Synthesis of novel glycoconjugates derived from alkynyl heterocycles through a click approach

Article abstract of DOI:10.1080/00397911.2011.637655

The synthesis of a series of novel 1,4-disubstituted 1,2,3-triazole compounds bearing a D-glucose derivative and an heteroaromatic system is described. Alkylation of isatin, 3-methyl-carbazole, and one tetrahydro-γ-carboline with propargyl bromide gave their N-propargyl derivatives in good yields. These compounds further reacted with acetylated D-glucose with the azide group in position 1 to give three final products and with peracetylated 6-azido-6-deoxy-α-D-methylglucoside, giving the corresponding derivative of tetrahydro-γ-carboline. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications to view the free supplemental file.

Full text of DOI:10.1080/00397911.2011.637655

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Synthesis of Novel Glycoconjugates
Derived From Alkynyl Heterocycles
through a Click Approach
Marília Silva a , João C. O. Gonçalves a , Ana M. F. Oliveira-Campos a
, Lígia M. Rodrigues a & Ana P. Esteves a
a Center of Chemistry, School of Sciences, University of Minho,
Campus de Gualtar, Braga, Portugal
Accepted author version posted online: 05 Jun 2012.Version of
record first published: 05 Mar 2013.
To cite this article: Marília Silva , João C. O. Gonçalves , Ana M. F. Oliveira-Campos , Lígia M.
Rodrigues & Ana P. Esteves (2013): Synthesis of Novel Glycoconjugates Derived From Alkynyl
Heterocycles through a Click Approach, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 43:10, 1432-1438
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Synthetic Communications1, 43: 1432–1438, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.637655
SYNTHESIS OF NOVEL GLYCOCONJUGATES DERIVED
FROM ALKYNYL HETEROCYCLES THROUGH
A CLICK APPROACH
´
Marılia Silva, Joao C. O. Gonc¸alves, Ana M. F. Oliveira-
Campos, Lıgia M. Rodrigues, and Ana P. Esteves
˜
´
Center of Chemistry, School of Sciences, University of Minho,
Campus de Gualtar, Braga, Portugal
GRAPHICAL ABSTRACT
Abstract The synthesis of a series of novel 1,4-disubstituted 1,2,3-triazole compounds
bearing a D-glucose derivative and an heteroaromatic system is described. Alkylation of isa-
tin, 3-methyl-carbazole, and one tetrahydro-c-carboline with propargyl bromide gave their
N-propargyl derivatives in good yields. These compounds further reacted with acetylated
D-glucose with the azide group in position 1 to give three final products and with peracety-
lated 6-azido-6-deoxy-a-D-methylglucoside, giving the corresponding derivative of tetrahy-
dro-c-carboline.
Supplemental materials are available for this article. Go to the publisher’s online edition
of Synthetic Communications1 to view the free supplemental file.
Keywords Alkynyl heterocycles; azido sugars; click chemistry; 1,2,3-triazoles
INTRODUCTION
Compounds containing the indole type or tetrahydro-c-carboline systems
frequently display biological activity of some sort, namely neuroleptic activity.[1]
Carbohydrates and glycoconjugates are involved in many normal and pathologic
biological processes including cellular recognition, tumor metastasis, and bacterial
and viral infections.[2] Glycosyl 1,2,3-triazole conjugates have appeared as interesting
Received October 21, 2011.
Address correspondence to Ana P. Esteves, Centre of Chemistry, School of Sciences, University of
Minho, Campus de Gualtar, 4710 057 Braga, Portugal. E-mail: aesteves@quimica.uminho.pt
1432

