Synthesis of biurets: Via TMSNCO addition to 1-aminosugars: Application in the de novo synthesis of dC oxidation products

Article abstract of DOI:10.1039/c8ob02810a

The reaction between 1-aminosugars and trimethylisocyanate (TMSNCO) was optimised as a one-step synthetic strategy for the synthesis of sugar biurets. This protocol was successfully applied to a number of 1-aminosugars, which exclusively provided the corresponding biurets in 67-99% yields. The new methodology was applied in the de novo synthesis of N¹-(2-deoxy-α/β-d-erythro-pentofuranosyl)biuret (dfBU) and N¹-(2-deoxy-α/β-d-erythro-pentopyranosyl)biuret (dpBU), two known DNA lesions arising from the hydroxyl radical induced decomposition of 2′-deoxycytidine (dCyd).

Full text of DOI:10.1039/c8ob02810a

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Biomolecular Chemistry
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Synthesis of biurets via TMSNCO addition to
-aminosugars: application in the de novo
synthesis of dC oxidation products†
1
Cite this: DOI: 10.1039/c8ob02810a
Veronika Tsoulougian, Emmanuel E. Psykarakis and Thanasis Gimisis
*
The reaction between 1-aminosugars and trimethylisocyanate (TMSNCO) was optimised as a one-step
synthetic strategy for the synthesis of sugar biurets. This protocol was successfully applied to a number of
1-aminosugars, which exclusively provided the corresponding biurets in 67–99% yields. The new method-
Received 10th November 2018,
Accepted 2nd January 2019
1
ology was applied in the de novo synthesis of N -(2-deoxy-α/β-D-erythro-pentofuranosyl)biuret (dfBU)
DOI: 10.1039/c8ob02810a
1
and N -(2-deoxy-α/β-D-erythro-pentopyranosyl)biuret (dpBU), two known DNA lesions arising from the
rsc.li/obc
hydroxyl radical induced decomposition of 2’-deoxycytidine (dCyd).
monitoring the release of nitrous oxide, is widely used today
for the synthesis of molecules bearing the biuret pattern.
Since the application of harsh synthetic conditions for the
Introduction
2
3–25
The biuret (carbamylurea) motif is present in many chemical
structures exhibiting important biological activity expressed synthesis of sugar-substituted biurets is not feasible due to the
through anticonvulsant, bacteriostatic, anti-inflammatory or sensitivity of the sugar substrates, an alternative synthetic
1
–7
cytotoxic properties. The same motif is found in lividine, an route was sought. An iterative process of building ureas,
8
amino acid isolated from Grateloupia livida (Fig. 1) and in the biurets and triurets from amines and trichloroacetylisocyanate
9
main product of ribosidation of 5-azauracil in E. coli culture,
as well as among DNA oxidation products.
has been recently reported as amenable to nucleoside sub-
1
0–14
7,26
In particular, strates
but we were interested in a more direct access to the
γ-irradiation of 2′-deoxycytidine (dCyd) in aerated aqueous biuret motif.
1
2
solution was reported to lead to N -(2-deoxy-α/β-D-erythro-pen-
In a recent patent, mono-substituted biurets were men-
1
tofuranosyl)biuret (dfBU, Fig. 1) and N -(2-deoxy-α/β-D-erythro- tioned as a low-yield (3%) by-product during the reaction
pentopyranosyl)biuret (dpBU, Fig. 1), formed as equimolar between primary amines and trimethylsilylisocyanate
1
1
6
anomeric mixtures.
To our knowledge, no information (TMSNCO). In a previous patent, the reaction of an arylamine
regarding in vivo formation, mutagenic potential or de novo with an excess (>9.5 equiv.) of TMSNCO in a pyridine :
synthetic access to these lesions has been reported to date. In tetrahydrofuran (1 : 4) mixture for 4 days led to the formation
continuation of our interest in the de novo synthesis of DNA of the corresponding biuret in 48% yield. We considered these
1
5,16
lesions,
access to dfBU and dpBU could be useful for mild conditions appropriate for the synthesis of the desired
analytical and biological studies in the areas of mutagenesis biurets from appropriate 1-aminosugars.
and genotoxicity.
In this paper, we report the development of synthetic con-
Since the first synthesis of mono-substituted biurets from ditions that provide direct and high yield access to sugar
1
7
the reaction of methyl allophanate with primary amines,
several synthetic strategies have been reported, which involve
high reaction temperatures and the use of either strong or
toxic reagents and multistep reactions, which often lead to by-
1
8–22
products.
The synthesis of 1-substituted biurets from
2
1
nitrobiuret and primary amines, which involves heating equi-
valent amounts of the reactants at high temperatures and
Organic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian
University of Athens, 10571 Athens, Greece. E-mail: gimisis@chem.uoa.gr
†
Electronic supplementary information (ESI) available: NMR spectra of urea 3a,
and biurets 2a–g, 8–10, 13 and 14. See DOI: 10.1039/c8ob02810a
Fig. 1 Biologically important biuret structures.
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biurets, utilising 1-aminosugars and TMSNCO, in one step. the concentration of the substrate from 0.25 to 0.40 M, in dry
The efficient and general methodology produced was applied THF the desired biuret product was isolated exclusively, in
to the synthesis of α/β anomeric mixtures of dfBU and 90% yield (entry 5). In dichloromethane (0.40 M), the urea/
1
0,11
dpBU.
biuret ratio decreases, but a mixture is still obtained (entry 6).
Increasing the equivalents of Et N leads to a slight increase of
3
the 2a yield. When pyridine was used as the base, the desired
biuret was obtained in 24% yield. For higher concentrations in
both solvents, lower yields are obtained, due to the reduced
solubility of amine 1a (entries 9 and 10). A modest increase of
the reaction temperature to 40 °C resulted, in both solvents, in
increased urea/biuret ratio mixtures (entries 11 and 12), and
when the reaction temperature was slowly raised to reflux, in
dry THF, the formed biuret disappeared, and the initial amine
Results
1
-Aminosugars were considered to be the most convenient
starting materials for the synthesis of the desired biurets due
to their ease of synthesis by the catalytic hydrogenation of the
2
7
corresponding azides in good yields. Sugar azides were, in
turn, synthesised from protected sugars under standard
2
7
conditions.
2,3,4,6-Tetra-O-acetyl-β-D-glucopyranosylamine
1
a was isolated intact (entry 13). A decrease in the excess of
TMSNCO led to a decrease in the yield of isolated biuret
entries 14 and 15). It was finally concluded that the optimal
2
8,29
(
1a)
was used as the model substrate in order to identify
the best reaction conditions for the synthesis of the corres-
ponding 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl biuret in the
presence of TMSNCO (Scheme 1, Table 1).
