Lipase-catalyzed enantioseparation of alcohols containing a tetrazole ring

Article abstract of DOI:10.1016/j.tetasy.2012.01.015

A simple chemoenzymatic method for the preparation of optically active (5-aryltetrazolyl-2)-4-butan-2-ol, (5-aryltetrazolyl-2)-propan-2-ol, and their acetates has been developed. The starting compounds (5-aryltetrazolyl-2)-4- butan-2-one and (5-aryltetraz

Full text of DOI:10.1016/j.tetasy.2012.01.015

Tetrahedron: Asymmetry 23 (2012) 136–143
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Tetrahedron: Asymmetry
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Lipase-catalyzed enantioseparation of alcohols containing a tetrazole ring
⇑
´
Edyta Łukowska-Chojnacka , Urszula Bernas, Jan Plenkiewicz
Faculty of Chemistry, Institute of Biotechnology, Warsaw University of Technology, Noakowskiego St. 3, 00-664 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple chemoenzymatic method for the preparation of optically active (5-aryltetrazolyl-2)-4-butan-2-
ol, (5-aryltetrazolyl-2)-propan-2-ol, and their acetates has been developed. The starting compounds (5-
aryltetrazolyl-2)-4-butan-2-one and (5-aryltetrazolyl-2)-propan-2-one were obtained by a Michael-type
addition of 5-aryl substituted tetrazoles to methyl vinyl ketone, and alkylation of 5-aryl substituted tet-
razoles with chloroacetone, respectively. Their reduction with sodium borohydride afforded racemic mix-
tures of (5-aryltetrazolyl-2)-4-butan-2-oles and (5-aryltetrazolyl-2)-propan-2-oles.
Received 8 December 2011
Accepted 20 January 2012
Available online 17 February 2012
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
analogues of natural amino acids, which exist as constituents of en-
zyme-modifier complexes with higher activities than the free en-
Tetrazoles and their derivatives constitute an interesting sub-
class of heterocycles, with a wide number of applications. They
are used in coordination chemistry as chelating agents,1 in agricul-
ture as plant growth regulators,2 and in the explosives industry3 as
useful highly energetic materials and propellants. Moreover, some
tetrazole derivatives play an important role in biochemistry and
medicinal chemistry.4–8 Such a wide range of applications is the re-
sult of their unique structure and ability to serve as bioisosters of the
carboxyl group. It is known that the replacement of a carboxyl group
in biologically active compounds with a similarly acidic tetrazolyl
fragment, may affect their biological activity. In particular, 5-substi-
tuted tetrazole derivatives, with anti-hypertensive activity, are used
as pharmacologically active drugs; for example Losartan,9–12 Cande-
sartan,11,12 Zolarsartan,11,12 and Valsartan.10 Moreover, there are
many known tetrazole derivatives involved in hyperlipoprotein-
emia and associated atherosclerotic diseases.13–15 Other tetrazole
derivatives exhibit antiallergic,16,17 antiinflammatory,18–20 antibac-
terial,21,22 and antifungal22 properties. Among the antibacterial and
antifungal agents, are 5-thio-substituted tetrazole derivatives such
as 1-benzyl-5-[(3-bromopropyl)thio]-1H-tetrazole and 5,50-[1,3-
propanediylbis(thio)]bis(1-benzyl-1H-tetrazole), with activities
similar to the standards ampicillin and intraconazole.22 The applica-
tion of tetrazole derivatives is highly diverse, because of their ability
to inhibit the action of many enzymes for example, human liver gly-
zyme, for example modifier complex of carboxypeptidase A.36
These findings suggest an unpredictable behavior for tetrazole
derivatives in enzyme catalyzed reactions, and even total enzyme
inhibition may be expected. We were unable to find any informa-
tion on the use of tetrazole derivatives in lipase-catalyzed reac-
tions in spite of the many papers on the reactions of other
azoles.37–40 Herein we report our findings on the specific proper-
ties of the tetrazole moiety.
2. Results and discussion
Herein, we describe a simple chemoenzymatic procedure for
the preparation of some new optically active 2,5-disubstituted tet-
razoles. The chemical step involves the synthesis of the necessary
substrates: ketones and alcohols, while the enzymatic step em-
ploys lipases as the chiral catalysts for the enantioseparation.
Two groups of alcohols, different in nature of the substituent at
the 2-position of the tetrazole ring, were prepared. One group
was (5-aryltetrazolyl-2)-4-butan-2-ols 3a–d. These compounds
were obtained from the appropriate 5-substituted tetrazoles
1a–d in a two step reaction. The first step involved the Michael
type addition of the appropriate 5-substituted tetrazoles 1a–d to
methyl vinyl ketone, yielding (5-aryltetrazolyl-2)-4-butan-2-ones
2a–d. The reaction was carried out in 2-propanol in the presence
of triethylamine at reflux (Scheme 1).
cosidase,23 human liver
a
-mannosidase,24 aromatase,25 protein
tyrosine phosphatases,26 HCV NS3 protease,27 cyclooxygenase-2,28
and others.29,30 Therefore, some tetrazole derivatives are used as
chemotherapeutic agents in certain types of cancer,31–33 and in
the treatment of AIDS.34,35 Moreover, there are known tetrazole
According to the literature data,41 the reaction took place regio-
selectively to solely give 2,5-disubstituted isomers 2a–d. The reflux
times and yields of the reaction depended on the benzene-ring
substituent and are summarized in Table 1. In the second step,
the required racemic alcohols 3a–d were obtained in high yields
(94–96%), by reduction of the appropriate ketones 2a–d with so-
dium borohydride in methanol at room temperature.
⇑
Corresponding author. Tel.: +48 22 6607570; fax: +48 22 628 2741.
E-mail address: elukowska@ch.pw.edu.pl (E. Łukowska-Chojnacka).
0957-4166/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2012.01.015

E. Łukowska-Chojnacka et al. / Tetrahedron: Asymmetry 23 (2012) 136–143
137
of 1H NMR chemical shifts recorded for diastereomeric esters pre-
pared from the enantiomerically enriched alcohol and the (R)- or
(S)-enantiomer of methoxyphenylacetic acid as shown in the
Experimental. Our investigations indicated that the alcohol (ꢀ)-
3a had an (R)-configuration. This means that alcohols (+)-3a–d
and acetates (ꢀ)-4a–d have (S)- and (R)-configurations, respec-
tively. This is in agreement with Kazlauskas’ rule.43
Among the three lipases tested, the best enantioselectivities
(E = 38–102) were obtained with Amano AK as the catalyst. Amano
PS and Novozym SP 435 showed poor selectivities (E = 0–7). In
addition, reactions catalyzed by lipase from Pseudomonas cepacia
(Amano PS) were very sluggish (7–12 days). Considering the re-
sults of the reactions catalyzed by Amano AK, substituents in the
benzene ring affect the rate and the enantioselectivity of the reac-
tion. The highest enantioselectivity (E = 102) was noted for com-
pound 3a without any substituent on the benzene ring. In
comparison, 4-methyl, 4-chloro, and 2-chloro substituents dimin-
ished the enantioselectivity of the reaction. The results presented
in Table 2 also show that the acetylation of 3d proceeded four
times slower than the other reactions investigated.