GLYCOCONJUGATES FROM ALKYNYL HETEROCYCLES
1433
target molecules because of their potential to act as inhibitors for galectins[3] and
RNA binding molecules.[4] In fact, 1,2,3-triazoles were reported as important hetero-
cyclic pharmacophores for developing antiviral,[5] anticancer,[6] and antibiotic
agents.[7] In addition, they are particularly promising because they can mimic the
amide bond and they are not cleaved hydrolytically, in contrast to amides present
in glycopeptides.[8] Azido sugars are known as versatile starting materials for several
biologically active compounds. In particular, glycosyl azides proved to be a very use-
ful substrate for the preparation of glycosyl 1,2,3-triazole derivatives by the ‘‘click
chemistry’’ approach.[9] The Cu(I)-catalysed azide–alkyne cycloaddition reaction
proved to be a powerful tool for the synthesis of glycoconjugates containing the
1,2,3-triazole moiety because of its efficiency at room temperature, regioselectivity
affording exclusively 1,4-disubstituted 1,2,3-triazoles in good yields.[10–15]
RESULTS AND DISCUSSION
In the present work the synthesis of 1,4-disubstituted 1,2,3-triazole compounds
of type 4 bearing a D-glucose derivative and an heteroaromatic system is described.
Starting materials for compounds 2 and 3 were obtained according to pub-
lished methods[1,16] and for compound 1 commercial isatin was used.
The propargyl derivatives 1–3 were obtained by alkylation using sodium
hydride and propargyl bromide in dimethylformamide (DMF). The yields ranged
from 51% for compound 2 to 72% for the isatin 1.
Compound 1 was recently reported and prepared by phase-transfer catalysis.[17]
The N-propargyl group is easily identified in the NMR by the appearance of a triplet
and a doublet with a coupling constant of 2.8 Hz, for example, for compound 2 at
2.26 and 5.02 ppm, respectively.
The formation of the 1,2,3-triazole ring was achieved by a Cu(I)-catalysed
cycloaddition process known as ‘‘click chemistry.’’[18] The first step was the prep-
aration of glucosyl azide, which was reacted with the propargyl derivatives 1–3
(Scheme 1), yielding the final compounds 4a–4c.[19] Another triazole derivative, 5,
analog of 4c, was prepared by a similar method[20] from acetylated methyl-a-
D-glucopyranoside with the azide group in position 6 (Scheme 2).
The final products were obtained in yields between 21% for 4c and 56% for 5.
All compounds were characterized by the usual analytical techniques and 1H and 13
C
nuclear magnetic resonance, including bidimensional techniques for the full assign-
ment of the spectra. The cyclization is confirmed by the appearance of a singlet in
the range 8.31–8.47 ppm for compounds 4 and 8.02 for derivative 5, due to the tria-
zole ring proton. The 1H NMR spectra for compounds 4 and 5 show some different
features. For example, the value of the chemical shift of H-10 for 5 is much lower

1434
M. SILVA ET AL.
Scheme 1. Preparation of compounds 4 and numbering of the atoms.
Scheme 2. Preparation of compound 5.
(4.72 ppm) than for compounds 4 (6.30 for 4a). The chemical shifts for protons 60 are
significantly lower for compounds 4 (3.98–4.04 ppm for 4c) than for 5 (4.75–
4.90 ppm).
CONCLUSIONS
