Enzyme-catalyzed resolution of aromatic ring fused cyclic tertiary alcohols

Article abstract of DOI:10.1016/j.tetasy.2008.12.002

An efficient chemoenzymatic route for the synthesis of optically active aromatic ring fused cyclic tertiary alcohols (S)-(-)-1-methyl-1,2,3,4-tetrahydronaphthalen-1-ol (-)-1b and (S)-(+)-1-methyl-2,3-dihydro-1H-inden-1-ol (+)-1a has been developed. Different lipases have been tested in the transesterification of these tertiary alcohols; CAL-A (Candida antarctica Lipase A) was found to be the best biocatalyst for 1b and CAL-A-CLEA (Lipase A, C. antarctica, cross-linked enzyme aggregate) for 1a, obtained with ee values of 20% and 45%, respectively, and the corresponding esters 2b and 2a with the ee values of 99% and 71%, respectively.

Full text of DOI:10.1016/j.tetasy.2008.12.002

Tetrahedron: Asymmetry 19 (2008) 2717–2720
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Tetrahedron: Asymmetry
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Enzyme-catalyzed resolution of aromatic ring fused cyclic tertiary alcohols
b
a
Devrim Özdemirhan a, , Serdar Sezer , Yasemin Sönmez
*
a
_
Department of Chemistry, Abant Izzet Baysal University, Bolu 14280, Turkey
b Department of Chemistry, Middle East Technical University, Ankara 06531, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient chemoenzymatic route for the synthesis of optically active aromatic ring fused cyclic tertiary
alcohols (S)-(ꢀ)-1-methyl-1,2,3,4-tetrahydronaphthalen-1-ol (ꢀ)-1b and (S)-(+)-1-methyl-2,3-dihydro-
1H-inden-1-ol (+)-1a has been developed. Different lipases have been tested in the transesterification
of these tertiary alcohols; CAL-A (Candida antarctica Lipase A) was found to be the best biocatalyst for
1b and CAL-A-CLEA (Lipase A, C. antarctica, cross-linked enzyme aggregate) for 1a, obtained with ee val-
ues of 20% and 45%, respectively, and the corresponding esters 2b and 2a with the ee values of 99% and
71%, respectively.
Received 10 November 2008
Accepted 1 December 2008
Available online 10 January 2009
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
( )-3-ethynyl-3-oxbutyryl quiniclidine which afforded (R)-(+)-3-
ethynyl-3-hydroxy quiniclidine and (S)-(ꢀ)-3-ethynyl-3-oxbutyryl
The construction of building blocks that contain chiral tertiary
alcohol moieties is of great importance in the field of natural prod-
uct synthesis and pharmaceuticals. Therefore, the synthesis of
enantiopure tertiary alcohols and their esters has attracted consid-
erable attention.1 In particular, chiral aromatic fused hydrocarbon
compounds, such as tetralin and indane have been classified as bio-
markers since their structure is similar to that of the structural
subunits of biological precursors, such as lipids and steroids.2
Moreover, oxygen-containing derivatives of indane and tetralin
are valuable intermediates for various chiral organic compounds,3
quiniclidine in 97% and 99% ee, respectively.8 Moreover, CAL-A was
found to be the most efficient enzyme for the resolution of ( )-2-
phenylbut-3-yn-2-ol while CRL showed low enantioselectivity.9
Herein, we report the results of the enzymatic resolution of
( )-1-methyl-2,3-dihydro-1H-inden-1-ol, ( )-1a and ( )-1-methyl-
1,2,3,4-tetrahydronaphthalen-1-ol, ( )-1b (Scheme 1).
