ω-Transaminases as efficient biocatalysts to obtain novel chiral selenium-amine ligands for Pd-catalysis

Article abstract of DOI:10.1039/b920946h

ω-Transaminases have been evaluated as biocatalysts in the reductive amination of organoselenium acetophenones to the corresponding amines, and in the kinetic resolution of racemic organoselenium amines. Kinetic resolution proved to be more efficient than the asymmetric reductive amination. By using these methodologies we were able to obtain both amine enantiomers in high enantiomeric excess (up to 99%). Derivatives of the obtained optically pure o-selenium 1-phenylethyl amine were evaluated as ligands in the palladium-catalyzed asymmetric alkylation, giving the alkylated product in up to 99% ee.

Full text of DOI:10.1039/b920946h

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
x-Transaminases as efficient biocatalysts to obtain novel chiral
selenium-amine ligands for Pd-catalysis†‡
Leandro H. Andrade,*a Alexandre V. Silva,a Priscila Milani,a Dominik Koszelewskib and Wolfgang Kroutilb
Received 6th October 2009, Accepted 1st February 2010
First published as an Advance Article on the web 3rd March 2010
DOI: 10.1039/b920946h
w-Transaminases have been evaluated as biocatalysts in the reductive amination of organoselenium
acetophenones to the corresponding amines, and in the kinetic resolution of racemic organoselenium
amines. Kinetic resolution proved to be more efficient than the asymmetric reductive amination. By
using these methodologies we were able to obtain both amine enantiomers in high enantiomeric excess
(up to 99%). Derivatives of the obtained optically pure o-selenium 1-phenylethyl amine were evaluated
as ligands in the palladium-catalyzed asymmetric alkylation, giving the alkylated product in up to
99% ee.
not suitable, because they afforded the amide group, which was
Introduction
not easily removed by standard hydrolysis conditions. A literature
Since the discovery of organoselenium compounds by Lo¨wig
survey revealed that chiral unprotected amines can be obtained
in 1836,1 these compounds have been largely used as synthetic
intermediates for the formation of several chemical species.
Among of them, we can mention the preparation of ketones
through a seleno-Pummerer reaction,2a carbon–carbon double
bonds from syn selenoxide elimination2b and the formation
of heterocycles through the seleniranium ion.2c Besides these
applications, it is worth remarking that these compounds possess
biological activities, such as anti-inflammatory and antioxidant.3a,b
More recently, chiral organoselenium compounds have been
widely used in asymmetric synthesis.4 Several chiral selenides and
diselenides have been applied as chiral ligands in asymmetric
hydrosilylation of ketones and imines,5a–c enantioselective addi-
tion of diorganozinc reagents to aldehydes,5d,e enantioselective
conjugate addition of organometallic reagents to enones,5c and
palladium-catalyzed asymmetric allylic alkylation.4c,5f –i Regarding
these applications, some synthetic tools have been developed to
synthesize organoselenium compounds in enantiomerically pure
form. Among them, we can mention the use of chiral precursors,6
selenocyclization,4a and more recently, enantioselective synthesis
mediated by enzymes.7 Organoselenium amine is one of the sub-
classes of selenium compounds that we have directed our efforts
to obtain in their optically active form using enzymes. By using
enzymatic kinetic resolution and chemoenzymatic dynamic kinetic
resolution of organoselenium amines with lipases, we have pre-
pared organoselenium amides in excellent enantiomeric excess (up
to 99%).8 However, at this moment, as we required the free amino
group for further synthetic transformation, these protocols were
through transamination reactions catalyzed by transaminases.9
Inspired by these reactions, we describe in this paper the stereos-
elective amination of organoselenium acetophenones and kinetic
resolution of the racemic organoselenium amines catalyzed by
transaminases to yield the corresponding chiral organoselenium
amines inenantiomericallypureform. Inaddition, weappliedboth
methodologies to prepare novel chiral organoselenium ligands,
which were evaluated in the palladium-catalysed asymmetric
substitution of 1,3-diphenyl-2-propenyl acetate with dialkyl mal-
onates.
Results and discussion
The synthesis of organoselenium acetophenones 2a–d and the
racemic organoselenium-1-phenylethanamines 3a–d were carried
out according to Scheme 1.
The in situ preparation of the diazonium salt from 1-(4-
aminophenyl)ethanone followed by addition of KSeCN afforded
the selenocyanate acetophenone 1 (64% yield). Then, the alky-
lation of the selenium atom was carried out with NaBH4 and
an appropriate alkyl halide to give the organoselenium acetophe-
nones 2a–d (up to 75% yield). The reductive amination of ketones
2a–d gave racemic amines 3a–d in up to 73% yield. In order to
facilitate the enantiomeric separation by chiral HPLC analysis,
the amines 3a–d were transformed to the corresponding amides
4a–d by reaction with acetic anhydride.
The stereoselective amination of organoselenium acetophe-
nones 2a–d with w-transaminases (ATA-117, ATA-113, ATA-114
and ATA-103) and alanine as amino donor was carried out under
different reaction conditions. In order to shift the equilibrium to
the product side, the co-product pyruvate was reduced by lactate
dehydrogenase (LDH) in the presence of NADH-recycling using
the glucose dehydrogenase/glucose system (Table 1).
aInstitute of Chemistry, University of Sa˜o Paulo, Av. Prof. Lineu Prestes,
748, CEP 05508-900, Sa˜o Paulo, SP, Brazil. E-mail: leandroh@iq.usp.br;
Fax: +55-11-3815-5579; Tel: +55-11-3091-2287
bResearch Centre Applied Biocatalysis, Department of Chemistry, Organic
and Bioorganic Chemistry, University of Graz, Graz, Austria
† This paper is part of an Organic & Biomolecular Chemistry web theme
issue on biocatalysis.
‡ Electronic supplementary information (ESI) available: Characterization
data (1H and 13C NMR, IR and mass spectrometry) for all compounds
and enantiomeric separation for chiral amides by chiral HPLC. See
DOI: 10.1039/b920946h
As we can see in Table 1, we evaluated different w-transaminases,
different amounts of biocatalyst (6, 10 or 15 mg) and the influence
of DMSO as a co-solvent (Table 1). Excellent enantioselectivities
were observed when biocatalysts ATA-117 and ATA-113 were used
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2043–2051 | 2043
©

View Article Online
Table 1 Stereoselective amination of organoselenium acetophenones 2a–da
Entry
ketone
ATA
Amount/mg
DMSO (% v/v)
Conv. (%)b
eeamine (%)c
1
2
3
4
6
7
8
9
10
11
13
14
15
16
17
18
19
20
22
23
24
25
26
27
29
30
2a
2b
2c
2d
2a
2b
2a
2b
2c
2d
2a
2b
2a
2b
2a
2b
2c
2d
2a
2b
2a
2b
2c
2d
2a
2b
117
117
117
117
117
117
113
113
113
113
113
113
113
113
114
114
114
114
114
114
103
103
103
103
103
103
6
6
6
6
10
10
6
6
6
—
—
—
—
10
10
—
—
—
—
10
10
10
10
—
—
—
—
10
10
—
—
—
—
10
10
5
4
nd
nd
nd
nd
>99 (R)
48 (R)
81 (S)
nd
nd
nd
nd
nd
nd
>99 (S)
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
<1
<1
17
27
30
14
2
<1
13
13
13
23
8
6
10
10
15
15
6
6
6
8
<1
<1
1
6
10
10
6
6
6
6
10
10
1
14
12
2
<1
3
9
nd
a Reaction conditions: Pi-buffer pH 7, pyridoxal-5¢-phosphate (1 mM), w-transaminase, L- or D-alanine (250 mM) (D-ala in the case of ATA-117, otherwise
L-ala), pyruvate reductase mix, ketone 2a–d (50 mM), 30 ◦C, 24 h. b Determined by GC. c Determined by chiral HPLC analysis after derivatization with
acetic anhydride. nd = not determined due to low conversion.
