ORGANIC
LETTERS
2011
Vol. 13, No. 23
6260–6263
Polarized Naphthalimide CH Donors
Enhance Clꢀ Binding within an
Aryl-Triazole Receptor
Kevin P. McDonald, Raghunath O. Ramabhadran, Semin Lee,
Krishnan Raghavachari, and Amar H. Flood*
Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington,
Indiana 47405, United States
Received October 11, 2011
ABSTRACT
The dipolar character of 1,8-naphthalimide together with polarization of the C4ꢀH and C5ꢀH donors has been utilized in receptor 1 to effectively bind
chloride alongside triazole and phenylene units. The Clꢀ binding strength of 1 shows that the naphthalimide provides greater anion stabilization than
an unactivated phenylene, and DFT calculations show that its collinear donor array can be a “urea-like” analog for CH anion interactions.
3 3 3
The 1,8-naphthalimide building block, specifically 4-amino-
1,8-naphthalimide, is typically employed as a reporter1 for
fluorescence sensing where binding of an analyte (cation,
anion, Hþ) affects the internal charge transfer from the
electron-rich naphthalene to the electron-deficient imide.1,2
While this phenomenon generates a highly polarized excited
state, the inherent dipole within the ground state of the 1,8-
naphthalimide moiety is also expected to generate polarized
CH donors for cooperative hydrogen bonding interactions
with anionic guests inside receptors.
the cooperative binding of anions alongside urea and
thiourea motifs. While engaging with this NH donor led
to enhanced affinities, further inspection of the 1H NMR
data showed a significant downfield shift (Δδ = 0.5 ppm)
in the adjacent naphthalimide CH resonance. Given the
growing evidence of effective CH Xꢀ interactions6
3 3 3
stemming from triazoles7 and other extrinsically polar-
ized aryl CH groups,6,8 this shift may have been a strong
Recent sensor designs3ꢀ5 only hinted at the potential CH
donors latent within 1,8-naphthalimide. These sensors utilized
the NH donor of the 4-amino substituted 1,8-naphthalimide in
(6) McDonald, K. P.; Hua, Y.; Flood, A. H. Top. Heterocyl. Chem.
2010, 24, 341–367.
(7) (a) Li, Y.; Flood, A. H. Angew. Chem., Int. Ed. 2008, 47, 2649–
2652. (b) Li, Y.; Flood, A. H. J. Am. Chem. Soc. 2008, 130, 12111–12122.
(c) Li, Y.; Pink, M.; Karty, J. A.; Flood, A. H. J. Am. Chem. Soc. 2008,
130, 17293–17295. (d) Bandyopadhyay, I.; Raghavachari, K.; Flood,
A. H. ChemPhysChem. 2009, 10, 2535–2540. (e) Zahran, E.; Hua, Y.;
Flood, A. H.; Bachas, L. G. Anal. Chem. 2010, 82, 368–375. (f) Lee, S.;
Hua, Y.; Park, H.; Flood, A. H. Org. Lett. 2010, 12, 2100–2101. (g) Hua,
Y.; Flood, A. H. Chem. Soc. Rev. 2010, 39, 1262–1271 and references
therein. (h) Hua, Y.; Ramabhadran, R. O.; Uduehi, E. O.; Karty, J. A.;
Raghavachari, K.; Flood, A. H. Chem.;Eur. J. 2011, 17, 312–321.
(8) (a) Bryantsev, V. S.; Hay, B. P. J. Am. Chem. Soc. 2005, 127,
8282–8283. (b) Bryantsev, V. S.; Hay, B. P. Org. Lett. 2005, 7, 5031–
5034. (c) Yoon, D. W.; Gross, D. E.; Lynch, V. M.; Sessler, J. L.; Hay,
B. P.; Lee, C.-H. Angew. Chem., Int. Ed. 2008, 47, 5038–5042. (d) Bruno,
G.; Cafeo, G.; Kohnke, F. H.; Nicolo, F. Tetrahedron 2007, 63, 10003–
10010. (e) Berryman, O. B.; Sather, A. C.; Hay, B. P.; Meisner, J. S.;
Johnson, D. W. J. Am. Chem. Soc. 2008, 130, 10895–10897.
(1) For a recent review of naphthalimide sensors: Duke, R. M.; Veale,
E. B.; Pfeffer, F. M.; Kruger, P. E.; Gunnaluagsson, T. Chem. Soc. Rev.
2010, 39, 3936–3953.
(2) De Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley,
A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997,
97, 1515–1566.
(3) (a) Gunnlaugsson, T.; Kruger, P. E.; Jensen, P.; Pfeffer, F. M.;
Hussey, G. M. Tetrahedron Lett. 2003, 44, 8909–8913. (b) Bao, X.-P.;
Wang, L.; Wu, L.; Li, Z.-Y. Supramol. Chem. 2008, 20, 467.
(4) Pfeffer, F. M.; Seter, M.; Lewcenko, N.; Barnett, N. W. Tetra-
hedron Lett. 2006, 47, 5241–5245.
(5) Pfeffer, F. M.; Buschgens, A. M.; Barnett, N. W.; Gunnlaugsson,
T.; Kruger, P. E. Tetrahedron Lett. 2005, 46, 6579–6584.
r
10.1021/ol202729z
Published on Web 11/04/2011
2011 American Chemical Society