Lipase mediated kinetic resolution of benzimidazolyl ethanols

Article abstract of DOI:10.1016/j.tetasy.2008.03.021

Enantioselective trans-acylation of the racemic benzimidazolyl ethanols was achieved via enzymatic kinetic resolution. A range of commercially available lipases were screened and Novozyme-435 was established as the optimal catalyst. N-Protection was found to be mandatory for effective transesterification. However, electron-withdrawing substituents reduced the enantioselectivity to some extent when compared to the other substituents.

Full text of DOI:10.1016/j.tetasy.2008.03.021

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Tetrahedron: Asymmetry 19 (2008) 901–905
Lipase mediated kinetic resolution of benzimidazolyl ethanols
Ravi Kumar Cheedrala,a Rachna Sachwanib and Palakodety Radha Krishnab,*
aDepartment of Chemistry, Biotech Center, Pohang University of Science and Technology (POSTECH),
San 31, Hyoja-Dong, Pohang 790-784, Republic of Korea
bD-206/B, Discovery Laboratory, Organic Chemistry Division-III, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 16 January 2008; accepted 20 March 2008
Abstract—Enantioselective trans-acylation of the racemic benzimidazolyl ethanols was achieved via enzymatic kinetic resolution. A
range of commercially available lipases were screened and Novozyme-435 was established as the optimal catalyst. N-Protection was
found to be mandatory for effective transesterification. However, electron-withdrawing substituents reduced the enantioselectivity to
some extent when compared to the other substituents.
Ó 2008 Published by Elsevier Ltd.
1. Introduction
recyclability, non-requirement of co-factors, low cost and
applicability to diverse reactions such as esterification,
transesterification, amidation and hydrolysis make them
popular biocatalysts in organic synthesis.6 They have been
frequently utilized for the kinetic resolution of diastereo-
meric and enantiomeric mixtures of primary, secondary
and allylic alcohols.7
The high biological potential of benzimidazole derivatives
has been well established.1 Their physiological action
include respiratory, analgesic, spasmolytic, anti-inflamma-
tory and antihypertensive activity, which makes them
important therapeutic agents to combat human and
veterinary diseases.2 As stereochemistry in a drug molecule
governs its biological activity, chirality is a key issue in
pharmaceutical research. Of the two enantiomers of 2-(a-
hydroxybenzyl) benzimidazole derivatives, the (R)-enantio-
mer is more active and selective than the (S)-enantiomer, as
demonstrated by QSAR studies and biological tests.3 Such
findings make the synthesis of chiral benzimidazole deriva-
tives an interesting area of research.
2. Results and discussion
Herein, we report the lipase mediated kinetic resolution
of benzimidazolyl ethanols. Preliminary studies were
performed on benzimidazolyl ethanol rac-1 with various
acetates as functionalized acyl donors (Scheme 1). The
acetates employed were vinyl acetate, isoprenyl acetate
and p-chlorophenyl acetate. Vinyl acetate was chosen as
the acetate of choice, since with the other two acetates the
reactions were found to be sluggish. The substrate was pre-
pared by a standard procedure as reported in the literature.8
The lipases examined herein were Pseudomonas cepacia
The application of enzymes as biocatalysts to obtain chiral
compounds in enantiomerically pure forms is quite well
known.4 Lipases have been successfully used in many bio-
transformations owing to their excellent regio- and stereo-
selectivities.5 Their wide substrate specificity, stability,
OAc
OH
OH
H
H
N
H
N
N
Lipase, acyl donor
Toluene, 27 oC
+
N
N
N
rac-1
(R)-1a
(S)-1
Scheme 1.
*
Corresponding author. Tel.: +91 40 27160123x2651; fax: +91 40 27160387; e-mail: prkgenius@iict.res.in
0957-4166/$ - see front matter Ó 2008 Published by Elsevier Ltd.
doi:10.1016/j.tetasy.2008.03.021

902
R. K. Cheedrala et al. / Tetrahedron: Asymmetry 19 (2008) 901–905
solvation sites.12 n-Hexane and toluene were considered
as suitable solvents and studied for the domino reaction.
Polar solvents did not give the expected conversions. Thus,
it was observed that the most effective resolution occurred
in toluene at 25 °C (Table 3). The configuration of the
remaining alcohol (S)-1 was determined by comparing
the rotation values. Alcohol (S)-1 has [a]D = À27.4 (c 0.9,
CH3OH) while the reported8 (S)-1 has [a]D = À34.1 (c
0.01, CH3OH) thus accounting for 80% ee. Conversely,
the resolved acetate 1a was assigned an (R)-configuration.