(
conditions for the synthesis of biurets from the corresponding
amines involved the use of 5 equiv. TMSNCO and 1 equiv.
The initial reaction, either in dry THF or DCM alone with
no additives, did not lead to any observed product (entries 1
and 2, Table 1). Carrying out the reaction in the presence of 5
Et
3
N in dry THF (0.4 M), at room temperature (entry 5).
In order to determine the scope of this reaction, we further
investigated the addition of TMSNCO under the optimised
conditions to a number of protected 1-aminosugars 1b–g, as
shown in Table 2.
Appropriate 1-aminosugars were prepared from their corres-
ponding protected precursors in two steps, under standard
conditions. More specifically, the peracetylated sugar sub-
equiv. TMSNCO and 1 equiv. Et N in dry dichloromethane at
3
room temperature afforded traces of the biuret 2a (entry 3).
When the solvent was replaced by dry THF, we observed the
formation of a mixture containing the biuret and urea deriva-
tives (entry 4). Subsequently, it was observed that by increasing
strates were converted to the corresponding azides (AcO)
4
-β-D-
2
7
30,31
27
Gal-N
3
,
(AcO)
4
-α-D-Man-N
3
,
(AcO)
3
-β-D-Xyl-N
3
,
(AcO) -
3
3
2
27
33
β-L-Ara-N3,
(AcO) -β-L-Fuc-N
and (AcO) -α-L-Rha-N ,
3
3
3
3
which were in turn catalytically hydrogenated to the desired
2
7
1
-aminosugars (AcO)
4
-β-D-Gal-NH
2
(1b), (AcO)
4
-α-D-Man-NH
2
3
4,35
27
(
(
1c)
AcO)
(AcO) -β-D-Xyl-NH (1d),
(AcO) -β-L-Ara-NH (1e),
3
2
3
2
2
7
36
3
-β-L-Fuc-NH
2
(1f)
and (AcO)
3
-α-L-Rha-NH
2
(1g).
Compounds 1b–g underwent reactions with TMSNCO, under
our optimised conditions, to afford the corresponding biuret
products in yields ranging from 67% for (AcO)
3
-β-L-Ara-biuret
Scheme 1 Optimisation of the reaction. Details in Table 1.
Table 1 Optimisation of the biuret formation reaction
(2e) to 99% for (AcO) -β-L-Fuc-biuret (2b) (Table 2).
4
a
a
#
TMSNCO (equiv.)
Base (equiv.)
Solvent (M)
Temp (°C)
2a (%)
3a (%)
b
b
b
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
5
5
5
5
5
5
5
5
5
5
5
5
5
3
2.5
—
—
DCM (0.25)
THF (0.25)
DCM (0.25)
THF (0.25)
THF (0.40)
DCM (0.40)
THF (0.40)
THF (0.40)
THF (0.50)
DCM (0.50)
DCM (0.40)
THF (0.40)
THF (0.40)
THF (0.40)
THF (0.40)
25
25
25
25
25
25
25
25
25
25
40
40
66
25
25
—
—
5
30
90
44
91
24
12
8
46
34
—
20
15
—
—
—
49
—
35
—
—
—
—
47
65
—
—
—
Et
Et
Et
Et
Et
3
3
3
3
3
N (1.0)
N (1.0)
N (1.0)
N (1.0)
N (2.0)
b
b
Py (10.0)
Et
Et
Et
Et
Et
Et
Et
3
3
3
3
3
3
3
N (1.0)
N (1.0)
N (1.0)
N (1.0)
N (1.0)
N (1.0)
N (1.0)
b
0
1
2
3
4
5
b
b
b
a
b
Isolated yields. 1a was also recovered quantitatively in entries 1, 2, and 13 and in 91, 57, 82, 91, 80 and 70% in entries 3, 8, 9, 10, 14 and 15,
respectively.
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Table 2 Synthesis of biurets 2b–2g
Structure
#
Yield
90%
2
b
c
d
e
f
2
2
2
2
2
73%
87%
67%
99%
69%
Scheme 2 (i) H
2
, 10% Pd/C then (ii) TMSNCO, Et
3
N, THF, 25 °C, 19 h:
(
8), 77%, (9) 44%, (13) 17%. (iii) TBAF, THF, 95%, α : β, 1.3 : 1. (iv) 7 N NH
3
,
MeOH, 76%,%, α : β, 1.4 : 1. (v) DMTCl, pyridine, DMAP, 0 °C, 3 h, 57%.
77% and 44%, respectively (two-step yield). Deprotection of 9,
g
via TBAF in THF, provided access to a 1.3 : 1 (α : β) anomeric
mixture of 10, the dfBU oxidation product of dCyd. Biuret 14
1
1
has also been isolated from the γ-irradiation of dCyd. The
protected pyranosyl biuret 13, was also obtained, albeit in a
low yield, from the corresponding azide 11 as shown in
Scheme 2. Deprotection of the acetyl protection was achieved
with methanolic ammonia to provide the dpBU lesion 14, as a
3
i. TMSNCO (5 equiv.), Et N (1 equiv.), THF (0.4 M), 25 °C.
1
.4 : 1 (α : β) mixture of anomers. Biuret 10 was finally con-
The final application of the optimised methodology
Scheme 2) started from 2,3,5-tri-O-acetyl-D-ribofuranosyl azide
verted to the 5′-DMT-protected derivative 15 (Scheme 2), in
order to examine the suitability of this lesion for insertion into
synthetic oligonucleotides via standard oligonucleotide syn-
thesis (see Discussion below).
(
(
3
7
4),
3,5-di-O-(tert-butyldimethylsilyl)-2-deoxy-α/β-D-ribofura-
3
8–40
nosyl azide (5)
or 3,4-di-O-acetyl-2-deoxy-α-D-ribopyranosyl
1
5
azide (11), to afford, through a protocol similar to the one
described above (Table 1, entry 5), the corresponding biuret
analogues 8, 9 and 13. The purpose of this final application
was to provide synthetic access to the known biuret DNA
Discussion
1
lesions dfBU (10) and dpBU (14) (Fig. 1, Scheme 2), oxidatively The H NMR spectra of dfBU (10) and dpBU (14) were in agree-
11,13
produced from dCyd.
ment with the reported spectra of the separated anomers, via
Isolation and characterisation of the intermediate amines RP chromatography, by Wagner et al. The detailed descrip-
, 7 and 12 was not possible due to their instability. Attempts tion of the published H NMR spectra allowed us to identify
1
1
1
6
to isolate these amines led to unidentified complex mixtures the α-anomers as the major isomer in both 10 (α : β, 1.3 : 1)
1
on TLC. We can only postulate that these mixtures consisted of and 14 (α : β, 1.4 : 1). Although the H NMR spectra contained
oligomers arising from the condensation of ring-opened only the furanosyl isomer in the case of 10 and only the pyra-
1
3
imine-alcohols, in equilibrium with the ring-closed amines.