O
N
HN
N
CH3COCH=CH2, NEt3
2-propanol, reflux
N
N
N
Y
N
Y
N
X
X
2a-d
1a-d
X
Y
NaBH4,
MeOH
a
b
c
d
H
H
H
H
CH3
Cl
H
Cl
OH
N
N
N
Y
N
X
( )-3a-d
Scheme 1.
Table 1
The reaction times and yields of ketones 2a–d
It also seemed worthwhile to investigate if the distance be-
tween the hydroxy group (center of the enzymatic reaction) and
the tetrazole ring significantly influenced the reaction course. For
this purpose, (5-aryltetrazolyl-2)-propan-2-ols 6a–d were pre-
pared from the appropriate ketones obtained by N-alkylation of
5-substituted tetrazoles 1a–d with chloroacetone. This procedure
is often used37 in the synthesis of other heterocyclic ketones. The
reaction was carried out in acetone, in the presence of K2CO3 at re-
flux (Scheme 3).
The results are summarized in Table 3. The yields of the reac-
tions (38–58%) are acceptable, but significantly lower than in prep-
arations of ketones 2a–d. Extending the reflux did not improve the
yields. Both reactions (Scheme 1 and Scheme 3) took place regiose-
lectively to give only one isomer.
The racemic mixtures of alcohols 6a–d were also prepared by
chemical reduction of ketones 5a–d. The progress of the reaction
was monitored by thin-layer chromatography (TLC), and the reac-
tion was stopped when the conversion reached 100%. Regardless of
the substituent type, all of the alcohols were obtained in a short
reaction time (1–3 h) and with excellent yields ranging between
90.5% and 95%.
The kinetic separation of enantiomers ( )-6a–d was carried out
only with the Amano AK lipase. The progress of each reaction was
monitored by TLC and the reaction was stopped at approximately
50% conversion of the substrate (Scheme 4).
Entry
X
Y
Reaction time (h)
Yield (%)
a
b
c
H
H
H
Cl
H
CH3
Cl
3
4
6
3
85
90
94
81
d
H
The racemic mixtures of alcohols ( )-3a–d were then used as
the substrates in a lipase-catalyzed acetylation. The influence of
the lipase type as well as the substituent on the aromatic ring on
the enantioselectivity of the reaction was estimated by determin-
ing the reaction enantioselectivity. The catalytic efficiency of three
commercially available lipases: Amano AK from Pseudomonas fluo-
rescens, Amano PS from Pseudomonas cepacia, and Novozym SP 435
from Candida antarctica were investigated as catalysts of the reac-
tions carried out at room temperature in tert-butyl methyl ether
(TBME) with vinyl acetate as an acyl donor (Scheme 2). The control
experiment revealed that the reaction did not proceed in the ab-
sence of the enzyme.
The progress of the reactions was monitored on TLC plates; ace-
tates (ꢀ)-4a–d and unreacted alcohols (+)-3a–d were separated by
silica gel column chromatography. The enantiomeric excess of the
remaining alcohols (+)-3a–d were determined by HPLC analysis
using a chiral column. In order to determine the enantiomeric ex-
cess of the esters formed, acetates (ꢀ)-4a–d were hydrolyzed to
the appropriate optically active alcohols (ꢀ)-3a–d, since applied
Chiracel OD-H column was inappropriate for acetate enantiomers
resolution. The hydrolysis was performed in methanol with 1 M
NaOH solution at room temperature. It seems reasonable to as-
sume that the enantiomeric excess of acetates (ꢀ)-4a–d were the
same or even higher than the alcohols prepared from them. The re-
sults are summarized in the Table 2. The absolute configurations of
the products, that is, alcohol (ꢀ)-3a [obtained by the hydrolysis of
ester (ꢀ)-4a], and acetate (ꢀ)-4a, were determined by a modified
Mosher’s method.42 The assignments arose from the comparison
The enantiomeric excess of the remaining alcohols (+)-6b–d
and acetates prepared (+)-7c–d was directly determined by HPLC
analysis using a chiral column. The enantiomeric excess of ester
(+)-7b was assigned after its hydrolysis to the corresponding alco-
hol. The enantiomeric excess of alcohol (+)-6a and ester (+)-7a was
not determined. The absolute configurations of the alcohols and es-
ters were determined by the modified Mosher’s method42 and
indicated an (S)-configuration for alcohol (+)-6d, and an (R)-config-
uration for acetate (+)-7d. The parameters and results of the reac-
tion, enantiomeric purities of the products, and enantioselectivities
OH
OH
OAc
N
enzyme, TBME
N
N
N
N
N
N
N
N
+
vinyl acetate,
Y
N
Y
Y
N
N
molecular sieves
X
X
X
3a-d
3a-d
( )-
(S)-(+)-
4a-d
(R)-(-)-
Scheme 2.

138
E. Łukowska-Chojnacka et al. / Tetrahedron: Asymmetry 23 (2012) 136–143
Table 2
The results of the lipase-catalyzed transesterifications of alcohols ( )-3a–d with vinyl acetate
b
b
Entry
a
X
Y
Enzyme
Time (h)
c (%)a
eesub (%)
eeprod (%)
Ea
H
H
H
Cl
H
CH3
Cl
Amano AK
24
24
27
96
42
43.5
39
70
72
59
98
96
93
91
80
102
59
38
H
55
40
b
c
H
H
H
Cl
H
CH3
Cl
Amano PS
168
168
192
288
30
19
33
30
15
26
69
65
52
7
5
4
H
Very low conversion, products were not isolated
H
H
H
Cl
H
CH3
Cl
Novozym SP 435
29
27.5
24
59
53
72.5
38.5
10
34
65
rac
7
30
26
rac
1
2.5
3
0
H
24
a
Conversion (c) and E values were calculated from the enantiomeric excess of the substrate (+)-3a–d (eesub) and the product (ꢀ)-4a–d (eeprod) using the formula:
E = ln[(1-eesub)(eeprod/(eesub+eeprod))]ln[(1+eesub)(eeprod/(eesub+eeprod))], c = eesub/(eesub+eeprod).
b
Determined by HPLC analysis using a Chiracel OD-H column.
