen for comparing the selectivities of sev-
eral lipases (Fig. 1, Table 1). Enzymatic acetylations in
vinyl acetate show applicable activity on rac-2 revealing
Novozym 435 as the most selective enzyme (E >250).
The high enantiomeric selectivity of this enzyme was
confirmed by preparative scale acetylation of rac-2
yielding enantiopure alcohol (S)-2 and acetate (R)-3
(ee >99.5%, each). In the hydrolysis of rac-3, catalyzed
by Novozym 435, the high degree of enantiomeric selec-
tivity was preserved resulting in enantiopure (R)-2 and
(S)-3 (ee >99.5%, each).
(S,S)-4
(S,S)-5
Novozym 435
H2O
N
N
OAc
OH
(R,R)-4
(R,R)-5
Figure 2. Preparation of pure meso-4, its diacetate meso-6 and the two
enantiomeric forms of monoacetates (S,S)-5 and (R,R)-5.

G. Szatzker et al. / Tetrahedron: Asymmetry 15 (2004) 2483–2490
Table 1. Lipase-catalyzed acetylation of 2-(1-hydroxyethyl)pyridine rac-2a
2485
Enzyme
Time (h)
c (%)
(S)-2 Eeb (%)
(R)-3 Eeb (%)
Ec
Novozym 435
Lipozyme TL IM
Lipase PS
24
24
24
24
24
24
24
24
24
24
24
50.0
18.7
11.9
8.1
>99.5
21.5
13.4
9.4
>99.5
99.0
98.6
98.0
96.7
89.5
68.5
63.9
36.0
34.4
<0.1
>250
ꢁ250
167
109
62
Lipozyme IM 20
PPL
Lipase AK
5.0
5.0
47.7
5.3
86.5
10.9
3.2
46
5.6
Candida cylindracae lipase
Lipase AY
5.7
4.7
3.0
Candida rugosa lipase
PLE
Candida antarctica lipase A
10.9
12.7
>99.0
5.7
5.2
2.2
ꢁ1.0
<0.1
a Reactions with c >5% within 24h. For details, see Experimental.
b Ee of (S)-2 and (R)-3 and c: GLC/Beta-DEX 120 column.
c Degree of enantiomeric selectivity (E) was calculated from c and ee3,15 and confirmed by independent calculation from ee2 and ee3 (due to
sensitivity to experimental errors, E-value over 500 is given as >250).
16
In a report on acetylation using Ac2O and Amano lipase
P for the separation of the stereoisomers of 4,13 it was
speculated that a highly stereoselective reaction would
result in a mixture of the less reactive enantiomer of 4
along with the diacetate 6 from its reactive enantiomer
and monoacetate 5 from meso-4. However, separation
and proper characterization of the stereoisomers 4 and
its acetate derivatives 5 and 6 is not a trivial task, as
the experimental part of this work13 indicated, stating
(S,S)-4 (85.56%), meso-4 (13.88%) and (R,R)-4 (0.56%)
is forming if one reduction step happens with a degree
of selectivity of 85% ee, whereas practically pure (S,S)-
4 (99.8%) is forming [along with traces of meso-4
(0.18%) and (R,R)-4 (0.01%)] if one reduction step pro-
ceeded with a degree of selectivity of 99.8% ee. Accord-
ingly, noncomplete stereoselectivity results in practically
inseparable mixtures of diastereomers, for which
accurate specific rotation determination is not really
possible.
1
that the 250MHz H NMR spectrum of meso-4 Ôwas
identical with that of the mixture of diol stereoisomersÕ
rac/meso-4.
The chiral Ru(II)-catalyzed stereoselective reduction of
2,6-diacetylpyridine 111 was not completely selective,
resulting in a 91:9 mixture of (S,S)-4 (99.6% ee by
HPLC) and meso-4. The rotation data reported for
(S,S)-4 (Table 2), therefore, was apparently determined
from this mixture.
On the basis of our results on the enantiomeric selectiv-
ity of the enzymatic acetylation of racemic 1-[6-(1-hyd-
roxy-ethyl)pyridin-2-yl]ethanone rac-2 (Table 1),
a
high degree of stereoselectivity was expected in the
acetylation of the isomeric mixture rac/meso-4 with the
most selective Novozym 435 in vinyl acetate. As ex-
pected, the reaction performed on a preparative scale
stopped after reaching the expected conversions to yield
a separable mixture of (S,S)-4, (R,S)-5 and (R,R)-6 in
It was supposed that the acetylation with Ac2O cata-
lyzed by lipoprotein lipase from Pseudomonas sp.