Scheme 1 Reagents and conditions: (i) NaNO2, HCl 2 M, pH 4.3, 0 ◦C, then KSeCN, 1 h; (ii) RBr, NaBH4, MeOH, 0 ◦C, 2 h; (iii) Ti(OCH(CH3)2)4,
NH3/EtOH (2 M), 12 h; (iv) NaBH4, 12 h, r.t.; (v) acetic anhydride, Et3N, CH2Cl2.
with substrates 2a and 2b. For example, by using ATA-117 (10 mg)
and 10% of DMSO as co-solvent, the amine (R)-3b was obtained
with >99% ee and 17% conversion. Employing the same reaction
conditions, the reductive amination of ketone 2a afforded amine
(R)-3a with 48% ee and 27% conversion.
On the other hand, by using ATA-113 as biocatalyst, we
observed the formation of the opposite enantiomer. The reductive
amination of ketone 2b by ATA-113 (6 mg) with no co-solvent
gave the amine (S)-3b with 30% conversion (81% ee). Using
the same enzyme (15 mg) and 10% of DMSO as co-solvent,
2044 | Org. Biomol. Chem., 2010, 8, 2043–2051
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 2 Kinetic resolution of racemic amines (3)a
Entry
Substrate
ATA
Conv. (%)b
eeamine (%)c
Ed
1
2
3
4
6
7
8
9
3a
3b
3c
3d
3a
3b
3c
3d
117
117
117
117
113
113
113
113
49
47
47
35
53
54
48
56
98 (S)
98 (S)
91 (S)
nd
>99 (R)
93 (R)
77 (R)
76 (R)
>200
>200
>200
—
>200
30
26
9
a Reaction conditions: Pi buffer pH 7, pyridoxal-5¢-phosphate (1 mM), w-transaminase, sodium pyruvate (50 mM), amines 3a–d (50 mM), 30 ◦C, 24 h.
b Determined by GC. c Determined by chiral HPLC analysis after derivatization with acetic anhydride. d E = ln[1 - c(1 + ee P)]/ln[1 - c(1 - ee P))], c =
conversion, P = product. nd = not determined due to low conversion.
the amine (S)-3a (>99% ee) was obtained with 23% conversion.
Organoselenium acetophenones 2c–d did not react satisfactorily
under these conditions. From these results, we deduced that the
size of the carbon chain attached to the selenium atom plays an
important role in the reaction. As the size of the carbon chain
increased, no reaction was observed.
DMSO as a co-solvent improved, in some cases, the rate of the
reaction (Table 1, e.g. entry 6 and 8). We also observed that the
amount of the biocatalyst influenced the conversion of the reaction
(Table 1, e.g. entry 14 and 16); thus, the more catalyst, the higher
the conversion.
allylic alkylation.10 Besides, it has been described that selenium-
containing imines11 and tertiary amines11a,12 can also be used as
ligands in palladium-catalyzed reactions.
Inspired by the selenium and nitrogen ability to form palla-
dium chelates, we envisioned novel Se–N derivatives, such as
amines, imines and amides, which can be prepared from 1-(2-
organoseleno-phenyl)ethanamines I (Fig. 1). Each compound can
chelate to palladium, affording six-membered ring chelates, which
can exhibit interesting catalytic potential. Of special interest are
the organoselenium amines I since they are modulable at the N
and Se atoms.
Alternatively to the reductive amination of organosele-
nium acetophenones, we studied the kinetic resolution of the
racemic 1-(organoseleno-phenyl)ethanamines 3a–d, catalyzed by
w-transaminases and sodium pyruvate, to achieve the optically
pure amines 3 (Table 2). In this reaction, the amines 3a–d act as the
amino donor, and pyruvate as the amine acceptor is transformed to
alanine. Thus, w-transaminases can convert one enantiomer from
amine to the corresponding ketone, leaving the other enantiomer
intact. The substrates 3a–d were treated with w-transaminases
ATA-113 and 117 and pyruvate in aqueous solution (Table 2).
As expected, the w-transaminases ATA-117 and ATA-113
showed opposite enantiopreference (Table 2). Thus, by changing
the biocatalyst we can obtain both enantiomers (R)- or (S)-3a–c
with high conversion and ee values (Table 2, entries 1–3 and 6–8).
In several cases the enantioselectivity (E-value) was higher than
200. For example, the kinetic resolution (KR) of the substrate
3d by ATA-113 afforded (R)-3d with 76% ee and 56% conversion
(Table 2, entry 9). ATA-117 showed, for all cases, that the substrate
was transformed with perfect enantioselectivity, while ATA-113
showed varied enantioselectivity depending on the substrate.
Recently, it was reported by Braga et al. that organoselenium
amides can complex to palladium ligands, affording chiral chelates
that exhibited efficient potential as catalysts for asymmetric
Fig. 1 Design of new chiral selenium ligands from a single chiral
precursor.
In order to evaluate our catalytic system, we decided to synthe-
size the organoselenium amine 6 using the same chemoenzymatic
protocol employed for compounds 2a–d and 3a–d (Scheme 2).
Initially, we tried to prepare the chiral organoselenium amine
6 by reductive amination of the ketone 5 using w-transaminases
117, 113, 114 and 103 and alanine as amino donor. However, this
methodology was not efficient to produce the desired selenium
amine 6 (conversion lower than 5%).
Alternatively, w-transaminases 117, 113, 114 and 103 were
used in the KR of amine (RS)-3e (Scheme 2). Fortunately, the
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2043–2051 | 2045
©

View Article Online
Scheme 2 Reagents and conditions: (i) NaNO2, HCl 2 M, pH 4.3, 0 ◦C, then KSeCN, 1 h; (ii) RBr, NaBH4, MeOH, 0 ◦C, 2 h; (iii) a. Ti(OCH(CH3)2)4,
NH3/EtOH (2 M), 12 h; b. NaBH4, 12 h, r.t.; (iv) DMAP, Et3N, acetyl chloride, CH2Cl2; (v) K2CO3, C2H5Br, CH2Cl2; (vi) 2-Cl-benzaldehyde, MgSO4,
CH2Cl2.
KR with w-transaminase 113 furnished excellent results and the
organoselenium amide 3e was obtained in enantiomerically pure
form (>99% ee and 50% conversion). The w-transaminases 117,
114 and 103 were not efficient (conversion lower than 5%, data
not shown).
After finding the appropriate w-transaminase, the KR was
repeated at 120 mg scale to obtain the optically active amine in a
larger quantity. The organoselenium amine (R)-6 was transformed
into amide (R)-7, substituted amine (R)-8 and imine (R)-9 in good
yields as shown in Scheme 2.
After the synthesis of the organoselenium compounds (R)-7–
9, we turned our attention to the investigation of their potential
as chiral ligands in the palladium-catalyzed asymmetric allylic
alkylation. The substitution reaction of 1,3-diphenyl-2-propenyl
acetate 10 with different nucleophiles derived from malonate was
the model reaction employed to evaluate the chiral selenium
compounds as new ligands, Table 3.
As we can see in Table 3, we initiated our investiga-
tion by using all of the organoselenium ligands 7–9, N,O-
bis(trimethylsilyl)acetamide (BisSi)/KOAc as base and CH2Cl2 as
solvent at 0 ◦C (Table 3, entries 1–3). The best result with respect
to yield was obtained with organoselenium amide 7 as ligand, in
which the nucleophile was transferred to the allyl system with high
yield and stereoselectivity (Table 3, entry 1). When organoselenium
amine 8 was used as ligand, no product was observed. However,
the organoselenium imine 9 furnished the substitution product
12 with 87% yield and high enantioselectivity, 82% ee (Table 3,
entry 3).
obtained in a reasonable yield (66%), but in racemic form (Table 3,
entry 6).
In addition, we turned our attention to investigating different
nucleophiles derived from malonate 11 and the ligand 7. The
substitution products 12 were obtained with different levels of
enantioselectivity but in low yield. The best result was obtained
with diethyl phenyl malonate, which furnished >99% of enan-
tiomeric excess (Table 3, entry 9).
