444
S. Kadotani et al. / Tetrahedron 75 (2019) 441e447
Table 4
Acyl donor preference on the reaction rate for the lipase-catalyzed transesterification of three types of alcohols.
Entry
Substrate
Acyl donor
native PS-C
IL1-PS
PYET-PS
Reaction ratea
Reaction ratea
Reaction ratea
1
2
3
4
5
6
7
8
(
(
(
)-1a
)-1g
)-1j
Vinyl acetate
Vinyl butanoate
Vinyl octanoate
2,2,2-trifluoroethyl octanoate
Vinyl acetate
Vinyl butanoate
Vinyl octanoate
2,2,2-trifluoroethyl octanoate
Vinyl acetate
Vinyl butanoate
19
19
26
7.1
11
7.2
46
7.1
7.2
12
24
6.3
884
917
1183
690
821
578
1019
616
372
487
752
504
799
497
911
618
1274
778
969
517
778
395
739
482
9
10
11
12
Vinyl octanoate
2,2,2-trifluoroethyl octanoate
a
Rate: mM hꢁ1 mg enzymeꢁ1
.
3. Conclusions
with ether, the filtrate was dried under reduced pressure at rt to
give 1-ethylpyridin-1-ium bromide (0.60 g, 3.2 mmol) in 32% yield.
We have synthesized three types of pyridinium cetyl-PEG10
sulfate ILs and evaluated their property for activation of Bur-
kholderia cepacia lipase by the coating process through lyophiliza-
tion. Among the tested IL-coated enzymes, the PYET-coated lipase
PS (PYET-PS) was especially suitable for the transesterification of 1-
(pyridin-4-yl)ethanol (1g), 1-(pyridin-3-yl)ethanol (1h), 1-(pyr-
idin-2-yl)ethanol (1i), and 4-phenylbut-3-en-2-ol (1j). To the best
of our knowledge, the fastest transesterification was accomplished
while maintaining a perfect enantioselectivity (E value > 200) and
this was postulated to be due to the increasing Kcat value. It should
be noted that the lipase reactivity could be enhanced only by
coating with these ionic liquids, and the cationic part of the IL plays
an important role in the substrate preference of the enzyme.
Mp 120 ꢀC, 1H NMR (500 MHz, ppm, CDCl3 J ¼ Hz)
d 1.75 (3H, t,
J ¼ 7.5), 5.10 (2H, q, J ¼ 7.5), 8.15 (2H, t, J ¼ 7), 8.53 (1H, s), 9.63 (2H,
d, J ¼ 6.5); 13C NMR (125 MHz, ppm, CDCl3 J ¼ Hz)
d 17.37, 57.12,
57.39, 128.48, 128.64, 144.74, 144.92, 145.08, 145.60.
A
mixture of 1-ethylpyridin-1-ium bromide (150 mg,
0.80 mmol) and ammonium cetyl-PEG10 sulfate [20] (624 mg,
0.80 mmol) in dichloromethane (CH2Cl2) (8.0 ml) was stirred at rt
for 24 h to form the precipitate of ammonium bromide (NH4Br).
The precipitate was removed by filtration and the extract was
diluted with CH2Cl2 and cooled to ꢁ25 ꢀC to form the precipitate of
NH4Br which was removed by filtration. This process was repeated
several times until no more precipitate was formed. The resulting
filtrate was dried by lyophilization to give 666 mg (0.77 mmol) of
PYET in 96% yield: mp 35.2 ꢀC (DSC); 1H NMR (500 MHz, ppm, CDCl3
J ¼ Hz)
d
0.88 (3H, t, J ¼ 7.5), 1.25e1.58 (28H, m) 1.73 (1H, t, J ¼ 7.5),
4. Experimental
2.77 (2H, s), 3.44 (2H, t, 7), 3.58e3.74 (40H, m), 3.59e3.73 (46Hþ
a
,
m), 5,03 (2H, q, J ¼ 7.5), 8.14 (2H, t, J ¼ 7.5), 8.50 (1H, t, 8), 9.47 (2H,
4.1. General procedures
d, J ¼ 5.5); 13C NMR (125 MHz, ppm, CDCl3)
d 14.10, 17.18, 22.64,
26.00, 29.30, 29.44, 29.56, 29.63, 31.86, 61.42, 69.92, 70.41, 71.49,
72.56, 128.44, 144.91; IR (neat, cmꢁ1) 2917, 2887, 2849, 1725, 1633,
1467, 1346, 1278, 1246, 1112, 965, 846, 781, 713, 686, 630, 580, 530;
ESI-MS m/z: 108.0802 (Mþ); calcd for C7H10Nþ (Mþ) 108.0814.
