A versatile method of tethering biomolecules to pyrrole precursors for functionalized magnetic polypyrrole core-shell nanoparticles

Article abstract of DOI:10.1055/s-0029-1218846

A mild and versatile method based on copper-catalyzed [3+2] cycloaddition (Meldal-Sharpless reaction) was developed to tether biomolecules, such as monosaccharides, biotin, cholesterol, or uridine to the N-atom of pyrrole. The required azido and alkyne functions can be placed in either reactant, i.e. in the pyrrole or the biomolecule. The products are interesting precursors for functionalized superparamagnetic polypyrrole core-shell nanoparticles. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0029-1218846

PAPER
3021
A Versatile Method of Tethering Biomolecules to Pyrrole Precursors for
Functionalized Magnetic Polypyrrole Core-Shell Nanoparticles
T
ethering Biom
e
olecules
t
b
P
yrrole Pre
a
cursors stian Karsten,a Mohamed A. Ameen,a,b Sabrina I. Kalläne,a Alexandrina Nan,c Rodica Turcu,c Jürgen Liebscher*a
a
Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany
Fax +49(30)20937552; E-mail: liebscher@chemie.hu-berlin.de
b
c
Department of Chemistry, Faculty of Science, El Minia University, El Minia 61519, Egypt
National Institute of Research and Development for Isotopic and Molecular Technologies,
Donath 65-103, 400293 Cluj-Napoca, Romania
Received 13 April 2010; revised 3 May 2010
nanoparticles. As compared with other tethering tools, the
Meldal–Sharpless cycloaddition method tolerates many
functional groups allowing the omission of protective
groups and, thus, it has also been widely applied for bio-
Abstract: A mild and versatile method based on copper-catalyzed
[3+2] cycloaddition (Meldal–Sharpless reaction) was developed to
tether biomolecules, such as monosaccharides, biotin, cholesterol,
or uridine to the N-atom of pyrrole. The required azido and alkyne
functions can be placed in either reactant, i.e. in the pyrrole or the logical molecules. So far, the copper-catalyzed [3+2] cy-
biomolecule. The products are interesting precursors for functional-
cloaddition of azides with alkynes has been employed in
ized superparamagnetic polypyrrole core-shell nanoparticles.
PPy chemistry only once when 1-decylpyrroles with a ter-
Key words: pyrroles, alkynes, azides, cycloaddition, biomolecules
minal azido or propargyl ether moiety were electro-poly-
merized. The resulting PPy electrode surfaces were
further functionalized by click reactions with histidine
tags and biomolecules.16
Superparamagnetic nanoparticles, in particular iron(II,III)
oxide (Fe3O4) nanoparticles, have gained wide interest in
biological and medical applications, such as in cancer
treatment by hyperthermia, as contrast reagents in diagno-
sis, and in the separation of biomaterials.1–8 In all of these
applications the nanoparticles are exposed to body fluids
and it is desirable that they are inert under these conditions
and preferably locate at the target tissues. The stability
against the biological environment can be improved by
covering Fe3O4 nanoparticles with polymer shells leading
to so-called core-shell nanoparticles.2,4,7,9 Tethering bio-
logical molecules to the polymer shell can make the core-
shell nanoparticles more tolerable to the biological system
and can help to target locations of interest if the biomole-
cules contain recognition functions.4,6,7 Several polymers,
e.g. polyvinyl alcohol, polyvinyl acetate, polyethylene-
glycol (PEG), dextran, or silica have been utilized for this
purpose. Polypyrroles (PPy) have rarely been used in this
field although they are known to be biocompatible10,11 and
can form proper shells with Fe3O4 nanoparticles and, thus,
protect them very well.12–14 There are only a few reports
where PPy-Fe3O4 core-shell nanoparticles were obtained
in which the polypyrrole shell is decorated with biomole-
cules.15 In these cases, amino acids or folic acid were teth-
ered to pyrrole rings by EDC coupling.
We demonstrate here that the Meldal–Sharpless reaction
gives straightforward access to pyrrole monomers
equipped with carbohydrate, nucleoside, biotin, and ste-
roid moieties and we provide proof that the products can,
in principle, be used for the preparation of functionalized
magnetic core-shell Fe3O4 nanoparticles.
To maintain the capability of pyrrole monomers to under-
go proper oxidative polymerization to polypyrroles, posi-
tions 2 and 5 of the pyrrole ring must be free, i.e. positions
3 and 4 and the ring nitrogen atom are available as tether-
ing sites for biomolecules. Since the introduction of func-
tional groups into positions 3 and 4 can suffer from the
formation of regioisomers (competing formation of 2- or
5-substituted pyrroles) the nitrogen atom of the pyrrole
ring is often the favored site for the attachment of substit-
uents and, thus, it was also chosen in the synthesis pre-
sented here. Either functionality, azido or alkyne moiety,
necessary for Meldal–Sharpless cycloaddition could be
introduced at the pyrrole nitrogen atom. Thus 1-(6-bromo-
hexyl)-1H-pyrrole (1) was transformed into the corre-
sponding hitherto unknown azide 2 by nucleophilic
substitution with sodium azide in acetonitrile. On the oth-
er hand 3-(1H-pyrrol-1-yl)propanoic acid (5),17 which is
easily available via addition of pyrrole to acrylonitrile and
subsequent basic hydrolysis, was transformed into the N-
propargylamide 6. Surprisingly, the very versatile alkyne
6 is previously unknown; it can be expected to play an im-
portant role in the chemistry of functionalized pyrroles in
the future. The biomolecules containing reactants 3 and 7
are known and all of them were easy to attain.
We became interested in how far the popular and widely
used copper-catalyzed [3+2] cycloaddition of azides and
alkynes to give 1,2,3-triazoles (Meldal–Sharpless ‘click’
reaction) can be applied for tethering biomolecules to pyr-
roles, which can later be used for the preparation of func-
tionalized shells of magnetic core-shell Fe3O4
The [3+2]-cycloaddition reactions (Schemes 1 and 2,
Table 1) were performed by applying established proce-
dures with copper sulfate as catalyst in the presence of so-
SYNTHESIS 2010, No. 17, pp 3021–3028
Advanced online publication: 30.06.2010
DOI: 10.1055/s-0029-1218846; Art ID: T08910SS
x
x.
x
x
.
2
0
1
0
© Georg Thieme Verlag Stuttgart · New York

3022
S. Karsten et al.
PAPER
dium ascorbate (Method A). High yields of products 4 and
8 were achieved in the majority of cases after long reac-
tion times (several days). Sometimes, tris[(1-benzyl-1H-
1,2,3-triazol-4-yl)methyl]amine18,19 (TBTA) had to be
used as a ligand for copper (Method B) in order to accel-
erate the reaction and to obtain reasonable yields in ac-
ceptable reaction times (within hours). However, this
procedure has the disadvantage of causing difficulties
during the separation of the polar [3+2]-cycloaddition
product from the ligand (see product 4b).
