Synthesis of C-glycosides from S-glycosyl phosphorothioates

Article abstract of DOI:10.1515/znb-2002-0217

Treatment of O-benzyl protected S-glucosyl phosphorothioates with 1,3,5-trimethoxybenzene in the presence of iodine or boron trifluoride etherate led to appropriate aryl C-β-D-glucosides. The reaction of O-benzyl and O-acetyl-protected phosphorothioates o

Full text of DOI:10.1515/znb-2002-0217

Synthesis of C-Glycosides from S-Glycosyl Phosphorothioates
W. Kudelska
Institute of Chemistry, Faculty of Pharmacy, Medical University of Ło´ dz´, 90Ð151 Ło´ dz´,
Muszyn´ skiego 1, Poland
Reprint requests to Dr. W. Kudelska.
Fax: 48-42-678-83-98. E-mail: kudelska@ich.pharm.am.lodz.pl
Z. Naturforsch. 57b, 243Ð247 (2002); received October 16, 2001
S-Glycosyl Phosphorothioates, C-Glycosides, Synthesis
Treatment of O-benzyl protected S-glucosyl phosphorothioates with 1,3,5-trimethoxyben-
zene in the presence of iodine or boron trifluoride etherate led to appropriate aryl C-ꢀ-D-
glucosides. The reaction of O-benzyl and O-acetyl-protected phosphorothioates of monosac-
charides with allyltrimethylsilane, using boron trifluoride etherate as activator, gave mainly
or exclusively, the corresponding 3-(α-D- glycopyranosyl)-1-propenes. C-Glucosidation of fu-
ran with O-benzyl protected S- glucosyl phosphorothioate in the presence of boron trifluo-
ride etherate afforded (2- furyl)-α-C-glucoside.
Introduction
Results and Discussion
Carbon-linked glycosides, stable analogues of
naturally occurring O- and N-glycosides, have be-
come the subject of considerable interest in bioor-
ganic and medicinal chemistry[1Ð5].
The O-benzyl-protected S-α-D-glycosyl phos-
phorothioates (1Ð3) and O-acetylated S-(ꢀ-D-gly-
cosyl)phosphorothioates (4Ð5), employed as
electrophiles are listed in Fig. 1. The donors 1Ð3
were prepared from the corresponding 2,3,4,6-
tetra-O-benzyl-D-glycopyranoses by Lewis acid-
catalyzed reaction with ammonium salt of O,O-
dialkylphosphorothioic acid [6,8], while donors 4Ð
5 - by condensation of ammonium salt of O,O-
dialkylphosphorothioic acid with O-acetylated gly-
cosyl halides [9].
Several approaches to the synthesis of C-glyco-
sides have been explored previously [2Ð5]. The
most common method for the carbon-carbon bond
formation at the anomeric center involves the cou-
pling of carbon nucleophiles with carbohydrate-
based electrophiles having diverse leaving groups
e.g. lactols, lactones, anomeric esters, halides, gly-
cosides, thioglycosides, imidates, glycals, enitols
and 1,2-anhydro sugars. Furthermore, procedures
employing transition metals Ð mediated couplings,
anomeric anions and concerted reactions, such as
[4+2] cycloadditions and sigmatropic rearrange-
ment have also been used to synthesize C-glyco-
sides. Recently, free radical chemistry has been ex-
tended to this area and to O5C-glycoside
rearrangements.
Here, we present a new efficient procedure for
the synthesis of C-glycosides using sugar phos-
phorothioates as the anomeric leaving group. In
the previous papers [6,7], we have already re-
ported the utility of S-glycosyl phosphorothioates
for the efficient and rapid formation of isomeric
1,2-O-(1-cyanoethylidene)-D-glycoses and glyco-
syl cyanides.
Fig. 1. S-Glycosyl phosphorothioates 1Ð5 applied as gly-
cosyl donors and C-glycosides formed 6, 12.