It is worth mentioning that the absolute configuration of all
alkylated products was enantiocomplementary to those products
reported by Braga et al., including the results related to diethyl
ethyl malonate and diethyl phenyl malonate (Table 3, entries 8
and 9).10
In summary, we have demonstrated that optically pure
organoselenium-1-phenylethanamines can be obtained by reduc-
tive amination of organoselenium ketones and kinetic resolution
of organoselenium amines using w-transaminases as biocatalysts.
Kinetic resolution showed to be more efficient than the asym-
metric reductive amination. We have applied both methodologies
to prepare novel chiral organoselenium ligands which were
evaluated in the palladium-catalysed asymmetric substitution
of 1,3-diphenyl-2-propenyl acetate with dialkyl malonates. The
substitution products were obtained in high yield (up to 94%)
and enantiomeric excess (up to >99%), which revealed that
the organoselenium amide and organoselenium imine prepared
from chiral 1-(2-(ethylselanyl)phenyl)ethanamine have promising
potential as chiral ligands.
After the evaluation of the ligands, we investigated different
reaction conditions and nucleophiles (Table 3, entries 4–9). For
example, if the reaction was performed at room temperature
using ligand 7 and base BisSi/KOAc, the substitution product
was obtained in good yield (89%) but with low enantioselectivity
(79%). On the other hand, performing the reaction at -20 ◦C,
no product was observed (Table 3, entry 5). By using the ligand
Experimental section
Unless otherwise noted, commercially available materials were
used without further purification. w-Transaminases were com-
mercially available from Codexis, Redwood, USA. All solvents
were HPLC or ACS grade. Solvents used for moisture sensitive
operations were distilled from drying reagents under a nitrogen
atmosphere: THF was distilled from Na/benzophenone, CH2Cl2
was distilled from MgSO4.
3
organoselenium amide 7 (10 mol %), [Pd(h -C3H5)Cl]2 (5 mol %),
NaH as base and THF as solvent, the substitution product 12 was
2046 | Org. Biomol. Chem., 2010, 8, 2043–2051
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
Table 3 Evaluation of novel chiral organoselenium compounds 7–9 as ligands in the palladium-catalyzed asymmetric allylic alkylationa
Entry
Ligand
Base
Solvent
R1
R2
Temp./◦C
Yield (%)b
ee (%)c
1
2
3
4
5
6
7
8
9
7
8
9
7
7
7
7
7
7
BisSi/KOAc
BisSi/KOAc
BisSi/KOAc
BisSi/KOAc
BisSi/KOAc
NaH
BisSi/KOAc
BisSi/KOAc
BisSi/KOAc
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
THF
CH2Cl2
CH2Cl2
CH2Cl2
Me
Me
Me
Me
Me
Me
Me
Et
H
H
H
H
H
H
Me
Et
Ph
0
0
0
r.t.
-20
r.t.
0
0
0
94
—
87
89
—
66
6
89 (S)
—
82 (S)
79 (S)
—
rac.
rac.
11
18
88 (nd)
>99 (nd)
Et
3
a Reaction conditions: [Pd(h -C3H5)Cl]2 (5 mol%), chiral ligand 7–9 (10 mol%), (E)-1,3-diphenylallyl acetate (0.25 mmol), appropriate malonate (dimethyl
malonate, diethyl ethyl malonate or diethyl phenyl malonate, 0.5 mmol), BisSi (N,O-bis(trimethylsilylacetamide, 0.75 mmol), potassium acetate (1 mol%).
b Isolated yield. c Determined by chiral HPLC analysis. nd = not determined.
Analytical thin-layer chromatography (TLC) was performed
by using aluminium-backed silica plates coated with a 0.25 mm
thickness of silica gel 60 F254 (Merck), visualized with an ultraviolet
light (l = 254 nm), followed by exposure to p-anisaldehyde
solution, potassium permanganate solution, or vanillin solution
and heating.
Optical rotations were measured on a Perkin Elmer-343 digital
polarimeter in a 1 mL cuvette with a 1 dm pathlength. All
values are reported in the following format: [a]D(temperature of
measurement) = specific rotation (concentration of the solution
reported in units of 10 mg sample per 1 mL solvent used).
Gas chromatography (GC) analyses for measurement of enan-
tiomeric excesses were obtained using a Shimadzu 17-A Gas
Chromatograph, equipped with autosampler, flame ionization
detector (FID), and a chiral column Varian CP-Chirasil-DEX
CB b-ciclodextrin (25 m ¥ 0.32 mm ¥ 0.25 mm). The temperature
of the detector and injector was 220 ◦C; flow = 100 kPa, H2.
High performance liquid chromatograph (HPLC) analyses
for measurement of enantiomeric excesses were performed on
a Shimadzu, LC-10AD liquid chromatograph equipped with
autosampler and a variable wavelength UV detector (deuterium
Standard chromatographic purification procedures were fol-
lowed using 35–70 mm (240–400 mesh) silica gel purchased from
R
Acros Organicsꢀ.
Nuclear magnetic resonance (NMR) spectra were recorded on a
Bruker DPX spectrometer at operating frequencies of 200, 300 or
500 MHz (1H NMR) and 50, 75 or 125 MHz (13C NMR). The 1H
NMR chemical shifts are reported in ppm relative to TMS peak.
Data are reported as follows: chemical shift (d), multiplicity (s =
singlet, d = doublet, t = triplet, q = quartet, sext = sextuplet, m =
multiplet, br = broadened signal), and coupling constant (J) in
Hertz and integrated intensity. The 13C NMR chemical shifts are
reported in ppm relative to CDCl3.
R
lamp 190–600 nm). Chiral columns: Chiralcelꢀ OJ-H (0.46 cmf ¥
R
R
25 cm), Chiralcelꢀ OD-H (0.46 cmf ¥ 25 cm), Chiralcelꢀ AD-H
R
(0.46 cmf ¥ 25 cm) or Chiralcelꢀ OD (0.46 cmf ¥ 25 cm) from
Infrared spectra were recorded from KBr discs or from a thin
film between NaCl plates on a Bomem Michelson model 101 FTIR
Daicel Chemical Ind. i-PrOH and hexane (60% n-hexane) HPLC
grade purchased from J. T. Baker were used as the eluting solvents.
spectrometer with internal referencing. Absorption maxima (nmax
)
are reported in wavenumbers (cm-1).
General procedure for synthesis of
1-((selenocyanate)phenyl)ethanones
Low-resolution mass spectra were obtained on a GC-MS
Shimadzu spectrometer, operating at 70 eV. High-resolution
mass spectra (HRMS) were acquired using a Bruker Daltonics
MicroTOF instrument, operating electrospray ionization (ESI)
mode.
To an Erlenmeyer flask, para or ortho-aminoacetophenone (3.51 g,
26 mmol) and an aqueous HCl solution (50 mL, 2 M) were added.
The solution was cooled to 0 ◦C and a water solution of NaNO2
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2043–2051 | 2047
©

View Article Online
(24 mmol, 12 mL, 2 M) was added dropwise. At 0 ◦C, sodium
acetate (8 g, 60 mmol) was added, followed by the addition of
acetate buffer solution until pH 4.3. The KSeCN (5 g, 35 mmol)
was then added under vigorous agitation and the solution was
kept at 0 ◦C for 1 h. Sodium acetate was added until pH 5.5. The
resulting solution was extracted with CH2Cl2 (3 ¥ 30 mL). The
combined organic phases were dried over MgSO4. The solvent was
removed in vacuum and the residue purified by silica gel column
chromatography, using a mixture of hexane and ethyl acetate (4 : 1)
as solvent. The solvent was removed to give the selenocyanate
acetophenone 1.
d: 7.84-7.79 (m, 2H), 7.49-7.45 (m, 2H), 3.01 (quart., J = 7.5 Hz,
2H), 2.57 (s, 3H), 1.48 (t, J = 7.5 Hz, 3H). 13C NMR (50 MHz) d:
196.72, 138.19, 134.15, 129.57, 128.03, 25.77, 19.79, 14.45. LRMS
[EI], m/z (relative abundance): 228 (M+, 84), 213 (100), 209 (18),
185 (44), 181 (26), 156 (17), 105 (18), 91 (11), 77 (22), 63 (12),
43 (86). HRMS [ESI(+)], calcd for [C10H12OSe + H]+: 229.0131,
found 229.0131; (M + Na)+; for [C10H12OSe + Na]: 250.9951, found
250.9946.