Table 4
N
N
HN
ClCH2COCH3, K2CO3
CH3COCH3, reflux
N
N
Results of amano AK catalyzed acetylation of alcohols ( )-6a–d
N
Y
N
O
Y
b
b
Entry
X
Y
Time (h)
ca(%)
eesub (%)
eeprod (%)
Ea
N
X
X
a
b
c
H
H
H
Cl
H
CH3
Cl
47
46
45
56
—
NDc
77
74
NDc
88
91
—
5a-d
1a-d
46
45
56
36
47
41
NaBH4,
MeOH
d
H
99
78
a
Conversion (c) and E values were calculated from the enantiomeric excess of
substrate (+)-6b–d (eesub using the formula:
)
and product (ꢀ)-7b–d (eeprod
)
N
E=ln[(1-eesub)(eeprod/(eesub+eeprod))]ln[(1+eesub)(eeprod/(eesub+eeprod))],
c = eesub/
N
N
(eesub+eeprod).
OH
b
Y
N
Determined by HPLC analysis using Chiracel OD-H column.
ND-not determined.
c
X
6a-d
( )-
Scheme 3.
5-aryl substituted tetrazoles to methyl vinyl ketone proceeded
regioselectively at the 2-position of the tetrazole ring. The result-
ing ketones were reduced to their corresponding alcohols. All reac-
tions proceeded with high yields under mild conditions. The
lipase-catalyzed transesterification of the alcohols with vinyl ace-
tate as the acyl donor was found to be a useful method for the
preparation of the corresponding optically active alcohols and es-
ters. The highest enantioselectivities of the reactions (E = 36–102)
were obtained in the presence of lipase Amano AK from Pseudomo-
nas fluorescens as the catalyst.
Table 3
The refluxing times and yields of ketones 5a–d
Entry
X
Y
Reflux time (h)
Yield (%)
a
b
c
H
H
H
Cl
H
CH3
Cl
2
5
2
1
55
54
38
58
d
H
of the reactions are presented in Table 4. The highest enantioselec-
tivity, E = 47, was obtained for the acetylation of alcohol ( )-6c.
Comparison of the data presented in Table 2 and Table 4 led us
to conclude that the length of the alkyl chain between the hydroxy
group and the tetrazole ring significantly affects the lipase cata-
lyzed reaction time, but only slightly affects the enantioselectivity
of the reaction.
4. Experimental
4.1. General
1H (400 MHz) and 13C NMR (100 MHz) spectra were recorded
on Varian Mercury 400 MHz spectrometer in CDCl3 solution;
chemical shifts (d) are reported in ppm; J values are given in Hertz.
IR Spectra were taken on a Carl Zeiss Specord M80 instrument. MS
spectra were recorded on a Micro-mass ESI Q-ToF Premier instru-
ment. Ee’s of the alcohols 3a–d, 6b–d, and esters 7c–d, were deter-
mined by HPLC analysis, which were performed on a Shimadzu
CTO-10ASV equipped with UV detector STD-20A and chiral column
Chiralcel OD-H (Diacel) (in hexane:iso-propanol 95:5; 0.8 ml/min
3. Conclusion
A series of new optically active 2,5-disubstituted tetrazole
derivatives were prepared. The alkylation of 5-aryl substituted tet-
razoles with chloroacetone, as well as a Michael-type addition of
N
N
N
N
N
enzyme, TBME
N
N
N
N
+
Y
OH
Y
OH
vinyl acetate,
OAc
N
Y
N
N
molecular sieves
X
X
X
6a-d
6a-d
(S)-(+)-
Scheme 4.
7a-d
(R)-(+)-
( )-

E. Łukowska-Chojnacka et al. / Tetrahedron: Asymmetry 23 (2012) 136–143
139
for alcohols 3a–d, 6c–d, and esters 7c–d; in hexane:iso-propanol
97:3, 0.8 ml/min for alcohol 6b) using the corresponding racemic
compounds as references. The retention times (tR/min) were as fol-
lows for alcohols: 3a 34.47 (S) and 40.79 (R), 3b 40.85 (S) and 56.96
(R), 3c 28.36 (S) and 35.41 (R), 3d 27.92 (S) and 29.83 (R), 6b 52.24
(S) and 54.22 (R), 6c 25.74 (R) and 28.49 (S), 6d 30.18 (R) and 34.26
(S) and were as follows for esters: 7c 18.97 (S) and 24.37 (R) 7d
18.38 (R) and 19.10 (S). Optical rotations were measured with an
AP-300 automatic polarimeter (ATAGO). The reactions were mon-
itored by TLC on silica gel 60 (230–400 mesh) plates. The 5-substi-
tuted tetrazoles 1a–d were prepared in high yields (64–91%) from
commercially available nitriles, NaN3, and NH4Cl in DMF according
to the described method.44 Amano AK, Amano PS were purchased
from Amano Co. and Novozym SP 435 (immobilized C. antarctica-
B lipase) was kindly granted by Novo-Nordisk. Solvents, reagents,
and chemicals were purchased from POCH, Merck, Fluka, and
Aldrich.
4.3. General procedure for the synthesis of (5-aryltetrazolyl-2)-
propan-2-ones 5a–d
To a solution of 5-substituted tetrazole 1a–d (0.059 mol) and
grounded K2CO3 (0.073 mol, 10.1 g) in acetone (85 mL), chloroace-
tone (0.067 mol, 5.5 mL) was added dropwise with stirring at room
temperature for 15 min. Then the reaction mixture was refluxed
(55–59 °C) for the time indicated in Table 3. The progress of the
reaction was monitored by TLC with chloroform–methanol (9:1
v/v) as the eluent. After completion of the reaction, the precipitate
was filtered off, washed with acetone (3 ꢁ 50 mL) and the solvent
and washings were evaporated under reduced pressure. To the res-
idue, 100 mL of water was added and the resulting solid was col-
lected by filtration. The product was recrystallized from methanol.
4.3.1. (5-Phenyltetrazolyl-2)-propan-2-one 5a
Colorless crystals, mp 132–134 °C, yield 55%. 1H NMR (CDCl3): d
ppm: 2.24 (s, 3H, CH3), 5.47 (s, 2H, CH2), 7.47–7.50 (m, 3H, C6H5),
8.13–8.16 (m, 2H, C6H5). 13C NMR (CDCl3): d ppm: 27.05, 60.86,
4.2. General procedure for the synthesis of (5-aryltetrazolyl-2)-
4-butan-2-ones 2a–d
126.87, 126.93, 128.88, 130.50, 165.63, 197.83. IR (Nujol, cmꢀ1
)
1719, 1070, 1040, 725, 680. MS [M+H]+ m/z calcd for C10H11N4O+
To a solution of 5-substituted tetrazole 1a–d (0.04 mol) in 2-
propanol (120 mL), triethylamine (0.03 mol, 4.17 mL) and methyl
vinyl ketone (0.08 mol, 6.5 mL) were added. The resulting reaction
mixture was refluxed for the time indicated in Table 1. The pro-
gress of the reaction was monitored by TLC with hexane–ethyl ace-
tate (1:1 v/v) as the eluent. After the appropriate time, the reaction
was stopped by filtering off the solid. The solvent was evaporated
under reduced pressure. The residue and earlier obtained solid
were recrystallized from ethanol.