nosyl isomer in the case of 14, the C NMR spectra of either
Therefore, the crude products from the hydrogenation of 10 or 14 contained smaller signals of 14 or 10, respectively,
azides 4, 5 and 11 were treated directly under the optimised indicating a partial isomerization of dfBU to dpBU (and vice
1
3
conditions. The biuret analogues 8 and 9 were produced in versa), during the C NMR experiment, through sugar-ring
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opening and re-cyclisation, in agreement with what has been signals were observed for each of 1-, 3- and 5-NHs, in the area
1
1
reported. A similar furanosyl to pyranosyl ring isomerisation between 6.5 and 9.0 ppm, which were clearly visible upon
was also observed (data not shown) when the 5′-DMT-protected heating the NMR samples in DMSO-d , allowing the deconvo-
6
dfBU 15 was subjected to standard deprotection conditions, lution of the broad peaks observed at room temp due to slow
utilised in solid-phase oligonucleotide synthesis (3% trichloro- bond rotation in the NMR timescale.
acetic acid in DCM).
As far as the differences in the physical properties of biuret
A few details regarding the synthesis of hexose biurets 2a–g 2a compared with the corresponding urea 3a are concerned, it
should be noted. A clear indication that the product of the was found that 2a was insoluble in ethyl acetate, whereas 3a
1
3
reaction under study was an N - and not an N -(β-D-pyranosyl) was perfectly soluble. This made their separation feasible by
1
biuret came from the H NMR spectra in DMSO-d
6
where the simply triturating the crude product with EtOAc and collecting
1
8
9
1
-NH proton was observed as a doublet centred around the precipitated 2a by filtration. Nevertheless, the biurets’
.2–8.4 ppm, coupled with the anomeric H-1′ with J’s around polar nature often created problems in their chromatographic
.3–10.1 Hz. The 3-NH appeared as singlet downfield from separation from impurities.
-NH, centred around 8.8–8.9 ppm and the 5-NH2 protons
It is interesting to postulate on the mechanism leading to
appeared as a broad singlet centred around 6.8–6.9 ppm (see the observed biurets. In an associated study of biurets contain-
4
1
also ESI†). The biuret 2a could be differentiated from urea 3a ing alkoxysilane polymeric functions, it was determined that,
both spectroscopically and by its physical properties. under the reported reaction conditions, biurets could revert
1
The H NMR spectrum of urea 3a contained two sets of back to the isocyanate and the amine if the reaction mixture
exchangeable signals, one for the NH group observed as a was heated sufficiently for a long period. This is also con-
doublet centred at 5.92 ppm and one corresponding to the NH
firmed by our studies (Table 1, entries 11–13). In the same
patent, it was also proposed that the biuret formation is
2
13
group buried under the sugar protons at 4.95 ppm. The
C
NMR spectrum of urea 3a contained a single carbonyl carbon at carried out in two steps, the fast urea formation from the first
58.3 ppm, whereas that of biuret 2a contained two carbonyl addition of TMSNCO followed by a second slower addition of
peaks at 154.1 and 155.1 ppm. The existence of a single set of TMSNCO to a silylated urea intermediate to afford the biuret
1
1
the above three, exchangeable with D
2
O, signals in the H NMR product (Scheme 3). The TMS group in intermediate I
4
2
spectra of 2a–g (see ESI†) indicated that these compounds were increases the nucleophilicity of the terminal NHSiMe group
3
obtained as single anomers and were anomerically stable as and the second TMSNCO addition may occur through the
their precursor amines 1a–g. The stereochemistry of the stabilization of a six-membered transition state such as II
anomeric center was therefore governed in all intermediates by (Scheme 3).
that of the precursor azides. These in turn were formed under The formed biurets do not undergo further substitution by
stereochemical control by the anchimeric assistance of the TMSNCO to form a corresponding triuret analogue. As shown
2
-acetyl group, in a 1,2-trans fashion, as expected.
in Scheme 3, this could be explained by the intramolecular
On the other hand, the ribosyl biurets 8–10, as well as hydrogen bond between the first carbonyl group and the term-
-deoxyribopyranosyl biurets 13 and 14, were obtained as inse- inal 5-NH of the biuret intermediate III which in combination
2
parable, under normal phase chromatography, anomeric mix-
tures, mirroring the anomeric instability of the precursor
amines 6, 7 and 12. As can be seen for 8 in Fig. 2, a pair of
1
Fig. 2 Deconvolution of H NMR signals of biuret 8 in DMSO-d
6
by
heating from 25 °C (top) to 60 °C (bottom spectrum).
Scheme 3 Proposed mechanism for the synthesis of sugar biurets.
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with the TMS substituents renders the terminal amide group was stirred under 1 atm H
2
gas until the reaction was com-
inaccessible to TMSNCO. The importance of the TMS group in plete. The Pd/C was removed by filtration through Celite, and
intermediate I for a successful second addition was further the filtrate was concentrated in vacuo to remove the THF. The
indicated by the fact that when the reaction between urea 3a residue was triturated with Et O to afford 1-aminosugars 1a–g.
2
and TMSNCO in the presence of Et N was attempted, no biuret
formation was observed.
2,3,4,6-Tetra-O-acetyl-β-D-glucopyranosylamine (1a). Starting
from peracetylated β-D-glucose (4.00 g, 10.24 mmol), the inter-
mediate azide was purified with flash column chromatography
3
(
3
PE/EtOAc, 50 : 50) to give 3.67 g (97%), which was converted to
1
.25 g (95%) of the title compound as a white solid, the H
Experimental
General information
1
3
28,29
and C NMR
published data. M.P. 123–125 °C (diethyl ether), lit.
20–122 °C.
,3,4,6-Tetra-O-acetyl-β-D-galactopyranosylamine (1b). Starting
data of which were in agreement with the
2
8
All reagents and solvents were purchased from commercial
sources and used without further purification, unless other-
wise stated. All reactions were carried out under an argon
atmosphere on a magnetic stirrer and monitored by thin-layer
chromatography. Compounds were purified by flash chromato-
graphy on silica gel 40–60 μm, 60 Å. NMR measurements were
performed with a Varian Mercury 200 nuclear magnetic reso-
1
2
from peracetylated β-D-galactose (2.10 g, 5.57 mmol), the inter-
mediate azide was purified with flash column chromatography
(
1
PE/EtOAc, 50 : 50) to give 1.95 g (98%), which was converted to
.32 g (82%) of the title compound as a white solid, the
1
13
28,43
H and C NMR
published data. M.P. 134–136 °C (diethyl ether), lit.
34–136 °C.
