Candida antarctica lipase A and Pseudomonas stutzeri lipase as a pair of stereocomplementary enzymes for the resolution of 1,2-diarylethanols and 1,2-diarylethanamines

Article abstract of DOI:10.1016/j.tetlet.2012.11.147

Candida antarctica lipase A (CALA) and Pseudomonas stutzeri lipase (PSL) displayed opposite enantioselectivities in the acylation of 1,2-diphenylethanol and 1,2-diphenylethanamine. CALA was (S)-selective while PSL was (R)-selective. In addition, fourteen different 1,2-diarylethanols were tested as the substrates of CALA. It was found that most of them were accepted by CALA with high enantioselectivity. The DKR of five representative substrates by the combination of CALA and a ruthenium-based racemization catalyst provided good yields (82-91%) and acceptable enantiopurities (87-94% ee).

Full text of DOI:10.1016/j.tetlet.2012.11.147

Tetrahedron Letters 54 (2013) 1185–1188
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Tetrahedron Letters
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Candida antarctica lipase A and Pseudomonas stutzeri lipase as a pair
of stereocomplementary enzymes for the resolution of 1,2-diarylethanols
and 1,2-diarylethanamines
⇑
⇑
Sol Kim, Yoon Kyung Choi, Jieun Hong, Jaiwook Park , Mahn-Joo Kim
Department of Chemistry, Pohang University of Science and Technology, San-31 Hyojadong, Pohang 790–784, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Candida antarctica lipase A (CALA) and Pseudomonas stutzeri lipase (PSL) displayed opposite enantioselec-
tivities in the acylation of 1,2-diphenylethanol and 1,2-diphenylethanamine. CALA was (S)-selective
while PSL was (R)-selective. In addition, fourteen different 1,2-diarylethanols were tested as the sub-
strates of CALA. It was found that most of them were accepted by CALA with high enantioselectivity.
The DKR of five representative substrates by the combination of CALA and a ruthenium-based racemiza-
tion catalyst provided good yields (82–91%) and acceptable enantiopurities (87–94% ee).
Ó 2012 Elsevier Ltd. All rights reserved.
Received 21 September 2012
Revised 28 November 2012
Accepted 30 November 2012
Available online 7 December 2012
Keywords:
Enzymatic catalysis
Lipase
Resolution
Alcohol
Amine
Among enzymes, lipases have been most frequently employed
as catalysts for enantioselective transformations in organic synthe-
sis.1 They accept a broad range of substrates and often display good
enantioselectivity. They are particularly useful in the kinetic reso-
lution (KR) of racemic alcohols and amines. The enzymatic KRs
provide two separated enantiomers with 50% theoretical maxi-
mum yield for each of them. The maximum yield can be improved
up to 100% if the enzymatic KR is coupled with in situ racemization
of substrate to transform all of the substrates to single enantio-
meric products. This process is called dynamic kinetic resolution
(DKR).2 In contrast to KR, DKR provides only one type of enantio-
mer (R or S) as the product depending on the stereospecificity of
enzyme employed. Accordingly, a pair of stereocomplementary en-
zymes should be available to prepare both (R)- and (S)-products via
DKR.3,4 We herein report that Candida antarctica lipase A (CALA)
and Pseudomonas stutzeri lipase (PSL) are a pair of stereocomple-
mentary enzymes for the resolution of 1,2-diarylethanols and
1,2-diarylethanamines.5
OH
OH
S
L
1
2
Figure 1. Faster-reacting enantiomer in the lipase-catalyzed transesterification of
secondary alcohols.
the transesterification of 1-phenylethanol. Interestingly, subtilisin
Carlsberg (SC, Bacillus licheniformis), a proteolytic enzyme, has been
known to accept (S)-enantiomer selectively in this case.7 The
empirical rule, however, is hardly applicable to sterically more
demanding secondary alcohols which have two similarly large sub-
stituents at the hydroxymethine center. As such a class of second-
ary alcohols, 1,2-diarylethanols 3a–o have one phenyl and one
benzyl at the hydroxymethine center (Fig. 2). In this case, it is dif-
ficult to tell which is the larger of two in terms of enzymatic
enantioselectivity. In this work, we indeed found that two lipases,
PSL and CALA, were opposite in the enantiopreference toward 1,2-
diarylethanols. PSL was (R)-selective so that it appears to recognize
the phenyl group as the larger substituent. In contrast to this, CALA
was (S)-selective.