OH
OH
OAc
enzyme
+
for example, a-tetralone has been used to synthesize b-keto esters
( )n
rac-1a-b
( )n
(S)-(+)-1a-b
( )n
vinyl acetate
and thermorubin, an influential antibiotic substance.4
To the best of our knowledge, the synthesis of optically active
tertiary alcohols of ketones (e.g.,
(S)-(+)-2a
(R)-(-)-2a-b
a-indanone and a-tetralone) is
generally limited. One type is the synthesis of (R)-(ꢀ)-1-methyl-
1,2,3,4-tetrahydronaphthalen-1-ol (ꢀ)-1b and (S)-(+)-1-methyl-
2,3-dihydro-1H-inden-1-ol (+)-1a via their chiral trichromium
complexes.5 The other involves the catalytic asymmetric addition
of alkylzinc reagents to ketones.6 Furthermore, the enzymatic reso-
lution of aromatic ring fused tertiary alcohols is also limited in the
literature since there is great steric hindrance with regard to these
molecules accepting the active site of the enzyme. It is well known
that the structure of the substrate strongly affects the enantioselec-
tivity. It has been reported that various hydrolases, PLE (Pig liver
esterase), PPL (Porcine pancreatic lipase), CRL (Candida rugosa
lipase), and CAL-A (Lipase A from Candida antarctica), are active
biocatalysts toward esters of tertiary alcohols.7 In particular, PLE
has been shown to be an active biocatalyst in the resolution of
2a: n =1
2b. n =2
1a: n =1
1b. n =2
Scheme 1. Transesterification of ( )-1-methyl-2,3-dihydro-1H-inden-1-ol 1a and
( )-1-methyl-1,2,3,4-tetrahydronaphthalen-1-ol 1b.
2. Results and discussion
It is well known that the enantioselectivity of enzymatic reac-
tions depends upon certain parameters, that is, temperature, cosol-
vent, and pH.10 All reactions were performed by changing these
parameters to determine the optimum conditions. Firstly, various
hydrolases were tested, for example, CAL-A-CLEA, CRL, CAL-A, CAL-
B, and Amano PS-C II, on ( )-1-methyl-1,2,3,4-tetrahydronaphtha-
len-1-ol ( )-1b by changing the substrate:enzyme ratio (w/w) from
1:1 to 1:0.25. Compound ( )-1b (100 mg) was subjected to transe-
sterification with CAL-A (25 mg) with 1 mL of vinyl acetate
(16 mmol equiv) and 1 mL of isooctane at room temperature
* Corresponding author. Tel.: +90 374 254 10 00; fax: +90 374 253 46 42.
E-mail address: ozdemirhan_d@ibu.edu.tr (D. Özdemirhan).
0957-4166/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2008.12.002

2718
D. Özdemirhan et al. / Tetrahedron: Asymmetry 19 (2008) 2717–2720
(25 °C) for 168 h. No conversion was observed. Several cosolvents,
for example, THF, hexane, and 1,4-dioxane, were also used but we
did not obtain any results. Without cosolvent under the same condi-
tions, no conversion was observed. Temperature effects were then
tested. The experiment was screened at the temperatures ranging
from 25 to 32 °C. (R)-(ꢀ)-1-Methyl-1,2,3,4-tetrahydronaphthalen-
1-yl acetate, (ꢀ)-2b was obtained with 20% conversion in 99% ee be-
side compound (S)-(+)-1b in 20% ee after shaking for 144 h at 32 °C.
Some unidentified decomposed products were also observed at
higher temperatures.
1a and ( )-1-methyl-1,2,3,4-tetrahydronaphthalen-1-ol, ( )-1b by
using various hydrolases, that is, CAL-A-CLEA, CAL-A, CRL, and
Amano PS-C II. According to the results obtained, CAL-A-CLEA
was the best biocatalyst for ( )-1-methyl-2,3-dihydro-1H-inden-
1-ol, ( )-1a in 45% ee and corresponding ester with 71% ee.
Furthermore, CAL-A was the best for ( )-1-methyl-1,2,3,4-tetra-
hydronaphthalen-1-ol, ( )-1b in 20% ee and the corresponding
ester with 99% ee. Temperature is an important parameter in reac-
tions catalyzed by enzymes.13,14 In this study, 32 °C was the opti-
mum temperature. Compounds ( )-2a–b were easily decomposed
at higher temperatures. In particular, the methodology should be
useful in the synthesis of chiral drugs and their building blocks.