,3,4,6-Tetra-O-acetyl-α-D-mannopyranosylamine
data of which were in agreement with the
1
13
2
8
nance spectrometer (at 200 MHz for H and at 50 MHz for C,
respectively). The deuterated solvents used for NMR spec-
1
troscopy were CDCl
3 6 3 2
, DMSO-d , CD OD and D O. Chemical
2
(1c).
shifts are given in ppm and were referenced on residual
Starting from peracetylated α-D-mannose (2.02 g, 5.13 mmol),
the intermediate azide was purified with PE/EtOAc, 50 : 50 to
give 1.90 g (99%), which was converted to 1.23 g (70%) of the
1
solvent peaks for CDCl
3
(δ 7.26 ppm for H NMR and
1
3
1
7
6
7.16 ppm for C NMR), DMSO-d (δ 2.50 ppm for H NMR
and 39.52 ppm for C NMR), CD OD (δ 3.31 ppm for H NMR
and 49.00 ppm for C NMR), whereas for D O, an external
2
1
3
1
1
13
34
3
title compound as a white solid, the H and C NMR data of
which were in agreement with the published data. M.P.
1
3
4
4
reference of 3-(trimethylsilyl)-1-propanesulfonic acid sodium
salt was used. Coupling constants were measured in Hz.
Hydrogen atom assignments, when given, are based on COSY
spectra. Whenever possible the component peaks corres-
ponding to the minor and major isomers of chromatographi-
cally inseparable anomeric mixtures are reported separately.
An asterisk (*) next to a peak indicates the minor isomer com-
ponent in almost equimolar anomeric mixtures. Melting
points are uncorrected. Optical rotations were measured at
room temperature in a 1.0 dm cell. Mass spectrometry experi-
ments were carried out in a Thermo Finnigan Surveyor MSQ
plus mass spectrometer, using the electron spray ionization
technique (ESI-MS). High-resolution mass spectrometry experi-
ments were carried out in a Q-TOF Bruker MaXis impact HR-
mass spectrometer.
1
48–151 °C (diethyl ether), lit. 145–147 °C (2-propanol).
2,3,4-Tri-O-acetyl-β-D-xylopyranosylamine (1d). Starting from
peracetylated β-D-xylose (1.00 g, 3.14 mmol), the intermediate
azide was purified with flash column chromatography (PE/
EtOAc, 50 : 50) to give 0.94 g (99%), which was converted to
1
0
.58 g (67%) of the title compound as a white solid, the H
1
3
28
and C NMR data of which were in agreement with the pub-
lished data. M.P. 101–102 °C (diethyl ether), lit. 101–102 °C.
,3,4-Tri-O-acetyl-β-L-arabinopyranosylamine (1e). Starting
2
8
2
from peracetylated β-L-arabinose (1.00 g, 3.14 mmol), the inter-
mediate azide was purified with flash column chromatography
(
PE/EtOAc, 60 : 40) to give 1.00 g (100%), which was converted
to 0.88 g (100%) of the title compound as a white solid. M.P.
1
1
5
30 °C (dec) (diethyl ether). H NMR (CDCl
3 H
, 200 MHz): δ
.36–5.23 (m, 1H, H-1), 5.06 (dd, J = 3.3, 0.5 Hz, 1H, H-3), 5.04
(
3
dd, J = 1.7, 0.8 Hz, 1H, H-2), 4.08 (dd, J = 4.8, 3.9 Hz, 1H, H-4),
.94 (dd, J = 13.4, 2.1 Hz, 1H, H-5′), 3.64 (dd, J = 13.4, 1.3 Hz,
General procedure for the synthesis of 1-aminosugars 1a–g
Trimethylsilyl azide (1.4 equiv.) was added to a solution of per- 1H, H-5), 2.15 (s, 3H, CH ), 2.08 (s, 3H, CH ), 2.01 (s, 3H,
3
3
1
3
acetylated sugar (1.0 equiv.) in anhydrous DCM (0.25 M) under CH
3
). C NMR (CDCl
3
, 50 MHz): δ
C
20.5, 20.7, 20.8, 64.9,
an argon atmosphere and the resulting mixture was stirred at 68.5, 70.0, 70.9, 85.4, 169.9, 170.1, 170.2. ESI + MS (m/z): 259.1
+
+
+
+
0
°C for 10 min. SnCl (0.3 equiv., 1 M solution in DCM) was [M − NH ] , 276.1 [M + H] , 294.1 [M + NH ] , 551.3 [2M + H] .
4
2
4
added dropwise to the mixture and the resulting solution was
2,3,4-Tri-O-acetyl-β-L-fucopyranosylamine (1f). Starting from
stirred at rt until the reaction was complete. The mixture was peracetylated β-L-fucose (0.90 g, 2.72 mmol), the intermediate
treated with an aqueous solution of 5% NaHCO (w/w), and azide was purified with flash column chromatography (DCM/
3
the resulting solution was extracted with EtOAc. The organic MeOH, 95 : 5) to give 0.70 g (81%), which was converted to
1
45
2 4
layer was washed with water and brine, dried over Na SO , fil- 0.60 g (92%) of the title compound as a white foam. H NMR
tered and concentrated in vacuo. The residue was purified by (CDCl , 200 MHz): δH 5.25 (dd, J = 2.7, 1.1 Hz, 1H, H-4), 5.05
3
flash chromatography to afford the desired azide. To a solution (dd, J = 3.0, 7.3 Hz, 1H, H-4), 5.00 (dd, J = 10.5, 7.6 Hz 1H,
of the azide (1.0 equiv.) in anhydrous THF (0.1 M) was added a H-2), 4.15 (d, J = 8.7 Hz, 1H, H-1), 3.81 (qd, J = 6.5, 1.0 Hz, 1H,
catalytic amount of 10% w/w Pd/C (0.06 equiv.). The mixture H-5), 2.17 (s, 3H, CH ), 2.08 (s, 3H, CH ), 1.99 (s, 3H, CH ),
3
3
3
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1
3
1
1
1
.18 (d, J = 6.5 Hz, 3H, CH
3
). C NMR (CDCl
3
, 50 MHz): δ
C
95 : 5) to give 0.50 g (90%) as a white solid. M.P. 112–117 °C.
2
0
1
6.1, 20.4, 20.5, 20.7, 69.5, 69.8, 70.5, 71.5, 84.6, 170.0, 170.3, [α] −7.5 (c 1.00, MeOH). H NMR (DMSO-d , 200 MHz): δ
D
6
H
+
+
70.4. ESI + MS (m/z): 273.1 [M − NH
2
] , 290.1 [M + H] , 579.4 8.79 (s, 1H, NH), 8.27 (d, J = 9.6 Hz, 1H, NH), 6.85 (bs, 2H,
NH ), 5.40–5.21 (m, 3H, H-1,3,4), 4.94 (t, J = 6.6 Hz, 1H, H-2),
,3,4-Tri-O-acetyl-α-L-rhamnopyranosylamine (1g). Starting 4.31 (t, J = 6.4 Hz, 1H, H-5), 4.03 (dd, J = 11.3, 6.2 Hz, 1H,
from peracetylated α-L-rhamnose (1.00 g, 3.01 mmol), 0.86 g H-6′), 3.95 (dd, J = 11.3, 6.6 Hz, 1H, H-6″), 2.12 (s, 3H, CH ),
). C NMR
which was converted to 0.77 g (97%) of the title compound as (CDCl , 50 MHz): δ 20.57, 20.64, 20.68, 20.78, 61.2, 67.2, 67.7,
+
+
[2M + H] , 601.2 [2M + Na] .