(Amano P) produced a mixture of monoacetate (R,S)-
5 and Ôoptically pureÕ diol (S,S)-4 and diacetate (R,R)-
6.13 However, NMR data of the bis-MTPA derivative
from (R,R)-4, which was obtained by hydrolysis of the
enzymatically produced (R,R)-6 published in the same
paper,13 indicated the presence of 18% meso-4 and
12% (S,S)-4 in the (R,R)-4 sample (Table 2).
1
high purity (ee >99%, each, by GLC and 500MHz H
NMR).
Similar to the simple kinetic resolution of rac-2 cata-
lyzed by Novozym 435, the high degree of stereoselectiv-
ity in the acetylation process was preserved in the
hydrolysis as well. Thus, from the mixture of diacetates
rac/meso-6 the opposite enantiomeric forms of pure
(R,R)-4, (S,R)-5 and (S,S)-6 (ee >99%, each, by GLC
When the enantiomeric composition was deduced from
the diastereomeric ratio after diastereomeric derivatiza-
tion of a compound, the different diastereomers may be
formed at significantly different rates. Therefore, a
strictly complete conversion of the original enantiomeric
mixture into the desired derivative is an essential
requirement in this case. No solid proof or definitive
statement on the total conversion, however, was found
for the MCF derivative of 210 or the di-MTPA deriva-
tive of 4.10
1
and 500MHz H NMR) were obtained without special
care of controlling the degree of conversion.
With the highly enantiopure samples in our hands, some
unexpected specific rotations were determined (Table 2).
In many cases, our results (we always observed higher
rotation values than reported previously) were in
disagreement with the existing data, which prompted
us to clarify this situation.
It is noteworthy that some other factors may also influ-
ence the specific rotation data. A strong concentration
dependency of the specific rotation in acetone was found
for diol (S,S)-4: [a]D = ꢀ48.0, ꢀ84.5 and ꢀ99.5 were
determined for a freshly prepared sample at c 0.5,
The effect of incomplete selectivity on the product com-
position of stereoselective bakerÕs yeast reduction of 2,6-
diacetyl-pyridine 1 was analyzed in detail:7 a mixture of

2486
G. Szatzker et al. / Tetrahedron: Asymmetry 15 (2004) 2483–2490
Table 2. Specific rotations of pure stereoisomers of 2–6a
25
½aꢂD
a
Compounda
Lit. [a]D (Ee %)
c 2, EtOH
c 2, acetone
(S)-2
(R)-2
ꢀ62.0
+61.8
ꢀ75.8
+75.1
ꢀ69.6
+70.0
ꢀ0.2
ꢀ91.3
ꢀ4.1 (99)b ꢀ7.5 (99.8)c ꢀ40.16 (>95)d
+91.2
+40.53 (>95)d
(S)-3
(R)-3
(S,S)-4
(R,R)-4
meso-4
(S,S)-5
(R,S)-5
(S,R)-5
(R,R)-5
(S,S)-6
(R,R)-6
meso-6
ꢀ99.5
+99.6
ꢀ0.3
ꢀ26.6 (99)e ꢀ26.84 (99.92)f ꢀ45.99 (>98)g ꢀ61.0 (99.6)h ꢀ63.6i
+44.01j +44.6 (>98)k
+10.21i
ꢀ138.1
+49.5
ꢀ49.8
+138.4
ꢀ181.9
+182.6
+0.2
ꢀ131.3
+56.5
ꢀ56.0
+131.2
ꢀ171.9
+172.6
+0.2
+29.43i
+73.33i
a Ee of all chiral stereoisomers in this work were >99% (GLC/Beta-DEX 120 or HP Chiral columns). Chemical purity of all stereoisomers were
checked by GLC and 500MHz 1H NMR.
b c 1.0, CHCl3 (Ee of (S)-2: HPLC/Chiralcel OB column).8
c c 1.5, CHCl3 (Ee: HPLC of di-p-bromobenzoate derivative of (S)-2/Chiracel OD column).7
d c ꢁ4, acetone (Ee: GLC of MCF derivative of 2/SBP-5 column)10
.
e c 0.51, CHCl3 (Ee of (S,S)-4: HPLC/Chiralcel OB column).8
f c 2.98, CHCl3 (Ee and diastereomeric composition: HPLC of bis-p-bromobenzoates of (S,S)-4 and meso-4/Chiracel OD column).7
g c 1.9, acetone (Ee: di-MTPA derivative of 4/19F NMR).10
h c 1.9, acetone (data refers to a 91:9 mixture of (S,S)-4 and meso-4).11
i c 2, acetone.13
j c 2, acetone {1H NMR of the di-MTPA derivative from (R,R)-4 of [a]D +44.01 indicated the presence of 18% meso-4 and 12% (S,S)-4}.13
k c 2.3, acetone (Ee: di-MTPA derivative of 4/19F NMR).10
1 and 2, respectively. Dependency of the rotation on the
solvent is indicated by the [a]D = ꢀ33.4 value deter-
mined for the same sample in chloroform, c 1.