It has been known that most lipases have the same stereospec-
ificity. In the transesterification of simple secondary alcohols, for
example, lipases accept the enantiomer (1) shown in Figure 1
selectively if the substrate has one small and one relatively larger
substituent at the hydroxymethine center.6 According to the
empirical rule, lipases accept (R)-enantiomer (2) selectively in
The stereopreferences of PSL and CALA were explored with the
transesterification of 1,2-diphenylethanol (3a). The CALA-cata-
lyzed transesterification reaction was performed in the presence
of trifluoroethyl butyrate (TFEB) as an acyl donor in acetonitrile8
⇑
Corresponding author. Tel.: +82 54 279 2112; fax: +82 54 279 0654.
E-mail address: mjkim@postech.ac.kr (M.-J. Kim).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.147

1186
S. Kim et al. / Tetrahedron Letters 54 (2013) 1185–1188
ence of ethyl methoxyacetate (EMA) in toluene (Scheme 2).11 The
R
OH
OH
OH
optical rotations of unreacted substrates from both reactions,
which were isolated at 40–41% conversion, gave opposite signs,
thus indicating that the stereopreferences of PSL and CALA were
opposite as well. It is noted that the selectivity of PSL was higher
(E = >200) than that of CALA (E = 22).
R
R
3a R = H
3b R = Me
3e R = F
3i R = Me
R = iPr
3j
3f
R = Me
R = OMe
R = iPr
3c
R = OMe
3g
3h
Previously, we reported that PSL accepted a wide range of 1,2-
diarylethanols with good enantioselectivity.3d For comparison in
substrate scope and stereospecificity between CALA and PSL, we
tested fourteen 1,2-diarylethanols (3b–o) as the additional sub-
strates of CALA in this work. Most of them reacted smoothly with
good to excellent enantioselectivity but two, 3i and 3j, were poorly
reactive, indicating that the substitution on 1-phenyl ring reduces
the reactivity significantly (Table 1). This is compared to the broad-
er specificity of PSL which tolerated the substitution on the 1-phe-
nyl ring well.3d It is particularly noted that in general a substitution
on the 2-phenyl ring and the replacement of 1-phenyl group by a
smaller ring (furyl) enhanced the enantioselectivity (compare 3a
with 3b–d or 3e–h, and also 3a,b,e,f,h with 3k–o, respectively).
As the stereocomplementary procedure to the PSL-catalyzed
DKR,3d CALA-catalyzed DKR was explored with five 1,2-diaryletha-
nols 3a,e–h (Table 2). Ru complex 8 was chosen as the racemiza-
tion catalyst. The Ru-catalyzed racemization of 3a in acetonitrile
turned out to be so sluggish. Accordingly, acetonitrile was replaced
by toluene for DKR to promote the racemization at the cost of
enzymatic activity and enantioselectivity. The DKR reactions were
3d R = OPh
R
OH
OH
O
O
R
3k R = H
3l
3m R = F
3n
3o
R = Me
R = Me
R = iPr
Figure 2. 1,2-Diarylethanols.
while the PSL-catalyzed reaction was carried out using vinyl buty-
rate (VB) as an acyl donor in toluene (Scheme 1).9 After the reac-
tions had been carried out to 48% conversion, acylated products
and unreacted substrates were separated to determine their enan-
tiopurities and optical rotations.8,9 It was found that the signs of
optical rotations for acylated products and recovered substrates
were opposite between two enzymatic reactions, indicating that
CALA is (S)-selective because the (R)–selectivity of PSL was previ-
ously reported.3d
performed with solutions containing substrate (0.1 mmol),
8
(4 mol %), CALA (60 mg), TFEB (1.5 equiv), and K2CO3 (1 equiv) in
toluene at room temperature for 48 h.14 Three portions of enzymes
(3 ꢀ 20 mg) were added periodically at t = 0, 12, and 36 h because
the enzymatic activity decreased gradually with time. All the DKR
reactions provided good yields (82–91%) with acceptable enantio-
purities (87–94% ee).
