Protein-mediated nitroaldol addition in aqueous media. Catalytic promiscuity or unspecific catalysis?

Article abstract of DOI:10.1021/op100130c

A high efficient and environmentally friendly procedure for the production of aromatic and heteroaromatic β-nitroalcohols has been developed. This synthetic approach involves the condensation of an appropriate aldehyde with 1-nitroalkanes in aqueous media

Full text of DOI:10.1021/op100130c

Organic Process Research & Development 2011, 15, 236–240
Protein-Mediated Nitroaldol Addition in Aqueous Media. Catalytic Promiscuity or
Unspecific Catalysis?
Eduardo Busto, Vicente Gotor-Fern a´ ndez, and Vicente Gotor*
Departamento de Qu ´ı mica Org a´ nica e Inorg a´ nica, Instituto UniVersitario de Biotecnolog ´ı a de Asturias, UniVersidad de OViedo,
c/Juli a´ n ClaVer ´ı a s/n, OViedo 33071, Spain
Abstract:
that the nitroaldol reaction can be performed efficiently in
4
5
aqueous media or under free solvent conditions using very
mild reaction conditions where the formation of unwanted
products is prevented. In addition sensitive functionalities such
as tetrahydropyranes, ketals, and furanes are maintained unaltered.
On the other hand, the importance of nonchemical methods
have increasingly grown in recent years, and for example
enzymatic sources have presented themselves as chemo-, regio-,
A high efficient and environmentally friendly procedure for the
production of aromatic and heteroaromatic ꢀ-nitroalcohols has
been developed. This synthetic approach involves the condensation
of an appropriate aldehyde with 1-nitroalkanes in aqueous media
using as catalyst the inexpensive carrier protein Bovine serum
albumin (BSA). According to the experimental data, the Henry
reaction between aromatic aldehydes and nitroalkanes in aqueous
media proceeds by unspecific protein catalysis rather than catalytic
promiscuity. By proper choice of the reaction conditions, the
corresponding nitroalcohols were obtained in yields up to 91% at
6
and stereoselective catalysts, creating a wealth of opportunities
for the production of very different chemical structures, facts
that have not gone unnoticed by a great number of organic
chemists. One of the emerging areas in biocatalysis is catalytic
promiscuity, based on the ability of a single enzyme active site
30 °C. Catalyst recycling and scale-up of the reactions have been
considered as important factors, in order to show this methodology
as a valuable synthetic approach.
7
to catalyze different transformations. For instance, the hydrox-
ynitrile lyase from HeVea brasilensis has been used by Griengl
and co-workers as a promiscuous catalyst for the asymmetric
Henry reaction between aromatic aldehydes and nitromethane
Introduction
8
in a water/TBME biphasic system. More recently, He and co-
The Henry or nitroaldol reaction is a widely used reaction
in organic synthesis, being essentially a coupling between a
carbonyl compound and an alkyl nitrocompound, leading to the
workers have reported the ability of the protein-glutamine
γ-glutamyltransferase (TGase) to promote the Henry reaction
9
also in a biphasic system composed of water and CH
2
Cl
2
. On
1
formation of a ꢀ-nitroalcohol. From a synthetic point of view,
the other hand, the research group of Lin have reported the
D-aminoacylase-catalyzed Henry reaction between nitroethane
ꢀ
-nitroalcohols are very interesting difunctional compounds
since they are versatile precursors for the preparation of a great
variety of manufactures such as pharmaceutically active ꢀ-ami-
noalcohols, 2-nitroketones, R-hydroxycarboxylic acids or ni-
10
and a variety of aldehydes in DMSO as organic solvent.
However, to the best of our knowledge the nonchemical
catalyzed Henry reaction using water as a unique solvent has
not been described yet.
2
troalkenes. Traditional syntheses of nitroalcohols involve the
base catalyzed condensation between aldehydes and nitroalkanes
in organic solvents. For these processes, commonly strong bases
such as sodium methoxide, sodium hydroxide, LDA, butyl
lithium, barium hydroxide or sodium carbonate are used as
catalysts, however the formation of undesired side products is
often observed due to their ability to catalyze competitive
reactions such as aldol addition, Cannizzaro reaction and water
(4) (a) Ballini, R.; Bosica, G. J. Org. Chem. 1997, 62, 425. (b) Reddy,
K. R.; Rajasekhar, C.V.; Krishna, G. G. Synth. Commun. 2007, 37,
1
971. (c) Ballini, R.; Barboni, L.; Fringuelli, F.; Palmieri, A.; Pizzo,
F.; Vaccaro, L. Green Chem. 2007, 9, 823. (d) Fan, J.; Sun, G.; Wan,
C.; Wang, Z.; Li, Y. Chem. Commun. 2008, 3792. (e) Jammi, S.; Ali,
M. A.; Sakthivel, S.; Rout, L.; Punniyamurthy, T. Chem. Asian J. 2009,
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, 314.