pyridin-2-yl]ethanone rac-2, Novozym 435 was found
to exhibit excellent selectivity. With the aid of this highly
selective enzyme, acetylation of a diastereomeric mixture
of racemic and meso-2,6-bis(1-hydroxy-ethyl)pyridine
rac/meso-4 with vinyl acetate resulted in a mixture of
enantiopure diol (S,S)-4, monoacetate (R,S)-5 and diac-
etate (R,R)-6. Using further chemical and enzymatic
steps all the possible enantiomers of alcohol 2, acetate
3, (S,S)-, (R,R)-, and meso-diols 4, all stereoisomers of
monoacetate 5 and diacetate 6 were also prepared and
characterized. Accurately measured optical rotation
data for the products and analysis of their deviation
from the previously reported values have also been
given.
Initiated by the deviations of our specific rotation data
from the reported ones (Table 2), we repeated rotation
measurements for several samples, which were stored
in stopped glass flasks at room temperature for four
weeks. It was surprising to learn that the optical rota-
tions for (S,S)-4, (R,S)-5 and (R,R)-6 differed signifi-
cantly from the previously measured values. For
example, [a]D = +67.3 (c 2, acetone) was observed for
a (R,S)-5 sample, which exhibited [a]D = +56.5 (c 2, ace-
tone) previously. TLC check of this sample indicated
substantial (ca. 70%) conversion into a novel less polar
product. Separation and structure elucidation revealed
that this ÔnovelÕ product was ketone (R)-2. This was fur-
ther confirmed by the specific rotation determinations,
because the separated (R,S)-5 and (R)-2 fractions exhib-
ited the previously determined [a]D = +56.5 and +91.3
(c 2, acetone) values, respectively (Table 2).
4. Experimental
4.1. Materials and methods
4.1.1. Reagents and solvents. Vinyl acetate, sodium
borohydride, acetic anhydride and triethyl amine were
purchased from Aldrich. 2,6-Diacetyl-pyridine 1 was
prepared according to the reported procedure.17 All sol-
vents were of analytical grade or freshly distilled while
the sodium phosphate buffer (pH7.0, 50mM) was
freshly made.
As final proof of the reproducibility, the Novozym 435
mediated acetylation of rac/meso-4 was repeated to give
(S,S)-4 (22%), (R,S)-5 (41%) and (R,R)-6 (20%), which
exhibited essentially the same [a]D = ꢀ98.9, +56.3 and
+173.0 (c 2, acetone), respectively, as determined in
the first experiment (Table 2).
4.1.2. Biocatalysts. Lipase AK, lipase AY, lipase F,
and lipase PS were obtained from Amano Europe. Lipo-
zyme IM 20, Lipozyme TL IM, Novozym 435 and Can-
dida antarctica lipase A (CAL A) were products of
Novozymes, Denmark. Lipases from Candida rugosa
and Pseudomonas fluorescens were purchased from
3. Conclusions
Among the several lipases tested for the enantiomeric
selective acetylation of racemic 1-[6-(1-hydroxyethyl)-

G. Szatzker et al. / Tetrahedron: Asymmetry 15 (2004) 2483–2490
2487
Fluka. PPL and lipase from Candida cylindracae were
obtained from Sigma. Pig liver acetone powder (PLE)
was prepared in our laboratory.
4.1.7. Novozym 435 catalyzed acetylation of 1-[6-(1-
hydroxyethyl)pyridin-2-yl]ethanone rac-2. Racemic 1-
[6-(1-hydroxyethyl)pyridin-2-yl]ethanone rac-2 (250mg,
1.52mmol) and Novozym 435 (150mg) in vinyl acetate
(4mL) were shaken at rt for 24h. After removing the
enzyme by filtration, vinyl acetate was evaporated off
under reduced pressure and the residue was purified by
column chromatography (silica gel/hexane:acetone
10:1) to yield (S)-2 (113mg, 45%) and (R)-3 (125mg,
40%) as colourless oils.