EDC
HOBt
DIPEA
N
O
N
O
H2N
CH2Cl2,
r.t., 19 h
OH
N
H
5
6 (90%)
Method Aa (68–99%)
Method Ba (87–92%)
N3 biomolecule
The 1,2,3-triazole-biomolecule pyrrole conjugates 4 and 8
appeared as colorless, stable products that are solids in
most cases. Their structures were confirmed by spectro-
scopic methods. In addition to the signals of the pyrrole,
the biomolecule, and the linker moieties, diagnostic sig-
nals for the 1,2,3-triazole ring were found in the NMR
spectra [d = 7.4–7.9 (1H NMR), d = 121–124 and 144–146
(13C NMR)]. For later applications, e.g. as a recognition
function, it is essential that the biomolecule moiety in the
polypyrrole copolymer is unprotected. Thus, the acetyl
groups found in the sugar units of 4d, 8b, and 8c, remain-
ing from the preparation of the starting 1-azido saccha-
rides, had to be removed. This could be achieved by
transesterification with methanol in the presence of sodi-
um methoxide providing the unprotected glycosides 9 in
high yields (Scheme 3).
7
N
O
N
biomolecule
N
a see Scheme 1
H
N
N
8
Scheme 2
OAc
AcO
O
cat. NaOMe
R
9a–c
AcO
MeOH,
30 min, r.t.
OAc
4d, 8b, 8c
R
N
N
NaN3
N
N
4d
N
N
N3
4
MeCN,
reflux, 21 h
O
Br
4
4
O
2 (99%)
1
8b,c
N
N
N
H
N
O
N
Method A: cat. CuSO4⋅5H2O,
Na-ascorbate, H2O–t-BuOH
or THF, r.t., 2–9 d
(45–71% yield)
OH
N
N
N
HO
HO
biomolecule
N
3
Method B: cat. CuSO4⋅5H2O,
Na-ascorbate, TBTA, H2O–
t-BuOH or THF, r.t., 1–3 h
(35–88% yield)
4
O
OH
9a (86%)
O
N
NH
OH
OH
N
O
HO
HO
N
N
N
N
4
OH
N
9b (98%)
N
O
N
biomolecule
NH
4
OH
O
Scheme 1
N
N
N
HO
OH
9c (81%)
From our results it can be concluded that the copper-cata-
lyzed azide–alkyne cycloaddition is a versatile method for
tethering biomolecules to pyrrole that is likely to be suc-
cessful also with other, more complex biological struc-
tures. As proof of the principle, the cholesterol-
functionalized pyrrole 4a was applied to the preparation
Scheme 3
of functionalized magnetic core-shell nanoparticles. Pyr-
role 4a was copolymerized with unsubstituted pyrrole
(4a/pyrrole, 1:2) by oxidation with ammonium persulfate
Synthesis 2010, No. 17, 3021–3028 © Thieme Stuttgart · New York

PAPER
Tethering Biomolecules to Pyrrole Precursors
3023
Table 1 [3+2]-Cycloaddition Products 4 and 8
Product
Methoda
Time
Yieldb (%)
A
B
2 d
3 h
71
88
H
4a
H
H
H
N
O
N
N
4
N
O
S
HN
NH
A
B
5 d
3 h
52
35
4b
N
H
H
N
N
H
N
N
4
O
OAc
N
N
A
B
2 d
2 h
45
77
4c
N
O
N
AcO
AcO
4
O
OAc
OAc
N
AcO
AcO
N
A
B
2 d
3 h
65
81
4d
N
O
N
4
O
OAc
O
NH
HO
N
O
O
8a
B
1 h
87
OH
N
H
N
N
N
N
O
O
N
A
B
4 d
3 h
99
92
8b
8c
NH
OAc
O
AcO
AcO
N
N
N
OAc
O
N
A
B
9 d
3 h
68
88
NH
OAc
AcO
AcO
O
N
N
N
OAc
a Method A: CuSO4·5 H2O (cat.), Na ascorbate, H2O–t-BuOH or H2O–THF, r.t., 2–9 d; Method B: CuSO4·5 H2O (cat.), Na ascorbate, TBTA,
H2O–t-BuOH or H2O–THF, r.t., 1–3 h.
b Yield of isolated product.
in the presence of a water-based magnetic Fe3O4-nanoflu- 2853 cm–1 ascribed to CH2 and CH3 asymmetric stretch-
id stabilized by a double layer of lauric acid (Scheme 4). ing)20,21 in addition to the typical polypyrrole bands at
The envisaged functionalized core-shell nanoparticles 10 1598–1681 cm–1 (collective mode of intra- and inter-ring
were obtained as a black powder after magnetic separation vibration) and the strong Fe3O4 band at 592 cm–1
and drying. The FT-IR spectrum clearly shows the incor- (Figure 1).
poration of the cholesterol moiety (bands at 2931 and
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3024
S. Karsten et al.
PAPER
This example demonstrates that pyrroles, wherein the
tethering position of biomolecules is the ring N-atom and
the tether unit contains a 1,2,3-triazole are suitable for the
preparation of functionalized magnetic core-shell nano-
particles. We presently apply the method to other func-
tionalized pyrrole monomers and approach investigations
of the resulting materials in biological systems, such in
therapy and diagnosis or in the separation of biological
materials.