5) (a) Ballini, R.; Castagnani, R.; Petrini, M. J. Org. Chem. 1992, 57,
160. (b) Bhattacharya, A.; Purohit, V. C.; Rinalda, F. Org. Process
(
2
3
elimination. In recent years, different research groups found
Res. DeV. 2003, 7, 254. (c) Gan, C.; Chen, X.; Lai, G.; Wang, Z.
Synlett 2006, 387. (d) Tanaka, K.; Hachiken, S. Tetrahedron Lett. 2008,
49, 2533.
*
Corresponding author. E-mail: vgs@fq.uniovi.es.
(
1) Luzzio, F. A. Tetrahedron 2001, 57, 915, and references cited therein.
(6) (a) Zaks, A.; Dodds, D. R. Drug DiscoVery Today 1997, 2, 513. (b)
Klibanov, A. M. Nature 2001, 409, 241. (c) Tang, S. L. Y.; Smith,
R. L.; Poliakoff, M. Green Chem. 2005, 7, 761. (d) Anastas, P.;
Eghbali, N. Chem. Soc. ReV. 2010, 39, 301.
(
b) Davies, A. V.; Driffield, M.; Smith, D. K. Org. Lett. 2001, 3, 3075.
c) Palomo, C.; Oiarbide, M.; Mielgo, A. Angew. Chem., Int. Ed. 2004,
(
4
3, 5442. (d) Concell o´ n, J. M.; Rodr ´ı guez-Solla, H.; Concell o´ n, C.;
Garc ´ı a-Granda, S.; D ´ı az, M. R. Org. Lett. 2006, 8, 5979. (e) Concellon,
J. M.; Bernad, P. L.; Rodr ´ı guez-Solla, H.; Concell o´ n, C. J. Org. Chem.
(7) (a) Bornscheuer, U. T.; Kazlauskas, R. J. Angew. Chem., Int. Ed. 2004,
43, 6032. (b) Hult, K.; Berglund, P. Trends Biotechnol. 2007, 25, 231.
(c) Babtie, A.; Tokuriti, N.; Hollfelder, F. Curr. Opin. Chem. Biol.
2010, 14, 200.
2
007, 72, 5421. (f) Palomo, C.; Oiarbide, M.; Laso, A. Eur. J. Org.
Chem. 2007, 2561. (g) Borwga, J.; Gogoi, N.; Partha, P.; Barua, N. C.
Tetrahedron: Asymmetry 2007, 17, 3315.
(8) (a) Purkarthofer, T.; Gruber, K.; Gruber-Khadjawi, M.; Waich, K.;
Skranc, W.; Mink, D.; Griengl, H. Angew. Chem., Int. Ed. 2006, 45,
3454. (b) Gruber-Khadjawi, M.; Purkarthofer, T.; Skranc, W.; Griengl,
H. AdV. Synth. Catal. 2007, 349, 1445.
(
2) (a) Ono, N. The Nitro Group in Organic Synthesis; Wiley-VCH: New
York, 2001; pp 30-69. (b) Kudyba, I.; Raczko, J.; Urbanczyk-
Lipkowska, Z.; Jurczak, J. Tetrahedron 2004, 60, 4807.
3) (a) Rosini, G.; Ballini, R. Synthesis 1988, 833. (b) Rosini, G.
ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds.;
Pergamon Press: Oxford, 1991; Vol. 2, pp 321-34. (c) Shvekhgeimer,
M. A. Russ. Chem. ReV. 1998, 67, 35.
(
(9) Tang, R.-C.; Guan, Z.; He, Y.-H.; Zhu, W. J. Mol. Catal. B: Enzym.
2010, 63, 62.
(10) Wang, J.-L.; Xia, L.; Hong-Yan, X.; Bo-Kai, L.; Xian-Fu, L.