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244
W. Kudelska · Synthesis of C-Glycosides from S-Glycosoyl Phosphorothioates
Reaction of glucosyl phosphorothioate 1 with 10, 11 [21Ð24] in 83% and 63% yield, respectively,
electron rich aromatic compound such as 1,3,5-tri- after purification by column chromatography.
methoxybenzene in the presence of iodine was Analysis of 13C NMR spectra of 10 and 11 re-
found to be an effective way to produce the steri- vealed that a ~7:1 mixture of α- and ꢀ-anomers
cally favored ꢀ-C-aryl-D-glucoside product 6 [10Ð was formed (Table 1) with preponderance of the
13] (Figure 1), exclusively. We obtained the same thermodynamically more stable α-isomer, despite
expedient result in the coupling of 1,3,5-trimethox- the presence of the C-2-O-acetyl groups. Recrys-
ybenzene with 1 in the presence of boron trifluo- tallization of the α/ꢀ mixture 11 gave pure α-an-
ride etherate as an activator. Both reactions were omer [21].
performed in acetonitrile solution at room temper-
Table 1. Stereoselective synthesis of 3-glycopyranosyl-
ature for a few days with an excess (~2 equiva-
lents) of acceptor and activator. After the usual
work-up, product 6 was obtained with good yield
after column chromatography.
prop-1-enes Bn = -CH2C6H5, Ac = -COCH3 a) the α/ꢀ
ratio was determined by 13C NMR, b) product isolated.
Per-O-Benzylated and per-O-acetylated phos-
phorothioates 1Ð5 were evaluated as donors in the
synthesis of C-allyl glycosides (Scheme 1). Reac-
tions were conducted with allyltrimethylsilane in
acetonitrile in the presence of boron trifluoride
etherate. The amounts of the activator were ad-
justed according to the nature of the O-protective
groups of sugar. O-Benzyl protected phosphoro-
thioates 1Ð3 were activated with 2 equivalents of
BF3·Et2O and coupled with allyltrimethylsilane at
room temperature to provide the corresponding
3-(O-benzyl-α-D-glycopyranosyl)prop-1-enes 7Ð9
[14Ð20], stereoselectively. Compunds 7Ð9 were
isolated in high yield by preparative TLC (Ta-
ble 1). After successful application of O-benzy-
lated glycosyl donors 1Ð3, synthesis of C-allyl gly-
cosides from O-acetylated galactosyl-4 and
glucosyl-phosphorothioate 5 was also investigated.
The reaction of 4 or 5 with allyltrimethylsilane and
BF3·Et2O (~1.5 equivalent) at room temperature
did not proceed even after 10 days. Having
increased the amount of BF3·Et2O to 10 equiva-
In expanding this methodology to other C-nu-
lents, C-allylation with 4 and 5 occured at room cleophiles, furan, a reactive electron-rich aromatic,
temperature, but even after several days some was used as acceptor in the reaction with the glu-
starting material were still present in the reaction cosyl donor 1. In the presence of boron trifluoride
mixture. Treatment of glycosyl donors 4 or 5 with etherate, in acetonitrile, the 2-(O-benzyl-α-D-glu-
allyltrimethylsilane and 10 equivalents of copyranosyl)furan (12) [25] (Fig. 1) was isolated in
BF3·Et2O at 80 ∞C for a few hours led to 3-(O- ~60% yield, after column chromatography.
acetylated α- and ꢀ-glycopyranosyl)prop-1-enes
In summary, the application of S-glycosyl phos-
phorothioates in the efficient synthesis of various
C-aryl, C-allyl and C-heterocyclic glycosides has
been demonstrated. Iodine was successfully em-
ployed as an activator in the conversion of S-gly-
cosyl phosphorothioates to C-glucosylarenes,
widespread in nature and having interesting physi-
ological properties (hedamycin [26], kyanamycin
Scheme 1.
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W. Kudelska · Synthesis of C-Glycosides from S-Glycosoyl Phosphorothioates
245
The reaction mixture was stirred for 4 d at r.t. The
reaction mixture was diluted with CH2Cl2 (50 ml)
and filtered through Celite. The filtrate was
washed with satd. NaHCO3 (2 ¥ 30 ml), water (1
¥ 30 ml), dried (MgSO4) and evaporated in vacuo
to obtain crude product. The oily residue was puri-
fied on silica gel column chromatography petro-
leum ether Ð ethyl acetate (4:1, v/v) to give 6
(0.149 g, 72% ) as colourless syrup.
