Synthesis, characterisation and antimicrobial activity of new benzo[a]phenoxazine based fluorophores

N-[5-(3-Aminopropylamino)-10-methyl-9H-benzo[a]phenoxazin-9-ylidene]ethanaminium chloride (Bze-NH2) was prepared and used as a precursor in the synthesis of new polycyclic cationic dyes. In addition to the potentiality of Bze-NH2 as a non-covalent fluorescent probe, the presence of a free amino group in its structure prompted us to study the application of this functionalised heterocycle in the covalent labelling of glycine and valine amino acids, as models of biomolecules. All compounds obtained showed strong absorbance and high emission at long-wavelengths (λem >640 nm). Furthermore, all benzo[a]phenoxazine derivatives synthesised were evaluated as antifungal agents against Saccharomyces cerevisiae, considering the commercial Nile Blue A (NB) as a lead compound. The results revealed that they exhibited good activity, which was usually superior to NB, the most effective compound displaying a minimum inhibitory concentration (MIC) value of 15 μM.

Reagents and conditions: (a) DCC/HOBt, rt; (b) 1 M NaOH/H2O, 0 °C and rt.