N
H
+
H
H
N
H
H
O
N
4
N
N
4a
3-(1H-Pyrrol-1-yl)propanoic acid (5),17 N,N,N-tris[(1-benzyl-1H-
1,2,3-triazol-4-yl)methyl]amine (TBTA),18,19 and the biomolecules
3 [cholesterol propargyl ether (3a),22,23 N-(prop-2-ynyl)biotinamide
(3b),24 2,3,4,6-tetra-O-acetyl-1-(prop-2-ynyl)-b-D-glucose (3c),25,26
2,3,4,6-tetra-O-acetyl-1-(prop-2-ynyl)-b-D-galactose (3d)27] and 7
[2¢-azido-2¢-deoxyuridine (7a),28 2,3,4,6-tetra-O-acetyl-1-azido-1-
deoxy-b-D-glucose (7b),29 1-azido-2,3,4,6-tetra-O-acetyl-1-deoxy-
b-D-galactose (7c)29] were prepared by the described procedures
and all analytical data of the products matched with those reported
in the literature. Other starting materials were purchased from
Aldrich and Acros. TLC analysis was performed on Merck silica gel
60 F254 plates and visualized by UV illumination and by charring
with phosphomolybdic acid, KMnO4, or ninhydrin. Silica gel 60
(0.035–0.070 mm, Acros) was used for preparative column chroma-
tography. Melting points were determined on a Boetius hot-stage
+ Fe3O4 nanofluid
(NH4)2S2O8, r.t., 24 h
10
cholesterol-functionalized
polypyrrole-Fe3O4 core-shell
nanoparticles
1
apparatus and are uncorrected. H and 13C NMR spectra were re-
Fe3O4 iron oxide nanoparticles core stably dispersed
in water by lauric acid double layer stabilization
corded at 300 and 75.5 MHz, respectively, on a Bruker AC-300 with
TMS as internal standard. Elemental analyses were ascertained with
a Euro EA analyzer. HRMS (ESI) were measured with a Thermo
Finnigan LTQ-FT-ICR-MS with MeOH as solvent. Optical rota-
tions were determined with a Perkin-Elmer-241 polarimeter. FT-IR
spectra were obtained with a Jasco FTIR 610 spectrophotometer.
polypyrrole shell covering the magnetic core
1-(6-Bromohexyl)-1H-pyrrole (1)
H
A 50% aq NaOH soln (25 mL) was added to a vigorously stirred
soln of pyrrole (671 mg, 10.0 mmol) and Bu4NHSO4 (340 mg,
1.0 mmol) in CH2Cl2 (30 mL) at 0 °C. After a few min, 1,6-dibro-
mohexane (6.10 mmol, 25.0 mmol) was added dropwise and the re-
sultant soln was stirred at 0 °C for 30 min. After this time the
reaction was allowed to come up to r.t. and stirred for 21 h. To this
mixture was added 1 M HCl (30 mL) and CH2Cl2 (20 mL) and the
organic layer was separated and extracted with CH2Cl2 (2 × 15 mL).
The combined organic layers were washed with sat. aq NaHCO3
(2 × 30 mL), H2O (30 mL), and brine (30 mL), dried (MgSO4), and
evaporated under reduced pressure. The crude product was purified
by flash column chromatography (silica gel) to give 1 (1.38 g,
6.0 mmol, 60%) as a red oil; Rf = 0.35 (cyclohexane–EtOAc, 95:5).
H
N
H
4
O
H
N
N
Scheme 4 Preparation of cholesterol-functionalized PPy-Fe3O4 10
core-shell nanoparticles by oxidative copolymerization
1H NMR (CDCl3): d = 1.30–1.40 (m, 2 H, CH2), 1.45–1.55 (m, 2 H,
CH2), 1.78–1.95 (m, 4 H, 2 CH2), 3.43 (t, J = 6.8 Hz, 2 H, CH2Br),
3.91 (t, J = 7.1 Hz, 2 H, Npy-CH2), 6.18 (t, J = 2.1 Hz, 2 H, 2 CHpy),
6.68 (t, J = 2.1 Hz, 2 H, 2 CHpy).
13C NMR (CDCl3): d = 25.9 (CH2), 27.8 (CH2), 31.4 (CH2), 32.6
(CH2), 33.8 (CH2Br), 49.5 (Npy-CH2), 108.0 (2 CHpy), 120.5 (2
CHpy).
1-(6-Azidohexyl)-1H-pyrrole (2)
NaN3 (452 mg, 6.95 mmol) was added to a soln of 1 (1.07 g,
4.63 mmol) in MeCN (12 mL). The mixture was heated to reflux for
21 h. The soln was allowed to cool to r.t. and H2O (100 mL) was
added. The aqueous layer was extracted with CH2Cl2 (3 × 100 mL)
and the combined organic layers were dried (Na2SO4) and evaporat-
ed under reduced pressure. Purification by flash column chromatog-
raphy (silica gel) gave 2 (879 mg, 4.57 mmol, 99%) as a clear
yellow oil; Rf = 0.40 (cyclohexane–EtOAc, 9:1).
Figure 1 FT-IR spectrum (in KBr) of cholesterol-functionalized
magnetic core-shell nanoparticles 10
Synthesis 2010, No. 17, 3021–3028 © Thieme Stuttgart · New York

PAPER
Tethering Biomolecules to Pyrrole Precursors
3025
1H NMR (CDCl3): d = 1.30–1.48 (m, 4 H, 2 CH2), 1.55–1.68 (m, 2
H, CH2), 1.77–1.87 (m, 2 H, CH2), 3.28 (t, J = 6.8 Hz, 2 H, CH2N3),
3.90 (t, J = 7.1 Hz, 2 H, Npy-CH2), 6.17 (t, J = 1.9 Hz, 2 H, 2 CHpy),
6.68 (t, J = 2.1 Hz, 2 H, 2 CHpy).
13C NMR (CDCl3): d = 26.4 (2 CH2), 28.8 (CH2), 31.5 (CH2), 49.5
(Npy-CH2), 51.4 (CH2N3), 107.9 (2 CHpy), 120.5 (2 CHpy).
(2 × 35 mL)] and column chromatography gave 4a (813 mg,
1.32 mmol, 88%).
Waxy white solid; mp 88–89 °C; Rf = 0.47 (cyclohexane–EtOAc,
1:1).
[a]D22 –17.1 (c 1.01, CHCl3).
1H NMR (CDCl3): d = 0.67 (s, 3 H, CCH3), 0.86 (dd, J1 = 1.3 Hz,
J2 = 6.6 Hz, 6 H, CHCH3), 0.88–2.31 (m, 41 H, OCHCH2C, 2
CCH3, 14 CH2, 6 CH), 2.38 (ddd, J1 = 2.1 Hz, J2 = 4.7 Hz, J3 = 13.2
Hz, 1 H, OCHCH2C), 3.23–3.42 (m, 1 H, OCHCH2C), 3.85 (t,
J = 7.0 Hz, 2 H, Npy-CH2), 4.30 (t, J = 7.1 Hz, 2 H, CH2Ntriazole),
4.68 (s, 2 H, OCH2Ctriazole), 5.35 (d, J = 5.2 Hz, 1 H, CCHCH2C),
6.13 (t, J = 2.1 Hz, 2 H, 2 CHpy), 6.62 (t, J = 2.1 Hz, 2 H, 2 CHpy),
7.49 (s, 1 H, CHtriazole).
