synthesized and their properties as photoswitches have
been reported.13À19 These systems have been also used to
photocontrol peptide conformations.20À22
and photochemical study of oxazolone analogs of the GFP
chromophore to test their ability to act as efficient mole-
cular photoswitches.
Another example of biomolecules that undergo photo-
induced Z/E isomerizations is the chromophore of the
green fluorescent protein (GFP), from Aequorea victoria
jellyfish. GFPs are intrinsically fluorescent molecules
whose optical properties are determined by a photoexci-
table green-light emitter chromophore.23 However, several
studies have revealed that the GFP chromophore also
undergoes nonradiative processes when irradiated with
light, such as a Z/E photoisomerization, which contributes
to reducing the luminescence quantum yield.24À27 Also,
different modifications of the imidazoline GFP chromo-
phore have been also reported to show photophysical and
photochemical relevant processes.25,28,29 Interestingly,
well-known intermediates in the synthesis of GFP deriva-
tives such as the oxazolone analogs have been only slightly
explored in terms of their photoswitching ability. Although
the photoisomerization of benzylidene lactones has been
known for some time,30,31 only recently have some re-
ports on the photophysical properties of these com-
pounds appeared, with a focus on the fluorescence and
its applications.32À34 Thus, we report herein the synthesis
The general structure of synthesized compounds is
shown in Figure 1, together with the GFP chromophore.
The main difference between them is that the GFP chro-
mophore and its derivatives present an amide function in
the five-membered ring (dihydroimidazolone), while the
compounds that we have studied have an ester function
instead (5(4H)-oxazolones). The structure of the GFP
chromophore can be easily achieved from the synthesized
structures through a single reaction step.25 The synthesis of
the new photoswitches with the structure based on the
GFP chromophore takes place under the classical condi-
tions for the formation of azalactones,35 which is repre-
sented in Scheme 1. Using this methodology a number of
photoswitches can be easily synthesized (Table 1). In all
cases, the Z isomer was the only product detected in the
reaction crude. The configuration assigment was made on
the basis of X-ray diffraction data for 2d (see Supporting
Information (SI) for details).
(13) Sampedro, D.; Migani, A.; Pepi, A.; Busi, E.; Basosi, R.;
Latterini, L.; Elisei, F.; Fusi, S.; Ponticelli, F.; Zanirato, V.; Olivucci,
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F.; Sinicropi, A.; Andruniow, T.; Ferre, N.; Basosi, R.; Olivucci, M.
Angew. Chem., Int. Ed. 2007, 47, 414.
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J.; Sharma, D.; Leonard, J.; Haacke, S.; Canizzo, A.; Chergui, M.;
Zanirato, V.; Fusi, S.; Santoro, F.; Basosi, R.; Ferre, N.; Olivucci, M.
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Figure 1. GFP chromophore (a) and oxazolone derivatives (b).
Scheme 1. Synthesis for GFP-Based Photoswitches
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Although this methodology can be used to prepare a
wide range of products, the use of certain benzaldehyde
derivatives, such as 2-carboxy- or 2-cyanobenzaldehyde,
and ketones is prevented. Next, the UVÀvis spectra for all
the synthesized compounds were measured. The values for
the maximum wavelengths and the extinction coefficients
of the bands found for each compound in acetonitrile are
displayed in Table S1. Interestingly, these compounds
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