203,0855, found 203,0644.
4.3.2. (5-(4-Methylphenyl)tetrazolyl-2)-propan-2-one 5b
Colorless crystals, mp 139–140 °C, yield 54%. 1H NMR (CDCl3): d
ppm: 2.23 (s, 3H, CH3), 2.40 (s, 3H, CH3), 5.46 (s, 2H, CH2), 7.28–
7.30 (m, 2H, C6H4), 8.02–8.04 (m, 2H, C6H4). 13C NMR (CDCl3): d
ppm: 21.45, 27.05, 60.84, 124.14, 126.80, 129.58, 140.74, 165.75,
197.97. IR (Nujol, cmꢀ1) 1720, 1175, 1040, 820, 745. MS [M+H]+
m/z calcd for C11H13N4O+ 217,1011, found 217,0716.
4.2.1. (5-Phenyltetrazolyl-2)-4-butan-2-one 2a
4.3.3. (5-(4-Chlorophenyl)tetrazolyl-2)-propan-2-one 5c
Colorless crystals, mp 180–182 °C, yield 38%. 1H NMR (CDCl3): d
ppm: 2.27 (s, 3H, CH3), 5.48 (s, 2H, CH2), 7.46–7.48 (m, 2H, C6H4),
8.08–8.10 (m, 2H, C6H4). 13C NMR (CDCl3): d ppm: 27.13, 60.93,
Colorless crystals, mp 61–63 °C (lit.41 62–63 °C), yield 85%. 1H
NMR (CDCl3): d ppm: 2.25 (s, 3H, CH3), 3.37 (t, 2H, CH2CO,
J = 7.2 Hz), 4.90 (t, 2H CH2N, J = 7.2 Hz), 7.45–7.47 (m, 3H, C6H5),
8.09–8.12 (m, 2H, C6H5). 13C NMR (CDCl3): d ppm: 30.05, 41.59,
47.56, 126.74, 127.23, 128.83, 130.29, 165.06, 204.04. IR (Nujol,
cmꢀ1) 1705, 1530, 1168, 930, 790, 760, 735, 699. MS [M+H]+ m/z
calcd for C11H13N4O+ 217,1011, found 217,0770.
125.48, 128.22, 129.23, 136.61, 164.84, 197.57. IR (Nujol, cmꢀ1
)
1725, 1175, 1085, 1040, 995, 832, 750. MS [M+H]+ m/z calcd for
10H10ClN4O+ 237,0465, found 237,0298.
C
4.3.4. (5-(2-Chlorophenyl)tetrazolyl-2)-propan-2-one 5d
Colorless crystals, mp 99–101 °C, yield 58%. 1H NMR (CDCl3): d
ppm: 2.25 (s, 3H, CH3), 5.53 (s, 2H, CH2), 7.38–7.42 (m, 2H, C6H4),
7.52–7.54 (m, 1H, C6H4), 7.96–7.98 (m, 1H, C6H4). 13C NMR (CDCl3):
d ppm: 27.09, 60.96, 126.05, 126.93, 130.81, 131.27, 131.38,
133.02, 163.78, 197.66. IR (Nujol, cmꢀ1) 1728, 1205, 1175, 1060,
1030, 795, 750. MS [M+H]+ m/z calcd for C10H10ClN4O+ 237,0465,
found 237,0241.
4.2.2. (5-(4-Methylphenyl)tetrazolyl-2)-4-butan-2-one 2b
Colorless crystals, mp 83–85 °C, yield 90%. 1H NMR (CDCl3): d
ppm: 2.25 (s, 3H, CH3), 2.39 (s, 3H, CH3), 3.26 (t, 2H, CH2CO,
J = 7.2 Hz), 4.88 (t, 2H CH2N, J = 7.2 Hz), 7.25–7.28 (m, 2H, C6H4),
7.97–8.00 (m, 2H, C6H4). 13C NMR (CDCl3): d ppm: 21.42, 30.05,
41.61, 47.50, 124.42, 126.65, 129.52, 140.45, 165.15, 204.09. IR
(Nujol, cmꢀ1) 1700, 1615, 1040, 830, 750. MS [M+H]+ m/z calcd
for C12H15N4O+ 231,1168, found 231,0700.
4.4. General procedure for the synthesis of alcohols ( )-3a–d
and ( )-6a–d
4.2.3. (5-(4-Chlorophenyl)tetrazolyl-2)-4-butan-2-one 2c
Colorless crystals, mp 91–93 °C, yield 94%. 1H NMR (CDCl3): d
ppm: 2.26 (s, 3H, CH3), 3.27 (t, 2H, CH2CO, J = 6.8 Hz), 4.89 (t, 2H
CH2N, J = 6.8 Hz), 7.43–7.45 (m, 2H, C6H4), 8.03–8.05 (m, 2H,
C6H4). 13C NMR (CDCl3): d ppm: 30.05, 41.53, 47.62, 125.74,
128.04, 129.14, 136.31, 164.20, 203.95. IR (Nujol, cmꢀ1) 1710,
1600, 1080, 1000, 840, 750. MS [M+H]+ m/z calcd for C11H12ClN4O+
251,0621, found 251,0348.
In a typical experiment, sodium borohydride (56 mmol, 2.12 g)
was added portionwise to a cooled (16 °C) and stirred mixture of
the appropriate ketone 2a–d or 5a–d (14 mmol) dissolved in
60 mL of methanol. The reaction mixture was stirred at room tem-
perature. The progress of the reaction was monitored by TLC, using
toluene–ethyl acetate (5:1 v/v) as the eluent. After completion of
the reaction (approximately 2.5 h), the solvent was evaporated
and to the resulting crude product, 40 mL of H2O was added. The
mixture was extracted with Et2O (3 ꢁ 50 mL) and the organic layer
was washed with water (3 ꢁ 50 mL), dried over anhydrous MgSO4,
and evaporated.