2
2
3
13
(
3 3 3
91%) of the intermediate azide was isolated as a colorless oil, 2.01 (s, 3H, CH ), 1.99 (s, 3H, CH ), 1.92 (s, 3H, CH
3
C
1
a white foam. H NMR (CDCl
.2 Hz, 1H, H-3), 5.08–4.87 (m, 2H, H-2, H-4), 4.40 (d, J = 1.1 (ESI/Q-TOF) m/z: [M + H] calcd for C16
Hz, 1H, H-1), 3.66–3.42 (m, 1H, H-5), 2.18 (s, 3H, CH ), 2.04 (s, found 434.1405.
3 H
, 200 MHz): δ 5.38 (dd, J = 2.7, 71.0, 72.0, 79.2, 154.9, 156.2, 169.9, 170.2, 170.5, 170.9. HRMS
+
1
24 3
H N O11 434.1405;
3
1
3
3
H, CH
3
), 1.97 (s, 3H, CH
, 50 MHz): δ
1.7, 81.4, 169.7, 169.8, 170.1. ESI + MS (m/z): 290.2 [M + H] , purified with flash column chromatography (DCM/MeOH,
3
), 1.22 (d, J = 6.2 Hz, 3H, CH
3
).
C
1-(2,3,4,6-Tetra-O-acetyl-α-D-mannopyranosyl)biuret
(2c).
NMR (CDCl
7
3
3
C
17.4, 20.4, 20.5 (2C), 70.3, 70.8, 70.9, Starting from 1c (0.45 g, 1.30 mmol), the title compound was
+
+
+
+
12.3 [M + Na] , 579.5 [2M + H] , 601.4 [2M + Na] .
95 : 5) to give 0.41 g (73%) as a white solid. M.P. 98–101 °C.
2
0
1
[
α] −33.0 (c 1.00, MeOH). H NMR (DMSO-d
6
, 200 MHz): δ
.88 (s, 1H, NH), 8.41 (d, J = 9.8 Hz, 1H, NH), 6.82 (bs, 2H,
), 5.61 (dd, J = 9.8, 0.7 Hz, 1H, H-1), 5.36 (dd, J = 10.0, 3.6
N (0.18 mL, 1.29 mmol) and Hz, 1H, H-3), 5.20 (dd, J = 3.6, 0.7 Hz, 1H, H-2), 4.98 (t, J = 9.9
TMSNCO (0.87 mL, 6.47 mmol). The reaction mixture was Hz, 1H, H-4), 4.10 (dd, J = 12.8, 8.1 Hz, 1H, H-6′), 4.02–3.93 (m,
stirred at 40 °C for 19 h, and concentrated in vacuo to remove 2H, H-5, H-6″), 2.17 (s, 3H, CH ), 2.01 (s, 6H, 2 × CH ), 1.91 (s,
, 50 MHz): δ 20.54, 20.58, 20.67,
H
4
6
D
1
-(2,3,4,6-Tetra-O-acetyl-β-D-glucopyranosyl)urea (3a)
8
To a 0.4 M solution of 1a (0.45 g, 1.29 mmol) in anhydrous NH
THF (3 mL) were added Et
2
3
3
3
1
3
the THF. The residue was triturated with EtOAc, filtered and 3H, CH
3
). C NMR (CDCl
3
C
washed with EtOAc to afford 2a (0.19 g, 34%) as a white 20.67, 63.4, 66.7, 71.2, 72.8, 74.5, 77.8, 155.5, 157.6, 171.4,
+
powder (see data below). The filtrate was concentrated to 171.5, 171.9, 172.4. HRMS (ESI/Q-TOF) m/z: [M + H] calcd for
1
afford 3a (0.33 g, 65%) as a white powder. H NMR (200 MHz,
CDCl ) δ 2.01 (s, 3H), 2.03 (s, 3H), 2.07 (s, 3H), 2.08 (s, 3H),
C
16
H
24
N
3
O
11 434.1405; found 434.140.
1-(2,3,4-Tri-O-acetyl-β-D-xylopyranosyl)biuret (2d). Starting
3
H
3
1
=
.82 (ddd, J = 10.1, 4.6, 2.2 Hz, 1H), 4.09 (dd, J = 12.5, 2.2 Hz, from 1d (0.45 g, 1.63 mmol), the title compound was purified
H), 4.31 (dd, J = 12.5, 4.6 Hz, 1H), 4.82–5.22 (m, 5H), 5.31 (t, J with flash column chromatography (DCM/MeOH, 95 : 5) to
1
3
20
9.4 Hz, 1H), 5.92 (d, J = 9.6 Hz, 1H). C NMR (50 MHz, give 0.52 g (87%) as a white solid. M.P. 106–108 °C. [α]D −15.6
1
CDCl
3
) δ
C
20.66, 20.69, 20.83 (2C), 62.0, 68.4, 70.4, 73.1 (2C), (c 1.00, MeOH). H NMR (DMSO-d
6
, 200 MHz): δ
H
8.84 (s, 1H,
), 5.31 (t,
J = 9.2 Hz, 1H), 5.17 (t, J = 9.1 Hz, 1H), 4.91–4.73 (m, 2H), 3.88
dd, J = 11.3, 6.0 Hz, H-5′), 3.47–3.59 (m, 1H, H-5″), 2.08 (s, 3H,
7
9.8, 158.3, 169.8, 170.0, 170.90, 170.96. ESI + MS (m/z): 391.0 NH), 8.20 (d, J = 9.9 Hz, 1H, NH), 6.81 (bs, 2H, NH
2
+
+
+
[M + H] , 408.2 [M + NH ] , 781.3 [2M + H] .