We are currently studying the enzymatic resolution of various
The results obtained from CAL-A prompted us to test the other
enzymes, that is, CAL-A-CLEA, in the transesterification of substrate
( )-1b. In the case of CAL-A-CLEA with the substrate:enzyme ratio
(w/w) 1:0.5, (R)-(ꢀ)-1-methyl-1,2,3,4-tetrahydronaphthalen-1-yl ace-
tate, (ꢀ)-2b, and (S)-(+)-1-methyl-1,2,3,4-tetrahydronaphthalen-1-ol,
(+)-1b were isolated in 85% and 35% ee, respectively, in 20% conversion
for 48 h. By changing the substrate:enzyme ratio (w/w) to 1:0.75, the ee
value of (R)-(ꢀ)-1-methyl-1,2,3,4-tetrahydronaphthalen-1-yl acetate,
(ꢀ)-2b was increased to 91% ee while that of the alcohol (S)-(+)-1b to
38% ee, at 25% conversion. The enzymatic resolution with Amano PS-C
II of ( )-1b was carried out by changing the substrate:enzyme ratio
(w/w) from 1:0.25 to 1:1. The best substrate:enzyme ratio (w/w) 1:1
afforded (R)-(ꢀ)-2b and (S)-(+)-1b in 80% ee and 15% ee, respectively,
after 15% conversion for 96 h. CRL has been used in the enantioselective
resolution of various esters of tertiary alcohols.11 It was also used in the
resolution of compound ( )-1b. The same optimization reactions were
retried and the best result was obtained with 10% conversion and 90%
ee of (R)-(ꢀ)-1-methyl-1,2,3,4-tetrahydronaphthalen-1-yl acetate, (ꢀ)-
2b at 32 °C for 145 h with a 1:1 substrate:enzyme ratio (w/w) (Table 1).
The enzymatic resolution of ( )-1-methyl-2,3-dihydro-1H-in-
den-1-ol, ( )-1a was also examined with the same enzymes. The
optimization reactions of ( )-1a were carried out by using CAL-
A-CLEA with the substrate:enzyme ratio (w/w) 1:0.25 to afford
(R)-(ꢀ)-2a in 71% ee with (S)-(+)-1a in 45% ee, respectively, after
20% conversion for 72 h. Amano PS-C II with substrate:enzyme ra-
tio (w/w) 1:1 yielded (S)-(+)-2a in 15% ee after 7% conversion for
140 h. CRL did not work efficiently with compound ( )-1a and
yielded (R)-(ꢀ)-2a in 15% ee after 5% conversion. Although CAL-A
(Lipase A C. antarctica) worked well in the enzymatic resolution
of compound ( )-1b, substrate 1a was isolated as a racemic mix-
ture. The results of the enzyme-catalyzed reaction of compound
( )-1a with various hydrolases are given in Table 2.
tertiary alcohols synthesized from a,b-unsaturated cyclic ketones.
4. Experimental
1H NMR and 13C NMR spectra were recorded in CDCl3 on a Bru-
ker Spectrospin Avance DPX-400 spectrometer and the chemical
shifts are given in ppm downfield from tetramethylsilane. Infrared
spectra were recorded on a Shimadzu 8400S FT-IR spectrophotom-
eter. Optical rotations were measured in a 1 dm cell Rudolph Re-
search Analytical Autopol III polarimeter. Melting points were
determined on an Electrothermal apparatus (Model No.: 9200)
and are uncorrected. High performance liquid chromatography
was performed with a Thermo Separation Products, P1500-SN-
4000-UV2000 instrument using Daicel Chiralcel OD-H and OJ-H
chiral columns. Column chromatography was performed on Silica
Gel (60-Mesh, Merck Silica). TLC was performed on Merck 0.2-
mm Silica Gel 60 F254 aluminum sheets. CAL-A (Lipase A, C. antarc-
tica, recombinant from Aspergillus oryzae) and CAL-A-CLEA (Lipase
A, C. antarctica, cross-linked enzyme aggregate) were purchased
from Fluka, CRL (Lipase from C. rugosa, Type VII, P700 unit/mg so-
lid) was purchased from Sigma. Amano Lipase PS-C II (immobilized
on ceramic) was purchased from Aldrich.
