F. D. Nasário et al. / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
5
4.6. Bioreduction of ketones
126.82, 128.63, 133.10, 144.27. ½a D20
ꢂ
¼ þ50 (c 0.5, CHCl3) 87% ee.
{Lit.24
½
a 2D0
ꢂ
¼ þ53:9 (c 0.5, CHCl3)}. The ee was determined by
At first, 40 mg of ketone dissolved in 0.5 mL of 2-propanol were
added to a suspension of 3 g of wet cells (C. albicans or L. brevis) in
10 mL of distilled water. The pH of reactions was constant at
approximately 5. The reaction was monitored by GC/MS and the
enantiomeric excess was quantified by GC/FID and HPLC.
GC-FID, with an oven temperature of 50–130 °C, 2 °C minꢁ1
and 130–180 °C, 10 °C minꢁ1 and kept constant for 2 min;
tR = 27.95 min [(R)-enantiomer]; tS 28.58 min [(S)-enantiomer].
4.8.3. (R)-1-(4-Fluorophenyl)ethanol (R)-1c
Colorless liquid. MS m/z (rel. intensity %): 140 (M+, 19), 125
(100), 123 (24), 97 (69), 96 (19), 95 (27), 77 (21), 75 (14), 43
(16), 32 (14). 1H NMR (400 MHz, CDCl3) d = 1.48 (d, J = 6.4 Hz,
3H), 1.79 (s, 1H), 4.89 (q, J = 6.4 Hz, 1H), 7.03 (t, J = 8.8 Hz, 2H),
7.22 (dd, J = 8.4 Hz, J = 5.4 Hz, 2H). 13C NMR (100 MHz, CDCl3)
4.7. Deracemizationof1-arylethanolsusingtwomicroorganisms
Two microorganisms were used in this process: alcohol dehy-
drogenase Prelog (C. albicans) and alcohol dehydrogenase anti-Pre-
log (L. brevis). The first step of the kinetic resolution used cells
immobilized in calcium alginate beads, followed by the removal
and rinsing of the beads with ether. Free cells of the other microor-
ganism responsible for the reduction of the ketone formed were
added to the remaining liquid phase.
d = 25.32, 69.81, 115.17, 115.39, 127.01, 127.09.
½
a 2D0
ꢂ
¼ þ26
(c 3.2, CH2Cl2) 99% ee. {Lit.25
½ ꢂ
a 2D0
¼ þ26:5 (c 3.2, CH2Cl2)}. The ee
was determined by GC-FID, with an oven temperature of 100 °C
for 3 min, then increased to180 °C at 1.5 °C minꢁ1 and kept con-
stant for 10 min; tR = 19.25 min [(R)-enantiomer]; tS = 20.39 min
[(S)-enantiomer].
(a) A solution of 1-phenylethanol (50 mg) dissolved in 0.150 mL
of acetone was added to a suspension of 15 g of C. albicans
beads in 10 mL of distilled water. After 30 min (complete
kinetic resolution), the beads were removed and rinsed with
ether, and 3 g of L. brevis wet cells were added to the remain-
ing liquid phase. The reaction was monitored by GC/MS and
the enantiomeric excess was quantified by GC/FID and HPLC.
(b) A solution of 1-phenylethanol (50 mg) dissolved in 0.150 mL
of acetone was added to a suspension of 15 g of L. brevis
beads in 10 mL of distilled water. After 24 h (complete
kinetic resolution), the beads were removed and rinsed with
ether, and 3 g of C. albicans wet cells were added to the
remaining liquid phase. The reaction was monitored by
GC/MS and the enantiomeric excess was quantified by GC/
FID and HPLC.
4.8.4. (R)-1-(4-Bromophenyl)ethanol (R)-1d
Colorless liquid. MS m/z (rel. intensity %): 202 (M+, 24), 200 (M+,
26), 186 (88), 184 (99), 158 (26), 156 (34), 121 (26), 78 (47), 77
(100), 75 (15), 51 (21), 50 (17), 43 (39). 1H NMR (400 MHz, CDCl3)
d = 2.55 (d, J = 6.8, 3H), 2.13 (s, 1H), 4.83 (q, J = 6.87, 1H), 7.22 (d,
J = 8.4 Hz, 2H), 7.45 (d, J = 8.8 Hz, 2H). 13C NMR (100 MHz, CDCl3)
d = 25.24, 69.76, 121.15, 127.17, 131.55, 144.78.
½
a 2D0
ꢂ
¼ þ26
(c 1.1, CHCl3) 99% ee. {Lit.26
½ ꢂ
a 2D0
¼ þ27:5 (c 1.1, CHCl3)}. The ee
was determined by GC-FID, oven temperature of 100 °C
for 3 min, then increased to 180 °C at 1.5 °C minꢁ1 and maintained
constant for 10 min; tR = 39.56 min [(R)-enantiomer]; tS =
40.69 min [(S)-enantiomer].
4.8.5. (R)-1-(4-Hydroxyphenyl)ethanol (R)-1e
White solid. Mp: 135–136 °C. MS m/z (rel. intensity %): 138 (M+,
29), 123 (100), 121 (14), 120 (30), 95 (51), 91 (20), 77 (40), 65 (16),
43 (16). 1H NMR: (400 MHz, DMSO-d6) d = 1.26 (d, J = 6.3 Hz, 3H),
4.60 (dq, J = 4.3, 6.3 Hz, 1H), 4.92 (d, J = 4.3 Hz, 1H), 6.68 (d,
J = 8.5 Hz, 2H), 7.12 (d, J = 8.5 Hz, 2H), 9.18 (s, 1H). 13C NMR:
(100 MHz, DMSO-d6) d = 26.0, 67.8, 114.6, 126.4, 137.7, 156.0.