4
(
General procedure for the synthesis of biurets 2a–g
13
3 3 6 C
CH ), 1.99 (s, 6H, 2 × CH ). C NMR (DMSO-d , 50 MHz): δ
To a 0.4 M solution of 1-aminosugar 1a–g (1.0 equiv.) in anhy- 20.41, 20.46, 20.57, 62.9, 68.6, 70.1, 71.8, 78.2, 154.2, 155.0,
+
drous THF were added Et
5 equiv.). The reaction mixture was stirred at 25 °C overnight, for C13
and then was concentrated in vacuo to remove the THF. The 1-(2,3,4-Tri-O-acetyl-β-L-arabinopyranosyl)biuret (2e). Starting
residue was purified by column chromatography to afford the from 1e (0.45 g, 1.64 mmol), the title compound was purified
biurets 2a–g. with flash column chromatography (DCM/MeOH, 95 : 5) to
3
N (1.0 equiv.) and TMSNCO 169.45, 169.55, 169.64. HRMS (ESI/Q-TOF) m/z: [M + Na] calcd
(
H
19
N
3
NaO 384.1014; found 384.1014.
9
2
0
1
-(2,3,4,6-Tetra-O-acetyl-β-D-glucopyranosyl)biuret (2a). Starting give 0.40 g (67%) as a white solid. M.P. 68–72 °C. [α] +23.3
D
1
from 1a (0.45 g, 1.29 mmol), the title compound was purified (c 1.00, MeOH). H NMR (DMSO-d
6
, 200 MHz): δ
H
8.81 (s, 1H,
with flash column chromatography (DCM/MeOH, 95 : 5) to NH), 8.29 (d, J = 9.6 Hz, 1H, NH), 6.84 (bs, 2H, NH
2
), 5.25 (dd,
2
0
give 0.50 g (90%) as a white solid. M.P. 119–120 °C. [α] −10.0 J = 9.5 Hz, 3.5 Hz, 1H), 5.21–5.06 (m, 2H), 4.93 (t, J = 8.8 Hz,
D
1
(
c 0.96, MeOH). H NMR (DMSO-d
6
, 200 MHz): δ
H
8.84 (s, 1H, 1H), 3.99–3.64 (m, 2H, H-5, H-5′), 2.10 (s, 3H, CH
3
), 2.02 (s,
1
3
NH), 8.19 (d, J = 9.3 Hz, 1H, 1-NH), 6.86 (bs, 2H, NH
2
), 5.40 (t, 3H, CH
3
), 1.90 (s, 3H, CH
3
). C NMR (DMSO-d
6
, 50 MHz): δ
C
J = 9.5 Hz, 1H, 3-H), 5.33 (t, J = 9.4 Hz, 1H, H-1), 4.92 (t, J = 9.6 20.61, 20.75, 20.87, 65.3, 68.0 (2C), 70.6, 79.4, 155.0, 156.2,
+
Hz, 1H), 4.84 (t, J = 9.6 Hz, 1H), 4.18–3.94 (m, 3H, H-5,6), 2.01 170.0, 170.3, 170.9. HRMS (ESI/Q-TOF) m/z: [M + H] calcd for
1
3
(
(
7
s, 3H, CH
3
), 1.98 (s, 6H, CH
3
), 1.94 ppm (s, 3H, CH
3
). C NMR
C
13
H
20
N
3
O
9
362.1194; found 362.1210.
1-(2,3,4-Tri-O-acetyl-β-L-fucopyranosyl)biuret (2f). Starting
2.5, 77.6, 154.1, 155.1, 169.4, 169.5, 169.6, 170.2. HRMS (ESI/ from 1f (0.45 g, 1.56 mmol), the title compound was purified
DMSO-d , 50 MHz): δ 20.4, 20.5, 20.6, 61.9, 68.1, 70.2, 72.0,
6
C
+
Q-TOF) m/z: [M + H] calcd for C16
34.1399.
-(2,3,4,6-Tetra-O-acetyl-β-D-galactopyranosyl)biuret
24 3
H N O11 434.1405; found with flash column chromatography (DCM/MeOH, 95 : 5) to
2
0
4
give 0.57 g (99%) as a white solid. M.P. 149–153 °C. [α] −6.7
D
1
1
(2b). (c 0.75, acetone). H NMR (DMSO-d
6
, 200 MHz): δ
H
8.78 (s, 1H,
), 5.25
purified with flash column chromatography (DCM/MeOH, (dd, J = 9.9, 3.5 Hz, 1H, H-3), 5.20–5.09 (m, 2H, H-1,4), 4.90 (t,
Starting from 1b (0.45 g, 1.29 mmol), the title compound was NH), 8.20 (d, J = 10.1 Hz, 1H, NH), 6.85 (bs, 2H, NH
2
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J = 9.6 Hz, 1H, H-2), 4.11 (q, J = 6.6 Hz, 1H, H-5), 2.15 (s, 3H, was added to the filtrate and the reaction mixture was stirred
CH ), 2.00 (s, 3H, CH ), 1.93 (s, 3H, CH ), 1.03 (d, J = 6.4 Hz, under an argon atmosphere for 20 h. The mixture was concen-
3
3
3
1
3
3
H, CH
3
). C NMR (DMSO-d
6
C
, 50 MHz): δ 20.6, 20.7, 20.9, trated in vacuo to remove the THF. The residue was dissolved
6
5.3, 68.0, 70.6, 79.4, 155.0, 156.2, 170.0, 170.3, 170.9. HRMS in EtOAc and washed with water (4×). The organic phase was
+
(ESI/Q-TOF) m/z: [M + H] calcd for C H N O 376.1351; dried over Na SO , filtered and concentrated. Purification by
14 22 3 9 2 4
found 376.1352.