J. Biotechnol. 2010, 145, 240.
2
36
•
Vol. 15, No. 1, 2011 / Organic Process Research & Development
10.1021/op100130c  2011 American Chemical Society
Published on Web 07/20/2010

Scheme 1. Protein-catalyzed Henry reaction between
p-nitrobenzaldehyde and nitromethane
Table 2. Effect of the water/nitromethane ratio in the
conversion of the BSA-catalyzed Henry reaction between
a
p-nitrobenzaldehyde and nitromethane
entry
H
2
O (%)
MeNO
2
(equiv)a
c (%)b
1
2
3
4
5
6
7
8
9
-
5
97
92
78
58
29
19
10
5
<3
80
20
40
70
80
90
95
98
93
97
Table 1. Catalytic activities of different proteins in the
nitroaldol addition between nitromethane and
p-nitrobenzaldehyde
>97
>97
>97 (91)
97
entry
protein
no protein
CAL-B
PSL-C
PPL
c (%)a
2
84
1
2
3
4
5
6
<3
<3
6
65
31
91
a
All reactions were performed using p-nitrobenzaldehyde (45 mg, 0.30 mmol),
water/nitromethane system (1.56 mL total volume).
BSA (50 mg), 1 and
a
b
Determined by H NMR of the reaction crude. Isolated yields in brackets of 3a.
b
PPL (denatured)
BSA
1
workup of the reaction, 83% conversion was detected by H
a
Determined by 1H NMR of the reaction crude. b Pretreated with urea at 140
C for 48 h.
NMR analysis of the reaction crude after 48 h. This fact provides
a strong evidence that the reaction could proceed Via unspecific
protein catalysis rather than specific promiscuous catalysis as
observed for the Henry reaction in DMSO by Lin and
co-workers. A plausible explanation for this observation could
be performed on the basis of the basic character of the amino
group present in the side chain of the lysine residue as occurs
in other processes catalyzed by BSA such as the decomposi-
tion of Meisenheimer complexes, hydrolysis of p-nitrophenyl
acyl esters and p-nitrophenylcarbonates, Kemp elimination,
tandem Kemp elimination/ꢀ-elimination, ꢀ-elimination of
°
In this contribution, we describe an environmentally friendly
methodology for the production of ꢀ-nitroalcohols under very
mild reaction conditions. Different nonchemical catalysts have
been considered to promote the Henry reaction between a series
of nitroalkanes and a wide family of aromatic aldehydes in
aqueous medium.
10
11
12
13
14
15
Results and Discussion
16
17
First of all, we decided to examine the condensation between
p-nitrobenzaldehyde (1a) and nitromethane (2) as a model
reaction. With this aim we selected a nitromethane/water, 8:2
umbelliferone, Morita-Baylis-Hillman reaction, or Michael
18
addition between methyl nitroacetate and 3-buten-2-one. First
of all, the basic amino group could remove the acidic hydrogen
of the nitrocompound obtaining the corresponding nitronate.
Next, the nucleophilic attack of the nitronate towards the
aldehydes would lead to the formation of the C-C bond leading
to the corresponding ꢀ-nitroalcohol.
Once we had demonstrated the ability of BSA to promote
the Henry reaction in aqueous media, we decided to look for
the optimal amount of nitromethane in order to raise the
conversion of the transformation. In this manner the reaction
was performed by employing different water/nitromethane ratios
(Table 2). No conversion was observed when the reaction was
performed in anhydrous nitromethane (entry 1), which means
that the presence of water is essential for the protein-mediated
Henry reaction. Interestingly, an acceleration of the reaction
rate was observed by increasing the amount of water (entries
2-8), achieving a complete conversion using water content
(v/v), biphasic system as the reaction medium and several
lipases operating at 30 °C (Scheme 1).
Just as we expected, no adduct formation was observed in
the absence of catalyst (Table 1, entry 1). On the other hand,
low conversion values were observed for Candida antarctica
lipase B (CAL-B, entry 2) and Pseudomonas cepacia lipase
supported on a ceramic support (PSL-C, entry 3); meanwhile,
65% yield was attained using porcine pancreas lipase (PPL,
entry 4). In order to exclude protein catalysis, we decided to
perform some control experiments where denaturalized PPL or
a carrier transport protein [bovine serum albumin (BSA)] was
used to mediate the desired transformation (entries 5-6).
Surprisingly, 31% conversion was reached with denatured PPL
(entry 5), and more interestingly, a very high conversion value
(91%) was achieved when the reaction was performed using
the carrier protein BSA (entry 6).