1-(4-(Butylselanyl)phenyl)ethanone (2c). Yield: 75%. IR (KBr)
cm-1: 2959, 2930, 1680, 1588, 1395, 1358, 1268, 1183, 1083, 956,
817, 606, 590, 458. NMR 1H (200 MHz, CDCl3) d: 7.83-7.79 (m,
2H), 7.49-7.27 (m, 2H), 2.99 (t, J = 6.2 Hz, 2H), 2.57 (s, 3H), 1.80-
1.66 (m, 2H), 1.54-1.36 (m, 2H), 0.93 (t, J = 7.02 Hz, 3H). NMR
13C (50 MHz) d: 197.37, 139.21, 134.72, 130.13, 128.65, 31.85,
26.62, 26.41, 22.94, 13.49. LRMS [EI], m/z (relative abundance):
256 (M+, 58), 241 (13), 200 (37), 185 (70), 154 (8), 77 (17), 57 (54),
43 (100). HRMS [ESI(+)], calcd for [C12H16OSe + H]+: 257.0445,
found 257.0444.
1-((4-Selenocyanate)phenyl)ethanone (1). Yield: 65%. IR
(KBr) cm-1: 3434, 3342, 2964, 2920, 2151, 1685, 1586, 1394, 1360,
1266, 1185, 960, 816, 587, 520, 464. 1H NMR (200 MHz, CDCl3)
d: 7.99-7.95 (m, 2H), 7.73-7.68 (m, 2H), 2.62 (s, 3H). 13C NMR
(50 MHz) d: 196.99, 137.73, 132.88, 129.40, 128.55, 100.62, 26.84.
LRMS [EI], m/z (relative abundance): 225 (M+, 50), 210 (100), 208
(71), 182 (47), 180 (23), 76 (31), 63 (19), 43 (82). HRMS [ESI(+)],
calcd for [C9H7NOSe + Na]+: 247.9591, found 247.9586.
1-(4-(Benzylselanyl)phenyl)ethanone (2d). Yield: 71%. IR
(KBr) cm-1: 3335, 3064, 2998, 1968, 1891, 1809, 1676, 1585,
1-((2-Selenocyanate)phenyl)ethanone. Yield: 60%. IR (KBr)
cm-1: 3439, 3072, 2994, 2144, 1645, 1582, 1555, 1430, 1363, 1300,
1280, 1265, 1026, 962, 703, 603, 481. 1H NMR (500 MHz, CDCl3)
d: 8.11-8.08 (m, 2H), 7.65-7.61 (m 1H), 7.53-7.50 (m, 1H), 2,70
(s 3H). 13C NMR (125 MHz) d: 199.90, 134.75, 132.74, 132.13,
131.56, 130.68, 127.71, 106.77, 25.75. LRMS [EI], m/z (relative
abundance): 225 (M+, 37), 210 (53), 208 (26), 182 (18), 180 (8), 43
(100). HRMS [ESI(+)], calcd for [C9H7NOSe + Na]+: 247.9591,
found 247.9584.
1
1359, 1278, 1181, 1060, 955, 811, 766, 696, 585, 459. NMR H
(200 MHz, CDCl3) d: 7.81-7.77 (m, 2H), 7.49-7.45 (m, 2H), 7.26
(s, 5H), 4.20 (s, 2H), 2.56 (s, 3H). NMR 13C (50 Hz) d: 197.42,
138.60, 137.51, 135.28, 131.28, 128.83, 128.65, 128.57, 127.18,
31.31, 26.45. LRMS [EI], m/z (relative abundance): 290 (M+, 4),
199 (1), 154 (1), 91 (100), 75 (1), 65 (11), 41 (1). HRMS [ESI(+)],
calcd for [C15H14OSe + H]+: 291.0289, found 291.0288; (M + Na)+;
calcd for [C15H14OSe + Na]+: 313.0108, found 313.0112.
1-(2-(Ethylselanyl)phenyl)ethanone (5). Yield: 65%. IR (KBr)
cm-1: 2960, 2923, 2850, 1665, 1585, 1455, 1431, 1359, 1251, 1038,
956, 753, 599, 468. 1H NMR (300 MHz, CDCl3) d: 7.91 (dd, J =
7.5 Hz, J = 1.5 Hz, 1H), 7.51-7.48 (m, 1H), 7.44-7.38 (m, 1H),
7.27-7.22 (m, 1H), 2.86 (quart., J = 7.5 Hz, 2H), 2.63 (s, 3H), 1.47
(t, J = 7.5 Hz, 3H). 13C NMR (75 MHz) d: 198.80, 138.24, 135.36,
132.30, 131.78, 128.26, 124.23, 27.52, 18.49, 13.65. LRMS [EI],
m/z (relative abundance): 228 (M+, 19), 199 (100), 182 (5),157
(9), 91 (40), 77 (17), 51 (10),43 (62). HRMS [ESI(+)], calcd for
[C10H12OSe + H]+: 229.0131, found 229.0124; (M + Na)+; calcd
for [C10H12OSe + Na]: 250.9951, found 250.9952.
General procedure for synthesis of
1-((alkylselanyl)phenyl)ethanones (2a–d and 5)
To a two necked round-bottomed flask under N2, selenocyanate
acetophenones 1 (225 mg, 1 mmol) and methanol (5 mL) were
added. The solution was cooled to 0 ◦C and alkyl halide (MeI,
EtBr, BuBr or BnBr, 4 mmol) was added, followed by the slow
addition of NaBH4 (42 mg, 1.1 mmol). The solution was stirred for
2 h at 0 ◦C. The solvent was removed in vacuum and the residue was
diluted in ethyl acetate (3 mL) followed by addition of saturated
aqueous solution of NH4Cl (3 mL). After phase separation, the
aqueous phase was extracted with ethyl acetate (2 ¥ 3 mL). The
combined organic phases were dried over MgSO4. The solvent was
removed in vacuum and the residue purified by silica gel column
chromatography, using a mixture of hexane and ethyl acetate (4 : 1)
as solvent. The solvent was removed to give the organoselenium
acetophenones 2a–d and 5.
General procedure for synthesis of
(RS)-1-((ethylselanyl)phenyl)ethanamines (3a–d and 6)
To a two necked round-bottomed flask under N2, alkylselenium
acetophenones 2a–d and 5 (1 mmol), titanium(IV) isopropoxide
(0.6 mL, 2 mmol) and a solution of NH3 in ethanol (5 mmol,
2.5 mL, 2 M) were added. The solution was stirred at room
temperature for 12 h. After this period, NaBH4 (57 mg, 1.5 mmol)
was added and the resulting solution was stirred for an additional
12 h. Finally, the reaction was quenched with aqueous ammonia
solution (2.5 mL, 2 M) and the resulting mixture was filtered
off under vacuum. The remaining solid was washed with ethyl
acetate (2 ¥ 3 mL). The phases were separated and the aqueous
phase was extracted with ethyl acetate (3 ¥ 3 mL). The organic
phases were combined and then extracted with an aqueous HCl
solution (3 ¥ 3 mL, 1 M). Saturated aqueous NaOH solution
was added to the resulting acidic aqueous phase until pH 10
and it was then extracted with ethyl acetate (4 ¥ 5 mL). The
1-(4-(Methylselanyl)phenyl)ethanone (2a). Yield: 53%. IR
(KBr) cm-1: 2999, 1669, 1587, 1396, 1353, 1279, 1268, 1189, 1084,
814, 591, 494, 456, 426. NMR 1H (200 MHz, CDCl3) d: 7.83-7.79
(m, 2H), 7.43-7.38 (m, 2H), 2.56 (s, 3H), 2.40 (s, 3H). NMR 13C
(50 MHz) d: 197.32, 140.10, 134.44, 128.64, 128.59, 26.36, 6.36.