4.2.4. (5-(2-Chlorophenyl)tetrazolyl-2)-4-butan-2-one 2d
Oil, yield 81%. 1H NMR (CDCl3): d ppm: 2.26 (s, 3H, CH3), 3.28 (t,
2H, CH2CO, J = 7.2 Hz), 4.94 (t, 2H CH2N, J = 7.2 Hz), 7.36–7.40 (m,
2H, C6H4), 7.50–7.52 (m, 1H, C6H4), 7.90–7.93 (m, 1H, C6H4). 13C
NMR (CDCl3): d ppm: 30.08, 41.48, 47.70, 126.33, 126.88, 130.77,
131.07, 131.27, 132.93, 163.23, 204.01. IR (film, cmꢀ1) 1720,
1600, 1170, 1065, 1040, 750. MS [M+H]+ m/z calcd for
4.4.1. (5-Phenyltetrazolyl-2)-4-butan-2-ol 3a
Oil, yield 94%. 1H NMR (CDCl3):
d
ppm: 1.26 (d, 3H,
C
11H12ClN4O+ 251,0621, found 251,0232.
CH3, JCH3CH = 6 Hz), 2.08–2.12 (m, 1H, CHaHb), 2.20–2.25 (m, 2H,

140
E. Łukowska-Chojnacka et al. / Tetrahedron: Asymmetry 23 (2012) 136–143
CHaHb + OH), 3.80–3.90 (m, 1H, CH), 4.78–4.85 (m, 2H, CH2N), 7.46–
7.48 (m, 3H, C6H5), 8.11–8.13 (m, 2H, C6H5). 13C NMR (CDCl3): d ppm:
23.61, 38.02, 50.14, 64.66, 126.74, 127.26, 128,81, 130.28, 165.02. IR
(film, cmꢀ1) 3400, 2980, 1520, 1445, 1130, 1015, 725, 688. MS
[M+H]+ m/z calcd for C11H15N4O+ 219,1168, found 219,0780.
4.4.8. (5-(2-Chlorophenyl)tetrazolyl-2)-propan-2-ol 6d
Oil, yield 91%. 1H NMR (CDCl3): d ppm: 1.35 (d, 3H, CH3,
JCH3CH = 6.4 Hz), 2.67 (s, 1H, OH), 4.45–4.48 (m, 1H, CH), 4.63 and
4.66 (dd, 1H, CHaHbN, JHaCH = 8 Hz, JHaHb = 14 Hz), 4.74 and 4.78
(dd, 1H, CHaHbN, JHbCH = 3.2 Hz), 7.39–7.425 (m, 2H, C6H4), 7.52–
7.54 (m, 1H, C6H4), 7,96–7.98 (m, 1H, C6H4). 13C NMR (CDCl3): d
ppm: 20.19, 59.80, 66.21, 126.09, 126.96, 130.86, 131.23, 131.28,
133.02, 163.30. IR (film, cmꢀ) 3420, 2985, 1595, 1455, 1125,
1060, 1030, 940, 775, 745. MS [M+H]+ m/z calcd for C10H12ClN4O+
239,0621, found 239,081.
4.4.2. (5-(4-Methylphenyl)tetrazolyl-2)-4-butan-2-ol 3b
Colorless crystals, mp 47–49 °C, yield 95%. 1H NMR (CDCl3): d
ppm: 1.26 (d, 3H, CH3, JCH3CH = 6 Hz), 2.07–2.13 (m, 1H, CHaHb),
2.17–2.23 (m, 2H, CHaHb + OH), 2.40 (s, 3H, CH3), 3.84–3.86 (m,
1H, CH), 4.77–4.84 (m, 2H, CH2N), 7.26–7.29 (m, 2H, C6H4), 7.99–
8.01 (m, 2H, C6H4). 13C NMR (CDCl3): d ppm: 21.43, 23.60, 38.02,
50.07, 64.67, 124.46, 126.67, 129.53, 140.44, 165.11. IR (Nujol,
cmꢀ1) 3470, 1115, 1062, 1040, 818, 740. MS MS [M+H]+ m/z calcd
for C12H17N4O+ 233,1324, found 233,0893.
4.5. General procedure for the enzyme-catalyzed
transesterification of alcohols ( )-3a–d and ( )-6a–d
In a typical experiment, the appropriate alcohol ( )-3a–d or
( )-6a–d (2 mmol) was dissolved in 10 mL of TBME. Then vinyl
acetate (2 mmol, 0.18 mL), molecular sieves 4 Å (200 mg), and
40 mg of enzyme were added. The mixture was stirred at room
temperature (20–25 °C) and the conversion monitored by TLC
with toluene–ethyl acetate (5:1 v/v) as the eluent. After the
appropriate time, the reaction was stopped by filtering off the
enzyme and molecular sieves. The solvent was evaporated under
reduced pressure. The mixture of acetate and unchanged alcohol
was separated by column chromatography on silica gel with a
toluene–ethyl acetate (5:1 v/v) mixture as the eluent. The enan-
tiomeric excess was determined by chiral HPLC analysis using a
Chiralcel OD-H column. NMR spectra of the enantiomerically
enriched alcohols (S)-(+)-3a–d were identical with those of
( )-3a–d. The specific rotations were measured in MeOH solu-
tion for the enantiomerically enriched alcohols and are as
follows:
4.4.3. (5-(4-Chlorophenyl)tetrazolyl-2)-4-butan-2-ol 3c
Colorless crystals, mp 70–73 °C, yield 96%. 1H NMR (CDCl3): d
ppm: 1.27 (d, 3H, CH3, JCH3CH = 6 Hz), 2.06–2.12 (m, 2H, CHaHb + OH),
2.19–2.23 (m, 1H, CHaHb), 3.84–3.89 (m, 1H, CH), 4.74–4.88 (m, 2H,
CH2N), 7.43–7.46 (m, 2H, C6H4), 8.04–8.08 (m, 2H, C6H4). 13C NMR
(CDCl3): d ppm: 23.68, 37.98, 50.22, 64.71, 125.80, 128.05, 129.16,
136.31, 164.18. IR (Nujol, cmꢀ1) 3465, 1608, 1120, 1090, 1070,
833, 755. MS [M+H]+ m/z calcd for C11H13ClN4O+ 253,0778, found
253,0589.
4.4.4. (5-(2-Chlorophenyl)tetrazolyl-2)-4-butan-2-ol 3d
Oil, yield 95%. 1H NMR (CDCl3): d ppm: 1.26 (d, 3H, CH3,
JCH3CH = 6.4 Hz), 2.02 (s, 1H, OH), 2.06–2.15 (m, 1H, CHaHb), 2.20–
2.28 (m, 1H, CHaHb), 3.86–3.90 (m, 1H, CH), 4.84–4.90 (m, 2H,
CH2N), 7.37–7.41 (m, 2H, C6H4), 7.52–7.54 (m, 1H, C6H4) 7.92–
7.95 (m, 1H, C6H4). 13C NMR (CDCl3): d ppm: 23.62, 38.01, 50.29,
64.73, 126.40, 126.92, 130.80, 131.09, 131.29, 132.99, 163.23. IR
(film, cmꢀ1) 3420, 2985, 1460, 1125, 1065, 1030, 745. MS [M+H]+
m/z calcd for C11H13ClN4O+ 253,0778, found 253,0719.