The stereocomplementary relationship between PSL and CALA
was also found in the acylation of 1,2-diphenylethanamine (5)
which is isosteric to 1,2-diphenylethanol. The CALA-catalyzed acyl-
ation of 5 was best performed in the presence of trifluoroethyl
butyrate (TFEB) in acetonitrile (Scheme 2).10 In contrast to this,
the PSL-catalyzed acylation of 5 proceeded smoothly in the pres-
OCOPr
OH
OCOPr
PSL
CALA
PrCO2CH=CH2
48% conv
PrCO2CH2CF3
48% conv
(R)-4a (97% ee)
[α]25D +23.8
E = > 200
(S)-4a (92% ee)
[α]25D -17.7
3a
E = 65
OH
OH
(S)-3a (91% ee)
[α]25D +51.8
(R)-3a (85% ee)
[α]25D -47.4
Scheme 1. Lipase-catalyzed acylation of 1,2-diphenylethanol.
NHCOCH2OMe
NH2
NHCOPr
PSL
CALA
MeOCH2CO2Et
PrCO2CH2CF3
41% conv
40% conv
(R)-7 (>99% ee)
[α]25D +21.7
(S)-6 (85% ee)
[α]25D -25.4
E = > 200
5
E = 22
NH2
NH2
(S)-5 (70% ee)
[α]25D +6.55
(R)-5 (57% ee)
[α]25D -5.32
Scheme 2. Lipase-catalyzed acylation of 1,2-diphenylethanamine.

S. Kim et al. / Tetrahedron Letters 54 (2013) 1185–1188
1187
Table 1
CALA-catalyzed transesterification of 1,2-diarylethanols (3b–o)a
Substrate
Product
ees (%)
eep (%)
Conv (%)
Eb
Substrate
Product
ees (%)
eep (%)
Conv (%)
Eb
3b
3c
3d
3e
3f
4b
4c
4d
4e
4f
91
91
95
98
92
94
94
95
96
95
91
96
96
96
49
49
50
52
49
49
49
128
156
133
97
168
197
187
3i
3j
4i
4j
ndc
ndc
>99
>99
>99
>99
>99
ndc
ndc
86
95
90
10d
ndc
ndc
80
227
117
>400
271
3d
3k
3l
3m
3n
3o
4k
4l
4m
4n
4o
54
51
53
50
51
3g
3h
4g
4h
99
96
a
b
c
The values of optical rotation of unreacted substrates and acylated products are described in Refs. 12,13.
E = ln[(1 ꢂ c)(1 ꢂ ees)]/ln[(1 ꢂ c)(1 + ees)] with c = ees/(ees + eep).
Not determined.
d
Determined by 1H NMR.
Table 2
2. (a) Martin-Matute, B.; Bäckvall, J. E. Curr. Opin. Biol. 2007, 11, 226–232; (b) Ahn,
Y.; Ko, S.-B.; Kim, M.-J.; Park, J. Coord. Chem. Rev. 2008, 252, 647–658; (c) Lee, J.
H.; Han, K.; Kim, M.-J.; Park, J. Eur. J. Org. Chem. 2010, 999–1015; (d) Kim, Y.;
Park, J.; Kim, M.-J. ChemCatChem 2011, 3, 271–277.
DKR of 1,2-diarylethanols with CALA
Ar
Ar
OCOAr 8 Ar = Ph-p-OMe
3. For the (R)-selective DKRs of simple secondary alcohols, see: (a) Kim, N.; Ko, S.-
B.; Kwon, M. S.; Kim, M.-J.; Park, J. Org. Lett. 2005, 7, 4523–4527; (b) Martín-
Matute, B.; Edin, M.; Bogár, K.; Kaynak, F. B.; Bäckvall, J.-E. J. Am. Chem. Soc.