(
11) (a) Peters, T. All about Albumin: Biochemistry, Genetics and Medical
With these results in hand we found a clear contradiction
between our observations and the results previously reported
by He and co-workers, where the possibility of protein catalysis
Applications; Academic Press: San Diego, 1996.
(12) (a) Taylor, R. P.; Vatz, J. B. J. Am. Chem. Soc. 1973, 95, 5819. (b)
Taylor, R. P.; Chau, V.; Bryner, C.; Berga, S. J. Am. Chem. Soc. 1975,
9
7, 1934.
9
is excluded. With the aim of validating the hypothesis of
(
13) (a) Østda, H.; Andersen, H. J. Food Chem. 1996, 55, 55. (b) Riva, S.;
Mendozza, M.; Carrea, G.; Chattopadhay, P.; Tramontano, A. Appl.
Biochem. Biotechnol. 1998, 75, 33.
unspecific protein catalysis, we decided to carry out two
experiments employing the initial (cyclohexane/water, 10:1) and
(
14) Hollfelder, F.; Kirby, A. J.; Tawfik, D. S. Nature 1996, 283, 60.
2 2
the optimized (CH Cl /water, 5:3) conditions reported by He
(15) Boucher, G.; Sylvain, R.; Fargeas, V.; Dintinger, T.; Mathe-Allainmat,
M.; Lebreton, J.; Tellier, C. ChemBioChem 2005, 6, 807.
and co-workers using the nonenzyme protein BSA as biocata-
lyst. In agreement with the previously reported results, low
conversion (21%) was detected under the initial reaction
conditions; however, when the Henry reaction was performed
under the optimized conditions, we observed that, after the
(
(
16) Klein, G.; Reymond, J. M. Bioorg. Med. Chem. Lett. 1998, 8, 1113.
17) Reetz, M. T.; Mondi e` re, R.; Carballeira, J. D. Tetrahedron Lett. 2007,
48, 1679.
(
18) Strohmeier, G. A.; Sovi c´ , T.; Steinkellner, G.; Hartner, F. S.;
Andryushkova, A.; Purkarthofer, T.; Glieder, A.; Gruber, K.; Griengl,
H. Tetrahedron 2009, 65, 5663.
Vol. 15, No. 1, 2011 / Organic Process Research & Development
•
237

Scheme 2. Catalytic nitroaldol addition between different
aromatic aldehydes and nitromethane
Table 3. Catalytic Henry reaction between nitromethane
and a series of aromatic aldehydes 1a-j including
a
spontaneous formation of Michael adducts 5a-j
t
c
3a-j
entry
R
catalyst
(1a) BSA
(h) (%) (%) 5a-j (%)b
b
c
Figure 1. Catalyst recycling experiments for the Henry reaction
between p-nitrobenzaldehyde and nitromethane. The reaction
was performed using 0.3 mmol of 1a, 2.97 mmol of 2, 50 mg of
BSA, and 1.44 mL of water. Conversion values were determined
1
2
3
4
5
6
7
8
9
4-NO
4-NO
4-NO
3-NO
2
2
2
2
-C
-C
-C
-C
6
6
6
6
H
H
H
H
4
4
4
4
16 >97
(1a) BSA (denatured) 16 >97
91
83
70
91
74
75
54
68
79
46
59
--
<3
5
25
5
10
5
21
5
13
<3
14
<3
<3
(1a) L-lysine
(1b) BSA
16 >97
16 >97
16 >97
16 >97
16 >97
16 >97
48 >97
72
72
72
4-CN-C
6
H
4
(1c)
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
1
by H NMR of the reaction crude after 16 h.
2-Pyridyl (1d)
3-Pyridyl (1e)
4-Pyridyl (1f)
On the other hand, different aromatic aldehydes were tested
in order to generalize the scope of the BSA-catalyzed Henry
reaction (entries 1 and 4-12). Complete conversion was
achieved for aldehydes bearing strong electron-withdrawing
groups (entries 1 and 4-8), especially for 1a,b yielding the
final products with excellent yields (entry 1 and 4), meanwhile
nitrocompounds 3c,d,f,g (entries 5, 6, 8, and 9) were recovered
in good isolated yields (68-79%). However, the 3-pyridyl
nitroalcohol 3e was obtained in moderate yield as an appreciable
amount of the dinitrocompound 5e (entry 7). As expected,
moderate yields were found for ꢀ-nitroalcohols with neutral or
electron-donating groups (entries 10-12) as the poor electro-
philic character of the carbonyl groups made the nucleophilic
attack of nitromethane less probable. Disappointingly, we could
not find any enantioselectivity grade in any of the BSA-
mediated experiments. It must be also mentioned that the BSA-
catalyzed nitroaldol addition between nitromethane and aliphatic
aldehydes such as n-hexanal and n-butanal led to very low
conversions (<5%) (data not shown).