13C NMR (CDCl3): d = 12.0 (CH3), 18.8 (CH3), 19.5 (CH3), 21.2
(CH2), 22.7 (CH3), 22.9 (CH3), 23.9 (CH2), 24.4 (CH2), 26.2 (2
CH2), 28.1 [CH(CH3)2], 28.3 (CH2), 28.4 (CH2), 30.2 (CH2), 31.4
(CH2CH2Ntriazole), 32.0 (CH), 32.1 (CH2), 35.9 (CH), 36.3 (CHCH2),
37.0 (CCH3), 37.3 (CH2), 39.2 (CHCH2), 39.6 (CH2), 39.9 (CH2),
42.4 (CCH3), 49.5 (Npy-CH2), 50.3 (CH, CH2Ntriazole), 56.3 (CH),
56.9 (CH), 61.8 (OCH2Ctriazole), 79.1 (CHOCH2Ctriazole), 108.0 (2
CHpy), 120.5 (2 CHpy), 122.0 (CCHCH2), 122.2 (CHtriazole), 140.8
(CCHCH2), 146.1 (Ctriazole).
HRMS (ESI): m/z [M + H]+ calcd for C10H17N4: 193.1448; found:
193.1457.
N-(Prop-2-ynyl)-3-(1H-pyrrol-1-yl)propanamide (6)
To a stirred soln of 3-(1H-pyrrol-1-yl)propanic acid (5, 1.39 g,
10.0 mmol) and propargylamine (606 mg, 11.0 mmol) in anhyd
CH2Cl2 (100 mL) was added 1-ethyl-3-[3-(dimethylamino)pro-
pyl]carbodiimide (EDC) (2.02 g, 13.0 mmol), HOBt (2.03 g,
15.0 mmol), and DIPEA (1.42 g, 11.0 mmol) under argon at r.t. The
mixture was stirred 19 h and then diluted with the same amount of
CH2Cl2. The organic layer was separated and washed with 3 M HCl
(2 × 50 mL) and H2O (2 × 65 mL), dried (MgSO4), and evaporated
under reduced pressure. The residue was purified by flash column
chromatography (silica gel) to give 6 (1.58 g, 8.97 mmol, 90%) as
an ivory-colored solid; mp 64–65 °C; Rf = 0.47 (CH2Cl2–MeOH,
95:5).
1H NMR (CDCl3): d = 2.21 (t, J = 2.6 Hz, 1 H, CH2C≡CH), 2.59 (t,
J = 6.7 Hz, 2 H, CH2CO), 3.97 (dd, J1 = 2.6 Hz, J2 = 5.3 Hz, 2 H,
CH2C≡CH), 4.21 (t, J = 6.7 Hz, 2 H, Npy-CH2), 6.02 (br s, 1 H,
CONH), 6.13 (t, J = 2.1 Hz, 2 H, 2 CHpy), 6.64 (t, J = 2.1 Hz, 2 H,
2 CHpy).
HRMS (ESI): m/z [M + H]+ calcd for C40H65N4O: 617.5153; found:
617.5156.
Anal. Calcd for C40H64N4O: C, 77.87; H, 10.46; N, 9.08. Found: C,
77.69; H, 10.46; N, 9.03.
13C NMR (CDCl3): d = 29.3 (CH2C≡CH), 38.6 (CH2CO), 45.4 (Npy-
CH2), 71.7 (CH2C≡CH), 79.3 (CH2C≡CH), 108.5 (2 CHpy), 120.6 (2
CHpy), 170.1 (C=O).
HRMS (ESI): m/z [M + H]+ calcd for C10H13N2O: 177.1022; found:
177.1015.
N-({1-[6-(1H-Pyrrol-1-yl)hexyl]-1H-1,2,3-triazol-4-yl}meth-
yl)biotinamide (4b)
According to the general procedure, method A, using azide 2
(304 mg, 1.58 mmol), alkyne 3b (445 mg, 1.58 mmol), CuSO4·5
H2O (79 mg, 0.32 mmol), and sodium ascorbate (125 mg,
0.63 mmol) in t-BuOH–H2O (1:1, 60 mL) for 5 d; separation
[CH2Cl2 (50 mL), CH2Cl2 (3 × 20 mL), H2O (2 × 35 mL)] and col-
umn chromatography gave 4b (390 mg, 0.82 mmol, 52%).
Anal. Calcd for C10H12N2O: C, 68.16; H, 6.86; N, 15.90. Found: C,
68.22; H, 6.96; N, 15.68.
1,3-Dipolar Cycloaddition; General Procedure
According to the general procedure, method B, using azide 2
(96 mg, 0.50 mmol), alkyne 3b (141 mg, 0.50 mmol), CuSO4·5
H2O (25 mg, 0.10 mmol), sodium ascorbate (40 mg, 0.20 mmol),
and TBTA (53 mg, 0.10 mmol) in t-BuOH–H2O (1:1, 26 mL) for
3 h; separation [CH2Cl2 (20 mL), CH2Cl2 (3 × 10 mL), H2O
(2 × 10 mL)] and column chromatography gave 4b (84 mg,
0.18 mmol, 35%); complete removal of TBTA failed.
Method A: A mixture of azide 2 or 7 (1.0 equiv) and alkyne 3 or 6
(1.0 equiv) was dissolved in distilled H2O–t-BuOH or H2O–THF
(1:1) (depending on solubility). To the stirred and degassed soln
was added successively CuSO4·5 H2O (0.2 equiv) and sodium
ascorbate (0.4 equiv) added at r.t. The resulting soln was stirred un-
til TLC indicated completion of the reaction. The soln was diluted
with CH2Cl2 and the aqueous layer was extracted with CH2Cl2 (3 ×)
The combined organic layers were washed with H2O, dried
(Na2SO4), and evaporated under reduced pressure. Purification by
flash column chromatography (silica gel) gave the desired com-
pounds 4a–d and 8a–c.
Cream-colored solid; mp 163–164 °C; Rf = 0.22 (CHCl3–MeOH,
9:1).
1H NMR (CDCl3): d = 1.26–1.33 (m, 4 H, 2 CH2), 1.35–1.48 (m, 2
H, CH2), 1.56–1.78 (m, 6 H, 2 CH2, CH2CH2Ntriazole), 1.79–1.90 (m,
2 H, CHbiotin-CH2), 2.18 (t, J = 6.4 Hz, 2 H, CH2CONH), 2.74 (d,
J = 12.7 Hz, 1 H, CHbiotin-CH2S), 2.90 (dd, J1 = 3.5 Hz, J2 = 12.5
Hz, 1 H, CHbiotin-CH2S), 3.11 (d, J = 3.1 Hz, 1 H, CHbiotin-CH2),
3.84 (t, J = 7.0 Hz, 2 H, Npy-CH2), 4.26 (t, J = 7.0 Hz, 2 H,
CH2Ntriazole), 4.29–4.42 (m, 2 H, NHbiotin-CHCHS, NHCH2Ctriazole),
4.45–4.55 (m, 2 H, NHbiotin-CHCH2S, NHCH2Ctriazole), 6.11 (t,
J = 2.1 Hz, 2 H, 2 CHpy), 6.61 (t, J = 2.1 Hz, 2 H, 2 CHpy), 6.75 (br
s, 1 H, CONH), 7.28 (s, 1 H, CONHbiotin), 7.57 (s, 1 H, CHtriazole),
7.95 (s, 1 H, CONHbiotin).
