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L.H. Andrade et al. / Journal of Molecular Catalysis B: Enzymatic 73 (2011) 63–66
O
O
O
RBr, NaBH4
MeOH, 0 ºC
NaNO2, HCl 2M
KSeCN, 0 ºC
H2N
NCSe
RSe
3a, 4-SeMe (55%)
2a, 4-SeCN (64%)
2b, 3-SeCN (28%)
2c, 2-SeCN (68%)
1a, 4-NH2
1b, 3-NH2
1c, 2-NH2
3b, 4-SeCH2Ph (71%)
3c, 3-SeMe (48%)
3d, 3-SeCH2Ph (45%)
3e, 2-SeMe (45%)
3f, 2-SeCH2Ph (41%)
Scheme 1.
dehydrogenase from Leuconostoc mesenteroides, glucose-6-
phosphate and NADPH were purchased from Sigma–Aldrich.
The organoselenium acetophenones (3a–f) were synthesized as
previously described [21].
2.3.4. 1-(3-(Benzylseleninyl)phenyl)ethanone (4d), orange oil
1H NMR (200 MHz, CDCl3) ı = 2.51 (s, 3H), 3.95 (d, J = 11.4 35 Hz,
1H), 4.19 (d, J = 11.2 Hz, 1H), 6.88–6.93 (m, 2H), 7.21–7.27 (m, 3H),
7.52–7.61 (m, 2H), 7.81 (d, J = 0.8 Hz, 1H), 8.05 (dd, J = 1.6 and 5.6 Hz,
1H). 13C NMR (50 MHz, CDCl3) ı = 26.59, 58.63, 126.02, 128.54,
129.44, 129.88, 130.30, 130.74, 137.58, 40 140.29, 196.74. HRMS
[ESI(+)], calcd [M+H]+: 307.0237, found: 307.0241.
2.2. General procedure for oxidation of the organoselenium
acetophenones (3a–f) using monooxygenase (PAMO)
2.3.5. 1-(2-(Methylseleninyl)phenyl)ethanone (4e), orange solid
1H NMR (200 MHz, CDCl3) ı = 2.72 (s, 6H), 7.68 (dt, J = 1.4 and
6.2 Hz, 1H), 7.90 (dt, J = 1.2 and 6.4 Hz, 1H). 13C NMR (50 MHz,
CDCl3) ı = 26.37, 38.33, 126.06, 130.76, 130.89, 134.67, 199.74.
HRMS [ESI(+)], calcd [M+H]+: 230.9924, found: 230.9915.
To an erlenmeyer flask (100 mL) containing the starting mate-
rial solution (0.047 mmol in 190 L of DMSO) was added Tris/Cl
aqueous buffer at pH 9.0 (50 mM, 19 mL), glucose-6-phosphate
(0.1 mmol), NADPH (0.002 mmol), glucose-6-phosphate dehydro-
genase (0.62 mM) and PAMO (2.5 mM). Reactions were shaken at
30 ◦C for 24 h, and then extracted with dichloromethane (3 × 5 mL).
The organic phase was dried over MgSO4, and the solvent was
evaporated under vacuum. The crude reaction was purified by
preparative thin-layer chromatography (eluent: ethyl acetate).
2.3.6. 1-(2-(Benzylseleninyl)phenyl)ethanone (4f), orange solid
1H NMR (200 MHz, CDCl3) ı = 2.70 (s, 3H), 4.02 (d, J = 11 Hz,
50 1H), 4.14 (d, J = 11 Hz, 1H), 7.06–7.18 (m, 5H), 7.55–7.7 (m,
2H), 7.94–8.1 (m, 2H). 13C NMR (50 MHz, CDCl3) ı = 26.45, 58.77,
127.13, 127.81, 128.12, 129.80, 130.54, 198.50. HRMS [ESI(+)], calcd
[M+H]+: 307.0237, found: 307.0225.