4.1.3. Analytical methods. NMR spectra were recorded
1
on a Bruker DRX-500 spectrometer (500MHz for H
and 125MHz for 13C; TMS; ppm on d scale) in CDCl3
if not stated otherwise. IR spectra were taken on a Spe-
cord 2000 spectrometer in film and the wave numbers re-
ported in cmꢀ1. GC analyses were carried out on Agilent
4890D or HP 5890 instruments equipped with FID
detector using H2 as the carrier gas (injector: 250ꢁC,
detector: 250ꢁC, head pressure: 12psi). For the separa-
tions HP Chiral (30m · 0.32mm · 0.25lm film of 20%
permethylated b-cyclodextrin, HP Part No.: 190916-
B213) with 1:50 split ratio or Beta-DEX 120
(30m · 0.25mm · 0.25lm film, Supelco Column No.:
16161-0413) with 1:80 split ratio were used. Optical rota-
tions were determined on a Perkin–Elmer 241 polarime-
ter. TLC was carried out on Kieselgel 60 F254 (Merck)
sheets. Spots were visualized by treatment with 5% etha-
nolic phosphomolybdic acid solution and heating of the
dried plates.
4.1.8. (S)-[6-(1-Hydroxyethyl)pyridin-2-yl]ethanone (S)-
25
D
2. ½aꢂ ¼ ꢀ62:0 (c 2.0 in EtOH) {lit.8 (>99% ee):
[a]D = ꢀ4.1
(c
1.0,
CHCl3);
lit.7
(>99.8%
ee): [a]D = ꢀ7.5 (c 1.5, CHCl3)}; IR, H and 13C NMR
1
data were indistinguishable from the spectra of rac-2.
4.1.9. (R)-[6-(1-Acetoxyethyl)pyridin-2-yl]ethanone (R)-
25
D
3. ½aꢂ ¼ þ75:1 (c 2.0, EtOH); IR: 1744, 1700, 1592,
1456, 1424, 1360, 1288, 1228, 1112, 1080, 1032, 952,
816; 1H NMR: 1.63 (2H, d, J = 6.7Hz, CH3), 2.14
(2H, s, CO–CH3), 2.71 (3H, s, CO–CH3), 5.98 (1H, q,
J = 6.7Hz, O–CH), 7.51 (1H, d, J = 7.7Hz, Py5–H),
7.81 (1H, t, J = 7.7Hz, Py4–H), 7.92 (1H, d,
J = 7.7Hz, Py3–H); 13C NMR: 20.65, 21.39, 25.80,
72.77, 120.21, 123.49, 137.39, 152.70, 159.61, 169.97,
199.83; Anal. Calcd for C11H13NO3: C, 63.76; H, 6.32;
N, 6.76. Found: C, 63.67; H, 6.38; N, 6.71.
4.1.4. Racemic 1-[6-(1-hydroxyethyl)-pyridin-2-yl]-etha-
none rac-2. To a solution of 2,6-diacetylpyridine 1 (4g,
25mmol) in anhydrous ethanol (120mL) NaBH4 (0.87g,
3.7mmol) was added portionwise at rt and the resulting
mixture stirred overnight. After evaporating the solvent
in vacuum, the residue was dissolved in ethyl acetate
(50mL) and washed by water (10mL), 5% HCl solution
(10mL), saturated NaHCO3 solution (10mL) and brine
(10mL) and dried over sodium sulfate. From this solu-
tion, ethyl acetate was distilled off by rotary evaporator
and the residue purified by column chromatography (sil-
ica gel/hexane:acetone 10:1) to give rac-2 (1.67g, 41%) as
a colourless oil. IR: 3448, 2958, 1700, 1588, 1448, 1416,
4.1.10. Racemic 1-[6-(1-acetoxyethyl)pyridin-2-yl]ethan-
one rac-3. Racemic 1-[6-(1-hydroxyethyl)pyridin-2-
yl]ethanone rac-2 (2.0g, 12.2mmol), acetic anhydride
(1.24g, 12.2mmol) and triethylamine (10mL) were stir-
red at 50ꢁC for 8h. The reaction mixture was diluted
with chloroform (50mL) and washed with water
(3 · 15mL), 5% HCl solution (15mL), saturated
NaHCO3 solution (15mL) and brine (15mL). The
organic solution was dried over sodium sulfate and
concentrated under reduced pressure. The residue was
purified by column chromatography (silica gel/hex-
ane:acetone 10:1) to give rac-3 (1.7g, 66%) as a colour-
less oil. IR, 1H and 13C NMR data were
indistinguishable from the spectra of (R)-3.
1
1360, 1288, 1224, 1120, 1080, 1020, 912, 816; H NMR:
1.53 (3H, d, J = 6.6Hz, CH3), 2.72 (2H, s, CO–CH3), 3.9
(1H, br s, OH), 4.95 (1H, q, J = 6.6Hz, O–CH), 7.48
(1H, d, J = 7.7Hz, Py5–H), 7.84 (1H, t, J = 7.7Hz,
Py4–H), 7.93 (1H, d, J = 7.7Hz, Py3–H); 13C NMR:
24.50, 26.10, 68.97, 120.27, 123.49, 137.81, 151.89,
162.64, 199.33; Anal. Calcd for C9H11NO2: C, 65.44;
H, 6.71; N, 8.48. Found: C, 65.37; H, 6.74; N, 8.44.