13C NMR (CDCl3): d = 25.5 (CH2), 26.2 (2 CH2), 28.1 (CH2), 28.3
(CH2), 30.1 (CHbiotin-CH2), 31.3 (CH2CH2Ntriazole), 34.4
(NHCH2Ctriazole), 35.9 (CH2CONH), 40.8 (CHbiotin-CH2S), 49.4
(Npy-CH2), 50.3 (CH2Ntriazole), 56.0 (CHbiotin-CH2CH2), 60.4
(NHbiotin-CHCH2S), 61.8 (NHbiotin-CHCHS), 108.0 (2 CHpy), 120.5
(2 CHpy). 122.6 (CHtriazole), 145.3 (Ctriazole), 164.9 (C=O), 173.6
(C=O).
Method B: Analogous to Method A, but using additional TBTA
(0.2 equiv).
4-[(Cholest-5-en-3b-yloxy)methyl]-1-[6-(1H-pyrrol-1-yl)hexyl]-
1H-1,2,3-triazole (4a)
According to the general procedure, method A, using azide 2
(288 mg, 1.50 mmol), alkyne 3a (637 mg, 1.50 mmol), CuSO4·5
H2O (75 mg, 0.30 mmol), and sodium ascorbate (119 mg,
0.60 mmol) in THF–H2O (1:1, 60 mL) for 2 d; separation [CH2Cl2
(50 mL), CH2Cl2 (3 × 20 mL), H2O (2 × 35 mL)] and column chro-
matography gave 4a (656 mg, 1.06 mmol, 71%).
According to the general procedure, method B, using azide 2
(288 mg, 1.50 mmol), alkyne 3a (637 mg, 1.50 mmol), CuSO4·5
H2O (75 mg, 0.30 mmol), sodium ascorbate (119 mg, 0.60 mmol),
and TBTA (159 mg, 0.30 mmol) in THF–H2O (1:1, 60 mL) for 3 h;
separation [CH2Cl2 (50 mL), CH2Cl2 (3 × 20 mL), H2O
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S. Karsten et al.
PAPER
HRMS (ESI): m/z [M + H]+ calcd for C23H36N7O2S: 474.2646;
found: 474.2646.
H, CH2Ctriazole), 5.00 (dd, J1 = 3.4 Hz, J2 = 10.5 Hz, 1 H, H3), 5.20
(dd, J1 = 7.9 Hz, J2 = 10.5 Hz, 1 H, H2), 5.38 (d, J = 2.9 Hz, 1 H,
H4), 6.09 (t, J = 2.1 Hz, 2 H, 2 CHpy), 6.60 (t, J = 2.1 Hz, 2 H, 2
CHpy), 7.46 (s, 1 H, CHtriazole).
13C NMR (CDCl3): d = 20.6 (CH3), 20.7 (2 CH3), 20.8 (CH3), 26.1
(CH2), 26.2 (CH2), 30.2 (CH2), 31.3 (CH2), 49.4 (Npy-CH2), 50.2
(CH2Ntriazole), 61.3 (CH2Ctriazole), 63.6 (CHCH2), 67.1 (C4), 68.8
(C2), 70.8 (C3, C5), 100.5 (C1), 108.0 (2 CHpy), 120.5 (2 CHpy),
122.6 (CHtriazole), 144.2 (Ctriazole), 169.5 (C=O), 170.1 (C=O), 170.3
(C=O), 170.4 (C=O).
1-[6-(1H-Pyrrol-1-yl)hexyl]-4-[(2,3,4,6-tetra-O-acetyl-b-D-glu-
copyranosyloxy)methyl]-1H-1,2,3-triazole (4c)
According to the general procedure, method A, using azide 2
(79 mg, 0.41 mmol), alkyne 3c (158 mg, 0.41 mmol), CuSO4·5 H2O
(20 mg, 0.08 mmol), and sodium ascorbate (32 mg, 0.16 mmol) in
t-BuOH–H2O (1:1, 25 mL) for 2 d; separation [CH2Cl2 (20 mL),
CH2Cl2 (3 × 10 mL), H2O (2 × 10 mL)] and column chromatogra-
phy gave 4c (107 mg, 0.18 mmol, 45%).
HRMS (ESI): m/z [M + H]+ calcd for C27H39N4O10: 579.2661;
found: 579.2666.
According to the general procedure, method B, using azide 2
(79 mg, 0.41 mmol), alkyne 3c (158 mg, 0.41 mmol), CuSO4·5 H2O
(20 mg, 0.08 mmol), sodium ascorbate (32 mg, 0.16 mmol), and
TBTA (44 mg, 0.08 mmol) in t-BuOH–H2O (1:1, 26 mL) for 2 h;
separation [CH2Cl2 (20 mL), CH2Cl2 (3 × 10 mL), H2O
(2 × 10 mL)] and column chromatography gave 4c (183 mg,
0.32 mmol, 77%).
N-[1-(2¢-Deoxyuridin-2¢-yl)]-1H-1,2,3-triazol-4-methyl)-3-(1H-
pyrrol-1-yl)propanamide (8a)
According to the general procedure, method B, using azide 7a
(242 mg, 0.90 mmol), alkyne 6 (159 mg, 0.90 mmol), CuSO4·5
H2O (45 mg, 0.18 mmol), sodium ascorbate (71 mg, 0.38 mmol),
and TBTA (96 mg, 0.18 mmol) in THF–H2O (1:1, 3 mL) for 1 h;
column chromatography gave 8a (355 mg, 0.78 mmol, 87%) as a
white foam; mp 88–92 °C; Rf = 0.27 (EtOAc–MeOH, 5:1).
Viscous yellow oil; Rf = 0.14 (cyclohexane–EtOAc, 1:4).
[a]D22 –14.7 (c 1.00 CHCl3).
