1
052
P. Traar, F. Belaj and K. A. Francesconi
Electrospray ionization mass spectra (ESIMS) were recorded on
an Agilent G1946D single quadrupole mass spectrometer with flow
injection using a mixture of water/acetonitrile (4 : 1 v/v) and MeOH as
solvents.
Melting points (uncorrected) were recorded on a Gallenkamp
melting point apparatus, rotation values on a Perkin Elmer Polarime-
ter 341, and elemental analysis on an Elemental Analyzer 1108, Fisons
Instruments.
X-Ray crystal structure analysis was performed with a modified
STOE four-circle diffractometer.
The structures for the well known intermediates 2, 7, 3, and 8, in
addition to the by-product 3a, were confirmed by NMR spectroscopy
(
see Accessory Materials).
Methyl Tri-O-acetyl-2-acetamido-2-deoxy-1-seleno-
β-D-hexopyranosides 4, 9
[
13]
diagram of 5 showing the atomic
Fig. 1. Stereoscopic ORTEP
numbering scheme. The probability ellipsoids are drawn at the 50%
probability level. Selected bond lengths and angles: Se1–C1 1.957(2),
For the introduction of the methylseleno group we followed in gen-
[10]
eral a known procedure used for glucopyranosides.
Thus, a mixture
Se1–C11 1.951(3), C2–N21 1.448(3), N21–C21 1.351(3), C21–O21
of dimethyl diselenide (470 mg, 2.5 mmol) and sodium borohydride
189 mg, 5 mmol)indryethanol(15 mL)underargonwasstirredatroom
◦
1
.240(3) Å; C11–Se1–C1 98.42(11), C21–N21–C2 123.0(2) .
(
temperature until the yellow-orange colour disappeared (5–10 min).The
◦
solution was then cooled to 0 C (ice bath) and the chloro sugar 3 or 8
(
crystallized directly from the clear reaction solution. To
600 mg, 1.64 mmol) was added. The mixture was allowed to warm to
obtain the chlorides 3 and 8 the use of hydrogen chloride
room temperature and stirred for 12 h. Acetic acid (0.5 mL) was added
and the mixture was stirred for an additional hour before the solvent
was removed by evaporation. The residue was taken up in ethyl acetate
[8]
in ether was favoured. On our first attempt (beginning
with 2), however, evaporation of the organic layer lead
to an oil which on work-up produced the hydrochloride
(
50 mL), the solution washed with water and saturated aqueous sodium
bicarbonate solution, and then quickly dried (MgSO4). Evaporation of
the organic layer gave the protected methylseleno sugar as a white solid.
Recrystallization from chloroform gave fine needles (4, 612 mg, 88%;
9, 584 mg, 84%).
[9]
3
a. This rearrangement has been described previously.
Subsequently, we performed the reaction under argon, and
the organic layer was evaporated followed by coevapora-
tion several times with chloroform (to remove all traces
of acetic acid), giving the chlorides as solids (3, 87%; 8,
◦
[4]
◦
20
D
Compound 4, mp 205–208 C (dec.; lit. 218–220 C), [α] −10
[
c 0.7 in (CH3)2SO] (Found: C 42.6, H 5.7, N 3.1. C15H23NO8Se
requires C 42.5, H 5.4, N 3.3%). δH (400 MHz, CDCl3) 5.53 (1H, d,
J 9.8, NH), 5.36 (1H, d, J 2.8, H4), 5.04 (1H, dd, J 10.2, 2.8, H3), 4.69
8
9%). These products, pure by NMR spectroscopy, were
used without further purification. For the introduction of the
selenium at the anomeric centre, we used an alkylselenide
(
1H, d, J 10, H1), 4.35 (1H, q, J 10, H2), 4.14–4.06 (2H, m, H6), 3.94
(1H, t, J 6, H5), 2.13 (3H, s, Me of OAc), 2.11 (3H, s, Me of SeMe),
2.01, 1.98 (6H, s, Me of OAc), 1.94 (3H, s, Me of NHAc). δ (100 MHz,
CDCl3) 170.8–170.3 (CO), 79.0 (C1), 75.5 (C5), 71.2 (C3), 66.9 (C4),
6
[10]
ion,
generated from dimethyl diselenide by reduction
C
with sodium borohydride, which was then reacted directly
in solution to give the methyl tri-O-acetyl-2-acetamido-2-
deoxy-1-seleno-β-d-hexopyranosides 4 and 9. Deprotection
1.6 (C6), 49.7 (C2), 23.3 (Me of NHAc), 20.7 (Me of OAc), 2.7 (Me of
+
80
+
80
+
SeMe). m/z (ESI , 10V) 464 [M( Se) + K] , 448 [M( Se) + Na] ,
80
+
+
−
4
26 [M( Se) + H] , 330 [M + H − CH3SeH] . m/z (ESI , 10 V) 460
[7]
80 80
−
−
of residual hydroxyl groups according to Zemplén in basic
medium lead to the desired methyl 2-acetamido-2-deoxy-1-
seleno-β-d-galactopyranoside 5 and methyl 2-acetamido-2-
deoxy-1-seleno-β-d-glucopyranoside 10. No purification by
column chromatography was needed during the synthesis,
and the overall yield was 56% for 5 and 52% for 10.