Table 1. Observed enantiomeric excess of various lipases for rac-1
Entry
Enzyme
eea (acetate)
1
2
3
Lipase PS-B
Lipase PS-C
Novozyme-435
30
50
70
a Based on chiral HPLC.
Table 2. Observed conversion rates of various lipases for rac-2
Entry
Enzyme
eea (acetate)
After the initial screening of commercial lipases and sol-
vents (Tables 2 and 3) for rac-2, we observed that Novo-
zyme-435 effectively catalyzed the kinetic resolution of
rac-2 in toluene at 27 °C (Scheme 2).
1
2
3
Lipase PS-B
Lipase PS-C
Novozyme-435
40
60
97
a Based on chiral HPLC.
The higher enantioselectivity observed in the case of rac-2
as compared to rac-1 inspired us to investigate the enzyme
compatibility for various substituents (Scheme 3) (Table 2).
To study the effects of diverse substituents, various deriva-
tives rac-3, rac-4, rac-5 and rac-6 were synthesized13 and
subjected to enzymatic kinetic resolution (Scheme 3). The
results obtained are shown in Table 4.
Table 3. Solvent studies for kinetic resolution of rac-2
Entry
Solvent
Reaction time (h)
ee (2a)a
ee (2)a
1
2
Hexane
Toluene
48
24
92
97
90
93
a Based on chiral HPLC.
The absolute stereochemistry of the newly created centre
was determined by comparing the [a]D values with the liter-
ature for (S)-1a.8 The configurations of the resulting ester
and the remaining alcohol for all the other examples were
assigned as (R)- and (S)-, respectively, by analogy. It is
noteworthy that certain substitutions on the nitrogen
enhanced the enantioselectivity. Thus, the ee was found
to be lower in case of electron-withdrawing substituents
such as benzoyl or p-toluene sulfonyl as compared to
methyl and benzyl substituents.
lipases PS-B and PS-C, and Candida antarctica lipase B
(Novozyme-435). It was observed that none of the chosen
lipases gave ee >70% for this substrate (Table 1).
However, the N-methylated derivative rac-2 gave signifi-
cantly better results with Novozyme-435 leading to a sub-
stantial increase in the enantiomeric excess by ꢀ27%
(Table 2).
Selection of the appropriate solvent is a critical factor for
biocatalysis,9 as organic solvents are known to change
the enzyme activity10 and enantioselectivity11 governing
the enzyme conformation by interacting with the hydration
layer essential for catalysis and by altering hydrophobic or
H-bonding in the core of the protein as well as protein
3. Conclusion
In conclusion, enzymatic transesterification was established
as an efficient technique for the kinetic resolution of
OH
N
OAc
OH
N
N
Novozyme-435,
Toluene, 27 oC
OAc
+
N
N
N
rac-2
(R)-2a
(S)-2
Scheme 2.
R
R
N
R
OH
R'
OAc
OH
R'
N
N
Novozyme-435,
Toluene, 27 oC
OAc
+
R'
N
N
N
(R)-3a-6a
(S)-3-6
rac-3, R = Bz, R' = Me
rac-4, R = Ts, R' = Me
rac-5, R = Bn, R' = Me
rac-6, R = Bz, R' = Ph
Scheme 3.

R. K. Cheedrala et al. / Tetrahedron: Asymmetry 19 (2008) 901–905
Table 4. Kinetic resolution of various benzimidazolyl ethanols
903
Entry
Substrate
Reaction time (h)
eea (acetate)
eea (alcohol)
% Conversionb
53
Ec
OH
OH
OH
OH
OH
OH
H
N
rac-1
24
70
80
14
N
N
N
rac-2
rac-3
rac-4
rac-5
24
24
24
24
24
97
79
75
95
77
93
88
86
97
87
49
53
53
51
53
225
25
Bz
N
N
Ts
N
19
N
Bn
N
165
22
N
Bz
N
rac-6
Ph
N
a Based on chiral HPLC.
b The % conversion was calculated from the enantiomeric excess of the starting material (ees) and the product (eep) according to % conversion = ees/
(ees + eep).
c The enantioselectivity E can be expressed in terms of ees and eepby E = ln[1 À ees/1 + (ees/eep)]/ln[1 + ees/1 + (ees/eep)].
benzimidazolyl ethanols. These enantiopure benzimidazol-
yl ethanols have proven to be valuable synthons for various
biologically active compounds.
graphic separation and purification of final products were
carried out on silica gel columns (60–120 mesh).