[26], bergenin [27Ð29], et.). Allylation of the gly-
cosyl phosphorothioates donors allowed the for-
mation of C-glycosylalkenes, useful carbohydrate
mimetics commonly employed as enzyme inhibi-
tors [19,20].
Experimental Section
General methods
Melting points were determined with Boetius
PHMK 05 apparatus and are uncorrected. IR
spectra were obtained by using the Infinity MI-60
FT-IR spectrometer. 1H, 13C and 31P NMR spectra
were measured in CDCl3 solution on a Bruker
DPX spectrometer operating at 250.13, 62.9 and
101.24 MHz, respectively. The following starting
materials were purchased from Aldrich Co: 1,3,5-
trimethoxybenzene, allyltrimethylsilane, furan and
boron trifluoride etherate. Preparative TLC was
performed on 20 ¥ 20 cm glass plates coated with
2 mm of silica gel 60 F254 (E. Merck); detection
was effected by UV lamp or by exposure to iodine
vapours. Column chromatography was performed
on Silica Gel 60 (E. Merck) (70Ð230 mesh,
ASTM).
General procedure. 3-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-
benzyl-α-D-glycopyranosyl)prop-1-enes (7Ð9)
To the solution of thiophosphate 1Ð3 (0.211 g,
0.3 mmol), in dry acetonitrile (3 ml), allyltrimeth-
ylsilane (1.5 mmol, 0.171 g, 0.24 ml) was added,
˚
then molecular sieves 4 A and finally BF3·Et2O
(0.085 g, 0.08 ml, 0.6 mmol). The resulting solution
was stirred for the time indicated in Table 1. The
reaction mixture was diluted with CH2Cl2 (50 ml)
and filtered through Celite. The filtrate was
washed with satd. NaHCO3 (2 x 30 ml), water (1
x 20 ml), dried (MgSO4) and evaporated in vacuo
to obtain the crude product. This product was dis-
solved with AcOEt and purified by preparative
thin layer chromatography using benzene Ð Et2O
(4:1, v/v) as the eluent.
2,4,6-Trimethoxy-1-(1Ј-deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-
benzyl-ꢀ-D-glucopyranosyl) benzene (6)
3-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-benzyl-α-D-
glucopyranosyl)prop-1-ene (7)
(A). To a solution of 1 (211 mg, 0.3 mmol) in
acetonitrile
(5 ml)
1,3,5-trimethoxybenzene
7 was obtained as colourless crystalline residue
(0.142 g, 84.2% ). M. p. 64Ð65∞ C (after crystalliza-
tion from hexane), (lit. [16] 64Ð65 ∞C). Ð 13C
NMR: δ = 29.7 (C-3), 68.8, 71.0, 73.0, 73.4, 73.6,
75.0, 75.4, 78.0, 80.0, 82.3, (pyranose-C, 4¥CH2 Ph
), 116.8 (C-1), 127.5Ð128.3 (4¥Ph), 134.7 (C-2),
138.0, 138.4, 138.7,(4 C, ipso Ph).Ð 1H NMR: δ =
2.47 (m, 2 H, 3-H), 3.59Ð3.82 (m, 6 H, 2Ј, 3Ј, 4Ј,
5Ј, 6Ј. 6Љ-H), 4.14 (m, 1 H, 1Ј-H), 4.44Ð4.95 (m, 8
H, 4¥CH2Ph), 5.09 (m, 2 H, 1a-H, 1b-H), 5.81 (m,
˚
(101 mg, 0.6 mmol) molecular sieves 4 A, and sub-
limated iodine (152 mg, 0.6 mmol) were added.