LRMS [EI], m/z (relative abundance): 214 (M+, 70), 199 (100), 184
(25), 171 (16), 104 (5), 91 (74), 76 (17), 43 (67). HRMS [ESI(+)],
calcd for [C9H10OSe + H]+: 214.1431, found 214.9978.
1-(4-(Ethylselanyl)phenyl)ethanone (2b). Yield: 63%. IR (KBr)
cm-1: 3438, 2966, 2929, 2870, 1677, 1586, 1393, 1357, 1269, 1234,
1182, 1083, 858, 812, 605, 588, 458. 1H NMR (200 MHz, CDCl3)
2048 | Org. Biomol. Chem., 2010, 8, 2043–2051
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
combined organic phases were washed once with brine (3 mL)
and dried over MgSO4. The solvent was removed in vacuum to
give the (RS)-organoselenium amines 3a–d and 6 in a pure form.
These compounds were employed directly in the enzymatic kinetic
resolution.
[ESI(+)], calcd for [C10H15NSe–NH2]+: 213.0182, found 213.0170;
calcd for [C10H15NSe + H]+: 230.0448, found 230.0441.
General procedure for synthesis of
N-(1-((alkylselanyl)phenyl)ethyl)acetamides (4a–d and 7)
To a Schlenck flask, organoselenium amines 3a–d and 6 (50 mg,
0.22 mmol), CH2Cl2 (1 mL), acetic anhydride (62 mL, 0.66 mmol)
and triethylamine (62 mL, 0.44 mmol) were added. The resulting
solution was stirred for 1 h at 50 ◦C. After this period, the reaction
mixture was diluted with CH2Cl2 (5 mL) and the resulting solution
was then washed with an aqueous HCl solution (2 ¥ 2 mL, 1
M). The organic phase was washed with brine (2 mL), dried
over MgSO4 and the solvent was removed in vacuum to give
organoselenium amides 4a–d and 7.
(RS)-1-(4-(Methylselanyl)phenyl)ethanamine (3a). Yield: 73%.
IR (KBr) cm-1: 3357, 2966, 1615, 1582, 1454, 1370, 1272, 1098,
1
1072, 1012, 904, 817, 722, 539. NMR H (200 MHz, CDCl3) d:
7.39-7.35 (m, 2H), 7.24-7.20 (m, 2H), 4.06 (quart., J = 6.6 Hz,
1H), 2.32 (s, 3H), 1.71 (s, 2H), 1.35 (d, J = 6.6 Hz, 3H). NMR
13C (50 MHz) d: 145.67, 130.51, 129.54, 126.31, 50.69, 25.41, 7.20.
LRMS [EI], m/z (relative abundance): 215 (M+, 22), 200 (100), 185
(39), 154 (3), 120 (13), 104 (22), 91 (17), 78 (22), 42 (32). HRMS
[ESI(+)], calcd for [C9H13NSe–NH2]+: 199.0025, found 199.0021.
(RS)-N-(1-(4-(Methylselanyl)phenyl)ethyl)acetamide
(4a).
(RS)-1-(4-(Ethylselanyl)phenyl)ethanamine (3b). Yield: 73%.
IR (KBr) cm-1: 3359, 3286, 3070, 2961, 2923, 2866, 1591, 1492,
1447, 1372, 1230, 1014, 822, 770, 541. 1H NMR (200 MHz, CDCl3)
d: 7.47-7.42 (m, 2H), 7.26-7.22 (m, 2H), 4.08 (quart., J = 6.5 Hz,
1H), 2.89 (quart., J = 7.5 Hz, 2H), 1.81 (s, 2H), 1.42 (t, J =
7.0 Hz, 3H), 1.37 (d, J = 6.6 Hz, 3H). 13C NMR (50 MHz) d:
146.52, 133.22, 128.42, 126.67, 51.15, 25.74, 21.66, 15.72. LRMS
[EI], m/z (relative abundance): 229 (M+, 27), 214 (100), 185 (39),
120 (20), 104 (21), 78 (33), 42 (42). HRMS [ESI(+)], calcd for
[C10H15NSe–NH2]+: 213.0182, found 213.0174.
Yield: 93%. IR (KBr) cm-1: 3282, 1640, 1546, 1367, 1120, 1010,
817, 740, 612, 586, 530. NMR 1H (300 MHz, CDCl3) d: 7.39-7.36
(m, 2H), 7.27-7.18 (m, 2H), 6.05 (s, 1H), 5.09-5.04 (m, 1H), 2.34
(s, 3H), 1.96 (s, 3H), 1.45 (d, J = 6.0 Hz, 3H). NMR 13C (75 MHz)
d: 169.21, 141.38, 130.70, 130.62, 126.93, 48.39, 23.36, 21.66,
7.34. LRMS [EI], m/z (relative abundance): 257 (M+, 40), 242
(21), 200 (82), 181(8), 120 (25), 104 (30), 91 (17), 77 (20), 43 (100).
HRMS [ESI(+)], calcd for [C11H15NOSe + Na]+: 280.0217, found
280.0216; (M + K)+; calcd for [C11H15NOSe + K]+: 295.9956,
found 295.9967.
(RS)-1-(4-(Butylselanyl)phenyl)ethanamine (3c). Yield: 19%.
IR (KBr) cm-1: 3357, 3287, 2959, 2929, 2871, 1592, 1492, 1463,
1371, 1202, 1014, 821, 721, 541. NMR 1H (200 MHz, CDCl3) d:
7.35-7.31 (m, 2H), 7.13-7.09 (m, 2H), 3.95 (quart., J = 6.6 Hz,
1H), 2.78 (t, J = 7.5 Hz, 2H), 1.83 (s, 2H), 1.65-1.50 (m, 2H),
1.40-1.23 (m, 5H), 0.79 (t, J = 7.5 Hz, 3H). NMR 13C (50 MHz) d:
145.70, 133.88, 132.28, 128.29, 126.11, 50.52, 31.87, 27.33, 25.15,
22.56, 13.23. LRMS [EI], m/z (relative abundance): 257 (M+, 21),
242 (100), 200 (6), 185 (24), 120 (22), 106 (21), 91 (10), 78 (29),
42 (40). HRMS [ESI(+)], calcd for [C12H19NSe–NH2]+: 241.0496,
found 241.0493.
(RS)-N-(1-(4-(Ethylselanyl)phenyl)ethyl)acetamide
(4b).
Yield: 97%. IR (KBr) cm-1: 3314, 3075, 2971, 2927, 2867, 2822,
1646, 1545, 1374, 1137, 816, 724, 535. 1H NMR (300 MHz,
CDCl3) d: 7.46-7.43 (m, 2H), 7.26-7.19 (m, 2H), 5.98 (s, 1H), 5.08
(quart., J = 7.2 Hz, 1H), 2.90 (quart., J = 7.0 Hz, 2H), 2.01 (s,
3H), 1.47 (d, J = 7.0 Hz, 3H), 1.42 (t, J = 7.2 Hz, 3H). 13C NMR
(75 MHz) d: 169.38, 141.70, 132.84, 129.25, 126.91, 48.60, 23.31,
21.62, 21.43, 15.51. LRMS [EI], m/z (relative abundance): 271
(M+, 61), 253 (39), 214 (99), 181 (18), 156 (14), 120 (45), 104 (33),
78 (26), 43 (100). HRMS [ESI(+)], calcd for [C12H17NOSe + H]+:
272.0554, found 272.0556.
(RS)-1-(4-(Benzylselanyl)phenyl)ethanamine (3d). Yield: 21%.