4-Br-C
4-Ph-C
6
H
4
(1g)
(1h)
10
11
12
13
6
H
4
55
77
30
2-Nf (1i)
1-Nf (1j)
d
4-NO
2
-C
6
H
4
(1a) BSA
26 >97
82
a
Entries 1-12: Reactions were performed using the corresponding aldehyde
(
0.30 mmol), BSA, or L-lysine (50 mg), water (1.44 mL), and nitromethane (160
µL, 2.98 mmol). Determined by H NMR of the reaction crude. Isolated yields
after flash chromatography. Reaction was performed using 1a (1.00 g, 6.60
mmol), BSA (1.10 g), water (31.68 mL), and nitromethane (3.52 mL, 65.56
mmol).
b
1
c
d
Scheme 3. Tandem Henry reaction/Michael addition
between aromatic aldehydes 1a-j and nitromethane (2)
In order to take advantage of this approach we have also
explored two important factors in the application of this
methodology in the industrial scale: scale up of the reaction
catalyst and catalyst recycling. The reaction between 4-ni-
trobenzaldehyde (1a) and nitromethane (2) was scaled up using
solutions between 70 and 90%, which means that only a 10-
fold excess of nitromethane is necessary to obtain complete
conversion (entries 5-7). A slight decrease of the conversion
was observed for water contents higher than 95%, probably due
to the insolubility of the starting material in the reaction medium
1
g of starting material (6.6 mmol), obtaining the nitroalcohol
3a in complete conversion and 82% isolated yield (entry 13).
Compared to the small-scale experiment (entry 1) additional
0 h were required to achieve complete conversion which could
(entries 8-9).
1
Once that we had in hand the optimized reaction conditions,
we decided to perform the nitroaldol addition between 1a and
be due to the fact that the orbital shaking is less efficient when
the reaction is performed with a higher volume of solvent;
additionally, a slight decrease on the reaction yield was
observed.
At the same time we have also investigated the possibility
of reusing the catalytic BSA. Figure 1 shows the efficiency of
the catalyst employed during five consecutive cycles to promote
the reaction between p-nitrobenzaldehyde (1a) and nitromethane
(2) under the previous optimized reaction conditions. Complete
conversion was observed up to third reaction cycle, and
interestingly only a very slight loss of activity was observed
for the fourth (97% conversion) and fifth (95% conversion)
catalytic cycles.
2
using denatured BSA (Scheme 2, Table 3, entry 2) or L-lysine
(entry 3) as catalysts with the aim of excluding the possibility
that a specific residue in a certain region of the protein was
responsible for the catalytic activity.
As expected, quantitative conversions were observed for both
processes which mean that nitroaldol addition proceeds Via
nonspecific catalysis rather than catalytic promiscuity. Interest-
ingly, higher isolated yields were recovered with BSA (entry
1) in comparison with L-lysine (entry 3), where an appreciable
amount of the dinitrocompound 5a was observed through a
tandem Henry/Michael reaction depicted in Scheme 3.
2
38
•
Vol. 15, No. 1, 2011 / Organic Process Research & Development

Scheme 4. BSA catalyzed nitroaldol addition between
crude was purified by flash chromatography (EtOAc/hexane
mixtures), yielding the corresponding nitroalcohols 3a-j.
4
-nitrobenzaldehyde and nitrocompounds 6a-b
1
9
2
-Nitro-1-(4-nitrophenyl)ethanol (3a): R
f
(20% EtOAc/
1
hexane) 0.25; H NMR (CDCl , 300.13 MHz): δ 2.25 (brs, 1H),
.58-4.61 (m, 2H), 5.63-5.68 (m, 1H), 7.64 (d, JHH ) 6.5
3
3
4
3
13
Hz, 2H), 8.26 (d, JHH ) 6.5 Hz, 2H); C NMR (CDCl
MHz): δ 70.4 (CH ), 81.0 (CH), 125.5 (2CH), 127.4 (2CH),
45.5 (C), 148.5 (C).