(S)-(+)-3a: ½a 2D2
ꢂ
¼ þ20:2 (c 2.43, CH3OH), ee = 70%;
¼ þ20:2 (c 2.52, CH3OH), ee = 72%;
¼ þ13:75 (c 2.91, CH3OH), ee = 59%;
¼ þ22:2 (c 2.12, CH3OH), ee = 98%;
¼ þ36:4 (c 2.35, CH3OH), ee = 68%;
¼ þ34:5 (c 2.42, CH3OH), ee = 74%;
ꢂ ¼ þ43:1 (c 1.95, CH3OH), ee = 99%.
(S)-(+)-3b: ½a 2D2
ꢂ
(S)-(+)-3c: ½a 2D2
ꢂ
(S)-(+)-3d: ½a 2D4
ꢂ
(S)-(+)-6b: ½a 2D9
ꢂ
4.4.5. (5-Phenyltetrazolyl-2)-propan-2-ol 6a
(S)-(+)-6c: ½a 2D6
ꢂ
Colorless crystals, mp 53–55 °C, yield 95%. 1H NMR (CDCl3): d
ppm: 1.34 (d, 3H, CH3, JCH3CH = 6.4 Hz), 3.02 (s, 1H, OH), 4.43–
4.47 (m, 1H, CH), 4.57 and 4.61 (dd, 1H, CHaHbN, JHaCH = 7.6 Hz,
JHaHb = 13.6 Hz), 4.66 and 4.69 (dd, 1H, CHaHbN, JHbCH = 3.6 Hz),
7.45–7.47 (m, 3H, C6H5), 8.06–8.09 (m, 2H, C6H5). 13C NMR (CDCl3):
d ppm: 20.22, 59.78, 66.18, 126.77, 126.93, 128.85, 130.41, 165.06.
IR (Nujol, cmꢀ1) 3325, 1125, 1060, 840, 775, 725, 685. MS [M+H]+
m/z calcd for C10H13N4O+ 205,1011, found 205,0980.
(S)-(+)-6d: ½a 2D5
4.5.1. (R)-(ꢀ)-(5-Phenyltetrazolyl-2)-4-butan-2-yl acetate 4a
Oil, yield 81.5%. 1H NMR (CDCl3): d ppm: 1.29 (d, 3H, CH3,
JCH3CH = 6.4 Hz), 2.01 (s, 3H, CH3CO), 2.29–2.35 (m, 2H, CH2),
4.70–4.73 (m, 2H, CH2N), 4.96–5.00 (m, 1H, CH), 7.45–7.50 (m,
3H, C6H5), 8.11–8.14 (m, 2H, C6H5). 13C NMR (CDCl3): d ppm:
19.85, 21.11, 35.13, 49.66, 67.94, 126.75, 127.30, 128.84, 130.26,
165.11, 170.36. IR (film, cmꢀ1) 1730, 1445, 1370, 1235, 1065,
728, 690. MS [M+H]+ m/z calcd for C13H17N4O2 261,1273, found
+
4.4.6. (5-(4-Methylphenyl)tetrazolyl-2)-propan-2-ol 6b
Colorless crystals, mp 85–87 °C, yield 92.5%. 1H NMR (CDCl3): d
ppm: 1.33 (d, 3H, CH3, JCH3CH = 6.4 Hz), 2.40 (s, 3H, CH3C6H4), 3.01
(s, 1H, OH), 4.42–4.46 (m, 1H, CH), 4.56 and 4.59 (dd, 1H, CHaHbN,
JHaCH = 7.6 Hz, JHaHb = 13,6 Hz), 4.64 and 4.68 (dd, 1H, CHaHbN,
JHbCH = 3.6 Hz), 7.25–7.27 (m, 2H, C6H4), 7.96–7.98 (m, 2H, C6H4).
13C NMR (CDCl3): d ppm: 20.20, 21.45, 59.73, 66.19, 124.14,
126.70, 129.55, 140.61, 165.16. IR (Nujol, cmꢀ1) 3330, 1135,
1070, 928, 828, 749. MS [M+H]+ m/z calcd for C11H15N4O+
219,1168, found 219,0672.
261,0687. ½a 2D2
¼ ꢀ22:6 (c 2.19, CH3OH) ee = 96%.
ꢂ
4.5.2. (R)-(ꢀ)-(5-(4-Methylphenyl)tetrazolyl-2)-4-butan-2-yl
acetate 4b
Oil, yield 86%. 1H NMR (CDCl3): d ppm: 1.29 (d, 3H, CH3,
JCH3CH = 6.0 Hz), 2.01 (s, 3H, CH3CO), 2.23–2.37 (m, 2H, CH2), 2.40
(s, 3H, CH3), 4.69–4.72 (m, 2H, CH2N), 4.94–5.02 (m, 1H, CH),
7.26–7.29 (m, 2H, C6H4), 8.00–8.02 (m, 2H, C6H4). 13C NMR
(CDCl3): d ppm: 19.85, 21.12, 21.45, 35.13, 49.62, 67.99, 124.49,
126.67, 129.54, 140.43, 165,10, 170.37. IR (film, cmꢀ1) 1735,
4.4.7. (5-(4-Chlorophenyl)tetrazolyl-2)-propan-2-ol 6c
1460, 1370, 1235, 1040, 825, 750. MS [M+H]+ m/z calcd for
Colorless crystals, mp 100–103 °C, yield 90.5%. 1H NMR (CDCl3):
d ppm: 1.35 (d, 3H, CH3, JCH3CH = 6.4 Hz), 2.79 (s, 1H, OH), 4.42–4.49
(m, 1H, CH), 4.58 and 4.61 (dd, 1H, CHaHbN, JHaCH = 7.6 Hz,
JHaHb = 13,6 Hz), 4.66 and 4.69 (dd, 1H, CHaHbN, JHbCH = 3.6 Hz),
7.42–7.45 (m, 2H, C6H4), 8.01–8.04 (m, 2H, C6H4). 13C NMR (CDCl3):
d ppm: 20.29, 59.87, 66.21, 125.47, 128.06, 129.18, 136.50, 164.23.
IR (Nujol, cmꢀ1) 3200, 1415, 1195, 1090, 935, 840, 755, 735. MS
[M+H]+ m/z calcd for C10H12ClN4O+ 239,0621, found 239,0238.
C
14H19N4O2 275,1430, found 275,0847. ½a D22
ꢂ
¼ ꢀ20:2 (c 2.35,
+
CH3OH) ee = 93%.