(RS)-N-(1-(4-(Butylselanyl)phenyl)ethyl)acetamide
(4c).
IR (KBr) cm-1: 3376, 3027, 2970, 1597, 1579, 1561, 1494, 1470,
Yield: 90%. IR (KBr) cm-1: 3278, 2960, 2930, 1650, 1549, 1494,
1454, 1372, 1294, 1136, 1014, 822, 540. NMR 1H (300 MHz,
CDCl3) d: 7.45-7.42 (m, 2H), 7.26-7.18 (m, 2H), 5.83 (s, 1H),
5.11-5.07 (m, 1H), 2.89 (t, J = 4.5 Hz, 2H), 1.97 (s, 3H), 1.71-1.65
(m, 2H), 1.47-1.39 (m,5H), 0.90 (t, J = 4.5 Hz, 3H). NMR
13C (75 MHz) d: 169.14, 141.73, 132.63, 129.57, 126.88, 48.41,
32.24, 27.70, 23.43, 22.95, 21.63, 13.56. LRMS [EI], m/z (relative
abundance): 299 (M+, 25), 281 (45), 242 (38), 207 (89), 184 (24), 133
(19), 120 (32), 104 (25), 96 (21), 73 (37), 43 (100). HRMS [ESI(+)],
calcd for [C14H21NOSe + Na]+: 322.0686, found 322.0688.
1
1453, 1361, 1324, 1268, 1011, 814, 759, 696, 535, 465. NMR H
(200 MHz, CDCl3) d: 7.26-7.22 (m, 2H), 7.04-7.02 (m, 7H), 3.90-
3.82 (m, 3H), 1.34 (s, 2H), 1.17 (d, J = 8.0 Hz, 3H). NMR 13C
(50 MHz) d: 146.62, 138.21, 133.20, 128.38, 127.93, 126.34, 126.00,
50.39, 31.79, 25.31. LRMS [EI], m/z (relative abundance): 291
(M+, 6), 276 (16), 200 (2), 120 (6), 104 (4), 91 (100), 78 (8), 65 (17),
42 (13). HRMS [ESI(+)], calcd for [C15H17NSe–NH2]+: 275.0339,
found 275.0324.
(RS)-1-(2-(Ethylselanyl)phenyl)ethanamine (6). Yield: 63%.
IR (KBr) cm-1: 3357, 3287, 3055, 2962, 2923, 2866, 1660, 1585,
1447, 1371, 1230, 1032, 755, 663, 598, 549, 462. 1H NMR
(300 MHz, CDCl3) d: 7.51-7.44 (m, 2H), 7.29-7.23 (m, 1H), 7.18-
7.12 (m, 1H), 4.59 (quart., J = 6.6 Hz,1H), 2.91 (quart., J =
5.7 Hz, 2H), 2.21 (s, 2H), 1.43 (t, J = 7.5 Hz, 3H), 1.39 (d,
J = 7.2 Hz, 3H). 13C NMR (75 MHz) d: 148.02, 132.38, 129.84,
127.42, 127.29, 125.28, 48.86, 24.34, 21.46, 15.20. LRMS [EI], m/z
(relative abundance): 229 (M+, 22), 214 (12), 200 (52), 183 (55), 157
(6), 119 (46), 104 (85), 91 (29), 77 (42), 51 (24), 44 (100). HRMS
(RS)-N-(1-(4-(Benzylselanyl)phenyl)ethyl)acetamide
(4d).
Yield: 92%. IR (KBr) cm-1: 3449, 3342, 2971, 2929, 1646, 1538,
1
1494, 1370, 1138, 819, 697, 539, 463, 425. NMR H (300 MHz,
CDCl3) d: 7.43-7.39 (m, 2H), 7.28-7.19 (m, 7H), 5.68 (s, 1H),
5.12-5.07 (m, 1H), 4.09 (s, 2H), 1.98 (s, 3H), 1.46 (d, J = 6.0 Hz,
3H). NMR 13C (75 MHz) d: 169.07, 142.40, 138.47, 133.65,
129.39, 128.83, 128.44, 126.88, 126.84, 48.38, 32.24, 23.46, 21.65.
LRMS [EI], m/z (relative abundance): 333 (M+, 29), 318 (1), 274
(4) 200 (4) 120 (3) 91 (100), 65 (5), 43 (4). HRMS [ESI(+)], calcd
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2043–2051 | 2049
©

View Article Online
for [C17H19NOSe + Na]+: 356.0530, found 356.0521; (M + K)+;
calcd for [C17H19NOSe + K]+: 372.0269, found 372.0266.
with w-transaminase (10 mg, ATA-113 or ATA-117). The reaction
mixture contained 50 mM of the corresponding amine 3 and
6 (Schemes 1 and 2). The conversion to ketone 2 and 5 was
followed by GC chromatography. The reaction was stopped by
adding aqueous NaOH (200 mL, 10 N), followed by extraction
with ethyl acetate (600 mL, twice). The combined organic phase
was dried (Na2SO4) before being analysed. Results are summarized
in Table 2.
(RS)-N-(1-(2-(Ethylselanyl)phenyl)ethyl)acetamide (7). Yield:
90%. IR (KBr) cm-1: 3432, 3272, 3079, 2965, 2923, 2856, 1646,
1558, 1443, 1373, 1305, 1033, 752, 512, 458. 1H NMR (300 MHz,
CDCl3) d: 7.52 (dd, J = 4.5 Hz, J = 0.6 Hz, 1H), 7.32 (dd, J =
4.5 Hz, J = 0.6 Hz, 1H), 7.27-7.23 (m, 1H), 7.19-7.16 (m, 1H), 6.36
(s, 1H), 5.46 (quart., J = 4.2 Hz, 1H), 2.94 (quart., J = 4.2 Hz,
2H), 2.02 (s, 3H), 1.49 (d, J = 4.2 Hz, 3H), 1.42 (t, J = 4.2 Hz,
3H). 13C NMR (75 MHz) d: 169.38, 144.68, 134.09, 130.22, 127.91,
127.54, 126.05, 49.68, 29.71, 22.13, 21.85, 15.29. LRMS [EI], m/z
(relative abundance): 271 (M+, 3), 228 (12), 183 (18), 162 (100),
120 (29), 104 (15), 77 (12), 43 (28). HRMS [ESI(+)], calcd for
[C12H17NOSe + H]+: 272.0554, found 272.0552.
Determination of the absolute configuration of the organoselenium
amines 3–6 and amides 4–7
The absolute configurations of the organoselenium amides 4 were
assigned by chromatographic comparison with standard samples
of (R)- and (S)-N-(1-phenylethyl)acetamide after removing the
organoselenium group from 4 with n-butyllithium according to
the procedure above.
General procedure for determination of the enantiomeric excess
To a two necked round-bottomed flask, the chiral organose-
lenium amides 4 (68 mg, 0.25 mmol), THF (10 mL) and n-
butyllithium (3.3 mmol)◦ at 0 ◦C were added, under N2. The
solution was stirred at 0 C for 2 h and, finally, the reaction was
quenched with brine (10 mL). The organic layer was separated and
the aqueous phase was extracted with ethyl ether (4 ¥ 3 mL). The
combined organic phases were washed once with brine (3 mL) and
dried over MgSO4. The solvent was removed in vacuum and the
product was readily analyzed by chiral GC and compared with
authentic samples of (R)- and (S)-N-(1-phenylethyl)acetamide.
GC conditions: injector 220 ◦◦C; detector: 220 ◦C; pressure: 100
kPa; column temperature: 70 C, 3 ◦C min-1 up to 180 ◦C. Reten-
tion times for (RS)-N-(1-phenylethyl)acetamide: (R) = 25.06 min,
(S) = 24.21 min.
(ee) by HPLC analysis
The enantiomeric purities of the organoselenium amides 4 were
measured by HPLC analysis. The analysis was carried out
on Chiralcel OD-H column and the peaks detected by a UV
detector at 254 nm. Eluent: hexane–isopropanol (95 : 5), flow rate:
1.0 mL min-1. Retention times:
(RS)-N-(1-(4-(methylselanyl)phenyl)ethyl)acetamide (4a): (R)-
4a = 25.11 min; (S)-4a = 31.68 min.