4.2. General procedure for the lipase-catalyzed transesteri-
fication of racemic alcohols
All racemic allylic alcohols were subjected to enzymatic
transesterification according to the same procedure. The
enzyme/substrate ratio of 50 mg of enzyme/mmol of sub-
strate was kept constant in all the cases. To a stirred mix-
ture of alcohol (0.1 mmol) and toluene (0.33 mL), vinyl
acetate (16 lL) and Novozyme-435 (5 mg) were added
and stirred at room temperature for 24 h. The reaction
was then filtered and concentrated in vacuo. Column chro-
matography of the crude product with a 20% ethyl acetate
in n-hexane as eluant gave enantiomerically pure alcohol in
32–43% yields.
4. Experimental
4.1. General methods
Solvents were dried over standard drying agents and
freshly distilled prior to use. Chemicals were purchased
and used without further purification. The enzymes were
purchased from Ms. Amano Enzyme Co. Japan. All col-
umn chromatographic separations were performed using
silica gel (Acme’s, 60–120 mesh). Organic solutions were
dried over anhydrous Na2SO4 and concentrated below
40 °C in vacuo. 1H NMR (300 MHz) and 13C NMR
(75 MHz) spectra were measured with a Bruker Avance
300 MHz with tetramethylsilane as internal standard for
solutions in deuteriochloroform. J values are given in
Hertz. IR spectra were recorded on a Perkin–Elmer IR-
683 spectrophotometer with NaCl optics. Optical rotations
were measured with JASCO DIP 300 digital polarimeter at
25 °C. Mass spectra were recorded on CEC-21-11013 or
Fannigan Mat 1210 double focusing mass spectrometers
operating at a direct inlet system or LC/MSD Trap SL
(Agilent Technologies). The enantiomeric excess of result-
ing esters and alcohols was determined by HPLC analysis
which was conducted by using chiral-OD column,
225 nm, i-PrOH/n-hexane solvent system. All chromato-
4.2.1. Enzymatic resolution of ( )-1-(1H-benzo[d]imidazol-
2-yl)ethanol 1. To a stirred mixture of alcohol 1 (0.16 g,
0.1 mmol) and toluene (0.33 mL), vinyl acetate (16 lL)
and Novozyme-435 (5 mg) were added and stirred at room
temperature for 24 h. The reaction was then filtered and
concentrated in vacuo. Column chromatography of the
crude product with a 1:1 EtOAc/n-hexane mixture as elu-
ant gave ester (R)-1a in 38% yield and 80% ee and alcohol
(S)-1 with 33% yield and 90% ee. (R)-1a: [a]D = +59.4 (c
0.9, CH3OH), HPLC (column, chiral-OD, 225 nm, 3%
i-PrOH/n-hexane); tR (major): 3.71 min; tR (minor):
4.31 min; IR (neat): 3100, 1738, 1025 cmÀ1
;
1H NMR
(300 MHz, CDCl3): d 9.73 (br s, 1H), 7.96–7.44 (m, 2H),

904
R. K. Cheedrala et al. / Tetrahedron: Asymmetry 19 (2008) 901–905
7.28–7.26 (m, 2H), 6.12–6.04 (m, 1H), 2.35 (s, 3H), 1.84 (d,
3H, J = 6 Hz); 13C NMR (75 MHz, CDCl3): d 170.32,
141.55, 138.92, 123.05, 115.33, 76.29, 21.97, 19.58; ESIMS
(m/z) (%): 227 (M+23): Anal. Calcd for C11H12N2O2: C,
64.69; H, 5.92; N, 13.72. Found: C, 64.33; H, 6.14; N,
13.83 and (S)-1: [a]D = À13.5 (c 1.1, CH3OH), HPLC
(column, chiral-OD, 225 nm, 4% i-PrOH/n-hexane); tR
(major): 10.46 min; tR (minor): 9.54 min; IR (neat): 3400,
HPLC (column, chiral-OD, 225 nm, 5% i-PrOH/n-hexane);
tR (major): 31.23 min; tR (minor): 27.54 min; IR (neat):
3366, 1692, 1029 cmÀ1 1H NMR (300 MHz, CDCl3): d
;
8.08–8.05 (m, 2H), 7.57–7.46 (m, 2H), 7.44–7.35 (m, 3H),
7.27–7.24 (m, 2H), 6.33–6.29 (m, 1H), 1.99 (d, 3H,
J = 6 Hz); ESIMS (m/z) (%): 267 (M+1): Anal. Calcd for
C16H14N2O2: C, 72.16; H, 5.30; N, 10.52. Found: C,
71.58; H, 5.54; N, 10.24.
