Click synthesis of N1-(β-D-ribofuranosyl)-C4-(coumarin-4″-yl)-1,2,3-triazoles

Article abstract of DOI:10.1080/00397911.2019.1657150

A series of eight N¹-(β-D-ribofuranosyl)-C⁴-(coumarin-4′′-yl)-1,2,3-triazoles have been synthesized by Cu(I)-catalyzed click reaction of 1-azido-1-deoxy-2,3,5-tri-O-benzoyl-β-D-ribofuranose with differently substituted 4-ethynylcouma

Full text of DOI:10.1080/00397911.2019.1657150

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Click synthesis of N1-(β-D-ribofuranosyl)-C4-
(coumarin-4″-yl)-1,2,3-triazoles
Vipin K. Maikhuri, Kapil Bohra, Smriti Srivastava, ꢀ Kavita & Ashok K. Prasad
To cite this article: Vipin K. Maikhuri, Kapil Bohra, Smriti Srivastava, ꢀ Kavita & Ashok K. Prasad
(2019): Click synthesis of N1-(β-D-ribofuranosyl)-C4-(coumarin-4″-yl)-1,2,3-triazoles, Synthetic
Communications, DOI: 10.1080/00397911.2019.1657150
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https://doi.org/10.1080/00397911.2019.1657150
Click synthesis of N1-(b-D-ribofuranosyl)-C4-(coumarin-400-yl)-
1,2,3-triazoles
Vipin K. Maikhuria, Kapil Bohrab, Smriti Srivastavaa, Kavitaa, and Ashok K. Prasada
b
aBioorganic Laboratory, Department of Chemistry, University of Delhi, Delhi, India; Department of
Chemistry, DDU College, University of Delhi, Delhi, India
ABSTRACT
ARTICLE HISTORY
A series of eight N1-(b-D-ribofuranosyl)-C4-(coumarin-400-yl)-1,2,3-tria-
zoles have been synthesized by Cu(I)-catalyzed click reaction of 1-
azido-1-deoxy-2,3,5-tri-O-benzoyl-b-D-ribofuranose with differently
substituted 4-ethynylcoumarins followed by debenzoylation of the
resulted N1-(20,30,50-tri-O-benzoyl-b-D-ribofuranosyl)-C4-(coumarin-400-
yl)-1,2,3-triazoles in 71 to 89% overall yields. The structures of all the
synthesized compounds were established on the basis of their spectral
data analysis that was further confirmed by X-ray data analysis of one
of the model benzoylated compounds, i.e. N1-(20,30,50-tri-O-benzoyl-
b-D-ribofuranosyl)-C4-(700-isopropoxycoumarin-400-yl)-1,2,3-triazole.
Received 10 June 2019
KEYWORDS
Click chemistry; 4-
ethynylcoumarins; coumari-
nyltriazolylglycosides; 1-
azido-1-deoxy-2,3,5-tri-O-
benzoyl-b-D-ribofuranose
GRAPHICAL ABSTRACT
Introduction
Organic scaffolds containing coumarin moiety displays a wide range of biological activ-
ities such as antimicrobial,[1] anticancer,[2] antiproliferative,[3] antitumor,[4] antioxi-
dant,[5] antiviral,[6] etc. The coumarin as well as sugar moieties have broad range of
applications and biocompatibility. Further, 1,2,3-triazoles are important class of N-het-
erocycles in medicinal as well as in organic chemistry.[7–11] Connecting triazole with
sugar and coumarin moiety could bring forth some interesting biological and photo-
physical properties. Few research groups have synthesized modified nucleosides con-
necting 1,2,3-triazole with coumarin and sugars (Figure 1).[12–15] These modified
scaffolds own a varied range of biological properties, such as anticancer, antibacterial,
antifungal and antiviral together with photophysical and other applications.[16–17] Often,
CONTACT Ashok K. Prasad
ashokenzyme@gmail.com
Bioorganic Laboratory, Department of Chemistry, University
of Delhi, Delhi 110007, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
ß 2019 Taylor & Francis Group, LLC