4.1. General procedure for the synthesis of ( )-1a–b
To a stirred solution of Mg turnings (15 mmol) and iodine (2
pieces) in dry diethyl ether (7 mL) at 25 °C equipped with a reflux
condenser was added dropwise
a mixture of iodomethane
(11 mmol) in anhydrous diethyl ether (5 mL). The mixture was al-
The absolute configurations of both (+)-1a and (+)-1b were as-
signed as (S), by comparison of their specific rotation values with
the literature data.5,12 Related to these results, the absolute configu-
rations of (+)-2a and (ꢀ)-2a were assigned as (S) and (R), respec-
tively, whereas those of (+)-2b and (ꢀ)-2b were assigned as (S) and
(R), respectively.
lowed to reflux for 30 min. The mixture was cooled down to 0 °C
and then corresponding ketone (1-indanone or
a-tetralone)
(10 mmol) in dry diethylether (3 mL) was added dropwise. The
resultant mixture was stirred for 2 h. The reaction mixture was
hydrolyzed with saturated ammonium chloride solution (10 mL)
and then with 1 M HCl (2 mL). The resultant mixture was extracted
with diethylether (3 ꢁ 30 mL). The combined organic phase was
washed with brine (20 mL) and dried over MgSO4 and evaporated
in vacuo. The crude products were purified by flash column chro-
matography with a mixture of solvents of ethyl acetate and hexane
at a ratio of 1:8 for 1a and 1:7 for 1b.
3. Conclusion
In this report, we have demonstrated the first enzyme-cata-
lyzed resolution of ( )-1-methyl-2,3-dihydro-1H-inden-1-ol, ( )-
Table 1
The results of enzymatic resolution of ( )-1-methyl-1,2,3,4-tetrahydronaphthalen-1-ol 1b
Conversiona
eep (%)
ees (%)
Ed
29
253
10
½
a 2D6
a 2D6
a 2D6
a 2D6
a 2D6
ꢂ
(prod.)/abs. conf.
½
a 2D6
a 2D6
a 2D6
a 2D6
ꢂ
(subs.)/abs. conf.
b
Enzyme
Time (h)
CAL-A-CLEA
CAL-A
Amano PS-C II
CRL
48
144
96
25
20
15
10
91
99
80
90
38
20
15
½
½
½
½
ꢂ
¼ ꢀ5:1 (c 0.60, CHCl3) (R)
¼ ꢀ14:3 (c 0.60, CHCl3) (R)
¼ ꢀ4:0 (c 1.30, CHCl3) (R)
¼ ꢀ4:5 (c 0.25, CHCl3) (R)
½
ꢂ
¼ þ7:2 (c 1, CHCl3) (S)
¼ þ4:5 (c 1, CHCl3) (S)
¼ þ2:1 (c 1, CHCl3) (S)
ꢂ
½
ꢂ
ꢂ
½
ꢂ
c
c
145
—
21
ꢂ
—
a
Conversions were determined using HPLC analysis.
b
c
Enantiomeric excesses were determined by Daicel Chiralcel OD-H and OJ-H column HPLC analysis.
Isolated as a racemate.
d
E values were calculated according to the literature.9

D. Özdemirhan et al. / Tetrahedron: Asymmetry 19 (2008) 2717–2720
2719
Table 2
The results of enzymatic resolution of ( )-1-methyl-2,3-dihydro-1H-inden-1-ol 1a
Conversiona
eep (%)
ees (%)
45
Ed
½
a 2D6
a 2D6
a 2D6
a 2D6
ꢂ
(prod.)/abs. conf.
½
a 2D6
ꢂ
(subs.)/abs. conf.
¼ þ7:9 (c 1, CHCl3) (S)
b
Enzyme
Time (h)
CAL-A-CLEA
Amano PS-C II
CRL
72
140
168
20
7
5
71
55
15
7
4
1.4
½
½
½
ꢂ
¼ ꢀ5:0 (c 0.25, CHCl3) (R)
¼ þ4:6 (c 0.25, CHCl3) (S)
¼ ꢀ1:1 (c 0.25, CHCl3) (R)
½
a 2D6
ꢂ
c
c
c
—
ꢂ
—
c
—
ꢂ
—
a
Conversions were determined using HPLC analysis.
b
c
Enantiomeric excesses were determined by Daicel Chiralcel OD-H and OJ-H column by HPLC analysis.
