Organic Letters
Letter
not aryl diazonium ion dependent, BSA was treated with both
(9) Kimani, F. W.; Jewett, J. C. Angew. Chem., Int. Ed. 2015, 54,
4
051−4054.
triazole 7 and azido-fluorophore 8. As expected, labeling of BSA
20
(10) Kimball, D. B.; Haley, M. M. Angew. Chem., Int. Ed. 2002, 41,
338−3351.
did not occur with the control compounds. We evaluated the
role of labeling time on the BSA and saw a clear increase of
fluorescence intensity up to 30 min of treatment with acidic
media (Figure 2c). At each time point the reactions were
quenched adding a large excess of resorcinol to react with
remaining free aryl diazonium ions and subsequently
neutralizing the solution to arrest release of additional aryl
diazonium ions. This timing trend is consistent with our
understanding of pH dependent release of the aryl diazonium
ions that occurs over several minutes and the subsequent rapid
3
(
11) Pratsch, G.; Wallaschkowski, T.; Heinrich, M. R. Chem. - Eur. J.
2
012, 18, 11555−11559.
12) Sakla, A. B.; Masoud, N. K.; Sawiris, Z.; Ebaid, W. S. Helv. Chim.
Acta 1974, 57, 481−487.
13) Singh, M. S.; Chowdhury, S.; Koley, S. Tetrahedron 2016, 72,
(
(
5257−5283.
(14) Turner, Z. R.; Bellabarba, R.; Tooze, R. P.; Arnold, P. L. J. Am.
Chem. Soc. 2010, 132, 4050−4051.
(
15) Fanghan
485−493.
16) Khramov, D. M.; Bielawski, C. W. J. Org. Chem. 2007, 72,
407−9417.
17) Ahad, A. M.; Jensen, S. M.; Jewett, J. C. Org. Lett. 2013, 15,
060−5063.
18) It should be noted that other proteins that were tried, such as
̈ ̈
el, E.; Hansel, R.; Hohlfeld, J. J. Prakt. Chem. 1977, 319,
9
reaction between that ion with tyrosine.
(
9
(
5
We reported a new triazabutadiene scaffold that enables us,
and others, to utilize the power of Cu-click chemistry to
perform late-stage functionalization reactions on this uniquely
reactive moiety. The key questions and concerns of
triazabutadiene compatibility with Cu-click chemistry were
address, and we went on to show the utility of such a strategy
by enabling the direct conjugation of a fluorophore to a model
protein. We expect that this chemistry will broaden the
applicability of the use of triazabutadienes as masked aryl
diazonium ions and offer chemists and chemical biologists more
options when designing coupling strategies.
(
lysozyme, did not label efficiently due to the poor water solubility of
5d. Our working hypothesis is that BSA did indeed help to solubilize
the triazabutadiene. The labeling observed was evidence of the aryl
diazonium ion formation, but cannot be solely attributed to tyrosine
because other adducts (such as triazenes) can form, albeit reversibly.
(
19) Jones, M. W.; Mantovani, G.; Blindauer, C. A.; Ryan, S. M.;
Wang, X.; Brayden, D. J.; Haddleton, D. M. J. Am. Chem. Soc. 2012,
34, 7406−7413.
20) We observed a low level of background labeling with all
1
(
ASSOCIATED CONTENT
Supporting Information
■
compounds. This background can be attributed to the ability of
hydrophobic pockets on BSA binding to small molecules.
*
S
Protocols for the synthesis and characterization of all
AUTHOR INFORMATION
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Jean-Laurent Blanche for assistance with synthesis
and Lindsay Guzman for assistance with revisions. This work
was supported in part by an NSF-CAREER award to J.C.J.
(CHE-1552568).
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