3150, 1045 cmÀ1 1H NMR (300 MHz, CDCl3): d 7.59–
;
7.54 (m, 2H), 7.22–7.17 (m, 2H), 5.15 (m, 1H), 1.72 (d,
3H, J = 6 Hz). ESIMS (m/z) (%): 163 (M+1): Anal. Calcd
for C9H10N2O: C, 66.65; H, 6.21; N, 17.27. Found: C,
66.98; H, 6.14; N, 17.37.
4.2.4. Enzymatic resolution of ( )-1-(1-tosyl-1H-benzo[d]-
imidazol-2-yl)ethanol 4. To a stirred mixture of alcohol 4
(0.33 g, 0.1 mmol) and toluene (0.33 mL), vinyl acetate
(16 lL) and Novozyme-435 (5 mg) were added and stirred
at room temperature for 24 h. The reaction was then fil-
tered and concentrated in vacuo. Column chromatography
of the crude product with a 1:9 EtOAc/n-hexane mixture as
eluant gave ester (R)-4a in 39% yield and 82% ee and alco-
hol (S)-4 with 37% yield and 86% ee. (R)-4a: [a]D = +23.4
(c 0.9, CH3OH), HPLC (column, chiral-OD, 225 nm, 4%
i-PrOH/n-hexane); tR (major): 3.74 min; tR (minor):
4.2.2. Enzymatic resolution of ( )-1-(1-methyl-1H-
benzo[d]imidazol-2-yl)ethanol 2. To a stirred mixture of
alcohol 2 (0.18 g, 0.1 mmol) and toluene (0.33 mL), vinyl
acetate (16 lL) and Novozyme-435 (5 mg) were added
and stirred at room temperature for 24 h. The reaction
was then filtered and concentrated in vacuo. Column
chromatography of the crude product with a 4:1 EtOAc/
n-hexane mixture as eluant gave ester (R)-2a in 42% yield
and 99% ee and alcohol (S)-2 with 40% yield and 99% ee.
(R)-2a: [a]D = +63.6 (c 1.0, CH3OH), HPLC (column,
chiral-OD, 225 nm, 4% i-PrOH/n-hexane); tR (major):
26.92 min; tR (minor): 41.07 min; IR (neat): 1735,
8.46 min; IR (neat): 1743, 1040 cmÀ1
;
1H NMR
(300 MHz, CDCl3): d 7.98–7.68 (m, 4H), 7.38–7.25 (m,
4H), 5.33 (br s, 1H) 3.66 (br s, 1H), 2.37 (s, 3H), 1.54 (d,
3H, J = 6.6 Hz); 13C NMR (75 MHz, CDCl3): d 157.49,
146.22, 141.34, 133.07, 130.29, 126.93, 125.45, 124.99,
120.42, 113.68, 64.31, 29.70, 23.15, 21.66; ESIMS (m/z)
(%): 359 (M+1). Anal. Calcd for C18H28N2O4S: C, 60.32;
H, 5.06; N, 7.82. Found: C, 60.25; H, 5.16; N, 7.78 and
(S)-4: [a]D = À21.8 (c 0.8, CH3OH), HPLC (column,
chiral-OD, 225 nm, 5% i-PrOH/n-hexane); tR (major):
31.32 min; tR (minor): 27.61 min; IR (neat): 3427,
1020 cmÀ1 1H NMR (300 MHz, CDCl3): 7.80–7.85 (m,
;
1H), 7.35–7.15 (m, 3H), 6.23–6.13 (m, 1H), 3.81 (s, 3H),
2.11 (s, 3H), 1.82 (d, 3H, J = 5.4 Hz); 13C NMR
(75 MHz, CDCl3): d 170.32, 152.27, 123.16, 122.39,
120.10, 109.43, 64.32, 29.96, 20.97, 18.84; ESIMS (m/z)
(%): 241 (M+23): Anal. Calcd for C12H14N2O2: C, 66.04;
H, 6.47; N, 12.84. Found: C, 65.88; H, 6.36; N, 12.97
and (S)-2: [a]D = À8.6 (c 1.0, CH3OH), HPLC (column,
chiral-OD, 225 nm, 5% i-PrOH/n-hexane); tR (major):
69.75 min; tR (minor): 56.31 min; IR (neat): 3350,
1
1023 cmÀ1; H NMR (300 MHz, CDCl3): d 7.87–7.68 (m,
4H), 7.38–7.26 (m, 4H), 5.52–5.48 (m, 1H), 2.38 (s, 3H),
1.76 (d, 3H, J = 6.2 Hz); ESIMS (m/z) (%): 317 (M+1):
Anal. Calcd for C16H16N2O3S: C, 60.74; H, 5.10; N, 8.85.