column chromatography (EtOAc) afforded the title compound
1-(2,3,4-Tri-O-acetyl-α-L-rhamnopyranosyl)biuret (2g). Starting as a white amorphous solid (0.23 g, 44%). It was obtained as
from 1g (0.45 g, 1.55 mmol), the title compound was purified an inseparable, 1.6 : 1 (α : β) anomeric mixture. R : 0.50
f
1
6 H
with flash column chromatography (EtOAc), to give 0.40 g (EtOAc). H NMR (DMSO-d , 200 MHz): both anomers: δ 8.74
69%) as a white solid. M.P. 159–163 °C. [α] +28.4 (c 1.00, (s, 1H, NH), 8.68* (s, 1H, NH), 8.52 (d, J = 9.4 Hz, 1H, NH),
MeOH). H NMR (DMSO-d , 200 MHz): δ 8.89 (s, 1H, NH), 8.02* (d, J = 9.3 Hz, 1H, NH), 6.77 (bs, 4H, NH ), 5.84–5.49 (m,
2
0
(
D
1
6
H
2
8
1
1
9
.34 (d, J = 9.7 Hz, 1H, NH), 6.91 (bs, 2H, NH
H, H-1), 5.27 (dd, J = 10.1, 3.6 Hz, 1H, H-3), 5.19 (dd, J = 3.7, 3.64–3.58 (m, 1H, H-4), 3.56–3.39 (m, 4H, H-5), 2.34 (ddd, J =
.4 Hz, 1H, H-2), 4.77 (t, J = 9.8 Hz, 1H, H-4), 3.75 (h, J = 12.2, 12.5, 6.3 Hz, 1H, H-2′), 2.04–1.55 (m, 3H, H-2′, H-2″), 0.87 (s,
2
), 5.59–5.44 (m, 2H, H-1), 4.42–4.18 (m, 2H, H-3), 3.93–3.79 (m, 1H, H-4),
1
3
.7, 5.8 Hz, 1H, H-5), 2.16 (s, 3H, CH
), 1.08 (d, J = 6.1 Hz, 3H, CH
0 MHz): δC 17.8, 20.6, 20.6, 20.7, 71.3, 71.5, 71.6 (2C), 18.4, 26.0 (2C), 40.1, 63.4, 73.5, 81.4, 87.3, 155.1, 156.2; minor
7.5, 155.5, 157.5, 171.4, 171.7, 171.9. HRMS (ESI/Q-TOF) m/z: anomer: δ −5.4, −5.3, −4.7 (2C), 18.0, 18.3, 25.8, 26.0, 40.5,
63.8, 72.8, 80.9, 87.0, 155.2, 156.5. HRMS (ESI/Q-TOF) m/z: [M
3
), 2.04 (s, 3H, CH
3
), 1.91 36H, 4 × SiC(CH
3
)
3
), 0.09–0.02 (s, 24H, 4 × Si(CH
3 2
) ). C NMR
1
3
(s, 3H, CH
3
3
). C NMR (CD OD, (CDCl , 50 MHz): major anomer: δ
3
3
C
−5.4, −5.3, −4.7 (2C), 18.3,
5
7
C
+
[M + H] calcd for C14
H
22
N
3
O
9
376.1351; found 376.1350.
−
−
H] calcd for C H N O Si 446.2512; found 446.2519.
19 41 3 5 2
1
-(2,3,5-Tri-O-acetyl-α/β-D-ribofuranosyl)biuret (8)
1-(2-Deoxy-α/β-D-ribofuranosyl)biuret (10)
To a solution of 2,3,5-tri-O-acetyl-D-ribofuranosyl azide 4
(0.40 g, 1.33 mmol) in anhydrous THF (10 mL) were added To a solution of biuret 9 (0.52 g, 1.16 mmol) in anhydrous
1
0
1
0% Pd/C (80 mg, 0.075 mmol) and Et
.66 mmol). The mixture was stirred under 1 atm H
h. The Pd/C was removed by filtration through Celite, and then concentrated in vacuo to remove THF. The residue was
3
N (0.09 mL, THF (14 mL) was added 1 M TBAF solution in THF (2.9 mmol,
2
gas for 2.9 mL). The reaction mixture was stirred at rt overnight and
the filtrate was used in the next step without further purifi- purified by column chromatography (DCM/MeOH, 8.5 : 1.5) to
1
cation. TMSNCO (0.59 mL, 4.80 mmol) was added to the fil- afford 11 (0.26 g, 100%) as a white solid, the H NMR data of
1
1
trate and the reaction mixture was stirred under an argon which were in agreement with the published data. It was
atmosphere for 20 h. The mixture was then concentrated obtained as a 1.3 : 1 (α : β) anomeric mixture. : 0.17
OD, 50 MHz): major
EtOAc and washed with water (4×). The organic phase was anomer: δC 40.5, 63.4, 73.1, 82.3, 88.0, 156.0, 157.9; minor
R
f
1
3
in vacuo to remove the THF. The residue was dissolved in (DCM : MeOH, 85 : 15). C NMR (CD
3
2 4 C
dried over Na SO , filtered and concentrated. Purification by anomer: δ 41.1, 63.6, 72.9, 82.1, 87.8, 156.1, 157.8. HRMS
column chromatography (EtOAc) afforded the title compound (ESI/Q-TOF) m/z: [M − H]− calcd for C
7
12 3 5
H N O 218.0782;
as a white amorphous solid (0.40 g, 77%). It was obtained as found 218.0775.
an inseparable 1 : 1 (α : β) anomeric mixture. R
f
: 0.30 (EtOAc).
, 200 MHz): both anomers: δ 8.98 (s, 1H),
.84* (s, 1H), 8.75 (d, J = 9.8 Hz, 1H), 8.39* (d, J = 9.3 Hz, 1H),
1
1-(3,4-Di-O-acetyl-2-deoxy-α/β-D-erythropentopyranosyl)biuret
13)
H NMR (DMSO-d
6
H
(
8
6
5
2
5
2
7
1
.80 (bs, 4H), 5.85 (dd, J = 9.8, 4.5 Hz, 1H), 5.46* (dd, J = 9.3, To a solution of azide 11 (0.80 g, 3.29 mmol), in anhydrous
.7 Hz, 1H), 5.29–5.09 (m, 3H), 4.27–4.00 (m, 5H), 2.08 (s, 6H), THF (30 mL), was added 10% Pd/C (100 mg, 0.094 mmol). The
.06 (s, 6H), 2.05 (s, 3H) 2.04 (s, 3H). C NMR (CDCl3, mixture was stirred under 1 atm H gas, for 1 h. The Pd/C was
1
3
2
0 MHz): both anomers: δ
C
20.36, 20.44, 20.50 (2C), 20.64, removed by filtration through Celite, and the filtrate was con-
0.71, 63.38, 63.41*, 69.7, 70.7*, 71.4, 73.0*, 78.36, 78.49*, centrated in vacuo. The residue was dissolved in THF (8 mL)
9.2, 82.8*, 154.7*, 155.0, 156.05*, 156.17, 169.48*, and TMSNCO (2.20 mL, 16.45 mmol) and Et N (0.46 mL,
3
69.96, 170.03, 170.07*, 170.70, 170.85*. HRMS (ESI/Q-TOF) 3.29 mmol) were added. The reaction mixture was stirred
−
m/z: [M − H] calcd for C13
H
19
N
3
O
9
360.1049; found 360.1052.
under an argon atmosphere for 19 h. The mixture was concen-
trated in vacuo to remove the volatiles. Purification by column
chromatography (DCM/MeOH, 90 : 10 v/v) afforded the title
compound as a white amorphous solid (0.17 g, 17%). It was
1-[3,5-Di-O-(tert-butyldimethylsilyl)-2-deoxy-α/β-D-ribofuranosyl]
biuret (9)
To a solution of 3,5-di-O-(tert-butyldimethylsilyl)-2-deoxy-α/ obtained as an inseparable, 1.15 : 1 (α : β) anomeric mixture.