2005, 127, 8817–8825; (c) Ko, S.-B.; Baburaj, B.; Kim, M.-J.; Park, J. J. Org. Chem.
2007, 72, 6860–6864; (d) Kim, M.-J.; Choi, Y. K.; Kim, S.; Kim, D.; Han, K.; Ko, S.-
B.; Park, J. Org. Lett. 2008, 10, 1295–1298; (e) Haak, R. M.; Berthiol, F.;
Jerphagnon, T.; Gayet, J. A.; Tababiono, C.; Postema, C. P.; Ritleng, V.; Pfeffer, M.;
Janssen, D. B.; Minnaard, A. J.; Feringa, B. L.; De Vries, J. G. J. Am. Chem. Soc.
2008, 130, 13508–13509; (f) Chen, Q.; Yuan, C. Chem. Commun. 2008, 5333–
5335; (g) Mavrynsky, D.; Päiviö, M.; Lundell, K.; Sillanpää, R.; Kanerva, L. T.;
Leino, R. Eur. J. Org. Chem. 2009, 1317–1320; (h) Do, Y.; Hwang, I. C.; Kim, M.-J.;
Park, J. J. Org. Chem. 2010, 75, 5740–5742; (i) Thalen, L. K.; Bäckvall, J.-E.
Beilstein J. Org. Chem. 2010, 6, 823–829; (j) Thalen, L. K.; Sumic, A.; Bogar, K.;
Norinder, J.; Persson, A. K. A.; Bäckvall, J.-E. J. Org. Chem. 2010, 75, 6842–6847;
(k) Lee, J. H.; Kim, N.; Kim, M.-J.; Park, J. ChemCatChem 2011, 3, 354–359; (l)
Lihammar, R.; Millet, R.; Bäckvall, J.-E. Adv. Synth. Catal. 2011, 353, 2321–2327;
(m) Ema, T.; Nakano, Y.; Yoshida, D.; Kamato, S.; Sakai, T. Org. Biomol. Chem.
2012, 10, 6299–6308; (n) Sato, Y.; Kayaki, Y.; Ikariya, T. Chem. Commun. 2012,
48, 3635–3637.
Ar
Ar
Cl
Ru
OC
R
R
OC
OH
OCOPr
CALA
PrCO2CH2CF3
K2CO3, toluene
25oC, 48 h
4a,e-h
3a e h
, -
Entry
Substrate
Product
Yielda (%)
eeb (%)
1
2
3
4
5
3a
3e
3f
3g
3h
4a
4e
4f
4g
4g
90
90
91
82
84
89
87
91
93
94
a
Determined by H NMR spectroscopy.
Determined by HPLC using a chiral column (Whelk-O1, Merck).
b
4. For the (S)-selective DKRs of simple secondary alcohols, see: (a) Kim, M.-J.;
Chung, Y. I.; Choi, Y. K.; Lee, H. K.; Kim, D.; Park, J. J. Am. Chem. Soc. 2003, 125,
11494–11495; (b) Kim, M.-J.; Kim, H. M.; Kim, D.; Ahn, Y.; Park, J. Green Chem.
2004, 6, 471–474; (c) Borén, L.; Martín-Matute, B.; Xu, Y.; Córdova, A.; Bäckvall,
J.-E. Chem. Eur. J. 2006, 12, 225–232; (d) Kim, M.-J.; Lee, H.; Park, J. Bull. Korean
Chem. Soc. 2007, 28, 2096–2098.