2.3. General procedure for oxidation of the organoselenium
acetophenones (3a–f) using sodium periodate [22]
3. Results and discussion
Methanol (3 mL) and water (1 mL) were mixed in a 50 mL
round-bottomed 5 flask containing organoselenium acetophe-
nones (3a–f). The reaction was cooled at 0 ◦C and sodium periodate
(1 mmol) was then added. The mixture was shaken at 0 ◦C for 1 h
and dichloromethane (5 mL) was added, and the resulting solution
10 was washed with aqueous NaCl saturated solution (2 × 5 mL).
The organic phase was dried over MgSO4, and the solvent was
evaporated under vacuum. The crude reaction was purified by
preparative thin-layer chromatography (eluent: ethyl acetate) pro-
viding the desired product (65–90%).
by PAMO, six selenium-containing acetophenones (3a–f) were
selected as substrates. The organoselenium acetophenones (3a–f)
were prepared from commercially available ortho-, meta- and para-
amino-acetophenones (1a–c) (Scheme 1). The in situ preparation
of diazonium salt from 1a–c followed by the addition of KSeCN
the alkylation of the selenium atom was carried out with NaBH4
and the appropriate alkyl halide to give the organoselenium ace-
tophenones (3a–f) (41–71%) [21].
investigation on PAMO-catalyzed reactions (Scheme 2). The oxi-
dation reactions were coupled to a second enzymatic reaction
catalyzed by glucose-6-phosphate dehydrogenase (G6PDH), in
order to regenerate the consumed NADPH [23]. All oxidations were
carried out in a Tris/Cl aqueous buffer at pH 9.0 (Table 1). The buffer
was saturated with oxygen for 5 min; otherwise the conversions
would be low.
The organoselenium acetophenones (3a–d) oxidation reaction
gave the corresponding selenoxides (4a–d) in high conversion after
24 h reactions. In all these reactions, PAMO was chemoselective
by only catalyzing selenium oxidation, leaving the ketone moiety
On the other hand, the PAMO-catalyzed reaction of 4-
hydroxyacetophenone, which contains an electron donor group,
yield ester (4-hydroxyphenyl acetate) in excellent conversion
(>99%) (see supporting material). As the methylselane and
2.3.1. 1-(4-(Methylseleninyl)phenyl)ethanone (4a), orange solid
1H NMR (200 MHz, CDCl3) ı = 2.65 (s, 6H), 7.85 (d, J = 8.6 Hz,
2H), 8.11 (d, J = 8.6 Hz, 2H). 13C NMR (50 MHz, CDCl3) ı = 26.74,
37.43, 125.79, 129.35, 139.45, 147.18, 197.03. HRMS [ESI(+)], calcd
[M+Na]+: 252.9744, found: 252.9735.
2.3.2. 1-(4-(Benzylseleninyl)phenyl)ethanone (4b), orange solid
1H NMR (200 MHz, CDCl3) ı = 2.64 (s, 3H), 3.98 (d, J = 11.4 Hz,
1H), 4.23 (d, J = 11.4 Hz, 1H), 6.94–6.97 (m, 2H) 7.24–7.30 (m, 3H),
7.49 (d, J = 8.4, 2H), 7.99 (d, J = 8.4, 2H). 13C NMR (50 MHz, CDCl3)
ı = 26.76, 59.08, 125.30, 126.50, 128.71, 128.78, 139.40, 197.18.
HRMS [ESI(+)], calcd [M+H]+: 307.0237, found: 307.0233.
2.3.3. 1-(3-(Methylseleninyl)phenyl)ethanone (4c), orange oil
1H NMR (200 MHz, CDCl3) ı = 2.67 (s, 6H), 7.65–7.72 (m, 1H), 30
7.98 (d, J = 7.2 Hz, 1H), 8.11 (d, J = 5.6 Hz, 1H), 8.30 (s, 1H). 13C NMR
(50 MHz, CDCl3) ı = 26.74, 125.28, 129.75, 130.14, 130.97, 138.23,
196.77. HRMS [ESI(+)], calcd [M+H]+: 230.9924, found: 230.9919.