-Nitro-1-(3-nitrophenyl)ethanol (3b): R
3
, 75.5
2
1
Furthermore, the scope of the procedure has been guaranteed,
20
2
f
(30% EtOAc/
performing the reaction between 4-nitrobenzaldehyde (1a) and
different nitrocompounds such as bromonitromethane (6a) or
nitroethane (6b) at 30 °C during 16 h (Scheme 4). In both cases,
the final adducts were isolated with high yields (86-88%);
furthermore, a slight diastereomeric induction was observed in
favor of the anti-diastereomer.
1
hexane) 0.25; H NMR (CD
3
OD, 300.13 MHz): δ 4.55-4.89
(
m, 2H), 5.51-5.57 (m, 1H), 7.81-7.89 (m, 1H), 7.75-7.83
13
(m, 1H), 8.15-8.23 (m, 1H), 8.41 (s, 1H); C NMR (CD
3
OD,
7
1
5.5 MHz): δ 69.8 (CH
30.0 (CH), 132.5 (CH) 142.9 (C), 148.8 (C).
-(1-Hydroxy-2-nitroethyl)benzonitrile (3c):
2
), 81.2 (CH), 121.1 (CH), 123.1 (CH),
21
4
R
f
(40%
1
EtOAc/hexane) 0.20; H NMR (CDCl
3
, 300.13 MHz): δ 3.21
(
brs, 1H), 4.50-4.59 (m, 2H), 5.50-5.56 (m, 1H), 7.81-7.89
Conclusions
3
3
(m, 1H), 7.53 (d, JHH ) 8.1 Hz, 2H), 7.71 (d, JHH ) 8.1 Hz,
In summary, we have developed a simple, mild, inexpensive
and green synthetic methodology to produce ꢀ-nitroalcohols
that are useful intermediates in organic synthesis. After an
exhaustive analysis of the reaction parameters we have found
that Bovine serum albumin (BSA) efficiently promotes the
nitroaldol addition between aromatic aldehydes and 1-nitroal-
kanes in aqueous medium in contradiction with previous
13
2
1
H); C NMR (CDCl
3 2
, 75.5 MHz): δ 70.6 (CH ), 81.3 (CH),
13.4 (2CH), 118.9 (2CH), 127.5 (C), 133.5 (C), 143.8 (C).
4
e
2
-Nitro-1-(pyridin-2-yl)ethanol (3d): R
f
(100% EtOAc)
1
0
4
7
.32; H NMR (CDCl
3
, 300.13 MHz): δ 3.41 (brs, 1H),
.61-4.83 (m, 2H), 5.41-5.55 (m, 1H), 7.17-7.47 (m, 2H),
13
3
.71-7.83 (m, 1H), 8.49-8.54 (m, 1H); C NMR (CDCl ,
9
75.5 MHz): δ 70.7 (CH ), 81.2 (CH), 121.4 (CH), 124.1 (CH),
1
observations reported. According to our observations, the Henry
2
38.0 (CH), 149.3 (CH), 157.0 (C).
reaction between aromatic aldehydes and nitroalkanes is possible
by unspecific protein catalysis rather than catalytic promiscuity.
Isolated yields of the final products were very dependent on
structural limitations, obtaining most of them with good to
excellent isolated yields (68-91%). More interestingly, the
reaction between 4-nitrobenzaldehyde and nitromethane has
been extensively studied, finding that BSA can be recycled and
reused for several times without a significant loss of activity.
Additionally we were able to scale up the reaction on a gram
scale, yielding the desired 2-nitro-1-(4-nitrophenyl)ethanol in
high yield.
20
2
-Nitro-1-(pyridin-3-yl)ethanol (3e):
R
f
(100% EtOAc)
, 300.13 MHz): δ 4.52-4.67 (m, 2H),
.41-5.55 (m, 1H), 6.03 (brs, 1H), 7.30-7.36 (m, 1H), 7.53
1
0
5
.22; H NMR (CDCl
3
3
13
(
(
1
d, JHH ) 6.5 Hz, 1H), 8.40 (s, 1H), 8.48 (s, 1H); C NMR
CDCl , 75.5 MHz): δ 68.4 (CH ), 81.3 (CH), 124.1 (CH),
34.7 (CH), 135.6 (CH), 147.1 (CH), 149.1 (C).