1H NMR (CDCl3): d = 1.28–1.34 (m, 4 H, 2 CH2), 1.70–1.79 (m, 2
H, CH2), 1.83–1.91 (m, 2 H, CH2), 1.96 (s, 3 H, CH3), 1.98 (s, 3 H,
CH3), 2.01 (s, 3 H, CH3), 2.07 (s, 3 H, CH3), 3.72 (ddd, J1 = 2.4 Hz,
J2 = 4.7 Hz, J3 = 9.9 Hz, 1 H, H5), 3.85 (t, J = 7.0 Hz, 2 H, Npy-
CH2), 4.13 (dd, J1 = 2.2 Hz, J2 = 12.5 Hz, 1 H, C5H-CH2), 4.22–
4.35 (m, 3 H, C5H-CH2, CH2Ntriazole), 4.67 (d, J = 7.9 Hz, 1 H, H1),
4.80 (d, J = 12.5 Hz, 1 H, CH2Ctriazole), 4.92 (d, J = 12.6 Hz, 1 H,
CH2Ctriazole), 5.00 (dd, J1 = 8.0 Hz, J2 = 9.4 Hz, 1 H, H2), 5.08 (t,
J = 9.6 Hz, 1 H, H4), 5.19 (t, J = 9.4 Hz, 1 H, H3), 6.11 (t, J = 2.1
Hz, 2 H, 2 CHpy), 6.61 (t, J = 2.1 Hz, 2 H, 2 CHpy), 7.47 (s, 1 H,
CHtriazole).
13C NMR (CDCl3): d = 20.7 (2 CH3), 20.8 (CH3), 20.9 (CH3), 26.1
(CH2), 26.2 (CH2), 30.2 (CH2), 31.3 (CH2), 49.4 (Npy-CH2), 50.3
(CH2Ntriazole), 61.9 (CH2Ctriazole), 63.1 (CH2O), 68.4 (C4), 71.3 (C2),
72.0 (C5), 72.8 (C3), 100.0 (C1), 108.0 (2 CHpy), 120.5 (2 CHpy),
122.7 (CHtriazole), 144.2 (Ctriazole), 169.4 (C=O), 169.5 (C=O), 170.3
(C=O), 170.7 (C=O).
1H NMR (CD3OD): d = 2.61 (t, J = 6.6 Hz, 2 H, CH2CO), 3.65–3.82
(m, 2 H, 5¢-CH2), 4.14 (t, J = 6.6 Hz, 2 H, Npy-CH2), 4.17–4.25 (m,
1 H, H4¢), 4.35 (s, 2 H, CH2Ctriazole), 4.47–4.57 (m, 1 H, H3¢), 4.55
(s, 1 H, CONH), 5.34 (t, J = 6.0 Hz, 1 H, H2¢), 5.70 (d, J = 8.0 Hz,
1 H, CHCHNuridine), 5.96 (t, J = 2.1 Hz, 2 H, 2 CHpy), 6.52 (d, J = 9.0
Hz, 1 H, H1¢), 6.59 (t, J = 2.1 Hz, 2 H, 2 CHpy), 7.73 (s, 1 H,
CHtriazole), 8.07 (d, J = 8.0 Hz, 1 H, CHNuridine).
13C NMR (CD3OD): d = 35.7 (CH2Ctriazole), 39.2 (CH2), 46.5 (Npy-
CH2), 62.2 (5¢-CH2), 67.3 (C2¢), 71.4 (C3¢), 87.9 (C4¢), 88.0 (C1¢),
103.4 (CHCHNuridine), 109.1 (2 CHpy), 121.6 (2 CHpy), 125.6
(CHtriazole), 141.9 (CHNuridine), 145.9 (Ctriazole), 152.1 (C=O), 165.9
(C=O), 173.4 (C=O).
HRMS (ESI): m/z [M + H]+ calcd for C19H24N7O6: 446.1783; found:
446.1773.
3-(1H-Pyrrol-1-yl)-N-{[1-(2,3,4,6-tetra-O-acetyl-b-D-gluco-
pyranosyl)-1H-1,2,3-triazol-4-yl]methyl}propanamide (8b)
According to the general procedure, method A, using azide 7b
(343 mg, 0.92 mmol), alkyne 6 (162 mg, 0.92 mmol), CuSO4·5
H2O (46 mg, 0.18 mmol), and sodium ascorbate (73 mg,
0.37 mmol) in t-BuOH–H2O (1:1, 44 mL) for 4 d; separation
[CH2Cl2 (32 mL), CH2Cl2 (3 × 20 mL), H2O (2 × 15 mL)] and col-
umn chromatography gave 8b (502 mg, 0.91 mmol, 99%).
HRMS (ESI): m/z [M + H]+ calcd for C27H39N4O10: 579.2661;
found: 579.2676.
1-[6-(1H-Pyrrol-1-yl)hexyl]-4-[(2,3,4,6-tetra-O-acetyl-b-D-ga-
lactopyranosyloxy)methyl]-1H-1,2,3-triazole (4d)
According to the general procedure, method A, using azide 2
(192 mg, 1.00 mmol), alkyne 3d (386 mg, 1.00 mmol), CuSO4·5
H2O (50 mg, 0.20 mmol), and sodium ascorbate (79 mg,
0.40 mmol) in t-BuOH–H2O (1:1, 50 mL) for 2 d; separation
[CH2Cl2 (45 mL), CH2Cl2 (3 × 18 mL), H2O (2 × 30 mL)] and col-
umn chromatography gave 4d (375 mg, 0.65 mmol, 65%).
According to the general procedure, method B, using azide 7b
(343 mg, 0.92 mmol), alkyne 6 (162 mg, 0.92 mmol), CuSO4·5
H2O (46 mg, 0.18 mmol), sodium ascorbate (73 mg, 0.37 mmol),
and TBTA (98 mg, 0.18 mmol) in t-BuOH–H2O (1:1, 50 mL) for
3 h; separation [CH2Cl2 (35 mL), CH2Cl2 (3 × 20 mL), H2O
(2 × 15 mL)] and column chromatography. To remove the ligand
completely a second column chromatography (EtOAc–MeOH,
98:2) was necessary to give 8b (465 mg, 0.85 mmol, 92%).
According to the general procedure, method B, using azide 2
(481 mg, 2.50 mmol), alkyne 3d (966 mg, 2.50 mmol), CuSO4·5
H2O (125 mg, 0.50 mmol), sodium ascorbate (198 mg, 1.00 mmol),
and TBTA (265 mg, 0.50 mmol) in t-BuOH–H2O (1:1, 120 mL) for
3 h; separation [CH2Cl2 (100 mL), CH2Cl2 (3 × 40 mL), H2O
(2 × 70 mL)] and column chromatography gave 4d (1.17 g,
2.02 mmol, 81%).
White solid; mp 172–173 °C; Rf = 0.39 (CH2Cl2–MeOH, 9:1).