The reaction mixture was stirred for 4 d at r.t. The
reaction mixture was diluted with CH2Cl2 (50 ml)
and filtered through Celite. The filtrate was
washed with Na2S2O3 (1 ¥ 30 ml) and water (1 ¥
30 ml), dried (MgSO4) and evaporated in vacuo to
obtain crude product: after column chromatogra-
phy product 6 was obtained as colourless syrup
(141 mg, 68.1% ). Ð 13C NMR: δ = 55.5 (OCH3),
56.0 (OCH3), 56.3 (OCH3), 69.3, 72.8, 73.3, 74.6,
75.3, 76.0, 78.6, 79.8, 80.1, 87.6, 90.9, 91.8 (pyra-
nose-C, 4¥CH2Ph), 107.7 (C-1), 127.3Ð128.5
(4Ph), 138.4, 138.6, 138.9, 139.0 (4C, ipso Ph),
158.8, 160.9, 161.4 [3C aromatic from
C6H2(OCH3)3]. - 1H NMR (selected): δ = 3.70 (s,
3 H, OCH3), 3.78 (s, 3 H, OCH3), 3.81 (s, 3 H,
1
1 H, 2-H), 7.01Ð7.31 (m, 20 H, 4¥Ph). H NMR
spectra are in agreement with lit. [15,16,18,19], 13
NMR spectra are in agreement with lit. [30].
C
3-(1Ј,3Ј,4Ј,6Ј-tetra-O-benzyl-α-D-
galactopyranosyl)prop-1-ene (8)
8 was obtained as a colourless syrup (0.125 g,
OCH3), 6.10 (d, J = 2.25 Hz, 1 H, C6H2), 6.16 (d, 74% ). Ð 13C NMR: δ = 29.6 (C-3), 67.1, 72.8, 72.9,
J = 2.0 Hz, 1 H, C6H2). 1H and 13C NMR data are 73.0, 74.1,( pyranose-C, 4¥CH2Ph), 76.3 (C-1Ј),
in agreement with the lit. data [10Ð12].
116.6 (C-1), 127.3Ð128.2 (4¥Ph), 135.0 (C-2),
(B). To a solution of 1 (211 mg, 0.3 mmol) in 138.1, 138.3, 138.4, 138.5, (4C, ipso Ph),- 1H NMR:
acetonitrile (5 ml),
1,3,5-trimethoxybenzene δ = 2.37 (m, 2 H, 3-H), 3.75Ð4.05 (m, 6 H, 2Ј, 3Ј,
˚
(101 mg, 0.6 mmol), molecular sieves 4 A and 4Ј, 5Ј, 6Ј, 6Љ-H), 4.11 (m, 1H, 1Ј-H), 4.49Ð4.71 (m,
BF3·Et2O (0.11 ml, 0.128 g, 0.9 mmol) were added. 8 H, 4¥PhCH2), 5.1 (m, 2 H, 1a-H, 1b-H), 5.74 (m,
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W. Kudelska · Synthesis of C-Glycosides from S-Glycosoyl Phosphorothioates
1
1 H, 2-H), 7.25Ð7.36 (m, 20 H, 4¥Ph). H and 13C 1 H, 3Ј-H), 5.28 (dd, J2,1 = 4.8 Hz, J2,3 = 9.3 Hz, 1
NMR spectra are in agreement with the lit. [14].
H, 2Ј-H), 5.42 (t, J3Ј,4Ј = 3.0 Hz, J4Ј,5Ј = 2.4 Hz, 1
H, 4Ј- H), 5.76 (m, 1 H, 2-H), in agreement with
1
the lit. [22,23] H NMR spectra.
3-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-benzyl-α-D-
mannopyranosyl)prop-1-ene (9)
3-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-acetyl-
glucopyranosyl)prop-1-ene (11)
9 was obtained as colourless syrup (0.144 g,
85.2% ). Ð 13C NMR: δ = 34.6 (C-3), 69.1, 71.4,
72.0, 72.2, 73.2, 73.6, 73.7, 74.8, 75.1, 76.8, (pyra-
nose-C, 4¥ CH2Ph), 117.1 (C-1), 127.4Ð128.3
(4¥Ph), 134.2 (C-2), 138.2, 138.3, (4C, ipso Ph),Ð
1H NMR: δ = 2.40 (m, 2 H, 3-H), 3.70Ð3.92 (m, 6
H, 2Ј, 3Ј, 4Ј, 5Ј, 6Ј, 6Љ-H), 4.11 (m, 1 H, 1Ј-H), 4.57Ð
4.77 (m, 8 H, 4¥CH2Ph), 5.01 (m, 2 H, 1a-H, 1b-
H), 5.82 (m, 1 H, 2-H), 7.26Ð7.41 (m, 20 H, 4¥Ph).