(RS)-N-(1-(4-(ethylselanyl)phenyl)ethyl)acetamide (4b): (R)-
4b = 20.44 min; (S)-4b = 24.93 min.
(RS)-N-(1-(4-(butylselanyl)phenyl)ethyl)acetamide (4c): (R)-
4c = 17.56 min; (S)-4c = 20.87 min.
(RS)-N-(1-(4-(benzylselanyl)phenyl)ethyl)acetamide (4d): (R)-
4d = 56.46 min; (S)-4d = 63.76 min.
Synthesis of (R)-N-(1-(2-(ethylselanyl)phenyl)ethyl)acetamide
(RS)-N-(1-(2-(ethylselanyl)phenyl)ethyl)acetamide (7): (R)-7 =
16.92 min; (S)-7 = 44.46 min.
(7). Yield: 90%. To
a Schlenck flask under N2, (R)-
organoselenium amine 6 (50 mg, 0.22 mmol), CH2Cl2 (1 mL),
acetyl chloride (0.66 mmol), triethylamine (0.44 mmol) and
DMAP (1 mol%) were added. The resulting solution was stirred
for 24 h at 40 ◦C. After this period, the reaction mixture was
diluted with CH2Cl2 (5 mL) and the resulting solution was then
washed with an aqueous HCl solution (2 ¥ 2 mL, 1 M). The
organic phase was washed with NaHCO3 aqueous solution (2 mL,
saturated), dried over MgSO4, and the solvent was removed in
vacuum to give organoselenium amide 7. The spectroscopy data
were equivalent to those reported above for the compound (RS)-
N-(1-(2-(ethylselanyl)phenyl)ethyl)acetamide. [a]2D5 +21.7 (c 0.50;
EtOAc).
General procedure for stereoselective amination of organoselenium
acetophenone 2 and 5 catalyzed by x-transaminases
All biocatalytic reactions were performed at 30 ◦C for 24 h
in sodium phosphate buffer (100 mM, pH 7) with pyridoxal-
5¢-phosphate (1 mM) in 2 mL eppendorf tubes. The reaction
buffer (1 mL) containing DMSO (Table 1) was mixed with w-
transaminase (ATA-113, ATA-114, ATA-117 or ATA-103), L- or
D-alanine (250 mM), pyruvate reductase mix (LDH is a mixture
of lactate dehydrogenase, glucose dehydrogenase, glucose, NAD+,
40 mg), and DMSO (150 mL). The reaction mixture contained
50 mM of the corresponding organoselenium acetophenones 2
and 5 (Schemes 1 and 2). The conversion to amines 3 and 6 was
followed by GC chromatography. The reaction was stopped by
adding aqueous NaOH (200 mL, 10 N), followed by extraction with
ethyl acetate (600 mL, twice). The combined organic phase was
dried (Na2SO4) and analysed. Results are summarized in Table 1.
Synthesis
of
(R)-N,N-diethyl-1-(2-(ethylselanyl)phenyl)-
ethanamine (8). To a Schlenck flask under N2, (R)-organosele-
nium amine 6 (0.13 mmol) and ethanol (0.14 mL) were added.
Then, the ethyl bromide was added (0.78 mmol) together with
K2CO3 (0.26 mmol). The resulting solution was stirred for 24 h
at 70 ◦C. After this period, the reaction mixture was diluted with
ethanol (1 mL) and the resulting solution was filtered off. After
that, the solvent was removed in vacuum and the residue purified
by silica gel column chromatography, using a mixture of hexane
and ethyl acetate (4 : 1) as solvent. The solvent was removed to
give (R)-N,N-diethyl-1-(2-(ethylselanyl)phenyl)ethanamine 8.
[a]2D0 +18.5 (c 1.7; CH2Cl2). Yield: 48%. IR (KBr) cm-1: 3056,
General procedure for kinetic resolution of organoselenium amines
3 and 6 catalyzed by x-transaminases
All biocatalytic reactions were performed at 30 ◦C for 24 h in
sodium phosphate buffer (100 mM, pH 7) with pyridoxal-5¢-
phosphate (1 mM) in 2 mL eppendorf tubes. The reaction buffer
(1 mL) containing sodium pyruvate 50 mM (1 equiv.) was mixed
1
2967, 2926, 1728, 1462, 1274, 757. NMR H (200 MHz, CDCl3)
2050 | Org. Biomol. Chem., 2010, 8, 2043–2051
This journal is
The Royal Society of Chemistry 2010
©

View Article Online
d: 7.42-7.38 (m, 2H), 7.17-7.14 (m, 2H), 4.12 (quart., J = 6.58 Hz,
1H), 2.91-2.84 (m, 2H), 2.60-2.56 (m, 4H), 1.46-1.27 (m, 6H),
1.00-0.93 (m, 6H). NMR 13C (50 MHz, CDCl3) d: 130.44, 127.90,
127.14, 126.88, 125.81, 59.18, 42.80, 20.31, 16.93, 11.98. LRMS
[EI], m/z (relative abundance): 285 (M, 16), 270 (67), 256 (83),
213 (33), 185 (21), 100 (100), 72 (49). HRMS [ESI(+)], calcd for
[C14H23NSe + H]+: 286.1074, found 286.1068.
(E)-Diethyl 2-(1,3-diphenylallyl)-2-phenylmalonate. Separa-
tion of enantiomers by HPLC analysis (Daicel Chiralcel AD-H
column; solvent, 99 : 1 hexane–isopropanol; flow rate 0.5 ml min-1;
254 nm detection). Retention times: (R or S) = 17.34 min; (R or
S) = 18.41 min.
Acknowledgements
Synthesis of (R)-N-(2-chlorobenzylidene)-1-(2-(ethylselanyl)-
phenyl)ethanamine (9). To a Schlenck flask under N2, (R)-
organoselenium amine 6 (48 mg, 0.2 mmol) and CH2Cl2 (0.2 mL)
were added. Then, the ortho-chlorobenzaldehyde (0.2 mmol) was
added together with MgSO4 (0.04 mg). The resulting solution was
We thank CNPq, CAPES, FAPESP, Province of Stryria, Codexis
and FFG for financial support.
References
◦
1 C. J. Lo¨wig, Pogg. Ann., 1836, 37, 552.
stirred for 24 h at 40 C. After this period, the reaction mixture
2 (a) S. L. Schreiber and C. Santini, J. Am. Chem. Soc., 1984, 106, 4038;
(b) T. Wirth, Angew. Chem., Int. Ed., 2000, 39, 3740; (c) M. Tiecco, L.
Testaferri, L. Bagnoli, F. Marini, C. Santi, A. Temperini, C. Scarponi,
S. Sternativo, R. Terlizzi and C. Tomassini, Arkivoc, 2006, 7, 186.
3 (a) G. Mugesh and H. B. Singh, Chem. Soc. Rev., 2000, 29, 347; (b) C. W.
Nogueira, G. Zeni and J. B. T. Rocha, Chem. Rev., 2004, 104, 6255.
4 (a) D. M. Browne and T. Wirth, Curr. Org. Chem., 2006, 10, 1893;
(b) A. L. Braga, D. S. Lu¨dtke, F. Vargas and R. C. Braga, Synlett, 2006,
1453; (c) A. L. Braga, D. S. Lu¨dtke and F. Vargas, Curr. Org. Chem.,
2006, 10, 1921; (d) T. Wirth, C. Santi, S. A. Shahzad, S. Santoro and
D. M. Freudendahl, Angew. Chem., Int. Ed., 2009, 48, 8409.
5 (a) Y. Nishibayashi, J. D. Singh, S. Segawa, S. Fukuzawa and S. Uemura,
J. Chem. Soc., Chem. Commun., 1994, 1375; (b) Y. Nishibayashi,
S. Segawa, J. D. Singh, S. Fukuzawa, K. Ohe and S. Uemura,
Organometallics, 1996, 15, 370; (c) E. M. McGarrigle, E. L. Myers, O.