In summary, we have demonstrated that CALA and PSL are ste-
reocomplementary in the acylation reactions of 1,2-diphenyletha-
nol and 1,2-diphenylethanamine: CALA was (S)-selective but PSL
was (R)-selective. CALA accepted 1,2-diarylethanols with good to
high enantioselectivity but its substrate scope was relatively nar-
rower than that of PSL reported previously. The DKR of 1,2-diaryl-
ethanols by the combination of CALA with a ruthenium-based
racemization catalyst was successful. Further applications of CALA
and PSL to dynamic kinetic resolution are in progress at this
laboratory.
5. Review on stereocomplementary enzymes: Wagner, U. G.; Faber, K.;
Mugford, P. F.; Jiang, Y.; Kazlauskas, R. J. Angew. Chem., Int. Ed. 2008, 47,
8782–8793.
6. For the empirical rules or active-site models for predicting the
enantioselectivity of some lipases, see: (a) Xie, Z.-F.; Suemune, H.; Sakai, K.
Tetrahedron: Asymmetry 1990, 1, 395–402; (b) Burgess, K.; Jennings, L. D. J. Am.
Chem. Soc. 1991, 113, 6129–6139; (c) Kazlauskas, R. J.; Weissfloch, A. N. E.;
Rappaport, A. T.; Cuccia, L. A. J. Org. Chem. 1991, 56, 2656–2665; (d) Kim, M.-J.;
Cho, H. J. Chem. Soc., Chem. Commun. 1992, 1411–1413; (e) Naemura, K.;
Fukuda, R.; Takahashi, N.; Konishi, M.; Hirose, Y. Tetrahedron: Asymmetry 1993,
4, 911–918; (f) Naemura, K.; Fukuda, R.; Konishi, M.; Hirose, K.; Tobe, Y. J. Chem.
Soc., Perkin Trans. 1 1994, 1253–1256; (g) Naemura, K.; Fukuda, R.; Murata, M.;
Konishi, M.; Hirose, K.; Tobe, Y. Tetrahedron: Asymmetry 1995, 6, 2385–2394;
(h) Naemura, K.; Murata, M.; Tanaka, R.; Yano, M.; Hirose, K.; Tobe, Y.
Tetrahedron: Asymmetry 1996, 7, 3285–3294; (i) Jing, Q.; Kazlauskas, R. J.
Chirality 2008, 20, 724–735.
7. Kazlauskas, R. J.; Weissfloch, A. N. E. J. Mol. Catal. B: Enzym. 1997, 3, 65–72.
8. CALA (trade name, Novozym-735) was immobilized on Celite before use as
follows. Lyophilized CALA (10 mg) and sucrose (6 mg) was dissolved in water
(10 mL), followed by the addition of celite (84 mg). The resulting mixture was
stirred for 30 min and water was removed under reduced pressure. The residue
was dried under vacuum for 1 day and then used in acylation. The acylation of
3a with CALA was performed with a solution containing 3a (0.2 mmol), CALA
on celite (8 mg), and TFEB (3 equiv) in acetonitrile (2 mL) at room temperature
Acknowledgment
Authors are grateful to the National Research Foundation of
Korea for its generous support of their works (2009-0074357 and
2012R1A1A2006595).
Supplementary data
for 24 h. (R)-3a: ½a D25
ꢁ
ꢂ47.4 (c 1.0, EtOH, 85% ee) (lit.3d
ꢂ17.7 (c 1.0, CHCl3, 92% ee).
½ ꢁ ꢂ53.8 (c 1.0, EtOH,
a 2D5
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
11.147.
98% ee). (S)-4a: ½a D25
ꢁ
9. PSL was used as received. The acylation of 3a with PSL was performed with a
solution containing 3a (0.2 mmol), PSL (24 mg), and VB (3 equiv) in toluene
(0.7 mL) at room temperature for 24 h. (S)-3a: ½a D25
ꢁ
+51.8 (c 1.0, EtOH, 91% ee)
(lit. ½a 2D0
ꢁ
+47.6 (c 0.50, EtOH, 94% ee; Xie, J.-B.; Xie, J.-H.; Liu, X.-Y.; Zhang, Q.-Q.;
References and notes
Zhou, Q.-L. Chem. Asian J. 2011, 6, 899–908). (R)-4a: ½a D25
ꢁ
+23.8 (c 1.0, CHCl3,
97% ee).