1H and 13C NMR spectra are in agreement with
the lit. [18,20].
Column chromatography, toluene Ð AcOEt
(4:1, v/v). 11 was obtained as a mixture (α/ꢀ =
ϳ 7:1). Ð 13C NMR (α-anomer): δ = 20.8, 20.9
(OAc), 30.7 (C-3), 62.3 (C-6Ј), 68.9 (C-4Ј, 5Ј), 70.3
(C-2Ј), 70.4 (C-3Ј) 72.0 (C-1Ј), 117.8 (C-1), 133.0
(C-2), 169.0, 169.6, 170.0, 170.6 (C=O); δ-anomer:
δ = ~ 20 (OAc), 36.0 (C-3), 62.4 (C-6Ј), 68.3 (C-
4Ј), 71.7 (C-2Ј), 74.5 (C-3Ј), 75.7 (C-5Ј), 77.4 (C-
1Ј), 117.4 (C-1), 133.0 (C-2), 169.4, 170.3, 170.8
(C=O), in agreement with the lit. [21] 13C NMR
spectra.
General procedure. 3-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-
acetyl-D-glycopyranosyl)prop-1-enes (10, 11)
Recrystalization (chloroform-hexane) gave 11
α, colorless needles. M. p. 107Ð108 ∞C (lit. [21]
1
To the solution of thiophosphate 4 or 5 (0.307 g,
0.6 mmol) in acetonitrile (10 ml), allyltrimethylsi-
lane (0.95 ml, 0.685 g, 6 mmol), molecular sieves 4
108 ∞C). Ð H NMR: δ = 2.03, 2.04, 2.05, 2.08,
(OAc), 2.62 (m, 1 H, 3-H), 2.29 (m, 1 H, 3-H), 3.86
(ddd, J5Ј,6Ј = 2.7 Hz, J4Ј,5Ј = 9.4 Hz, 1 H, 5Ј- H),
˚
A, and finally BF3·Et2O (0.76 ml, 0.85 g, 6 mmol)
4.08 (dd, 1 H, 6Ј-H), 4.21 (dd, J5Ј,6Ј = 5.4 Hz, J6Ј,6Љ
12.1 Hz, 1 H, 6Ј-H), 4.28 (ddd, J3,1Ј = 4.6 Hz, J3,1Ј
=
=
were added. The resulting solution was refluxed
(4, 5) for the times indicated in Table 1. The reac-
tion mixture was cooled, diluted with CH2Cl2
(50 ml), filtered (Celite), and washed with CH2Cl2.
The organic layer was washed with satd. NaHCO3
(2 x 30 ml) water (1 x 30 ml), and dried (MgSO4).
The solvent was removed under reduced pressure,
and the crude product was purified by column
chromatography.
10.8 Hz, 1 H, 1Ј-H), 4.98 (t, 1 H, J3Ј,4Ј = 9.4 Hz, 4Ј-
H), 5.09 (dd, J1Ј,2Ј = 5.7 Hz, J2Ј.3Ј = 9.5 Hz, 1 H, 2Ј-
H), 5.12 (ddd, J = 1.3 Hz, J = 2.7 Hz, J = 10.2 Hz,
1 H, 1-H), 5.15 (ddd, J = 1.5 Hz, J = 2.7 Hz, J =
17.1 Hz, 1 H, 1-H), 5.34 (t, J = 9.1 Hz, 1 H, 3Ј-H),
5.75 (m, 1 H, H-2), in agreement with the lit.
1
[21,24] H NMR spectra.
