ARS | Publication request: Synthesis and photochemistry of pH-sensitive GFP chromophore analogues

Submitted to: Tetrahedron Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 24, 2010
Publication Date: April 27, 2011
Citation: Kartritzky, A.R., Yoshioka-Tarver, M., El-Gendy, B.M., Hall, C. 2011. Synthesis and photochemistry of pH-sensitive GFP chromophore analogues. Tetrahedron Letters. 52(17):2224-2227.

Interpretive Summary: Green fluorescent protein (GFP) is an established monitoring method to detect small concentrations of different biological activities such as ligands, inhibitors, and antigens. Several studies have been performed to understand the high fluorescent activity of GFP; however, isolated GFPs, or synthesized GFP chromophores, have relatively small fluorescent activities due to photoisomerization of the exo-methylnene group. Our goal was to design pH sensitive GFP chromophore analogues based on photoisomerization properties. Four analogues containing heterocyclic rings, such as furan, thiophene, pyrrole, or pyridine, were designed and synthesized. The analogue’s fluorescent activity was reduced in neutral and basic media but enhanced in acidic media by protonating a nitrogen atom and inhibiting the photoisomerization of the exo-methylene group.

Technical Abstract: Nobel GFP chromophore analogues containing 2-thienyl-, 5-methyl-2-furyl-, 2-pyrryl, and 6-methyl-2-pyridyl-groups were synthesized, and their fluorescence spectra were recorded across pH range of 1 to 7. The GFP chromophores prevent photoisomerizaiton in acidic media and increase their fluorescent activities. NMR studies showed that protonation of 2-thienyl system inhibited photoisomerization (Z to E) at the exocyclic double bond and the protonation of stereomeric mixtures (E + Z) of 2-pyrryl system gave only the E-isomer. Fluorescence studies revealed enhancement of fluorescence intensity of 5-methyl-2-furyl-and 2-pyrryl system below pH 2.5 and gave a similar result for 6-methyl-2-pyridy system below pH 6.