fluorescent detection of molecules that react with the fluorogenic
molecules.1 For example, fluorogenic maleimides are nonfluo-
rescent or very weakly fluorescent until they react with thiols;
the reaction products are highly fluorescent, allowing fluorescent
detection or fluorescent visualization of thiols and thiol-
containing molecules.1a–c When intrinsically fluorescent mol-
ecules are used for bond-forming reactions, separation of product
molecules from unreacted fluorescent molecules is required
before analysis; an advantage of use of fluorogenic molecules
is that the reaction products can be analyzed without need for
a separation step.1,2 Although there are many types of fluoro-
genic molecules,1,2 fluorogenic molecules for reactions of
phenols have not been reported.4 The phenol functionality is
present in tyrosine, a building block of proteins, and in many
natural products.5 Tyrosine residues on folded proteins have
been used as modification sites.4 Therefore, fluorogenic mol-
ecules that react with phenols would be useful for screening of
catalysts and reaction conditions for the bond-forming reactions
with phenols including phenol-bearing biomolecules and for
fluorescent labeling and detection of molecules possessing
accessible phenols. Here, we report the first examples of
fluorogenic molecules for Mannich-type reactions of phenols
in aqueous buffers.
Fluorogenic Imines for Fluorescent Detection of
Mannich-Type Reactions of Phenols in Water
Hai-Ming Guo, Maki Minakawa, and Fujie Tanaka*
Department of Molecular Biology, The Scripps Research
Institute, 10550 North Torrey Pines Road,
La Jolla, California 92037
ReceiVed February 8, 2008
Since imines and iminiums react with phenols through
Mannich-type reactions in aqueous buffers or water-containing
solvents under mild conditions,4a,b we chose imines as phenol-
Fluorogenic imines and their precursor amines that can be
used for fluorescent visualization of Mannich-type reactions
of phenols in aqueous buffers have been developed. The
precursor amines are aniline derivatives that are covalently
conjugated to fluorophores. These amines and their imine
derivatives were nonfluorescent or very weakly fluorescent.
On the other hand, addition products of the imines to phenols
showed more than 100-fold higher fluorescence than the
imines and the precursor amines.
(2) (a) Tanaka, F.; Thayumanavan, R.; Barbas, C. F., III J. Am. Chem. Soc.
2003, 125, 8523. (b) Tanaka, F.; Mase, N.; Barbas, C. F., III J. Am. Chem. Soc.
2004, 126, 3692. (c) Tanaka, F.; Thayumanavan, R.; Mase, N.; Barbas, C. F.,
III Tetrahedron Lett. 2004, 45, 325. (d) Mase, N.; Tanaka, F.; Barbas, C. F., III
Org. Lett. 2003, 5, 4369. (e) Mase, N.; Tanaka, F.; Barbas, C. F., III Angew.
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Fluorogenic molecules that afford fluorescent products upon
bond-forming reactions allow monitoring the progress of the
reactions by increase in fluorescence.1–3 Evaluation of chemical
transformations with these fluorogenic molecules accelerates
characterization and screening of catalysts and/or reaction
conditions.1,2 In addition, these fluorogenic molecules enable
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3964 J. Org. Chem. 2008, 73, 3964–3966
10.1021/jo8003293 CCC: $40.75 2008 American Chemical Society
Published on Web 04/23/2008