2-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-benzyl-α-D-
glucopyranosyl)furan (12)
3-(1Ј-Deoxy-2Ј,3Ј,4Ј,6Ј-tetra-O-acetyl-D-
galactopyranosyl)prop-1-ene (10)
To the solution of thiophosphate 1 (0.211 g,
Column chromatography, gradient toluene Ð 0.3 mmol) in dry acetonitrile (5 ml) furan (0.11 ml,
AcOEt, (1:0 5 3:1, v/v). 10 was obtained as a mix- 0.102 g, 1.5 mmol) was added, then molecular
˚
ture (α/ꢀ = ~ 7:1). Ð IR (film): ν = 2961 (=CH2), sieves 4 A and finally BF3·Et2O (0.11 ml, 0.128 g,
1746 (C=O), 1643 (C=C), 1435, 1372, 1233, 1102, 0.9 mmol). The mixture was allowed to react for
1053, 984, 912 (=CH2), 756, 590, 500 cmÐ1. - 13C 24 h at r.t. The reaction mixture was diluted with
NMR (α Ð anomer): δ = 20.2, 20.3, 20.4 (OAc), CH2Cl2 (50 ml) and filtered through Celite The
30.5 (C-3), 61.1 (C-6Ј), 71.1 (C-1Ј), 67.3, 67.6, 67.8, filtrate was washed with satd. NaHCO3 (2 ¥
67.9 (C2ЈÐC5Ј), 117.2 (C-1), 133.2 (C-2), 169.4, 30 ml), water (1 ¥ 20 ml), dried (MgSO4) and
169.5, 169.7, 170.1 (C=O); ꢀ-anomer: δ = ~ 20.0 evaporated in vacuo to obtain crude product,
(OAc), 35.6 (C-3) 61.3 (C-6Ј), 67.4, 68.8, 71.8, 73.7, which was purified by column chromatography pe-
77.2 (C-1Ј), 117.0 (C-1), 133.0 (C-2), 169.3, 169.7, troleum ether Ð AcOEt (19:1, v/v). 12 was ob-
169.9 (C=O), in agreement with the lit. [22,23]. - tained as colourless crystals (0.105 g, 59.3% ). M.
1H NMR: δ = 2.08, 2.05, 2.04 (OAc), 2.29 (m, 1 H, p. 92Ð3 ∞C, [after crystallization (hexane)], lit. [25]
3-H), 2.46 (m, 1 H, 3-H), 4.09 (m, 2 H, 5Ј,6Ј-H), 92Ð3 ∞C. Ð 13C NMR: δ = 68.8, 70.0, 72.8, 73.2,
4.21 (dd, J5Ј,6Ј = 7.2 Hz, J6Ј,6Ј = 12.6 Hz, 1 H, 6Ј- 73.4, 75.0, 75.4, 75.6, 78.0, 79.4, 82.8 (pyranose-C,
H), 4.31 (ddd, J1’,2Ј = 5.1 Hz, J1Ј.3’ = 10.5 Hz, 4¥CH2Ph), 110.0, 116.6 (C-3, C-4), 127.4Ð128.2
J1Ј.3Ј = 5.4 Hz, 1 H, 1Ј-H), 5.10Ð5.16 (m, 2 H, 1a- (4Ph), 138.1, 138.5, 138.8 (4-C, ipso Ph), 142.6 (C-
1
H, 1b-H), 5.22 (dd, J3Ј,4Ј = 3.0 Hz, J2Ј,3Ј = 9.3 Hz, 5), 150.7 (C-2). Ð H NMR: δ = 3.45Ð3.69 (m, 4
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W. Kudelska · Synthesis of C-Glycosides from S-Glycosoyl Phosphorothioates
247
H, 4Ј, 5Ј, 6Ј, 6Љ-H), 3.88 (dd, J1Ј,2Ј = 6.6 Hz, J2Ј,3Ј
9.5 Hz, 1 H, 2Ј-H), 4.15 (dd, J2Ј,3Ј = 9.5 Hz, J3Ј,4Ј
=
=
Acknowledgements
Financial support from the Medical University
of Ło´ dz´ (502Ð13Ð682) is gratefully acknowledged.
Author is greatly indebted to Prof. M. Michalska
for her kind interest in this work.
9.2 Hz, 1 H, 3Ј-H), 4.94Ð4.36 (m, 8 H, 4¥CH2Ph),
5.05 (d, J1Ј2Ј = 6.6 Hz, 1 H, 1Ј-H), 6.28 (dd, J = 1.8
Hz, J = 3.3 Hz, 1 H, 4-H), 6.46 (d, J = 3.3 Hz, 1 H,
3-H), 7.03Ð7.27 (m, 20 H, 4C6H5), 7.36 (dd, J = 1
Hz, 1 H, 5-H). 1H and 13C NMR are in agreement
with the lit. data [25].
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