Fluorescent Probes from Aromatic Polycyclic Nitrile Oxides: Isoxazoles versus Dihydro-1λ3,3,2λ4-Oxazaborinines

Anthracenenitrile oxide undergoes 1,3-dipolar cycloaddition
reaction with propargyl bromide affording the expected
isoxazole as single regioisomer, suitably synthetically elaborated
and functionalized with a protected triple bond. The introduction
of a bromine atom at the position C10 of the anthracene
moiety allows for inserting a variety of aromatic and heterocyclic
substituents through Suzuki coupling. A two-way synthetic
route can lead to simple isoxazole derivatives or, after
N@O bond reductive cleavage and BF3 complexation, enamino
ketone boron complexes. The photophysical properties of both
the substituted isoxazoles and the corresponding boron
complexes were investigated to show the potentialities for the
employment as fluorescent tags in imaging techniques. The
quite good quantum yield values confirm the suitability of
these compounds in the cellular environment. Scope and
limitations of the methodology are discussed.