4.5.3. (R)-(ꢀ)-(5-(4-Chlorophenyl)tetrazolyl-2)-4-butan-2-yl
acetate 4c
Colorless crystals, mp 46–48 °C, yield 97%. 1H NMR (CDCl3): d
ppm: 1.29 (d, 3H, CH3, JCH3CH = 6 Hz), 2.01 (s, 3H, CH3CO), 2.29–
2.34 (m, 2H, CH2), 4.69–4.73 (m, 2H, CH2N), 4.93–5.01 (m, 1H,

E. Łukowska-Chojnacka et al. / Tetrahedron: Asymmetry 23 (2012) 136–143
141
CH), 7.44–7.46 (m, 2H, C6H4), 8.05–8.07 (m, 2H, C6H4). 13C NMR
(CDCl3): d ppm: 19.86, 21.11, 35.11, 49.74, 67.87, 125.80, 128.05,
129.16, 136.30, 164.25, 170.34. IR (Nujol, cmꢀ1) 1720, 1605,
1240, 1085, 1060, 1040, 1010, 948, 830, 750. MS [M+H]+ m/z calcd
4.6. General procedure for the synthesis of racemic mixtures of
acetates ( )-4a–d and ( )-7a–d
A mixture of the appropriate alcohol 3-a–d or 6a–d (1 mmol)
and anhydrous pyridine (0.63 mL) in acetic anhydride (0.63 mL)
was stirred at room temperature for 24 h. The progress of the reac-
tion was monitored by TLC with toluene–ethyl acetate (5:1 v/v) as
the eluent. After completion of the reaction the mixture was cooled
in an ice bath. The product was extracted with ethyl acetate
(3 ꢁ 10 mL), and the organic layer was washed with 5% HCl solu-
tion (3 ꢁ 10 mL), with NaHCO3 solution (3 ꢁ 10 mL), and dried
over anhydrous MgSO4. The product was purified by chromatogra-
phy on a short silica gel column with toluene–ethyl acetate (5:1
v/v).
for C13H16ClN4O2+ 295,0884 found 295,0381. ½a 2D2
¼ ꢀ24:9 (c 2.38,
ꢂ
CH3OH) ee = 91%.
4.5.4. (R)-(ꢀ)-(5-(2-Chlorophenyl)tetrazolyl-2)-4-butan-2-yl
acetate 4d
Colorless crystals, mp 42–44 °C, yield 96.5%. 1H NMR (CDCl3): d
ppm: 1.29 (d, 3H, CH3, JCH3CH = 6.4 Hz), 2.01 (s, 3H, CH3CO), 2.31–
2.38 (m, 2H, CH2), 4.74–4.78 (m, 2H, CH2N), 4.96–5.01 (m, 1H,
CH), 7.35–7.42 (m, 2H, C6H4), 7.51–7.53 (m, 1H, C6H4), 7.91–7.94
(m, 1H, C6H4). 13C NMR (CDCl3): d ppm: 19.83, 21.12, 35.10,
49.81, 67.92, 126.40, 126.88, 130.77, 131.04, 131.28, 132.97,
163.30, 170.34. IR (Nujol, cmꢀ1) 1721, 1245, 1060, 750. MS
4.7. General procedure for the chemical hydrolysis of acetates
(R)-(ꢀ)-4a–d and (R)-(+)-7b
+
[M+H]+ m/z calcd for C13H16ClN4O2 295,0884 found 295,0191.
½
a 2D4
ꢂ
¼ ꢀ16:7 (c 3, CH3OH) ee = 80%.
To the appropriate ester (0.4 mmol) dissolved in methanol
(2 mL), a solution of 1 M NaOH (2 mL) was added. The mixture
was stirred at room temperature for 24 h. The progress of the reac-
tion was monitored by TLC with toluene-ethyl acetate (5:1 v/v) as
the eluent. The product was extracted with CHCl3 (4 ꢁ 10 mL) and
the organic layer washed with water (3 ꢁ 50 mL), dried over anhy-
drous MgSO4, and evaporated. The alcohol was purified by chroma-
tography on a short silica gel column with toluene–ethyl acetate
(5:1 v/v) as the eluent. The specific rotations were measured in
MeOH solution for the prepared enantiomerically enriched alco-
hols and are as follows:
4.5.5. (R)-(+)-(5-Phenyltetrazolyl-2)-propan-2-yl acetate 7a
Oil, yield 95%. 1H NMR (CDCl3): d ppm: 1.36 (d, 3H, CH3,
JCH3CH = 6.4 Hz), 2.01 (s, 3H, CH3CO), 4.77–4.79 (m, 2H, CH2N),
5.42–5.47 (m, 1H, CH), 7.46–7.50 (m, 3H, C6H5), 8.13–8.15 (m,
2H, C6H5). 13C NMR (CDCl3): d ppm: 17.43, 20.89, 56.27, 67.84,
126.79, 127.19, 128.86, 130.35, 165.21, 170.03. IR (film, cmꢀ1
)
1745, 1450, 1370, 1235, 790, 730, 690. MS [M+H]+ m/z calcd for
+
C
12H15N4O2 247,1117 found 247,0660.
(R)-(ꢀ)-3a: ½a 2D8
ꢂ
¼ ꢀ29:7 (c 1.60, CH3OH), ee = 96%;
¼ ꢀ25:6 (c 1.76, CH3OH), ee = 93%;
¼ ꢀ22:95 (c 1.22, CH3OH), ee = 91%;
¼ ꢀ21:8 (c 2.36, CH3OH), ee = 80%;
ꢂ ¼ ꢀ52:0 (c 1.50, CH3OH), ee = 83%;
4.5.6. (R)-(+)-(5-(4-Methylphenyl)tetrazolyl-2)-propan-2-yl
acetate 7b
(R)-(ꢀ)-3b: ½a 2D2
ꢂ
(R)-(ꢀ)-3c: ½a 2D2
ꢂ
Oil, yield 79%. 1H NMR (CDCl3): d ppm: 1.35 (d, 3H, CH3,
JCH3CH = 6.8 Hz), 2.00 (s, 3H, CH3CO), 2.40 (s, 3H, CH3), 4.73 and
4.76 (dd, 1H, CHaHbN, JHaCH = 2.4 Hz, JHaHb = 14 Hz), 4.77 and
4.80 (dd, 1H, CHaHbN, JHbCH = 1.6 Hz), 5.41–5.46 (m, 1H, CH),
7.26–7.29 (m, 2H, C6H4), 8.00–8.03 (m, 2H, C6H4). 13C NMR
(R)-(ꢀ)-3d: ½a 2D4
ꢂ
(R)-(ꢀ)-6b: ½a 2D6
NMR Spectra of the enantiomerically enriched alcohols (S)-(ꢀ)-
3a–d and (S)-(ꢀ)-6b were identical with those of ( )-3a–d and
( )-6b.
