As a continuation of our previous work on the func-
tional molecules based on triterpenoids,9b,15 we report
the synthesis of a tweezer 1 (Figure 1) based on uracil-
appended glycyrrhetinic acid linked by 1,2,3-triazole and
its gelation properties with stimuli-responsive behavior of
ions attributed to the 1,2,3-triazole and uracil.16
Figure 1. Glycyrrhetinic acid-based tweezer 1 and compound 2
as a control.
the different reversible solꢀgel transitions in gelators
responsive to light,4 redox,5 counterions, or molecules6
and pH7 were reported. The reversibility as a crucial
feature of supramolecular materials enables these smart
gels superior to conventional ones and brings accessibility
for designing new functional materials.
Figure 2. State changes during the melting process of the gel 1
(0.7 g/100 cm3) in 1,2-dichloroethane: (a) gel obtained at 20 °C;
(b) gelꢀsol phase at 42 °C; (c) solution above 42 °C (the Tgel of 1
in 1,2-dichloroethane).
Glycyrrhetinic acid, a facile natural pentacyclic triterpe-
noid, possesses special characteristics such as a chiral rigid
skeleton, relative low toxicity, and biocompatibility. It is
mainly used for anti-inflammation, antivirus, and antitu-
mor treatments.8 Recently, there have been more reports
about using the triterpenoids as building blocks in supra-
molecular recognition9 and assembly10 since their special
characteristics could offer diversity spacer and unique
spatial structure arrangement. Meanwhile, nucleobases
involved in the self-assembly of DNA and RNA are being
investigatedforsupramolecular behavior11 towarda better
understanding of how molecules interact with each other.
In particular, uracil was reported as the building block in
constructing functional molecules not only in biology but
also in supramolecular chemistry and nanotechnology.12
In addition, 1,2,3-triazoles are being explored as binding
sites13 in addition to being attractive connecting units by
click reaction.14
Compound 1 was synthesized from the 2,3-dihydroxy-
glycyrrhetinic acid methyl ester9b (Scheme 1 in the Sup-
porting Information). The gelation behaviors of 1 were
determined in various solvents by a “stable to inversion of
the test tube” method,17 and transparent, stiff, and thermo-
reversible gels were observed in a series of halohyro-
carbon solvent (Figure 2), which were stable and
remained for more than 3 months at room temperature
without any changes (Table 1; Figure S1, Supporting
Table 1. Physical Data for Gels of 1 in Various Organic Solvents
entry
solvent
statea
MGC (g/100 cm3)b
1
2
CH2Cl2
G
G
G
G
I
1.8
(8) (a) Liu, D.; Song, D. D.; Guo, G.; Wang, R.; Lv, J. L.; Jing, Y. K.;
Zhao, L. X. Bioorg. Med. Chem. 2007, 15, 5432. (b) Tatsuzaki, J.;
Taniguchi, M.; Bastow, K. F.; Nakagawa-Goto, K.; Morris-Natschke,
S. L.; Itokawa, H.; Baba, K.; Lee, K. H. Bioorg. Med. Chem. 2007, 15,
6193. (c) Chadalapaka, G.; Jutootu, I.; McAlees, A.; Stefanac, T.; Safe,
S. Bioorg. Med. Chem. Lett. 2008, 18, 2633.
(9) (a) Bag, B. G; Pramanik, S. R; Maity, G. C. Supramol. Chem.
2005, 17, 297. (b) Hu, J.; Zhang, M.; Yu, L. B.; Ju, Y. Bioorg. Med.
Chem. Lett. 2010, 20, 4342. (c) Bag, B. G.; Dinda, S. K.; Dey, P. P.
Langmuir 2009, 25, 8663.
(10) (a) Bag, B. G.; Maity, G. C.; Pramanik, S. R. Pramana 2005, 65,
925. (b) Bag, B. G.; Maity, G. C.; Pramanik, S. R. Supramol. Chem.
2005, 17, 383. (c) Bag, B. G.; Maity, G. C.; Dinda, S. K. Org. Lett. 2006,
8, 5457.
(11) (a) Sivakova, S.; Rowan, S. J. Chem. Soc. Rev. 2005, 34, 9.
(b) Wang, X. G.; Zhou, L. P.; Wang, H. Y.; Luo, Q.; Xu, J. Y.; Liu, J. Q.
J. Colloid Interface Sci. 2011, 353, 412. (c) Sukul, P. K.; Malik, S. Soft
Matter 2011, 47, 4418.
CHCl3
3.8
3
1,2-dichloroethane
1,3-dibromopropane
CCl4
0.33
0.45
4
5
6
methanol
P
I
7
isopropyl alcohol
acetonitrile
acetone
8
P
S
S
S
I
9
10
11
12
13
14
15
THF
DMF
toluene
chlorobenzene
1,2-dichlorobenzene
nitrobenzene
S
S
S
a G = stable gel, S = soluble, I = insoluble, P = precipitate. b MGC
is the minimum gelator concentration at which gelation was observed to
restrict the flow of the medium at 25 °C.
(12) (a) Sessler, J. L.; Jayawickramarajah, J. Chem. Commun. 2005,
1939. (b) Iwaura, R.; Yoshida, K.; Masuda, M.; Yase, K.; Shimizu, T.
Chem. Mater. 2002, 14, 3047. (c) Snip, E.; Shinkai, S.; Reinhoudt, D. N.
Tetrahedron Lett. 2001, 42, 2153.
(13) (a) Li, Y. J.; Huffman, J. C.; Flood, A. H. Chem. Commun. 2007,
2692. (b) Meudtner, R. M.; Ostermeier, M.; Goddard, R.; Limberg, C.;
Hecht, S. Chem.;Eur. J. 2007, 13, 9834.
(14) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2001, 40, 2004.
Information). The results showed that 1,2-dichloroethane
is one of the best solvents for the gelation process by
Org. Lett., Vol. 13, No. 13, 2011
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