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V. K. MAIKHURI ET AL.
Figure 1. Few examples of coumarinyltriazolylglycosides and similar compounds of biological and
photophysical interest.
Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction have been used to link two
molecular entities with a triazole ring for the synthesis of novel bioconjugates with envi-
able properties.[18–20]
Coumarinyltriazolylglycosides reported by Srivastava et al. had shown good antituber-
cular activity against sensitive reference strain H37Rv as well as multidrug resistant clin-
ical isolate 591 of Mycobacterium tuberculosis.[13] Coumarins conjugated to sugar
triazoles developed by Rajaganesh et al. have displayed good photophysical proper-
ties.[21] Herein we report the synthesis of small library of N1-(b-D-ribofuranosyl)-C4-
(coumarin-400-yl)-1,2,3-triazoles using click chemistry approach. These compounds can
be further used for medicinal and photophysical studies.
Results and discussion
The synthesis of N1-(b-D-ribofuranosyl)-C4-(coumarin-400-yl)-1,2,3-triazoles 6a–h has
been attained by Cu(I)-catalyzed click reaction between 1-azido-1-deoxy-2,3,5-tri-O-ben-
zoyl-b-D-ribofuranose (4) with 4-ethynylcoumarins 3a–h, followed by debenzoylation of
the resulting tribenzoylated coumarinyltriazolylglycosides 5a–h with NaOMe in metha-
nol in 71-89% yields. The 1-azido-1-deoxy-2,3,5-tri-O-benzoyl-b-D-ribofuranose (4) was
synthesized by the reaction of commercially available 1-O-acetyl-2,3,5-tri-O-benzoyl-
b-D-ribofuranose with azido trimethylsilane in the presence of tin(IV) chloride in 87%
yield following the literature procedure.[22]
4-Hydroxycoumarin (2a) was acquired from Sigma-Aldrich Chemicals Pvt. Limited,
India and other seven substituted 4-hydroxycoumarins 2 b–h were synthesized either by
Friedel-Crafts acetylation of appropriate phenols followed by the reaction of resulted

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3
Scheme 1. Synthesis of 4-ethynylcoumarins
Scheme 2. Synthesis of coumarinyltriazolylglycosides
substituted acetophenones with diethyl carbonate or by the reaction of substituted phe-
nols with malonic acid ester following literature procedure.[23–27] Further, 4-hydroxy-
coumarins 2a–h were converted to their corresponding 4-trifluoromethanesulfonate by
reacting them with trifluoromethanesulfonic anhydride in the presence of base which

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V. K. MAIKHURI ET AL.
Figure 2. ORTEP diagram of the N1-(20,30,50-tri-O-benzoyl-b-D-ribofuranosyl)-C4-(700-isopropoxycou-
marin-400-yl)-1,2,3-triazole (5e).
on reaction with trimethylsilylacetylene under Sonogashira coupling condition afforded
4-trimethylsilylacetynylcoumarins that in turn on desilylation with n-Bu4NF in THF
afforded the desired 4-acetynylcoumarins 3a–h in good to excellent yields
(Scheme 1).[28–32]
The alkynylcoumarins 3a–h and benzoylated azidosugar 4 on Cu(I)-catalyzed 1,3-
dipolar cycloaddition reaction using CuSO4.5H2O (0.4 equiv.) and sodium ascorbate
(0.9 equiv.) in t-BuOH:THF:H2O (1:1:1) yielded N1-(20,30,50-tri-O-benzoyl-b-D-ribofura-
nosyl)-C4-(coumarin-400-yl)-1,2,3-triazoles 5a–h in 84 to 92% yields. The debenzoylation
of coumarinyltriazolylglycosides 5a–h in presence of sodium methoxide in methanol
afforded N1-(b-D-ribofuranosyl)-C4-(coumarin-400-yl)-1,2,3-triazoles 6a–h in 84-97%
yields (Scheme 2).
The structures of all the synthesized compounds were unambiguously established on
the basis of their spectral (1H, 13C, HRMS and IR) data analysis. The structure of
known compounds 2 b–h[23–27], 3a–c[28,30–32], 3e[32] and 3 h[29,30] were confirmed on
the basis of comparison of their physical and spectral data with those reported in the
literature. The structures of 5a–h and 6a–h were also confirmed on the basis of single
crystal X-ray diffraction studies on one of the model tribenzoylated coumarinyltriazolyl-
glycosides, i.e. N1-(20,30,50-tri-O-benzoyl-b-D-ribofuranosyl)-C4-(700-isopropoxycoumarin-
400-yl)-1,2,3-triazole (5e). The ORTEP diagram of crystal structure of compound 5e has
been shown in Figure 2.