PYBU and PYMP were prepared by a similar method.
The reagents and solvents were purchased from common
commercial sources and used as received or purified by distillation
over the appropriate drying agents. Burkholderia cepacia lipase
(native PS-C) was purchased from Amano Enzyme Ltd. The re-
actions requiring anhydrous conditions were carried out under
argon with dry, freshly distilled solvents, and magnetic stirring. The
reactions, except for the preparation of the ionic liquids, were
monitored by thin layer chromatography using a silica gel plate and
GC. Thin layer chromatography was performed with the indicated
solvents and Wako gel B-5F. The 1H NMR spectra and 13C NMR
spectra were recorded by a JEOL JNM MH-500 (500 MHz for 1H and
125 MHz for 13C). Chemical shifts are expressed in ppm downfield
from tetramethylsilane (TMS) in CDCl3 as the internal reference.
The IR spectra were obtained using a SHIMADZU FT-IR 8000
spectrometers. High resolution mass spectra were recorded by a
Thermo Fisher Scientific EXACTIVE mass spectrometer. The rate
was determined by a gas chromatography analysis (Quadrex
PYBU: mp 33.5 ꢀC (DSC); 1H NMR (500 MHz, ppm, CDCl3 J ¼ Hz)
d
0.88 (3H, t, J ¼ 7.5), 0.96 (3H, t, J ¼ 7.5), 1.25e1.41 (28H, m), 1.55
(2H, d, J ¼ 7.0) 1.98 (2H, m), 3.42 (2H, t, J ¼ 7.0), 3.55e3.72 (40H, m)
4.16(1H, t, J ¼ 4.5), 4.89 (2H, t, J ¼ 7.0), 8.12 (2H, t, J ¼ 7.0), 8.48 (1H, t,
J ¼ 7.5), 9.33 (2H, d, J ¼ 5.5); 13C NMR (125 MHz, ppm, CDCl3)
d
13.49, 14.08, 19.34, 22.65, 26.04, 29.31, 29.46, 29.58, 29.65, 31.38,
33.69, 61.56, 61.89, 66.28, 69.98, 70.19, 70.36, 70.49, 71.51, 72.50,
128.38, 144.92,145.26; IR (neat, cmꢁ1) 2917, 2887, 2852, 2470,1636,
1464, 1343, 1281, 1237, 1109,1033, 962, 846, 775, 719, 689, 719, 689,
630, 580, 541; ESI-MS m/z: 136.1113 (Mþ); calcd for C9H14Nþ (Mþ)
136.1127.
PYMP: mp 35.4 ꢀC (DSC); 1H NMR (500 MHz, ppm, CDCl3 J ¼ Hz)
d
0.88 (3H, t, J ¼ 7.5), 1.25e1.28 (26H, m), 1.57 (2H, q, J ¼ 6.5), 2.34
bonded fused silica methyl silicone,
optical purity was determined by HPLC analysis using Daicel OD,
OD-H, OB, AD, or OJ-H.
f
0.25 mm ꢂ 25 m, N2). The
(2H, m), 3.24 (3H, s), 3.45 (4H, m), 3.57e3.74 (38Hþ
a, m), 4.16 (1H,
t, J ¼ 5), 5.01 (2H, t, J ¼ 6.5), 8.10 (2H, t, J ¼ 7.5), 8.50 (1H, t, J ¼ 7.5),
9.36 (2H, d, J ¼ 6.0); 13C NMR (125 MHz, ppm, CDCl3)
d 14.06, 22.63,
26.02, 29.29, 29.44, 29.56, 29.63, 31.14, 31.85, 58.62, 59.79, 61.59,
66.27, 68.55, 69.98, 70.18, 70.22, 70.49, 71.49, 72.48, 128.13, 145.00,
145.54; IR (neat, cmꢁ1) 2914, 2887, 2852, 1636, 1464, 1346, 1281,
1106, 1027, 959, 843, 772, 716, 630, 580, 530, 476; ESI-MS m/z:
152.1060 (Mþ); calcd for C9H14NOþ (Mþ) 152.1076.
4.2. Preparation of PYET
A mixture of pyridine (0.80 g, 10 mmol) and bromoethane
(1.30 g, 12 mmol) was stirred ar rt for 43 h, then the mixture was
washed with ether twice and treated with active charcoal for 12 h
by stirring. After removing active charcoal by filtration and washed