(CDCl3):
d ppm: 17.43, 20.89, 21.45, 56.21, 67.86, 124.39,
126.71, 129.54, 140.52, 164.20, 170.03. IR (film, cmꢀ1) 1740,
1615, 1460, 1370, 1235, 825, 750. MS [M+H]+ m/z calcd for
4.8. Assignment of the absolute configuration of alcohol (ꢀ)-3a
a 2D9
ꢂ
¼ þ7:3 (c 2.18,
+
and its acetate and alcohol (+)-6c and its acetate
C13H17N4O2 261,1273 found 261,0865.
½
CH3OH) ee = 83%.
The enantiomerically enriched alcohol (ꢀ)-3a [obtained by
hydrolysis of ester (ꢀ)-4a, isolated from the reaction of lipase Ama-
no AK catalyzed transesterification of the racemate ( )-3a], was
used in reaction with optically pure (R)- and (S)-enantiomer of
methoxyphenylacetic acid (MPA)42 (Scheme 5). The 1H NMR spec-
tra of the resulting esters were taken in CDCl3 solution:
(R)–MPA-Ester, d ppm: 1.31 (d, 3H, CH3, JCH3CH = 6.4 Hz), 2.17–
2.25 (m, 2H, CH2), 3.42 (s, 3H, CH3), 4.24–4.30 (m, 2H, CH2N),
4.77 (s, 1H, CH), 5.01–5.03 (m, 1H, CH), 7.32–7.39 (m, 3H, Ar),
7.45–7.49 (m, 5H, Ar), 8.09–8.11 (m, 2H, Ar);
(S)-MPA-Ester, d ppm: 1.16 (d, 3H, CH3, JCH3CH = 6.4 Hz), 2.30–
2.35 (m, 2H, CH2), 3.39 (s, 3H, CH3), 4.63–4.67 (m, 2H, CH2N),
4.69 (s, 1H, CH), 5.01–5.09 (m, 1H, CH), 7.33–7.49 (m, 8H, Ar),
8.12–8.14 (m, 2H, Ar).
The differences in the proton chemical shifts (DdRS) observed
for the esters prepared from the (R)- and (S)-acids, respectively,
4.5.7. (R)-(+)-(5-(4-Chlorophenyl)tetrazolyl-2)-propan-2-yl
acetate 7c
Colorless crystals, mp 66–68 °C, yield 96%. 1H NMR (CDCl3): d
ppm: 1.35 (d, 3H, CH3, JCH3CH = 6.4 Hz), 2.00 (s, 3H, CH3CO), 4.72–
4.81 (m, 2H, CH2N), 5.40–5.46 (m, 1H, CH), 7.43–7.47 (m, 2H,
C6H4), 8.05–8.08 (m, 2H, C6H4). 13C NMR (CDCl3): d ppm: 17.45,
20.88, 56.37, 67.79, 125.70, 128.09, 129.16, 136.38, 164.36,
170.00. IR (Nujol, cmꢀ1) 1740, 1600, 1225, 1082, 1055, 1040, 839,
+
750. MS [M+H]+ m/z calcd for C12H14ClN4O2 281,0727 found
281,0343. ½a 2D6
¼ þ5:2 (c 2.31, CH3OH) ee = 91%.
ꢂ
4.5.8. (R)-(+)-(5-(2-Chlorophenyl)tetrazolyl-2)-propan-2-yl
acetate 7d
Oil, yield 96%. 1H NMR (CDCl3): d ppm: 1.37 (d, 3H, CH3,
JCH3CH = 6.8 Hz), 2.01 (s, 3H, CH3CO), 4.78 and 4.81 (dd, 1H,
CHaHbN, JHaCH = 6.8 Hz, JHaHb = 14 Hz), 4.84 and 4.87 (dd, 1H,
CHaHbN, JHbCH = 4.4 Hz), 5.41–5.49 (m, 1H, CH), 7.35–7.42 (m,
were calculated separately for the protons bonded to each carbon
3H, C6H5), 7.50–7.55 (m, 1H, C6H4), 7.92–7.96 (m, 1H, C6H4) .13
C
H
H
RS>0
L1
L2
δ
NMR (CDCl3): d ppm: 17.43, 20.88, 56.40, 67.86, 126.32, 126.88,
MPA
O
MPA
O
(R)
130.78, 131.10, 131.29, 133.04, 163.39, 170.01. IR (film, cmꢀ1
)
δ
RS<0
1740, 1455, 1370, 1230, 1060, 745. MS [M+H]+ m/z calcd for
+
C
12H14ClN4O2 281,0727 found 281,0220. ½a D26
ꢂ
¼ þ8:8 (c 2.85,
CH3OH) ee = 78%.
Figure 1.

142
E. Łukowska-Chojnacka et al. / Tetrahedron: Asymmetry 23 (2012) 136–143
L1 = Me (1' )
L2 = CH2 (2' ), CH2 (3' )
OH
3'
N
N
OMe
COOH
1'
OMe
COOH
2'
N
N
Ph
Ph
3a
(-)- ee=96%
(R)-MPA
(S)-MPA
(S)-MPA-Ester
(R)-MPA-Ester
or
DCC, DMAP,
CH2Cl2
DCC, DMAP,
CH2Cl2
2'
1'
N
N
N
OH
N
Cl
(+)-6d
ee=99%
L1 = Me (1' )
L2 = CH2 (2' )
Scheme 5.
for Advanced Studies. This work was also financially supported
by Warsaw University of Technology.
H
H
RS>0
L2
L1
δ
MPA
O
MPA
O
(S)
δ
RS<0
References
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Figure 2.
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equations:
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D
D
d
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RSL1 ¼ dRL1 ꢀ dSL1 ¼ 1:31 ꢀ 1:16 ¼ þ0:15ppm
RSL2 ¼ dRL2 ꢀ dSL2 ¼ ð2:21 ꢀ 2:32Þ þ ð4:27 ꢀ 4:65Þ
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alcohol (+)-6d isolated from the racemate ( )-6d (Scheme 5). 1H
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The differences in the chemical shifts (DdRS) observed for the
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D
D
d
d
RSL1 ¼ dRL1 ꢀ dSL1 ¼ 1:25 ꢀ 1:42 ¼ ꢀ0:17ppm
RSL2 ¼ dRL2 ꢀ dSL2 ¼ 4:85 ꢀ 4:73 ¼ þ0:12ppm
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DdRS, which corresponds to the signal of
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(+)-6d according to Figure 2.
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This work has been supported by the European Union in the
framework of European Social Fund through the Warsaw Univer-
sity of Technology Development Programme, realized by Center

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