IIIa, M. A. Shaw, S. L. Riches and V. K. Aggarwal, Chem. Rev., 2007,
107, 5841; (d) T. Wirth, Tetrahedron Lett., 1995, 36, 7849; (e) T. Wirth,
K. J. Kulicke and G. Fragale, Helv. Chim. Acta, 1996, 79, 1957; (f) A. L.
Braga, F. Vargas, J. A. Sehnem and L. A. Wessjohann, Eur. J. Org.
Chem., 2006, 22, 4993; (g) F. Vargas, J. A. Sehnem, F. Z. Galetto and
A. L. Braga, Tetrahedron, 2008, 64, 392; (h) A. L. Braga, V. Nascimento,
P. Milani and J. A. Sehnem, Synthesis, 2008, 1262; (i) X-L. Hou, X-W.
Wu, L-X. Dai, B-X. Cao and J. Sun, Chem. Commun., 2000, 1195.
6 (a) C. Zhu and Y. Huang, Curr. Org. Chem., 2006, 10, 1905; (b) T. Wirth
and G. Fragale, Chem.–Eur. J., 1997, 3, 1894.
was diluted with CH2Cl2 (1 mL) and the resulting solution was
filtered off. After that, the solvent was removed in vacuum to give
the (R)-organoselenium imine 9.
[a]2D0 -76.9 (c 0.9; CH2Cl2). Yield: 99%. IR (KBr) cm-1: 3057,
2967, 2923, 1635, 1467, 1440, 1051, 1033, 755. NMR 1H (200 MHz,
CDCl3) d: 8.85 (s, 1H), 8.14-8.12 (m, 1H), 7.74-7.70 (m, 1H),
7.51-7.15 (m, 6H) 5.16 (quart., J = 6.58 Hz, 1H), 2.91 (quart.,
J = 7.46 Hz, 2H), 1.56 (d, J = 6.58 Hz, 3H), 1.47-1.39 (m, 3H).
NMR 13C (50 MHz, CDCl3) d: 156.63, 146.23, 135.13, 133.43,
132.56, 131.38, 129.64, 128.56, 127.85, 127.31, 127.20, 126.89,
68.19, 24.63, 21.66, 15.19. LRMS [EI], m/z (relative abundance):
351 (M, 2), 322 (100), 185 (18), 183 (76), 140 (54), 104 (39). HRMS
[ESI(+)], calcd for [C17H18ClNSe + H]+: 352.0371, found 352.0365;
calcd for [C17H18ClNSe + Na]+: 374.0191, found 374.0183.
General procedure for asymmetric allylic alkylation catalysed by
palladium
To a two necked round-bottomed flask under N2, a solution
3
containing [Pd(h -C3H5)Cl]2 (0.0125 mmol, 5 mol%) and the
7 (a) J. V. Comasseto, C. E. Da Costa, I. H. S. Crusius, L. H. Andrade
and A. L. M. Porto, J. Mol. Catal. B: Enzym., 2007, 45, 135; (b) J. V.
Comasseto, L. H. Andrade, A. T. Omori, L. F. Assis and A. L. M. Porto,
Tetrahedron: Asymmetry, 2007, 18, 1048; (c) J. V. Comasseto, G. C.
Clososki, C. E. Costa, L. J. Missio and Q. B. Cass, Synth. Commun.,
2004, 34, 817; (d) J. V. Comasseto, C. E. Da Costa, G. C. Closoki,
H. B. Barchesi, S. P. Zanotto and M. G. Nascimento, Tetrahedron:
Asymmetry, 2004, 15, 3945; (e) J. V. Comasseto and R. A. Gariani,
Tetrahedron, 2009, 65, 8447.
chiral ligand 7, 8 or 9 (0.025 mmol or 10 mol%) in CH2Cl2
(1 mL) were stirred for 1 h. Then, a solution of (E)-1,3-
diphenylallyl acetate (0.25 mmol) in CH2Cl2 (2 mL) was added.
The resulting solution was stirred for 30 min followed by addi-
tion of appropriate malonate (dimethyl malonate, diethyl ethyl
malonate or diethyl phenyl malonate, 0.5 mmol), BisSi (N,O-
bis(trimethylsilylacetamide) (0.75 mmol) and potassium acetate
(1 mol%). The resulting solution was stirred for 48 h at the
appropriate time (Table 3). After this period, NH4Cl aqueous
solution (3 mL, saturated) was added, and then the reaction media
was extracted with CH2Cl2 (3 ¥ 5 mL). The organic layer was dried
with MgSO4, the solvent was removed in vacuum and the residue
purified by silica gel column chromatography, using a mixture
of hexane and ethyl acetate (9 : 1) as solvent. After removing the
solvent, the product was readily analyzed by HPLC.
8 (a) L. H. Andrade and A. V. Silva, Tetrahedron: Asymmetry, 2008, 19,
1175; (b) L. H. Andrade, A. V. Silva and E. C. Pedrozo, Tetrahedron
Lett., 2009, 50, 4331.
9 (a) M. D. Truppo, N. J. Turner and J. D. Rozzell, Chem. Commun.,
2009, 2127; (b) D. Koszelewski, I. Lavandera, D. Clay, D. Rozzell and
W. Kroutil, Adv. Synth. Catal., 2008, 350, 2761; (c) M. Ho¨hne, S. Ku¨hl,
K. Robins and U. T. Bornscheuer, ChemBioChem, 2008, 9, 363; (d) R. L.
Hanson, B. L. Davis, Y. Chen, S. L. Goldberg, W. L. Parker, T. P. Tully,
M. A. Montana and R. N. Patel, Adv. Synth. Catal., 2008, 350, 1367;
(e) D. Koszelewski, I. Lavandera, D. Clay, G. M. Guebitz, D. Rozzell
and W. Kroutil, Angew. Chem., Int. Ed., 2008, 47, 9337; (f) S. Buchholz
and H. Gro¨ger, in Biocatalysis in the Pharmaceutical and Biotechnology
Industries, ed. R. N. Patel, CRC Press, Boca Raton, 2007, pp. 829–847;
(g) U. Kaulmann, K. Smithies, M. E. B. Smith, H. C. Hailes and J. M.
Ward, Enzyme Microbiol. Technol., 2007, 41, 628; B.-Y. Hwang, B.-
K. H. Cho, Y. K. Koteshwar and B. G. Kim, J. Mol. Catal. B: Enzym.,
2005, 37, 47; (h) J. D. Stewart, Curr. Opin. Chem. Biol., 2001, 5, 120.
10 A. L. Braga, F. Vargas, R. C. Braga and J. A. Sehnem, J. Org. Chem.,
2005, 70, 9021.
(E)-Dimethyl 2-(1,3-diphenylallyl)malonate. Separation of
enantiomers by HPLC analysis (Daicel Chiralcel OD-H column;
solvent, 99 : 1 hexane–2-propanol; flow rate 1.0 mL min-1; 254 nm
detection). Retention times: (R) = 9.67 min; (S) = 10.45 min.
(E)-Diethyl 2-(1,3-diphenylallyl)-2-ethylmalonate. Separation
of enantiomers by HPLC analysis (Daicel Chiralcel AD-H col-
umn; solvent, 50 : 50 hexane–isopropanol; flow rate 0.5 mL min-1;
254 nm detection). Retention times: (R or S) = 3.60 min; (R or
S) = 6.02 min.
11 (a) M. Zielin´ska-Blajet, R. Siedlecka and J. Skarzewski, Tetrahedron:
Asymmetry, 2007, 18, 131; (b) A. L. Braga, M. W. Paixa˜o and G. Marin,
Synlett, 2005, 1675.
12 E. Wojaczynska and J. Skarzewski, Tetrahedron: Asymmetry, 2008, 19,
2252.
This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 2043–2051 | 2051
©