4.1.11. Novozym 435 catalyzed hydrolysis of 1-[6-(1-
acetoxyethyl)pyridin-2-yl]ethanone rac-3. 1-[6-(1-Acet-
4.1.5. Analytical scale enzymatic acetylation of racemic 1-
[6-(1-hydroxyethyl)pyridin-2-yl]ethanone rac-2. Enzyme
(5mg, see Table 1) was added to a solution of racemic
1-[6-(1-hydroxyethyl)-pyridin-2-yl]ethanone rac-2 (5mg)
in vinyl acetate (1mL) and the resulting suspension sha-
ken at rt/1000rpm in a sealed glass vial for the time indi-
cated in Table 1, after which the reaction was analyzed
by GC. The conversion and enantiomeric compositions
of the resulting alcohol (S)-2 and acetate (R)-3 are listed
in Table 1.
oxyethyl)pyridin-2-yl]ethanone
rac-3
(250mg,
(1.21mmol) and Novozym 435 (150mg) in 50mM
pH7.0 sodium phosphate buffer were shaken at rt/
1000rpm for 48h. The enzyme was filtered off and the
filtrate extracted with chloroform (3 · 3mL). The com-
bined extracts were washed with brine (3mL), dried over
sodium sulfate and concentrated under reduced pres-
sure. The residue was purified by column chromatogra-
phy (silica gel/hexane:acetone 10:1) to yield (R)-2
(90mg, 45%) and (S)-3 (115mg, 46%) as colourless oils.
4.1.6. Chiral GC analysis of acylation reactions from
racemic 1-[6-(1-hydroxyethyl)pyridin-2-yl]ethanone rac-
2. Rt (Beta-DEX 120; 125–150ꢁC, 1ꢁC/min)/min:
20.59 (S)-2 and 21.26 (R)-2 (base line separation);
22.24 (S)-3 and 22.56 (R)-3 (base line separation).
4.1.12.
(R)-[6-(1-Hydroxyethyl)pyridin-2-yl]ethanone
25
(R)-2. ½aꢂ ¼ þ61:8 (c 2.0, EtOH); IR, 1H and 13C
D
NMR data were indistinguishable from the spectra of
(S)-2.

2488
G. Szatzker et al. / Tetrahedron: Asymmetry 15 (2004) 2483–2490
4.1.13. (S)-[6-(1-Acetoxyethyl)pyridin-2-yl]ethanone (S)-
21.13, 24.42, 69.45, 72.55, 117.64, 118.10, 137.34,
158.55, 165.00, 169.53; Anal. Calcd for C11H15NO3: C,
63.14; H, 7.23; N, 6.69. Found: C, 63.25; H, 7.18; N,
6.73.
25
1
3. ½aꢂ ¼ ꢀ75:8 (c 2.0, EtOH); IR, H and 13C NMR
D
data were indistinguishable from the spectra of (R)-3.
4.1.14. Bis(1-hydroxyethyl)-pyridine rac/meso-4. To a
solution of 2,6-diacetylpyridine 1 (4g, 25mmol) in anhy-
drous ethanol (120mL), NaBH4 (1.75g, 7.5mmol) was
added portionwise at rt and the resulting mixture stirred
overnight. After evaporating the solvent in vacuum, the
residue was dissolved in ethyl acetate (50mL) and
washed by water (10mL), 5% HCl solution (10mL), sat-
urated NaHCO3 solution (10mL) and brine (10mL),
and dried over sodium sulfate. From this solution, ethyl
acetate was distilled off by rotary evaporator and the
residue purified by column chromatography (silica gel/
hexane:acetone 10:1) to give rac/meso-4 (2.55g, 66%)
as a white solid. Mp 49–51ꢁC; IR: 3360, 1596, 1576
4.1.18. (R,R)-2,6-Bis(1-acetoxyethyl)pyridine (R,R)-
25
D
25
D
6. ½aꢂ ¼ þ182:6 (c 2.0, acetone), ½aꢂ ¼ þ172:6 (c
2.0, EtOH) {lit.13 (ꢁ50% ee): [a]D = +73.33 (c 0.58,
CHCl3)} IR: 1746, 1662, 1644, 1586, 1464, 1370, 1240,
1158, 1080, 1030, 950, 810; H NMR (DMSO-d6): 1.49
1
(6H, d, J = 6.7Hz, 2 CH3), 2.08 (6H, s, 2 CO–CH3),
5.77 (2H, q, J = 6.7Hz, 2 O–CH), 7.32 (2H, d,
J = 7.7Hz, Py3,5–H), 7.81 (1H, t, J = 7.7Hz, Py4–H);
13C NMR (DMSO-d6): 20.30, 20.82, 72.05, 118.67,
137.48, 158.90, 169.21; Anal. Calcd for C13H17NO4: C,
62.14; H, 6.82; N, 5.57. Found: C, 62.07; H, 6.96; N,
5.61.