Isolated as a racemate.
d
E values were calculated according to the literature.9
4.1.1. ( )-1-Methyl-2,3-dihydro-1H-inden-1-ol 1a
4.3. General procedure for the transesterification reaction of
( )-1a–b
Yellow solid, mp 52–55 °C, 1.39 g, 83% yield. IR mmax (neat,
cmꢀ1): 3327, 2964, 2378, 1485. 1H NMR (400 MHz, CDCl3): d
7.34–7.37 (m, 1H), 7.23–7.26 (m, 3H), 2.99–3.07 (m, 1H), 2.80–
2.87 (m, 1H), 2.14–2.27 (m, 2H), 1.78 (br s, 1H) 1.57 (s, 3H); 13C
NMR (100.6 MHz, CDCl3): d 148.3, 142.6, 128.2, 126.9, 125.0,
122.2, 81.3, 42.4, 29.4, 27.3. Anal. Calcd for C10H12O: C, 81.04; H,
8.16. Found: C, 80.82; H, 8.15.
To 100 mg of substrate ( )-1a–b and 1 mL (16 mmol equiv) of
vinyl acetate, the corresponding enzyme (i.e., 25 mg of CAL-A,
50 mg of CAL-A-CLEA, 100 mg of Amano PSC-II, 100 mg of CRL)
was added, followed by shaking at 32 °C. The mixture was then
monitored by TLC. When the reaction was completed, the mixture
was filtered and the filtrate concentrated in vacuo. Purification was
done by flash column chromatography using ethyl acetate/hexane
as an eluent.
4.1.2. ( )-1-Methyl-1,2,3,4-tetrahydronaphthalen-1-ol 1b
White solid, mp 68–70 °C, [lit.12 mp 69 °C], (1.45 g, 87%) IR mmax
(neat, cmꢀ1): 3323, 2931, 2314, 1441, 1310. 1H NMR (400 MHz,
CDCl3): d 7.59 (dd, J = 1.6 and 7.6 Hz, 1H), 7.14–7.25 (m, 2H),
7.07 (d, J = 7.2 Hz, 1H), 2.72–2.86 (m, 2H), 1.90–1.98 (m, 3H),
1.77–1.88 (m, 1H), 1.75 (br s, 1H), 1.56 (s, 3H); 13C NMR
(100.6 MHz, CDCl3): d 142.9, 136.3, 128.8, 127.1, 126.4, 126.3,
70.6, 39.8, 30.7, 29.9, 20.4. Anal. Calcd for C11H14O: C, 81.44; H,
8.70. Found: C, 81.29; H, 8.65.
4.3.1. (S)-(+)-1-Methyl-2,3-dihydro-1H-inden-1-ol, (S)-(+)-1a
Yellow solid, 52 mg, (52% yield), ½a D26
¼ þ7:9 (c 1, CHCl3), 45%
ꢂ
ee. The enantiomeric excess of the product was determined by
HPLC analysis (Daicel Chiralcel OD-H, n-hexane/2-propanol 98:2,
flow rate 0.5 mL/min, k = 214 nm, t1(S) = 19.8 min, t2(R) = 23.8 min).
4.3.2. (S)-(+)-1-Methyl-1,2,3,4-tetrahydronaphthalen-1-ol,
(S)-(+)-1b
4.2. General procedure for the acetylation of ( )-1a–b
White solid, 50 mg, (50% yield), ½a D26
¼ þ7:2 (c 1, CHCl3), 38% ee.
ꢂ
The enantiomeric excess of the chiral product was determined by
HPLC analysis (Daicel Chiralcel OJ-H, n-hexane/2-propanol 98:2,
flow rate 0.5 mL/min, k = 214 nm, t1(R) = 18.2 min, t2(S) = 21.6 min).