[M( Se) + Cl] , 424 [M( Se) − H] .
◦
20
Compound 9, mp 192–195 C (dec.), [α] −31 [c 1.2 in (CH3)2SO]
D
(
Found: C 42.7, H 5.6, N 3.2. C15H23NO8Se requires C 42.5, H 5.4,
N 3.3%). δH (500 MHz, CDCl3) 5.62 (1H, d, J 9.8, NH), 5.09–5.05
2H, m, H3, H4), 4.65 (1H, d, J 10, H1), 4.23–4.19 (2H, m, H2, H6),
.11 (1H, AB part of an ABX dd, J 12.3, 2, H6), 3.68–3.64 (1H, m,
H5), 2.10 (3H, s, Me of SeMe), 2.07, 2.03 (9H, s, Me of OAc), 1.93
(
4
(
(
3H, s, Me of NHAc). δC (125 MHz, CDCl3) 171.2–169.3 (CO), 78.4
The described synthesis has provided quantities of two
important selenium metabolites that will be used in our future
studies on the biotransformation of selenium in humans.
C1), 77.3 (C5), 73.8, 68.3 (C3, C4), 62.3 (C6), 53.4 (C2), 23.2 (Me of
+
NHAc), 20.7–20.6 (Me of OAc), 2.7 (Me of SeMe). m/z (ESI , 50V)
4
80
+
−
80
−
48 [M( Se) + Na] . m/z (ESI , 50V) 460 [M( Se) + Cl] .
Experimental
Methyl 2-Acetamido-2-deoxy-1-seleno-β-D-hexopyranosides 5, 10
d-Galactosamine hydrochloride was purchased from Lactan/Roth
For removal of the acetyl groups the general deacylation procedure
[
7]
(
Graz), d-glucosamine hydrochloride from Lancaster (Frankfurt),
according to Zemplén was chosen. To the protected methylseleno
sugar 4 or 9 (500 mg, 1.18 mmol) in dry methanol (10 mL), 1 M NaOMe
solution (60 µL) was added. The mixture was kept at room temperature
and stirred for approx. 15 min (monitored by TLC) and then neutralized
dimethyl diselenide from Acros-Organics (Geel), and sodium boro-
hydride (p.a.) was obtained from Merck (Darmstadt). Organic solvents
were freshly distilled.
Thin-layer chromatography was performed on Merck TLC plastic
sheets of silica gel 60 F254 using ethyl acetate as eluent. For visu-
alization of the compounds, a dip solution of vanillin (1.5 g)/H2SO4
+
with AMBERLITE IR 120 H . The mixture was filtered and concen-
trated under vacuum. Recrystallization from water gave the selenosugar
as white crystals (5, 310 mg, 88%; 10, 316 mg, 90%).
◦
[4]
◦
20
D
(
20 mL)/water (150 mL)/ethanol (125 mL) was used.
Compound 5, mp 247–250 C [dec.; lit. 255–257 C (dec.)], [α]
1
13
77
[4]
24
H, C, and Se NMR spectra were recorded with Varian (400
+23 (c 0.8 in H2O) lit. [α] +16.4 (c 0.51 in H2O) (Found: C 35.9, H
D
and 600 MHz) and Bruker (360 and 500 MHz) instruments. Chemical
5.6, N 4.6. C9H17NO5Se requires C 36.2, H 5.7, N 4.7%). δH [400 MHz,
(CD3)2SO] 7.59 (1H, d, J 9.8, NH), 4.49 (1H, d, J 10, H1), 3.90 (1H,
q, J 10, H2), 3.71 (1H, d, J 2.8, H4), 3.49 (2H, dd, J 5.6, 2, H6), 3.39
1
shifts are given in ppm. Calibration H: CHCl3 7.24 ppm, (CH3)2SO
2
.49 ppm, SeO2 1300 ppm; 13C: CDCl3 77 ppm, (CH3)2SO 39.7 ppm.