1
1448, 1432, 1400, 1368, 1120, 1076, 1016, 928, 816; H
NMR: 1.51 (6H, d, J = 6.5Hz, 2 CH3), 4.11 (2H, br s,
4.1.19. Chiral GC analysis of 2,6-bis(1-hydroxyethyl)-
pyridine rac/meso-4 and its acetylated derivatives 5,
6. Rt (HP Chiral; 125–155ꢁC, 1ꢁC/min)/min: 14.36
(S,S)-4, 15.07 meso-4, 16.00 (R,R)-4, 16.38 (S,S)-5,
16.56 (R,S)-5, 16.62 (S,R)-5, 16.76 (R,R)-5, 21.64
(S,S)-6, 21.83 (R,R)-6, 21.95 meso-6.
2 OH), 4.90 (2H, m(q), 2 O-CH), 7.23 (2H, m, Py3,5
–
H), 7.63 (1H, m(t), Py4–H); 13C NMR: 24.31/24.35,
69.30/69.32, 118.39, 137.86/137.90, 161.97; GC Rt
(min) (HP Chiral; 125–155ꢁC, 1ꢁC/min): 14.36 (S,S)-4
(28.2%), 15.07 meso-4 (44.0%), 16.00 (R,R)-4 (27.8%);
Anal. Calcd for C9H13NO2: C, 64.65; H, 7.84; N, 8.38.
Found: C, 64.81; H, 7.72; N, 8.41.
4.1.20. 2,6-Bis(1-acetoxyethyl)pyridine rac/meso-6. 2,6-
(2.0g,
Bis(1-acetoxyethyl)-pyridine
rac/meso-4
4.1.15. Novozym 435 catalyzed acetylation of 2,6-bis(1-
hydroxyethyl)-pyridine rac/meso-4. 2,6-Bis(1-hydroxy-
ethyl)pyridine rac/meso-4 (2.0g, 10mmol) and Novozym
435 (0.5g) in vinyl acetate (20mL) were shaken at rt/
1000 rpm for 24h. The enzyme was filtered off and the
filtrate concentrated under reduced pressure. The resi-
due was purified by column chromatography (silica
gel/hexane:acetone 10:1) to give (S,S)-4 (414mg, 21%),
(R,S)-5 (999mg, 40%) and (R,R)-6 (581mg, 20%) as col-
ourless oils.
12.1mmol), acetic anhydride (2.84g, 27.8mmol) and tri-
ethylamine (10mL) were stirred at 50ꢁC for 8h. The
reaction mixture was diluted with chloroform (50mL)
and washed with water (3 · 15mL), 5% HCl solution
(15mL), saturated NaHCO3 solution (15mL) and brine
(15mL). The organic solution was dried over sodium
sulfate and concentrated under reduced pressure. The
residue was purified by column chromatography (silica
gel/hexane:acetone 10:1) to give rac/meso-6 (2.49g,
82%) as colourless oil. IR: 1748, 1664, 1648, 1588,
1464, 1372, 1240, 1160, 1080, 1032, 952, 812; 1H
NMR: 1.58 (ꢁ3.3H, d, J = 6.7Hz, CH3), 1.59 (ꢁ2.7H,
d, J = 6.7Hz, CH3), 2.13 (6H, s, 2 CO–CH3), 5.94
(2H, m, O–CH), 7.25 (2H, m, Py3,5–H), 7.68 (1H, m,
Py4–H); 13C NMR: 20.93, 21.44, 72.96, 118.82/118.87,
137.38/137.48, 159.61, 169.95; Anal. Calcd for
C13H17NO4: C, 62.14; H, 6.82; N, 5.57. Found: C,
62.25; H, 6.79; N, 5.52.