A 35% KH (4 mmol) suspension was washed with dry hexane
three times, then 5 mL of dry THF was added. Compounds ( )-
1a–b (2 mmol) were dissolved in 5 mL of dry diethyl ether and
then put into the reaction mixture. After 2 h, the dropwise addition
of acetic anhydride (4 mmol) with tetrabutylammonium iodide
(0.2 mmol) was performed. The reaction mixture was stirred for
an additional 2 h, then filtered by washing with CH2Cl2, dried over
MgSO4, and finally evaporated in vacuo. The crude products were
purified by flash column chromatography with a mixture of sol-
vents of ethyl acetate and hexane at a ratio of 1:8 for 2a and 1:7
for 2b.15
4.3.3. (R)-(ꢀ)-1-Methyl-2,3-dihydro-1H-inden-1-yl acetate,
(R)-(ꢀ)-2a
Yellow oil, 17 mg, (13% yield), ½a D26
¼ ꢀ5:0 (c 0.25, CHCl3), 45%
ꢂ
ee. The enantiomeric excess of the product was determined by
HPLC analysis (Daicel Chiralcel OD-H, n-hexane/2-propanol 98:2,
flow rate 0.5 mL/min, k = 214 nm, t1(R) = 9.5 min, t2(S) = 10.9 min).
4.3.4. (R)-(ꢀ)-1-Methyl-1,2,3,4-tetrahydronaphthalen-1-yl
acetate, (R)-(ꢀ)-2b
4.2.1. ( )-1-Methyl-2,3-dihydro-1H-inden-1-yl acetate 2a
Yellow oil, 20 mg, (16% yield), ½a D26
¼ ꢀ14:3 (c 0.6, CHCl3), 99%
ꢂ
Yellow oil, (0.71 g, 55%) IR m
max (neat, cmꢀ1): 2957, 2860, 1746,
ee. The enantiomeric excess of the product was determined by
HPLC analysis (Daicel Chiralcel OD-H, n-hexane/2-propanol 98:2,
flow rate 0.5 mL/min, k = 214 nm, t1(S) = 10.0 min, t2(R) = 10.6 min).
1452, 1238. 1H NMR (400 MHz, CDCl3): d 7.35–7.37 (m, 1H), 7.16–
7.25 (m, 3H), 2.95–3.02 (m, 1H), 2.74–2.81 (m, 1H), 2.45–2.52 (m,
1H), 2.26–2.33 (m, 1H), 2.01 (s, 3H), 1.70 (s, 3H); 13C NMR
(100.6 MHz, CDCl3): d 170.8, 145.4, 143.5, 128.4, 126.0, 124.7,
123.9, 90.2, 37.9, 30.2, 25.1, 22.5. Anal. Calcd for C12H14O2: C,
75.76; H, 7.42. Found: C, 75.58; H, 7.35.
Acknowledgment
We thank the Scientific and Technological Research Council of
Turkey for the grant [TBAG-105T431].
4.2.2. ( )-1-Methyl-1,2,3,4-tetrahydronaphthalen-1-yl acetate
2b16
References
Yellow oil, (0.77 g, 61%) IR m
max (neat, cmꢀ1): 2924, 2850, 2384,
1730, 1475, 1435, 1236. 1H NMR (400 MHz, CDCl3): d 7.37–7.39 (m,
1H), 7.15–7.18 (m, 2H), 7.06–7.08 (m, 1H), 2.84–2.92 (m, 1H), 2.73
(td, J = 4.8 and 16.4 Hz, 1H), 2.55 (dt, J = 3.2 and 12.0 Hz, 1H), 2.09–
2.15 (m, 1H), 2.00 (s, 3H), 1.93–1.99 (m, 1H), 1.75–1.80 (m, 1H),
1.74 (s, 3H); 13C NMR (100.6 MHz, CDCl3): d 169.9, 140.3, 136.5,
128.7, 127.0, 126.1, 125.9, 81.4, 34.5, 29.7, 29.6, 22.5, 20.8. Anal.
Calcd for C13H16O2: C, 76.44; H, 7.90. Found: C, 76.32; H, 7.85.
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