1. (a) Enzyme Catalysis in Organic Synthesis: A Comprehensive Handbook; Drauz, K.,
Waldmann, K., Eds.; Wiley-VCH: Weinheim, Germany, 2002. Vols. I–III; (b)
Borncheuer, U. T.; Kazlauskas, R. J. Hydrolases in Organic Synthesis, 2nd ed.;
Wiley-VCH: Weinheim, Germany, 2006; (c) Asymmetric Organic Synthesis with
Enzymes; Gotor, V., Alfonso, I., Garcia-Urdiales, E., Eds.; Wiley-VCH: Weinheim,
Germany, 2008.
10. The acylation of 5 with CALA was performed with a solution containing 5
(0.2 mmol), CALA on celite (8 mg), and TFEB (3 equiv) in acetonitrile (2 mL) at
room temperature for 24 h. (R)-5: ½a D25
ꢂ5.32 (c 2.0, CHCl3, 57% ee) (lit. ½aꢁD
ꢁ
ꢂ10.1 (c 1.96, CHCl3, 91% ee; Eddine, J. J.; Cherqaoui, M. Tetrahedron:
Asymmetry 1995, 6, 1225–1228). (S)-6: ½a D25
ꢂ25.4 (c 2.0, CHCl3, 85% ee).
ꢁ

1188
S. Kim et al. / Tetrahedron Letters 54 (2013) 1185–1188
11. The acylation of 5 with PSL was performed with a solution containing 5
14. The procedure for the DKR of 3a is described as the representative. Alcohol 3a
(19.8 mg, 0.1 mmol), 8 (3.4 mg, 4 mol %), and K2CO3 (13.8 mg, 0.1 mmol) were
added in a Schlenk flask and dried for 1 h. And then, dry and degassed toluene
(0.2 M, 0.5 mL) was added under argon atmosphere and stirred at 60 °C for
30 min. The color of solution was changed from yellow to brown. CALA (20 mg)
(0.2 mmol), PSL (40 mg), and EMA (2 equiv) in toluene (2 mL) at room
temperature for 24 h. (S)-5: ½a D25
ꢁ
+6.55 (c 2.0, CHCl3, 70% ee) (lit. ½a D20
ꢁ
+10.7
(c 1.05, CHCl3, >99% ee; Berger, M. L.; Schweifer, A.; Rebernik, P.;
Hammerschmidt, F. Bioorg. Med. Chem. 2009, 17, 3456–3462). (R)-6: ½a D25
ꢁ
+21.7 (c 1.4, CHCl3, >99% ee).
and trifluoroethyl butyrate (30 lL, 0.2 mmol) was added and the resultant
12.
13.
½
a 2D5
ꢁ
(c 1.0, EtOH) for recovered substrates: 3b, ꢂ33.9; 3c, ꢂ31.7; 3d, ꢂ50.9; 3e,
solution was stirred at 25 °C under argon atmosphere. A portion of fresh
enzyme (20 mg) was added once after 12 and one more after 36 h. The reaction
was stopped after 48 h. The solution was filtered through a celite-pad and then
analyzed by 1H NMR spectroscopy and HPLC using a chiral column (Whelk-O1,
Merck).
ꢂ34.9; 3f, ꢂ50.0; 3g, ꢂ41.5; 3h, ꢂ43.2; 3k, +8.18; 3l, +7.29; 3m, +6.98; 3n,
+8.24; 3o, +8.08
½ ꢁ (c 1.0, CHCl3) for acylated products: 4b, ꢂ16.2; 4c, ꢂ17.3; 4d, ꢂ2.0; 4e,
a 2D5
ꢂ24.0; 4f, ꢂ16.6; 4g, ꢂ12.5; 4h, ꢂ15.7; 4k, ꢂ70.4; 4l, ꢂ80.4; 4m, ꢂ80.4 4n,
ꢂ74.8; 4o, ꢂ69.7.