Found: C, 60.58; H, 5.08; N, 8.64.
1
1047 cmÀ1; H NMR (300 MHz, CDCl3): d 7.74–7.72 (m,
1H), 7.30–7.24 (m, 3H), 5.15–5.10 (m, 1H), 3.81 (s, 3H),
1.73 (d, 3H, J = 6 Hz); ESIMS (m/z) (%): 177 (M+1):
Anal. Calcd for C10H12N2O: C, 68.16; H, 6.86; N, 15.90.
Found: C, 68.58; H, 6.54; N, 15.37.
4.2.5. Enzymatic resolution of ( )-1-(1-benzyl-1H-benzo[d]-
imidazol-2-yl)ethanol 5. To a stirred mixture of alcohol 5
(0.25 g, 0.1 mmol) and toluene (0.33 mL), vinyl acetate
(16 lL) and Novozyme-435 (5 mg) were added and stirred
at room temperature for 24 h. The reaction was then fil-
tered and concentrated in vacuo. Column chromatography
of the crude product with a 1:4 EtOAc/n-hexane mixture as
eluant gave ester (R)-5a in 34% yield and 95% ee and alco-
hol (S)-5 with 32% yield and 97% ee. (R)-5a: [a]D = +12.2
(c 0.8, CH3OH), HPLC (column, chiral-OD, 225 nm, 4%
i-PrOH/n-hexane); tR (major): 3.67 min; tR (minor):
4.2.3. Enzymatic resolution of ( )-(2-(1-hydroxyethyl)-1H-
benzo[d]imidazol-1-yl)(phenyl) methanone 3. To a stirred
mixture of alcohol 3 (0.27 g, 0.1 mmol) and toluene
(0.33 mL), vinyl acetate (16 lL) and Novozyme-435
(5 mg) were added and stirred at room temperature for
24 h. The reaction was then filtered and concentrated in
vacuo. Column chromatography of the crude product with
a 1:4 EtOAc/n-hexane mixture as eluant gave ester (R)-3a
in 35% yield and 85% ee and alcohol (S)-3 with 33% yield
and 88% ee. (R)-3a: [a]D = +27.8 (c 1.0, CH3OH), HPLC
(column, chiral-OD, 225 nm, 4% i-PrOH/n-hexane); tR
(major): 8.17 min; tR (minor): 10.26 min; IR (neat): 1728,
3.84 min; IR (neat): 1734, 1042 cmÀ1
;
1H NMR
(300 MHz, CDCl3): d 7.32–7.26 (m, 6H), 7.03–7.01 (m,
2H), 6.23–6.12 (m, 1H), 5.82–5.38 (m, 2H), 1.80 (s, 3H),
1.72 (d, 3H, J = 6.6 Hz); 13C NMR (75 MHz, CDCl3): d
166.63, 154.27, 138.97, 129.11, 128.76, 125.83, 123.04,
115.39, 69.92, 55.73, 22.95; ESIMS (m/z) (%): 317
(M+23): Anal. Calcd for C18H18N2O2: C, 73.45; H, 6.16;
N, 9.52. Found: C, 73.85; H, 6.08; N, 9.35 and (S)-5:
[a]D = À15.1 (c 0.9, CH3OH), HPLC (column, chiral-OD,
225 nm, 5% i-PrOH/n-hexane); tR (major): 15.49 min; tR
1698, 1038 cmÀ1 1H NMR (300 MHz, CDCl3): d 8.06–
;
8.04 (m, 2H), 7.63–7.60 (m, 3H), 7.45–7.39 (m, 2H),
7.27–7.24 (m, 2H), 6.37–6.20 (m, 1H), 2.11 (s, 3H), 1.98
(d, 3H, J = 6.6 Hz); 13C NMR (75 MHz, CDCl3): d
152.24, 133.63, 129.86, 128.50, 123.10, 115.49, 67.22,
18.14; ESIMS (m/z) (%): 309 (M+1). Anal. Calcd for
C18H16N2O3: C, 70.12; H, 5.23; N, 9.09. Found: C, 69.85;
H, 5.66; N, 8.78 and (S)-3: [a]D = À36.0 (c 1.0, CH3OH),
1
(minor): 8.38 min; IR (neat): 3520, 1021 cmÀ1; H NMR
(300 MHz, CDCl3): d 7.28–7.16 (m, 6H), 7.15–7.02 (m,
2H), 5.45 (s, 2H), 5.29–5.06 (m, 1H), 3.62 (br s, 1H), 1.69
(d, 3H, J = 5 Hz); ESIMS (m/z) (%): 253 (M+1): Anal.