Our results showed that the click reaction proved to be a useful approach in the
synthesis of novel D-glucose-based heteroaromatic compounds bearing a 1,2,3-
triazole unit as a linker. All the compounds were obtained in moderate yields after
purification by flash chromatography and=or recrystallization.

GLYCOCONJUGATES FROM ALKYNYL HETEROCYCLES
1435
EXPERIMENTAL
Melting points were determined on a Gallenkamp melting-point apparatus and
are uncorrected. 1H NMR (300 MHz) and 13C NMR (75.4 MHz) spectra were
recorded on a Varian Unity Plus spectrometer at 298 K or on a Bruker Avance III
1
400 spectrometer (400 MHz for H and 100.6 MHz for 13C). Chemical shifts are
reported in parts per million (ppm) relative to solvent peak or tetramethylsilane
(TMS); coupling constants (J) are given in hertz (Hz). Double resonance, HMQC
(heteronuclear multiple quantum coherence) or HSQC (heteronuclear single quan-
tum coherence) and HMBC (heteronuclear multiple bond correlation) experiments
were carried out for complete assignment of 1H and 13C signals in the NMR spectra.
Electrospray ionization (ESI) mass spectrum was obtained on a LC-MS Finnigan
LXQ spectrometer. High-resolution mass spectra (HRMS) were obtained on a
Bruker FTMS APEXIII (ESI-TOF) or on a Waters-Micromass Autospec (FAB)
spectrometer. Thin-layer chromatography (TLC) was carried out on plates coated
with silica gel 60 F254. Column chromatography was performed on silica gel
(230–400 mesh) with light petroleum and ethyl acetate mixtures of increasing
polarity, unless other conditions are described. Light petroleum refers to the fraction
boiling in the range 40–60 ꢀC.
Synthesis of Alkynyl Heterocycle Derivatives 1–3
NaH (80%, 1.5 equiv.) was added at 0–5 ꢀC to a solution of the appropriate
heterocyclic compound (1.0 mmol) in dimethylformamide (DMF; 4 mL), and the
mixture was left stirring for 5 min. Propargyl bromide (1.0–1.8 equiv.: 1.0 for 1;
1.8 for 2 and 3) was added, and the mixture was left stirring for 3–10 h (4 h for 1,
10 h for 2, and 3 h for 3). Ice water was added and a solid precipitated out (for 1
and 2). It was filtered and dried (oven, 80 ꢀC). For compound 3 the workup
procedure was slightly different, as described in the Supplementary Information
available online.
General Method for the Preparation of Compounds 4a–4c
Sodium azide was added (0.034 g, 0.517 mmol) to a solution of a-acetobromo-
glucose (0.177 g, 0.431 mmol), in dimethylsulfoxide (DMSO; 2.16 mL). The reaction
mixture was left stirring at room temperature for 30 min (followed by TLC using
ethyl ether–light petroleum 1:1 as eluent), and the alkyne (0.646 mmol), 1 M sodium
L-ascorbate solution (1.08 mL), and 1 M CuSO4 ꢁ 5H2O solution (1.08 mL) were
added. The reaction mixture was left stirring for 4 h at room temperature. The reac-
tion was monitored by TLC (ethyl acetate–light petroleum 2:1 as eluent), and then it
was filtered. The filtrate was extracted with ethyl acetate. The combined extracts
were washed with water, dried (MgSO4), filtered, and evaporated to dryness. The
product was either recrystallized by an appropriate solvent or submitted to column
chromatography.
All experimental details are described in the Supplementary Information,
available online.