3
2
2
0
2
-Nitro-1-(pyridin-4-yl)ethanol (3f):
R
f
(20% EtOAc/
1
hexane) 0.27; H NMR (CD
3
OD, 300.13 MHz): δ 4.63-4.95
3
13
(
(
1
m, 2H), 7.65 (d, JHH ) 5.7 Hz, 2H), 8.65 (brs, 2H); C NMR
CD OD, 75.5 MHz): δ 67.5 (CH ), 78.9 (CH), 119.9 (2CH),
47.3 (2CH), 149.9 (C).
-Nitro-1-(4-bromophenyl)ethanol (3g): R
3
2
22
2
f
(20% EtOAc/
, 300.13 MHz): δ 3.15 (brs, 1H),
.41-4.55 (m, 2H), 5.39-5.48 (m, 1H), 7.61 (m, 1H), 7.23
Experimental Section
1
hexane) 0.27; H NMR (CDCl
4
3
Bovine serum albumine (BSA, 41 U/mg for the transforma-
tion of 1a in 3a) was purchased from Sigma-Aldrich (see
Supporting Information for the determination of the specific
activity). Chemical reagents were purchased from different
commercial sources and used without further purification.
Solvents were distilled over an adequate desiccant under
nitrogen. Flash chromatographies were performed using silica
3
3
13
(d, JHH ) 6.5 Hz, 2H), 7.52 (d, JHH ) 6.5 Hz, 2H); C NMR
(
(
CDCl
2CH), 132.6 (2CH), 137.5 (C).
-(Biphenyl-4-yl)-2-nitroethanol (3h):
3 2
, 75.5 MHz): δ 70.7 (CH ), 81.3 (CH), 123.3 (C), 128.0
22
1
f
R (20% EtOAc/
1
hexane) 0.19; H NMR (CDCl , 300.13 MHz): δ 2.85 (brs, 1H),
4
7
3
.52-4.65 (m, 2H), 5.40-5.52 (m, 1H), 7.32-7.37 (m, 1H),
1
13
gel 60 (230-240 mesh). H and C NMR experiments were
3
.42-7.47 (m, 4H), 7.55-7.60 (m, 2H), 7.61 (d, JHH ) 8.1
1
obtained using a Br u¨ ker AV-300 spectrometer ( H, 300.13 MHz
13
Hz, 2H); C NMR (CDCl
3 2
, 75.5 MHz): δ 71.2 (CH ), 81.6
13
and C, 75.5 MHz).
(CH), 126.8 (2CH), 127.5 (2CH), 128.1 (2CH), 128.2 (CH)
General Procedure for the Preparation of Nitroalcohols.
A typical experiment procedure is as follows: Over a suspension
of the corresponding aldehyde (0.30 mmol) in water (1.40 mL)
were added nitromethane (160 µL, 2.98 mmol) and BSA (50
mg). The mixture was shaken at 30 °C and 250 rpm for the
corresponding time (see Table 3). After that time the reaction
1
29.3 (2CH), 137.0 (C), 140.3 (C), 141.8 (C).
21
1
-(Naphthalen-2-yl)-2-nitroethanol (3i): R
f
(20% EtOAc/
, 300.13 MHz): δ 3.15 (brs, 1H),
.41-4.55 (m, 2H), 5.39-5.48 (m, 1H), 7.48-7.55 (m, 3H),
1
hexane) 0.23; H NMR (CDCl
4
3
(19) Noole, A.; Lippur, K.; Metsala, A.; Loop, M.; Kanger, T. J. Org. Chem.
2
010, 75, 1313.
was quenched by adding H
extracted with CH Cl
(3 × 5 mL). The organic phases were
combined, dried over Na SO and filtered, and the solvent was
removed by distillation under reduced pressure. The reaction
2
O (5 mL) and the aqueous phase
(
20) Zhang, G.; Yashima, E.; Woggon, W.-D. AdV. Synth. Catal. 2009,
351, 1255.
2
2
(
(
21) Liu, S.; Wolf, C. Org. Lett. 2008, 10, 1831.
22) Kowalczyk, R.; Kwiatkowski, P.; Skarewski, J.; Jarczak, J. J. Org.
Chem. 2009, 74, 753.