1
β-D-ribofuranosyl azide 5 (0.45 g, 1.16 mmol) in anhydrous
THF (9 mL) were added 10% Pd/C (70 mg, 0.066 mmol) and both anomers: δ
Et N (0.17 mL, 1.16 mmol). The mixture was stirred under 1 J = 8.9 Hz, 1H, NH), 8.18* (d, J = 9.1 Hz, 1H, NH), 6.87 (bs, 4H,
R
f
: 0.44 (DCM : MeOH, 90 : 10). H NMR (DMSO-d
6
, 200 MHz):
H
8.71 (s, 1H, NH), 8.67* (s, 1H, NH), 8.40 (d,
3
atm H
through Celite, and the filtrate was used in the next step 1H), 3.82–3.59 (m, 4H), 2.07* (s, 3H, CH
without further purification. TMSNCO (0.68 mL, 5.45 mmol) 1.99 (s, 3H, CH ), 1.98* (s, 3H, CH ), 1.86–1.63 (m, 2H).
2 2
gas, for 1 h. The Pd/C was removed by filtration 2 × NH ), 5.31–4.94 (m, 4H), 4.87* (ddd, J = 8.4, 4.6, 3.4 Hz,
3
), 2.06 (s, 3H, CH
3
),
C
1
3
3
3
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NMR (CD
3
OD, 50 MHz): major anomer: δ
C
20.8 (2C) 32.6, 65.0, dation products of 2′-deoxycytidine. Although the highly polar
6
2
1
8.0, 69.5, 77.3, 155.8, 157.6, 171.7, 172.0; minor anomer: δC nature of these lesions has so far hampered their study, their
0.7, 20.8, 34.2, 63.2, 68.0, 68.5, 75.9, 155.9, 157.7, 171.8, direct synthetic access may permit studies on derivatisation
+
71.9. HRMS (ESI/Q-TOF) m/z: [M
+
Na] calcd for and appropriate protection that would allow the investigation
of their mutagenic potential. The furanosyl to pyranosyl ring-
isomerisation, that was observed upon the deprotection of
DMT-dfBU 15, indicates that the protection of the biuret func-
C H N NaO 326.0959; found 326.0960.
1
1
17
3
7
1
-(2-Deoxy-α/β-D-ribopyranosyl)biuret (14)
A solution of biuret 13 (100 mg, 0.33 mmol) in NH
7 N, 1.4 mL) was stirred at rt for 18 h and concentrated this lesion suitable for oligonucleotide synthesis. A related
/MeOH tion is necessary in order to hamper ring opening and make
3
(
in vacuo. The residue was dissolved in MeOH, triturated with study is currently in progress and the results will be reported
DCM and filtered to afford biuret 14 as a white foam (60 mg, in due course.
1
7
6%), the H NMR data of which were in agreement with the
1
1
published data. It was obtained as a 1.4 : 1 (α : β) anomeric
1
3
mixture. R
CD OD) major anomer: δC 35.0, 66.3, 68.2, 68.9, 77.1, 155.9,
f
: 0.10 (DCM : MeOH, 90 : 10). C NMR (50 MHz, Conflicts of interest
3
There are no conflicts of interest to declare.
1
1
57.8; minor anomer: δC 37.2, 65.6, 67.7, 68.2, 75.4, 156.0,
57.8.
Acknowledgements
1
-(2-Deoxy-5-dimethoxytrityl-α/β-D-ribofuranosyl)biuret (15)
DfBU (10, 320 mg, 1.46 mmol) was dried with three successive This research has been co-financed by the European Union
cycles of dissolution in pyridine (5 mL) and evaporation. To (European Social Fund – ESF) and Greek national funds
this was added pyridine (14 mL) followed by DMTCl (743 mg, through the Operational Program “Education and Lifelong
2
.19 mmol) and DMAP (17 mg, 0.155 mmol), at 0 °C, and the Learning” of the National Strategic Reference Framework
resulting solution was stirred for 3 h. The reaction was diluted (NSRF) – Research Funding Program: Heraclitus II, “Investing
with methanol and toluene and the volatiles were evaporated in knowledge society through the European Social Fund”.
under reduced pressure in a rotary evaporator. Column chrom- V. T. and E. E. P. acknowledge funding (COST Action 1201
atography of the residue (CHCl
3
: MeOH, 9 : 1) yielded an inse- “Biomimetic Radical Chemistry”) and generous hosting
parable anomeric mixture of the title compound (434 mg, (Dr Carla Ferreri) for an STSM visit to ISOF Institute, Bologna,
1
5
7%) as a white foam. R : 0.17 (DCM : MeOH, 96 : 6). The H Italy.
f
NMR spectrum indicated the presence of a 2 : 1 mixture of
1
3
anomers but only a single set of peaks was observed in the
C
1
NMR. Both anomers: H NMR (DMSO-d , 200 MHz): δ 1.68 References
6
H
(
d, J = 13.2 Hz, 1H), 1.79–2.08* (m, 2H), 2.26 (ddd, J = 12.7, 6.4,
1
M. D. Altman, B. M. Andresen, K. L. Arrington,
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6
1
5
.4 Hz, 1H), 2.85–2.99 (m, 2H), 3.40 (bs, 1H), 4.00–4.09 (m,
H), 5.18* (d, J = 4.3 Hz, 1H, OH), 5.32 (d, J = 3.1 Hz, 1H, OH),
.61–5.78 (m, 1H), 6.79–6.91 (m, 6H), 7.16–7.44 (m, 9H), 8.05*
d, J = 9.4 Hz, 1H), 8.29 (d, J = 9.1 Hz, 1H), 8.68* (s, 1H), 8.85
s, 1H). C NMR (CD OD, 50 MHz): δC 40.3, 55.6 (2C), 65.3,
3.6, 81.9*, 82.4, 86.99, 87.28, 114.0 (4C), 127.7, 128.7 (2C),
29.1 (2C), 131.1 (4C), 136.97, 137.04, 146.2, 155.8, 157.8,
59.8 (2C). ESI + MS (m/z): 303.2 [DMT] , 522.2 [M + H] , 544.4
(
(
1
3
3
7
1
1
+
+
+
[M + Na] .
2
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F. Deroose, Novel 3-indol substituted derivatives, pharma-
ceutical compositions and methods for use, WO 2015/
140717A1, 2015.
Conclusions
In conclusion, we have developed and optimised an efficient
and convenient reaction for the synthesis of anomeric sugar
biurets in one step from their corresponding 1-aminosugars
utilising TMSNCO. The conditions were optimised with
respect to the base, solvent, temperature and reagent equiv.
utilised, in order to produce a high yielding protocol with
biurets as the sole products of the reaction. Furthermore, the
application of this method on 2-deoxy-D-ribose led to the syn-
thesis of 1-(2-deoxy-α/β-D-ribofuranosyl)biuret (dfBU, 10) and
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1a adrenergic receptor antagonists, US 6376503B1, 2002.
1
-(2-deoxy-α/β-D-ribopyranosyl)biuret (dpBU, 14), known oxi-
Org. Biomol. Chem.
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