1436
M. SILVA ET AL.
1-f[100-(2’,3’,4’,6’-Tetra-O-acetyl-b-D-glucopyranosyl)-1H-100,200,300-triazolyl-
400-yl]methylg-indoline-2,3-dione (4a). The title compound was obtained, follow-
ing the general procedure, as an orange oily solid (76%). After crystallization
(dichloromethane–light petroleum) the pure compound 4a was isolated in 49% yield,
1
mp 101.9–102.5 ꢀC. H NMR (300 MHz, DMSO-d6): dH 1.67 (3H, s, OAc), 1.93
(3H, s, OAc), 1.97 (3H, s, OAc), 2.00 (3H, s, OAc), 4.04 (1H, dd, J ¼ 12.4 and
2.1 Hz, H-6b0), 4.11 (1H, dd, J ¼ 12.4 and 5.4 Hz, H-6a0), 4.29–4.38 (1H, m,
H-50), 4.98 (2H, s, N-CH2), 5.12 (1H, t, J ¼ 9.6 Hz, H-30), 5.46–5.60 (2H, m, H-20
and H-40), 6.30 (1H, d, J ¼ 9.0 Hz, H-10), 7.05 (1H, d, J ¼ 8.1 Hz, H-4 or H-7),
7.12 (1H, t, J ¼ 7.2 Hz, H-5 or H-6), 7.53–7.64 (2H, m, ArH), 8.47 (1H, s, H-500).
13C NMR (75.4 MHz, DMSO-d6): dC 19.75, 20.22, 20.36, 20.49 (OAc), 34.93
(CH2), 61.72 (C-60), 67.49 (C-30), 70.15 and 72.02 (C-20 and C-40), 73.28 (C-50),
83.77 (C-10), 111.10 (C-7), 117.62 (C-3a), 122.90 (C-500), 123.40 (C-5), 124.47
(C-4), 138.06 (C-6), 142.24 (C-400), 149.98 (C-7a), 157.82 (C-2), 168.32 (OCH2-
COCH3), 169.35 (CO), 169.54 (CO), 170.01 (CO), 182.98 (C-3). Anal. calcd. for
1
C25H26N4O11 ꢁ 2H2O: C, 52.90; H, 4.80; N, 9.87%. Found: C, 52.67; H, 4.71; N,
9.70%; HRMS (ESI-TOF) calcd. for C25H26N4NaO11: 581.14903. Found:
581.14962.
3-Methyl-9-f[100-(2’,3’,4’,6’-tetra-O-acetyl-b-D-glucopyranosyl)-1H-100,200,300-
triazolyl-400-yl]methylg-9H-carbazole (4b). The compound was obtained, following
the general procedure, as a yellowish oil. After flash chromatography (ethyl ether),
the pure product 4b was isolated as a yellow solid (50%), mp 218.1–218.4 ꢀC (dec).
1H NMR (300 MHz, DMSO-d6): dH 1.62 (3H, s, OAc), 1.92 (3H, s, OAc), 1.93
(3H, s, OAc), 1.99 (3H, s, OAc), 2.46 (3H, s, CH3), 3.95–4.15 (2H, m, H-60),
4.23–4.32 (1H, m, H-50), 5.10 (1H, t, J ¼ 9.6 Hz, H-30), 5.46 (1H, t, J ¼ 9.6 Hz, H-20
or H-40), 5.57 (1H, t, J ¼ 9.6 Hz, H-20 or H-40), 5.64 (2H, s, N-CH2), 6.26 (1H, d,
J ¼ 9.3 Hz, H-10), 7.16 (1H, dt, J ¼ 1.2 and 8.1 Hz, H-6 or H-7), 7.26 (1H, dd,
J ¼ 1.0 and 7.0 Hz, H-2), 7.41 (1H, dt, J ¼ 1.2 and 8.1 Hz, H-7 or H-6), 7.57 (1H, d,
J ¼ 8.1 Hz, H-1 or H-8), 7.65 (1H, d, J ¼ 8.4 Hz, H-1 or H-8), 7.92 (1H, s, H-4),
8.08 (1H, d, J ¼ 7.5 Hz, H-5), 8.31 (1H, s, H-500). 13C NMR (75.4 MHz, DMSO-d6):
dC 19.69, 20.20, 20.34, 20.44 (OAc), 20.99 (CH3), 37.51 (CH2), 61.69 (C-60), 67.45
(C-30), 69.95 and 72.13 (C-20 and C-40), 73.23 (C-50), 83.65 (C-10), 109.30 and
109.46 (C-1 and C-8), 118.81 (C-7), 120.02 (C-4), 120.10 (C-5), 122.08 (C-4a),
122.26 (C-500), 122.38 (C-4b), 125.52 (C-6), 126.97 (C-2), 127.79 (C-3), 138.08
(C-9a), 139.95 (C-8a), 143.91(C-400), 168.25 (OCH2COCH3), 169.30 (CO), 169.51
(CO), 169.95 (CO). Anal. calcd. for C30H32N4O9: C, 60.80; H, 5.44; N, 9.45%. Found:
C, 61.01; H, 5.36; N, 9.09%.
Ethyl 5-f[100-(2’,3’,4’,6’-tetra-O-acetyl-b-D-glucopyranosyl)-1H-100,200,300-
triazol-400-yl]methylg-3,4-dihydro-1H-yrido[4,3-b]-indole-2(5H)-carboxylate (4c).
The title compound was obtained, following the general procedure, as a green oil.
After flash chromatography (ethyl ether–acetone 8:1) the pure product 4c was iso-
1
lated as a yellow solid (21%), mp 99.5–100.2 ꢀC. H NMR (400 MHz, DMSO-d6):
dH 1.20 (3H, t, J ¼ 7.2 Hz, CH3), 1.67 (3H, s, OAc), 1.93 (3H, s, OAc), 1.95 (3H, s,
OAc), 2.00 (3H, s, OAc), 2.89 (2H, s, H-4), 3.78 (2H, t, J ¼ 7.6 Hz, H-3), 3.98 ꢂ 4.04
(2H, m, H-60), 4.08 (2H, q, J ¼ 7.6 Hz, CH2), 4.26-4.33 (1H, m, H-50), 4.57 (2H, br s,