[a]D22 –28.1 (c 1.02, CHCl3).
1H NMR (CDCl3): d = 1.84 (s, 3 H, CH3), 2.02 (s, 3 H, CH3), 2.06
(s, 3 H, CH3), 2.07 (s, 3 H, CH3), 2.61 (t, J = 6.8 Hz, 2 H, CH2CO),
4.00 (ddd, J1 = 2.1 Hz, J2 = 4.8 Hz, J3 = 10.1 Hz, 1 H, H5), 4.14 (dd,
J1 = 2.1 Hz, J2 = 12.6 Hz, 1 H, C5H-CH2), 4.22 (t, J = 6.7 Hz, 2 H,
Npy-CH2), 4.31 (dd, J1 = 4.8 Hz, J2 = 12.7 Hz, 1 H, C5H-CH2), 4.45
(d, J = 5.8 Hz, 2 H, CH2Ctriazole), 5.22–5.30 (m, 1 H, H3), 5.38–5.46
(m, 2 H, H2, H4), 5.83 (dd, J1 = 2.7 Hz, J2 = 6.6 Hz, 1 H, H1), 6.10
(t, J = 2.1 Hz, 2 H, 2 CHpy), 6.31 (t, J = 5.7 Hz, 1 H, CONH), 6.62
(t, J = 2.1 Hz, 2 H, 2 CHpy), 7.64 (s, 1 H, CHtriazole).
Viscous yellow oil; Rf = 0.22 (cyclohexane–EtOAc, 3:7).
[a]D22 –22.2 (c 1.01, CHCl3).
1H NMR (CDCl3): d = 1.26–1.34 (m, 4 H, 2 CH2), 1.67–1.78 (m, 2
H, CH2), 1.80–1.91 (m, 2 H, CH2), 1.95 (s, 3 H, CH3), 1.96 (s, 3 H,
CH3), 2.03 (s, 3 H, CH3), 2.12 (s, 3 H, CH3), 3.85 (t, J = 7.0 Hz, 2
H, Npy-CH2), 3.93 (t, J = 6.5 Hz, 1 H, H5), 4.11–4.19 (m, 2 H, C5H-
CH2), 4.29 (t, J = 7.1 Hz, 2 H, CH2Ntriazole), 4.63 (d, J = 7.9 Hz, 1 H,
H1), 4.78 (d, J = 12.5 Hz, 1 H, CH2Ctriazole), 4.95 (d, J = 12.5 Hz, 1
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Tethering Biomolecules to Pyrrole Precursors
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13C NMR (CDCl3): d = 20.3 (CH3), 20.6 (CH3), 20.7 (CH3), 20.8
(CH3), 35.0 (CH2Ctriazole), 38.7 (CH2CO), 45.6 (Npy-CH2), 61.6
(C5H-CH2), 67.7 (C3), 70.5 (C4), 72.7 (C2), 75.2 (C5), 85.8 (C1),
108.5 (2 CHpy), 120.7 (2 CHpy), 121.0 (CHtriazole), 145.4 (Ctriazole),
168.9 (C=O), 169.4 (C=O), 170.0 (C=O), 170.3 (C=O), 170.6
(C=O).
(m, 3 H), 3.62–3.76 (m, 2 H), 3.81–3.85 (m, 3 H), 4.25–4.35 (m, 3
H, CH2Ntriazole, H1), 4.72 (d, J = 12.5 Hz, 1 H, CH2Ctriazole), 4.89 (d,
J = 12.5 Hz, 1 H, CH2Ctriazole), 6.00 (t, J = 2.1 Hz, 2 H, 2 CHpy), 6.63
(t, J = 2.1 Hz, 2 H, 2 CHpy), 7.79 (s, 1 H, CHtriazole).
13C NMR (CD3CN): d = 26.4 (CH2), 26.6 (CH2), 30.6 (CH2), 31.9
(CH2), 49.7 (Npy-CH2), 50.8 (CH2Ntriazole), 62.2 (C5H-CH2), 62.6
(CH2Ctriazole), 69.7 (C4), 72.0 (C2), 74.3 (C3), 75.8 (C5), 103.4 (C1),
108.3 (2 CHpy), 121.2 (2 CHpy), 124.5 (CHtriazole), 144.8 (Ctriazole).
HRMS (ESI): m/z [M + H]+ calcd for C24H32N5O10: 550.2144;
found: 550.2150.
Anal. Calcd for C24H31N5O10: C, 52.46; H, 5.69; N, 12.74. Found:
C, 52.62; H, 5.80; N, 12.56.
HRMS (ESI): m/z [M + H]+ calcd for C19H31N4O6: 411.2238; found:
411.2237.
3-(1H-Pyrrol-1-yl)-N-{[1-(2,3,4,6-tetra-O-acetyl-b-D-galacto-
pyranosyl)-1H-1,2,3-triazol-4-yl]methyl}propanamide (8c)
According to the general procedure, method A, using azide 7c
(188 mg, 0.50 mmol), alkyne 6 (88 mg, 0.50 mmol), CuSO4·5 H2O
(25 mg, 0.10 mmol), and sodium ascorbate (40 mg, 0.20 mmol) in
t-BuOH–H2O (1:1, 26 mL) for 9 d; separation [CH2Cl2 (20 mL),
CH2Cl2 (3 × 10 mL), H2O (2 × 10 mL)] and column chromatogra-
phy gave 8c (188 mg, 0.34 mmol, 68%) as a foam.
N-{[1-(b-D-Glucopyranosyl)-1H-1,2,3-triazol-4-yl]methyl}-3-
(1H-pyrrol-1-yl)propanamide (9b)
Following the general procedure using 8b (1.18 g, 2.14 mmol) gave
9b (801 mg, 2.10 mmol, 98%) as a white solid; mp 94–97 °C (dec.);
Rf = 0.27 (MeCN–H2O, 9:1).
[a]D22 +1.5 (c 1.01, MeOH).
1H NMR (DMSO-d6): d = 2.58 (t, J = 6.9 Hz, 2 H, CH2CO), 3.20–
3.26 (m, 1 H), 3.35–3.49 (m, 3 H), 3.65–3.76 (m, 2 H, C5H-CH2,
H2), 4.12 (t, J = 6.9 Hz, 2 H, Npy-CH2), 4.31 (d, J = 5.4 Hz, 2 H,
CH2Ctriazole), 5.48 (d, J = 9.3 Hz, 1 H, H1), 5.97 (t, J = 2.1 Hz, 2 H,
2 CHpy), 6.71 (t, J = 2.1 Hz, 2 H, 2 CHpy), 7.85 (s, 1 H, CHtriazole),
8.45 (t, J = 5.7 Hz, 1 H, CONH).