2
4
Vol. 15, No. 1, 2011 / Organic Process Research & Development
•
239

7
(
(
(
.81-7.95 (m, 2H); 13C NMR (CDCl
CH ), 81.6 (CH), 123.6 (CH), 125.8 (CH), 127.1 (CH), 127.2
CH), 128.2 (CH), 128.5 (CH), 129.4 (CH), 133.6 (C), 133.8
C), 135.8 (C).
-(Naphthalen-1-yl)-2-nitroethanol (3j): R
3
, 75.5 MHz): δ 71.6
(brs, 1Hsyn+1Hanti), 5.50 (d, 3JHH ) 9.3 Hz, 1Hanti), 5.55 (d,
3
3
3
2
JHH ) 3.5 Hz, 1Hsyn), 5.93 (d, JHH ) 9.3 Hz, 1Hanti), 6.15 (d,
JHH ) 3.7 Hz, 1Hsyn), 7.61-7.73 (m, 2Hsyn+2Hanti), 8.22-8.29
13
(m, 2Hsyn+2Hanti); C NMR (CDCl , 75.5 MHz): δ anti 75.1
3
2
2
1
f
(10% EtOAc/
, 300.13 MHz): δ 3.55 (brs, 1H),
.41-4.55 (m, 2H), 6.11-6.23 (m, 1H), 7.45-7.65 (m, 3H),
(CH), 80.3 (CH), 123.9 (2CH), 128.6 (2CH), 142.8 (C), 148.5
(C). δ syn 73.4 (CH), 85.0 (CH), 124.0 (2CH), 127.6 (2CH),
143.0 (C), 148.3 (C).
1
hexane) 0.21; H NMR (CDCl
4
7
3
3
3
.75 (d, JHH ) 7.9 Hz, 1H), 7.85 (d, JHH ) 8.0 Hz, 1H), 7.91
3
3
13
(
(
1
1
d, JHH ) 8.0 Hz, 1H), 8.06 (d, JHH ) 8.0 Hz, 1H); C NMR
CDCl , 75.5 MHz): δ 68.3 (CH ), 80.8 (CH), 121.8 (CH),
23.9 (CH), 125.5 (CH), 126.1 (CH), 127.1 (CH), 129.3 (CH),
29.6 (C), 133.5 (C), 133.6 (C).
-Nitro-1-(4-nitrophenyl)propan-1-ol (7a): R
Acknowledgment
3
2
We thank Novozymes for the generous gift of CAL-B
(Novozyme 435). This work was supported by the Spanish
Ministerio de Ciencia e Innovaci o´ n (Projects CTQ 2007-61126).
V.G.-F. thanks MICINN for a personal grant (Ram o´ n y Cajal
Program).
2
3
2
f
(20% EtOAc/
1
3
hexane) 0.29; H NMR (CDCl
)
3
, 300.13 MHz): δ 1.35 (d, JHH
3
7.1 Hz, 3Hsyn), 1.52 (d, JHH ) 7.1 Hz, 3Hanti), 3.20 (brs,
1H
syn+1Hanti), 4.59-4.72 (m, 1Hsyn+1Hanti), 5.20 (d, 3JHH
)
3
Supporting Information Available
9.3 Hz, 1Hsyn), 5.55 (d, JHH ) 3.5 Hz, 1Hanti), 7.58-7.63 (m,
13
Determination of BSA specific activity is described. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1H
3
syn+1Hanti), 8.21-8.35 (m, 1Hsyn+1Hanti); C NMR (CDCl ,
7
5.5 MHz): δ anti 11.7 (CH
3
), 72.3 (CH), 86.6 (CH), 123.8
),
4.9 (CH), 87.7 (CH), 124.0 (2CH), 127.8 (2CH), 145.5 (C),
48.1 (C).
-Bromo-1-(4-nitrophenyl)propan-1-ol (7b):
(2CH), 126.9 (2CH), 145.2 (C), 148.1 (C). δ syn 16.1 (CH
3
7
1
Received for review May 12, 2010.
OP100130C
2
4
2
R
f
(20%
1
EtOAc/hexane) 0.21; H NMR (CDCl
3
, 300.13 MHz): δ 3.45
(
23) Blay, G.; Domingo, L. R.; Hern a´ ndez-Olmos, V.; Pedro, J. R.
Chem.sEur. J. 2008, 14, 4725.
(24) Blay, G.; Hern a´ ndez-Olmos, V.; Pedro, J. R. Chem. Commun. 2008,
4840.
2
40
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Vol. 15, No. 1, 2011 / Organic Process Research & Development