R. K. Cheedrala et al. / Tetrahedron: Asymmetry 19 (2008) 901–905
905
Eberle, J.; Le Cloarec, A. Y.; Raynaud, G.; Dorme, N. Chem.
Abstr. 1973, 79, 137156f; (c) Fauran, C.; Turin, M.; Raynaud,
G.; Sergant, M. Chem. Abstr. 1976, 84, 135658x; (d) Jpn
Kokai Takkyo Koho JP 61, 145, 165; Chem. Abstr. 1987, 106,
18565e.
Calcd for C16H16N2O: C, 76.16; H, 6.39; N, 11.10. Found
C, 76.28; H, 6.56; N, 11.24.
4.2.6. Enzymatic resolution of ( )-(2-(hydroxy(phenyl)-
methyl)-1H-benzo[d]imidazol-1-yl)(phenyl)methanone
6.
3. Kadin, S. B.; Eggers, H. J.; Tamm, I. Nature 1964, 201, 639–
640.
To a stirred mixture of alcohol 6 (0.33 g, 0.1 mmol) and
toluene (0.33 mL), vinyl acetate (16 lL) and Novozyme-
435 (5 mg) were added and stirred at room temperature
for 24 h. The reaction was then filtered and concentrated
in vacuo. Column chromatography of the crude product
with a 1.5:8.5 EtOAc/n-hexane mixture as eluant gave ester
(R)-6a in 41% yield and 84% ee and alcohol (S)-6 with 43%
yield and 87% ee. (R)-6a: [a]D = +2.5 (c 1.1, CH3OH),
HPLC (column, chiral-OD, 225 nm, 4% i-PrOH/n-hexane);
tR (major): 3.58 min; tR (minor): 4.21 min; IR (neat): 1738,
1686, 1039 cmÀ1; 1H NMR (300 MHz, CDCl3): d 8.12–7.59
(m, 3H), 7.51–7.37 (m, 3H), 7.36–7.24 (m, 4H), 7.10–7.05
(m, 4H), 6.86 (s, 1H), 2.13 (s, 3H); 13C NMR (75 MHz,
CDCl3): d 167.82, 153.45, 141.55, 138.94, 130.87, 129.37,
127.72, 115.36, 72.08; ESIMS (m/z) (%): 371 (M+1): Anal.
Calcd for C23H18N2O3: C, 74.58; H, 4.90; N, 7.56. Found:
C, 73.98; H, 4.66; N, 7.64 and (S)-6: [a]D = À6.6 (c 1.3,
CH3OH), HPLC (column, chiral-OD, 225 nm, 5%
i-PrOH/n-hexane); tR (major): 17.06 min; tR (minor):
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8.16 min; IR (neat): 3357, 1690, 1023 cmÀ1 1H NMR
;
8. Katritzky, A. R.; Aslan, D. C.; Leeming, P.; Steel, P. J.
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(300 MHz, CDCl3): d 8.09–8.03 (m, 2H), 7.50–7.43 (m,
3H), 7.34–7.05 (m, 9H), 6.37–6.21 (m, 1H); ESIMS (m/z)
(%): 329 (M+1): Anal. Calcd for C21H16N2O2: C, 76.81;
H, 4.91; N, 8.53. Found C, 76.58; H, 4.96; N, 8.64.
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Acknowledgement
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Mozhaev, V. V.; Khmelnitsky, Y. L.; Sergeeva, M. V.;
Belova, A. B.; Klyachko, N. L.; Levashov, A. V.; Martinek,
K. Eur. J. Biochem. 1989, 184, 597–602.
One of the authors (R.S.) thanks CSIR, New Delhi, for
financial support in the form of a fellowship.
13. (a) Dubey, P. K.; Ravi Kumar, C.; Babu, B. Indian J. Chem.,
Sect. B 2003, 42B, 3128; (b) Ramaiah, K.; Dubey, P. K.;
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