Abstract

The present work investigated the preparation of phenoxazinone derivatives
and evaluated their performances for the detection of pathogenic bacteria.
The first method investigated the condensation of nitroaminophenol with
tetrahalogenobenzoquinones; the corresponding nitrohalogenophenoxazinones were
all characterised and evaluated for the detection of nitroreductase activity in a range
of clinically important microorganisms. The detection of nitroreductase activity has
been previously suggested for the monitoring of bacterial growth; however,
nitrohalogenophenoxazinones were proven to be less suitable for this purpose than
other, previously reported, nitroreductase substrates.
The second route investigated the synthesis of phenoxazinone derivatives via
the oxidative cyclisation of diamino-dihydroxydiphenylethers and of
diaminobenzoquinones. The reactive intermediates were trapped and characterised
in order to rationalize the mechanism of formation of aminophenoxazinones via this
route. 7- and 8-Aminophenoxazinones derivatives were prepared and further
derivatised with b-alanine. Similarly, some nitrohalogenophenoxazinones were
reduced to their corresponding aminophenoxazinones and derivatised with b-alanine.
Thirteen new chromogenic substrates were prepared, characterised and
evaluated for their sensitivity to detect b-alanine aminopeptidase on agar medium;
this enzyme is expressed by only three types of bacteria, the most important being
Pseudomonas aeruginosa, a pathogen commonly known to affect cystic fibrosis
sufferers. Their performance for the detection of Pseudomonas aeruginosa were
compared to the lead compound (7-N-(b-alanyl)amino-1-pentylphenoxazin-3-one),
the substrate contained in a commercially available medium, chromIDTM ID Ps.
aeruginosa. The substrates, if hydrolysed, resulted in a low colouration of the
colonies when compared to the lead compound; however, 2-pentyl substituted
aminophenoxazinones were found to be less toxic and had an excellent affinity for
the bacterial colonies.
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