4.1.16. (S,S)-2,6-Bis(1-hydroxyethyl)pyridine (S,S)-
25
25
4. ½aꢂ ¼ ꢀ69:6 (c 2.0, acetone), ½aꢂ ¼ ꢀ99:5 (c
D
D
2.0, EtOH) (lit.8 (>99% ee): [a]D = ꢀ26.6 (c 0.51,
CHCl3), lit.7 (99.92% ee): [a]D = ꢀ26.84 (c 2.98, CHCl3),
lit.10 (>98% ee): [a]D = ꢀ45.99 (c 1.9, acetone), lit.11
(99.6% ee): [a]D = ꢀ61.0 (c 1.9, acetone), lit.13 (64%
ee): [a]D = ꢀ63.6 (c 2, acetone); IR: 3376, 1596, 1576,
1
1448, 1432, 1400, 1368, 1120, 1076, 1016, 928, 816; H
NMR: 1.44 (6H, d, J = 6.6Hz, 2 CH3), 4.29 (2H, br s,
2 OH), 4.83 (2H, q, J = 6.6Hz, 2 O–CH), 7.16 (2H, d,
J = 7.7Hz, Py3,5–H), 7.63 (1H, t, J = 7.7Hz, Py4–H);
13C NMR: 24.05; 69.14, 118.00, 137.38, 161.76; Anal.
Calcd for C9H13NO2: C, 64.65; H, 7.84; N, 8.38. Found:
C, 64.31; H, 7.77; N, 8.36.
4.1.21. Novozym 435 catalyzed hydrolysis of 2,6-bis(1-
acetoxyethyl)-pyridine rac/meso-6. 2,6-Bis-(1-acetoxy-
ethyl)pyridine rac/meso-6 (500mg, 1.99mmol) and
Novozym 435 (250mg) in 10mL of 50mM pH7.0
sodium phosphate buffer were shaken at rt/1000rpm
for 48h. The enzyme was filtered off and the reaction
mixture was extracted with chloroform (3 · 5mL). The
combined extracts were washed with brine (5mL), dried
over sodium sulfate and concentrated under reduced
pressure. The residue was purified column chromatogra-
phy (silica gel/hexane:acetone 10:1) to give (R,R)-4
(59mg, 18%), (S,R)-5 (150mg, 36%) and (S,S)-6
(85mg, 17%) as colourless oils.
4.1.17.
(R,S)-1-[6-(1-Hydroxyethyl)pyridin-2-yl]ethyl
25
25
D
acetate (R,S)-5. ½aꢂ ¼ þ49:5 (c 2.0, acetone), ½aꢂ
¼
D
þ58:5 (c 2.0, EtOH) {lit.13, [a]D = +29.43 (c 2, acetone)};
IR: 3400, 1740, 1596, 1464, 1372, 1244, 1080, 1044, 816;
1H NMR (DMSO-d6): 1.35 (3H, d, J = 6.5Hz, CH3),
1.48 (3H, d, J = 6.7Hz, CH3), 2.08 (3H, s, CO–CH3),
4.72 (1H, m, O–CH), 5.35 (1H, d, OH), 5.74 (1H, q,
J = 6.7Hz, O–CH), 7.23 (1H, d, J = 7.7Hz, Py5–H),
7.43 (1H, d, J = 7.7Hz, Py3–H), 7.78 (1H, t,
J = 7.7Hz, Py4–H); 13C NMR (DMSO-d6): 20.77,
4.1.22.
(R,R)-Bis-(1-hydroxyethyl)pyridine
(R,R)-
25
D
25
D
4. ½aꢂ ¼ þ70:0 (c 2.0, acetone), ½aꢂ ¼ þ99:6 (c
2.0, EtOH) {lit.13 (64% ee): [a]D = +44.01 (c 2, acetone),

G. Szatzker et al. / Tetrahedron: Asymmetry 15 (2004) 2483–2490
2489
lit.10 (>98% ee): [a]D = +44.6 (c 2.3, acetone)}; IR,
1H and 13C NMR data were indistinguishable from
the spectra of (R,R)-4.
hexane:acetone 10:1) to yield (R,R)-5 (264mg, 79%) as
25
a
colourless oil. ½aꢂ ¼ þ138:4 (c 2.0, acetone),
D
25
D
½aꢂ ¼ þ131:2 (c 2.0, EtOH); IR: 3432, 1740, 1596,
1
1464, 1372, 1240, 1080, 1048, 816; H NMR: 1.43 (3H,
d, J = 6.5Hz, CH3), 1.53 (3H, d, J = 6.7Hz, CH3),
2.06 (3H, s, CO–CH3), 4.4 (1H, br s, OH), 4.81 (1H,
m, O-CH), 5.86 (1H, q, J = 6.7Hz, O–CH), 7.11 (1H,
d, J = 7.7Hz, Py5–H), 7.17 (1H, d, J = 7.7Hz, Py3–H),
7.62 (1H, t, J = 7.7Hz, Py4–H); 13C NMR: 20.71,
21.38, 24.23, 68.38, 72.73, 118.58, 118.59, 137.47,
158.51, 162.06, 169.95; Anal. Calcd for C11H15NO3: C,
63.14; H, 7.23; N, 6.69. Found: C, 63.07; H, 7.26; N,
6.65.