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SYNTHETIC COMMUNICATIONSV
5
Conclusion
Sixteen novel benzoylated and corresponding hydroxyl-coumarinyltriazolylglycosides
have been synthesized by using a straightforward Cu(I)-mediated click chemistry reac-
tion between 1-azido-1-deoxy-2,3,5-tri-O-benzoyl-b-D-ribofuranose and 4-ethynylcou-
marins in good yields and their structure has been unambiguously established on the
basis of X-ray diffraction studies on one of the model compounds, i.e. N1-(20,30,50-tri-O-
benzoyl-b-D-ribofuranosyl)-C4-(700-isopropoxycoumarin-400-yl)-1,2,3-triazole. These com-
pounds can be studied for the evaluation of their biological properties as they have
never been synthesized earlier.
Experimental
General procedure for the synthesis of benzoylated coumarinyltriazolylglycosides
(5a–h)
To a 50 mL R. B. flask, 4-ethynylcoumarins (3a–h, 2.77 mmol) and 1-azido sugar (4,
3.08 mmol) was dissolved in THF:t-BuOH:Water (1:1:1 ratio, 9 mL). Copper sulfate pen-
tahydrate (1.23 mmol) and sodium ascorbate (2.46 mmol) were further added to the
resulting reaction mixture. The reaction mixture was stirred for 15–20 h at room tem-
perature and on completion as indicated by TLC check the reaction mixture was con-
centrated on rota vapor and co-evaporated with toluene (2 ꢀ 15 mL) to remove water
from the reaction mixture. The crude product thus obtained was purified by silica gel
chromatography using methanol in chloroform as gradient solvent system.
N1-(20,30,50-tri-O-benzoyl-b-D-ribofuranosyl)-C4-(coumarin-400-yl)-1,2,3-triazole (5a)
It was obtained as yellow fluffy solid (1.605 g) in 88% yield, using 2% MeOH in CHCl3
as an eluent; m.p. ¼ 144–146 ꢁC; IR (cmꢂ1, KBr): 3014, 2116, 1727, 1604, 1266, 1120,
1
1095, 710; H NMR (400 MHz, DMSO-d6): d 9.20 (s, 1 H), 8.42 (d, J ¼ 7.8 Hz, 1 H),
7.95-7.87 (m, 6 H), 7.67–7.35 (m, 12 H), 6.83 (d, J ¼ 2.4 Hz, 1 H), 6.76 (s, 1 H), 6.34 (dd,
J ¼ 5.0, 2.6 Hz, 1 H), 6.20–6.17 (m, 1 H), 5.01–4.98 (m, 1 H), 4.73 (dd, J ¼ 12.3, 3.1 Hz,
1 H), 4.57 (dd, J ¼ 12.3, 4.2 Hz, 1 H); 13C NMR (100.6 MHz, DMSO-d6): d 165.4, 164.7,
164.5, 159.7, 153.8, 142.4, 142.1, 134.2, 134.0, 133.5, 132.5, 131.6, 131.5, 129.6, 129.5,
129.3, 129.1, 129.0, 128.9, 128.8, 128.7, 128.5, 128.4, 127.3, 126.7, 124.6, 117.1, 116.8,
113.8, 89.8, 80.1, 74.8, 70.9, 63.2; HRMS (ESI): m/z ¼ 680.1637, calculated for
[C37H27N3O9þNa]þ ¼ 680.1640.
General procedure for the synthesis of hydroxyl-coumarinyltriazolylglycosides
(6a–h)
In a R.B. flask of 25 mL, compound (5a–h, 1.83 mmol) and NaOMe (5.55 mmol) was
dissolved in MeOH (10 mL) and the reaction mixture was stirred at 25 ꢁC for 3-4 h. On
completion of reaction as indicated by TLC check, seralite SRC-120 (Hþ) was added
into the reaction to neutralize and the mixture was filtered. Solvent was removed under

6
V. K. MAIKHURI ET AL.
vacuum and the crude product thus obtained was purified using silica gel column chro-
matography in methanol-chloroform mixture as gradient solvent system.
N1-(b-D-ribofuranosyl)-C4-(coumarin-400-yl)-1,2,3-triazole (6a)
It was obtained as white solid (0.588 g) in 90% yield, using 10% MeOH in CHCl3 as an
1
eluent; m.p. ¼ 96–98 ꢁC; IR (cmꢂ1, KBr): 3422, 2928, 2372, 1688, 1400, 1122, 751; H
NMR (400 MHz, DMSO-d6): d 9.11 (s, 1 H), 8.50 (d, J ¼ 7.9 Hz, 1 H), 7.66 (t, J ¼ 8.3 Hz,
1 H), 7.46-7.38 (m, 2 H), 6.82 (s, 1 H), 6.03 (d, J ¼ 4.3 Hz, 1 H), 5.72 (brs, 1 H), 5.31 (brs,
1 H), 5.04 (brs, 1 H), 4.44 (t, J ¼ 4.5 Hz, 1 H), 4.16 (t, J ¼ 4.7 Hz, 1 H), 3.99 (dd, J ¼ 8.5,
4.2 Hz, 1 H), 3.64 (dd, J ¼ 11.9, 3.4 Hz, 1 H), 3.52 (dd, J ¼ 12.0, 4.1 Hz, 1 H); 13C NMR
(100.6 MHz, DMSO-d6): d 159.8, 153.9, 142.7, 142.0, 132.5, 127.3, 125.1, 124.7, 117.1,
116.8, 113.4, 92.6, 86.1, 75.3, 70.1, 61.1; HRMS (ESI): m/z ¼ 346.1028, calculated for
[C16H15N3O6þH]þ ¼ 346.1034.
Acknowledgments
We are grateful to University of Delhi for providing financial support under DU-DST Purse
Grant and under scheme to strengthen Research & Development; Vipin K. Maikhuri and Kavita
thank CFEES-DRDO and CSIR, New Delhi for the award of Junior Research Fellowships. We are
also thankful to CIF-USIC, University of Delhi for providing NMR, other spectral and crystallo-
graphic data recording facility.
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