GLYCOCONJUGATES FROM ALKYNYL HETEROCYCLES
1437
H-1), 5.12 (1H, t, J ¼ 10.0 Hz, H-30), 5.37 (2H, s, N-CH2), 5.49 (1H, t, J ¼ 9.6 Hz,
H-20 or H-40), 5.60 (1H, t, J ¼ 9.2 Hz, H-20 or H-40), 6.27 (1H, d, J ¼ 9.0 Hz, H-10),
7.00 (1H, dt, J ¼ 0.8 and 8.0 Hz, H-7), 7.09 (1H, dt, J ¼ 1.2 and 7.6 Hz, H-8), 7.42
(1H, d, J ¼ 7.6 Hz, H-6), 7.51 (1H, d, J ¼ 8.0 Hz, H-9), 8.32 (1H, s, H-500). 13C
NMR (100.6 MHz, DMSO-d6): dC 14.63 (CH3), 19.74, 20.21, 20.35, 20.46 (OAc),
22.09 (C-4), 37.47 (CH2-N), 40.84, 40.90 (C-1 and C-3), 60.88 (CH2), 61.69 (C-60),
67.48 (C-30), 70.02, 72.09 (C-20 and C-40), 73.23 (C-50), 83.73 (C-10), 106.22 (C-9b),
109.64 (C-9), 117.45 (C-6), 119.06 (C-7), 120.94 (C-8), 122.20 (C-500), 124.81
(C-9a), 133.58 (C-4a), 135.87 (C-5a), 144.39 (C-400), 155.02 (COOEt), 168.37 (CO),
169.34 (CO), 169.52 (CO), 169.97 (OCH2COCH3). HRMS (ESI-TOF) calcd. for
C31H37N5NaO11: 678.23818. Found: 678.23926.
Ethyl 5-f100-[2’,3’,4’-Tri-O-acetyl-6’-deoxy-6’-(100,200,300-triazolyl-
400-yl)methyl]-a-D-Methylglucosideg-3,4-dihydro-1H-pyrido[4,3-
b]indole-2(5H)-carboxylate (5)
The alkyne (0.198 g, 0.701 mmol), 1 M sodium L-ascorbate solution
(1.60 mL) and 1 M CuSO4 ꢁ 5H2O solution (1.60 mL) were added to a solution of
the azide in position 6 of the sugar moiety prepared by known methods6 (0.220 g,
0.637 mmol) in DMSO (3.2 mL). The reaction mixture was left stirring for 4 h at
room temperature (the reaction was monitored by TLC; ethyl acetate–light petrol
2:1) and then filtered, and the filtrate was extracted with ethyl acetate. The com-
bined extracts were washed with water, dried (MgSO4), filtered, and evaporated
to dryness, giving an oil. After flash chromatography (ethyl ether–acetone, 7:1)
the pure product 5 was isolated as a yellow solid (0.225 g, 56%), mp
104.3–104.8 ꢀC. 1H NMR (300 MHz, DMSO-d6): dH 1.20 (3H, t, J ¼ 6.9 Hz,
CH3), 1.93 (3H, s, OAc), 1.96 (3H, s, OAc), 1.97 (3H, s, OAc), 2.80 (3H, br s,
OCH3), 2.94 (2H, t, J ¼ 5.4 Hz, H-4), 3.77 (2H, t, J ¼ 5.4 Hz, H-3), 3.98–4.10
(1H, m, H-50), 4.08 (2H, q, J ¼ 6.9 Hz, CH2), 4.42 (1H, dd, J ¼ 8.7 and 17.1 Hz,
H-60a), 4.48–4.60 (3H, m, H-60b and H-1), 4.72 (1H, d, J ¼ 3.6 Hz, H-10), 4.78
(1H, dd, J ¼ 3.9 and 10.2 Hz, H-20), 4.84 (1H, t, J ¼ 9.9 Hz, H-40), 5.22 (1H, t,
J ¼ 9.3 Hz, H-30), 5.35 (2H, s, N-CH2), 6.98 (1H, dt, J ¼ 0.9 and 7.2 Hz, H-7),
7.08 (1H, dt, J ¼ 1.2 and 7.5 Hz, H-8), 7.40 (1H, d, J ¼ 7.8 Hz, H-6), 7.52 (1H,
d, J ¼ 8.4 Hz, H-9), 8.02 (1H, s, H-500). 13C NMR (75.4 MHz, DMSO-d6): dC
14.67 (CH3), 20.32, 20.39, 20.46, (OAc), 21.94 (C-4), 37.51 (N-CH2), 40.41
(C-3), 40.86 (C-1), 49.82 (C-60), 54.35 (OCH3), 60.93 (CH2), 67.36 (C-50), 69.37
(C-30), 69.50 (C-20), 69.68 (C-40), 95.82 (C-10), 106.10 (C-9b), 109.75 (C-9),
117.43 (C-6), 119.03 (C-8), 120.86 (C-7), 123.84 (C-500), 124.86 (C-9a), 133.54
(C-4a), 135.82 (C-5a), 143.74 (C-400), 155.04 (COOEt), 169.38 (CO), 169.64
(CO), 169.70 (CO). HRMS (ESI-TOF) calcd. for C30H38N5O10: 628.26132
[M þ 1]þ. Found: 628.26089.
ACKNOWLEDGMENTS
We gratefully acknowledge the financial support from FCT (Fundac¸a˜opara a
Ciencia e Tecnologia) and FEDER for National NMR Network (Bruker Avance
ˆ
II 400) and REEQ=630=QUI=2005 (LC=MS instrument).

1438
M. SILVA ET AL.
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