4.1.23.
(S,R)-1-[6-(1-Hydroxyethyl)pyridin-2-yl]ethyl
25
D
25
D
acetate (S,R)-5. ½aꢂ ¼ ꢀ49:8 (c 2.0, acetone), ½aꢂ
¼
ꢀ56:0 (c 2.0, EtOH); IR, H and 13C NMR data were
1
indistinguishable from the spectra of (R,S)-5.
4.1.24.
(S,S)-2,6-Bis(1-acetoxyethyl)pyridine
(S,S)-
25
D
25
D
6. ½aꢂ ¼ ꢀ181:9 (c 2.0, acetone), ½aꢂ ¼ ꢀ171:9 (c
2.0, EtOH); IR, H and 13C NMR data were indistin-
guishable from the spectra of (S,R)-5.
1
4.1.25. meso-2,6-Bis(1-hydroxyethyl)pyridine meso-4.
A
4.1.28. (S,S)-1-[6-(1-Hydroxyethyl)-pyridin-2-yl]ethyl acet-
ate with enzymatic reaction (S,S)-5. (S,S)-2,6-Bis(1-hy-
droxyethyl)-pyridine (S,S)-4 (150mg, 0.89mmol) and
CAL-A (15mg) in vinyl acetate (2mL) were shaken at
rt/1000rpm for 3h. The enzyme was filtered off and
the filtrate concentrated under reduced pressure. The
residue was purified by column chromatography (silica
mixture of (S,R)-1-[6-(1-hydroxyethyl)pyridin-2-yl]ethyl
acetate (S,R)-5 (200mg, 0.96mmol) and aqueous so-
dium hydroxide (5%, 5mL) was heated to 60ꢁC for
15min. The reaction mixture was extracted with chloro-
form (4 · 5mL). The combined extracts were washed
with brine (3mL), dried over sodium sulfate and concen-
trated under reduced pressure to give meso-4 (158mg,
98%) as white solid. mp 58–59ꢁC; IR: 3412, 1598,
1576, 1450, 1434, 1404, 1370, 1122, 1078, 1020, 930,
gel/hexane:acetone 10:1) to give (S,S)-5 (126mg, 68%)
25
D
as a colourless oil. ½aꢂ ¼ ꢀ131:8 (c 2.0, acetone),
25
½aꢂ ¼ ꢀ131:3 (c 2.0, EtOH); IR, 1H and 13C NMR data
1
D
were indistinguishable from the spectra of (R,R)-5.
820; H NMR (DMSO-d6): 1.35 (6H, d, J = 6.5Hz, 2
CH3), 4.70 (2H, m, 2 O–CH), 5.30 (2H, d, 2 OH), 7.35
(2H, d, J = 7.7Hz, Py3,5–H), 7.75 (1H, t, J = 7.7Hz,
Py4–H); 13C NMR (DMSO-d6): 24.32, 69.26, 116.91,
136.71, 163.88; Anal. Calcd for C9H13NO2: C, 64.65;
H, 7.84; N, 8.38. Found: C, 64.72; H, 7.77; N, 8.25.
Acknowledgements
The authors thank the National R&D Project, Ministry
of Education (NKFP3-35-2002) and the Hungarian Sci-
entific Research Found (OTKA T-038393) for financial
support. Thanks are due to Unilever Hungary Rt. for
donating a HP 5890 gas chromatograph.
4.1.26. meso-2,6-Bis(1-acetoxyethyl)-pyridine meso-
6. A mixture of (R,S)-1-[6-(1-hydroxyethyl)pyridin-2-
yl]ethyl acetate (R,S)-5 (150mg, 0.72mmol), acetic
anhydride (144mg, 1.44mmol) and triethylamine
(5mL) was stirred at rt for 6h. The reaction mixture
was diluted with 15mL chloroform and washed with
water (3mL), 5% HCl solution (3mL), saturated NaH-
CO3 solution (3mL) and brine (3mL). The organic solu-
tion was dried over sodium sulfate and concentrated
under reduced pressure. The residue was purified by col-
umn chromatography (silica gel/hexane:acetone 10:1) to
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a colourless oil.
25
D
25
D
½aꢂ ¼ þ0:2 (c 2.0, acetone), ½aꢂ ¼ þ0:2 (c 2.0, EtOH);
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(200mg) in 5mL of 50mM pH7.0 sodium phosphate
buffer were shaken at rt/1000rpm for 48h. The enzyme
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chloroform (3 · 5mL). The combined extracts were
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