On a preparative scale, 200 mg of substrate were added to a
250 mL Erlenmeyer flask containing 45 g of C. albicans in beads in
40 mL of water. After 45 min (complete kinetic resolution), the
beads were removed and rinsed with ether, after which 12 g of L.
brevis wet cells were added to the remaining liquid phase. The
crude reaction was extracted with ethyl acetate (three times),
and the organic layer was dried over anhydrous sodium sulfate.
The solvent was removed by rotary evaporator, and the product
was obtained after purification by silica gel chromatography using
hexane/ethyl acetate as the mobile phase.
½
a 2D0
ꢂ
¼ þ29 (c 3.4, ethanol) 99% ee. {Lit.27
½
a 2D0
ꢂ
¼ ꢁ47 (c 4.2, etha-
nol) for the (S)-1e}. The ee was determined by GC-FID, oven tem-
perature 80 °C for 3 min, 80–170 °C, 0.4 °C minꢁ1 and 170–180 °C,
2 °C minꢁ1 and kept constant for 3 min; tR = 184.64 min [(R)-
enantiomer]; tS = 186.53 min [(S)-enantiomer].
4.8. Isolated products from biocatalysis
4.8.6. (R)-1-(4-Methylphenyl)ethanol (R)-1f
White solid. Mp: 219–220 °C. MS m/z (rel. intensity %): 136 (M+,
40), 121 (100), 118 (15), 117 (19), 93 (67), 92 (15), 91 (59), 77 (28),
43 (16). 1H NMR (500 MHz, CDCl3) d = 1.52 (d, J = 6.5 Hz, 3H), 2.38
(s, 3H), 4.90 (q, J = 6.5 Hz, 1H), 7.19 (d, J = 7.5 Hz, 2H), 7.30 (d,
J = 7.5 Hz, 2H), 7.09 (t, J = 7.5 Hz, 1H). 13C NMR (125 MHz, CDCl3)
d = 21.11, 25.11, 70.30, 125.37, 129.20, 137.20, 142.89.
4.8.1. (R) and (S)-1-phenylethanol (R)-1a and (S)-1a
Colorless liquid. MS m/z (rel. intensity %): 122 (M+, 13), 107
(100), 105 (18), 104 (15), 103 (11), 79 (94), 78 (26), 77 (64), 51
(25), 50 (11), 43 (24), 40 (17), 32 (16). 1H NMR (250 MHz, CDCl3)
d = 1.49 (d, J = 6.5 Hz, 3H), 4.89 (q, J = 6.5 Hz, 1H), 7.25–7.37 (m,
5H). 13C NMR (125 MHz, CDCl3) d = 25.2, 70.5, 125.4, 127.5,
½
a 2D0
ꢂ
¼ þ53 (c 0.4, CHCl3) 99% ee. {Lit.28
½
a 2D0
ꢂ
¼ þ56 (c 0.4, CHCl3)}.
128.5, 145.8. ½a D20
ꢂ
¼ þ55 (c 1.0, CHCl3) 99% ee for the (R)-1a,
The ee was determined by GC-FID, oven temperature of 50–130 °C,
2 °C minꢁ1 and 130–180 °C, 10 °C minꢁ1 and maintained constant
for 2 min; tR = 21.68 min [(R)-enantiomer]; tS = 22.42 min [(S)-
enantiomer].
½
a 2D0
ꢂ
¼ ꢁ44 (c 0.5, CHCl3) 97% ee for the (S)-1a. {Lit.23
½
a 2D0
ꢂ
¼ þ58
(c 1.0, CHCl3) for the (R)-1a}. The ee was determined by HPLC anal-
ysis using a 15 cm ꢀ 2.1 mm ꢀ 5
lm Supelco Astec cellulose DMP
column (eluent hexane/2-propanol 98:2, flow rate 0.5 mL minꢁ1
)
and 215 nm UV detector; tR = 3.59 min [(R)-enantiomer]; tS
4.53 min [(S)-enantiomer].
4.8.7. (R)-1-(4-Methoxyphenyl)ethanol (R)-1g
Colorless liquid. MS m/z (rel. intensity %): 152 (M+, 30), 137
(100), 135 (20), 134 (51), 119 (26), 109 (35), 94 (20), 91 (25), 77
(23), 65 (14). 1H NMR (500 MHz, CDCl3): d 1.51 (d, J = 6.5 Hz, 3H),
3.85 (s, 3H), 4.89 (q, J = 6.5 Hz, 1H), 6.92 (d, J = 8.5 Hz, 2H), 7.34
(d, J = 8.5 Hz, 2H). 13C NMR (125 MHz, CDCl3): d 25.05, 55.32,
4.8.2. (R)-1-(4-Chlorophenyl)ethanol (R)-1b
Colorless liquid. MS m/z (rel. intensity %): 156 (M+, 24), 143
(31), 141 (100), 139 (13), 113 (31), 77 (77), 43 (19). 1H NMR
(500 MHz, CDCl3) d = 1.47 (d, J = 6.5 Hz, 3H), 4.87 (q, J = 6.5 Hz,
1H), 7.31 (m, 4H). 13C NMR (125 MHz, CDCl3) d = 25.29, 69.77,
70.03, 113.81, 126.69, 138.03, 159.03. ½a D20
¼ þ43 (c 0.5, CHCl3)
ꢂ
99% ee. {Lit.29
½
a 2D0
ꢂ
¼ þ43 (c 0.5, CHCl3)}. The ee was determined