Phenanthridinium compounds

Perhaps the most well-recognized fluorescent dye for detection of DNA hybridization is ethidium bromide (EtBr). EtBr is a cationic phenanthridinium compound that can bind to DNA by intercalation. This dye has an excitation maxima at 518 nm when bound to double-stranded DNA (dsDNA). Excitation of EtBr is often done by use of an argon ion laser, making this fluorophore a viable choice for applications in optical sensors as well as confocal scanning laser microscopy and fluorometry [41]. The structure of ethidium bromide is shown in Fig. 6. 

Although phenanthridine was discovered in the late nineteenth century1, 2 neither the parent base nor its derivatives attracted attention until useful therapeutic activity was established in certain quaternary phenanthridinium compounds.3 A substantial number of substituted phenanthridines (and many phenanthridinium salts) have now been described and lists of compounds appearing in the literature from 1884 until 1955 are available.4, 6 Phenanthridines have attracted surprisingly little systematic attention, although the system is of considerable theoretical interest and, with its nine nonequivalent carbon atoms, may be expected to provide a rigorous test of molecular orbital reactivity correlations. Naturally occurring derivatives include several Amaryllidaceae and Papaveraceae alkaloids, notably, lycorine, haemanthamine, and chelidonine the chemistry of the phenanthridine alkaloids has been reviewed.6... 

Quaternary phenanthridinium compounds are reduced to the corresponding A-alkyldihydrophenanthridines by hydrogenation over Adams catalyst. The reaction forms part of the modified Emde sequence284 shown below. 

In a preliminary study of caranine, it was found that a modified Oppenauer oxidation of the base gave the phenanthridinium compound XXX which was identical with one of the oxidation products of lycorine (102). From this oxidation it was postulated that caranine possesses the lycorine ring system with a hydroxyl group in the 1-position. Subsequent... 

Fukunaga, M. Yielding, L. W. Structure-function characterization of phenanthridinium compounds as mutagens in Salmonella. Mutat. Res. 1983, 121, 89-94. 

Several JV-(quinonylalkyl)enaminones have served as model compounds for an intramolecular Nenitzescu reaction demonstrating the ambident reactivity of both the enaminone and the quinone. The compounds cyclized unexpectedly, mainly to heterocyclic spiro-compounds146,147. A phenanthridinium salt and benzofuranoazocine are also obtained, depending on the length of the chain connecting the quinone and the enaminone moieties (equation 95). 

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