Abstract
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We present the synthesis,
photophysical properties, and biological
application of nontoxic 3-azo-conjugated BODIPY dyes as masked fluorescent
biosensors of hypoxia-like conditions. The synthetic methodology is
based on an operationally simple N=N bond-forming protocol,
followed by a Suzuki coupling, that allows for a direct access to
simple and underexplored 3-azo-substituted BODIPY. These dyes can
turn on their emission properties under both chemical and biological
reductive conditions, including bacterial and human azoreductases,
which trigger the azo bond cleavage, leading to fluorescent 3-amino-BODIPY.
We have also developed a practical enzymatic protocol, using an immobilized
bacterial azoreductase that allows for the evaluation of these azo-based
probes and can be used as a model for the less accessible and expensive
human reductase NQO1. Quantum mechanical calculations uncover the
restructuration of the topography of the S1 potential energy
surface following the reduction of the azo moiety and rationalize
the fluorescent quenching event through the mapping of an unprecedented
pathway. Fluorescent microscopy experiments show that these azos can
be used to visualize hypoxia-like conditions within living cells.
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