13C NMR (DMSO-d6): d = 34.2 (CH2Ctriazole), 37.3 (CH2), 44.9 (Npy-
CH2), 60.8 (C5H-CH2), 69.6 (C4), 72.1 (C2), 77.0 (C3), 80.0 (C5),
87.5 (C1), 107.6 (2 CHpy), 120.6 (2 CHpy), 121.7 (CHtriazole), 144.9
(Ctriazole), 169.8 (C=O).
According to the general procedure, method B, using azide 7c
(392 mg, 1.05 mmol), alkyne 6 (185 mg, 1.05 mmol), CuSO4·5
H2O (52 mg, 0.21 mmol), sodium ascorbate (83 mg, 0.42 mmol),
and TBTA (111 mg, 0.21 mmol) in t-BuOH–H2O (1:1, 60 mL) for
3 h; separation [CH2Cl2 (35 mL), CH2Cl2 (3 × 20 mL), H2O
(2 × 15 mL)] and column chromatography. To remove the ligand
completely a second column chromatography (EtOAc–MeOH,
98:2) was necessary to give 8c (507 mg, 0.92 mmol, 88%) as a
foam.
HRMS (ESI): m/z [M + H]+ calcd for C16H24N5O6: 382.1721; found:
382.1727.
Foam; mp 69–71 °C; Rf = 0.20 (CH2Cl2–MeOH, 95:5).
[a]D22 –7.1 (c 1.01, CHCl3).
1H NMR (CDCl3): d = 1.87 (s, 3 H, CH3), 2.01 (s, 3 H, CH3), 2.03
(s, 3 H, CH3), 2.24 (s, 3 H, CH3), 2.61 (t, J = 6.6 Hz, 2 H, CH2CO),
4.06–4.28 (m, 5 H, H5, CH5-CH2, Npy-CH2), 4.36–4.57 (m, 2 H,
CH2Ctriazole), 5.25 (dd, J1 = 3.4 Hz, J2 = 10.2 Hz, 1 H, H3), 5.47–
5.58 (m, 2 H, H2, H4), 5.80 (d, J = 9.3 Hz, 1 H, H1), 6.13 (m, 3 H,
2 CHpy, CONH), 6.63 (t, J = 2.1 Hz, 2 H, 2 CHpy), 7.71 (s, 1 H,
CHtriazole).
13C NMR (CDCl3): d = 20.4 (CH3), 20.6 (CH3), 20.7 (CH3), 20.8
(CH3), 35.1 (CH2Ctriazole), 39.0 (CH2CO), 45.7 (Npy-CH2), 61.4
(C5H-CH2), 67.0 (C4), 68.1 (C2), 70.9 (C3), 74.2 (C5), 86.5 (C1),
108.6 (2 CHpy), 120.7 (2 CHpy), 121.0 (CHtriazole), 145.3 (Ctriazole),
169.1 (C=O), 170.0 (C=O), 170.2 (C=O), 170.3 (C=O), 170.5
(C=O).
N-{[1-(b-D-Galactopyranosyl)-1H-1,2,3-triazol-4-yl]methyl}-3-
(1H-pyrrol-1-yl)-propanamide (9c)
Following the general procedure using 8c (448 mg, 0.82 mmol)
gave 9c (252 mg, 0.66 mmol, 81%) as a light brown hygroscopic
solid; mp 126–130 °C (dec); Rf = 0.15 (MeCN–H2O, 9:1).
[a]D24 +15.2 (c 1.00, MeOH).
1H NMR (DMSO-d6–D2O, 14:1): d = 2.56 (t, J = 6.9 Hz, 2 H,
CH2CO), 3.44–3.60 (m, 3 H), 3.68–3.72 (m, 1 H), 3.75–3.77 (m, 1
H), 3.97–4.03 (m, 1 H), 4.11 (t, J = 6.9 Hz, 2 H, Npy-CH2), 4.23–
4.39 (m, 2 H, CH2Ctriazole), 5.44 (d, J = 9.2 Hz, 1 H, H1), 5.97 (t,
J = 2.0 Hz, 2 H, 2 CHpy), 6.70 (t, J = 2.0 Hz, 2 H, 2 CHpy), 7.88 (s,
1 H, CHtriazole), 8.40–8.48 (m, 1 H, CONH).
13C NMR (DMSO-d6–D2O, 14:1): d = 34.3 (CH2Ctriazole), 37.4
(CH2), 44.9 (Npy-CH2), 60.5 (C5H-CH2), 68.5 (C4), 69.4 (C2), 73.8
(C3), 78.4 (C5), 88.1 (C1), 107.7 (2 CHpy), 120.5 (2 CHpy), 121.5
(CHtriazole), 144.9 (Ctriazole), 169.9 (C=O).
HRMS (ESI): m/z [M + H]+ calcd for C24H32N5O10: 550.2144;
found: 550.2128.
Deprotection of Tetraacetates 4d and 8b,c; General Procedure
Dry NaOMe–MeOH soln (0.1 equiv) (freshly prepared 1.0 M soln)
was added to a stirred (0.1 M) soln of the glycoside tetraacetate 4 or
8 (1.0 equiv) in MeOH at r.t. The mixture was stirred for 30 min
(TLC showed complete conversion). Neutralization by addition of
DOWEX 50 × 8 ion-exchange resin (pH 6), followed by filtration
and evaporation of the filtrate to dryness, afforded the pure unpro-
tected products 9a–c.
HRMS (ESI): m/z [M + H]+ calcd for C16H24N5O6: 382.1721; found:
382.1724.
Acknowledgment
We thank Prof. Dr. Ladislau Vekas, Romanian Academy of Sci-
ence, Timisoara Branch, for providing magnetic Fe3O4 nanofluid.
We further acknowledge Saltigo GmbH, Bayer Services GmbH &
Co. OHG, BASF AG, and Sasol GmbH for the donation of chemi-
cals.
4-[(b-D-Galactopyranosyloxy)methyl]-1-[6-(1H-pyrrol-1-
yl)hexyl]-1H-1,2,3-triazole (9a)
Following the general procedure using 4d (579 mg, 1.00 mmol)
gave 9a (355 mg, 0.86 mmol, 86%) as a brown oil; Rf = 0.24
(MeCN–H2O, 9:1).
[a]D20 –12.4 (c 1.01, CH2Cl2).
1H NMR (CD3CN): d = 1.14–1.40 (m, 4 H, 2 CH2), 1.63–1.75 (m, 2
H, CH2), 1.76–1.88 (m, 2 H, CH2), 3.36 (br s, 4 H, 4 OH), 3.43–3.53
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