Naturally occurring phenoxazines

Even before the first synthesis of phenoxazine—reported in 1887 by Bernthsen1—two dyestuffs with the phenoxazine ring system, Meldola s blue and gallocyanine, were commercially available. After its discovery, however, the chemistry of the phenoxazines lay dormant for nearly half a century. Only during the last 10 years has this class of compound aroused renewed interest, as evidenced by the discovery of naturally occurring and biologically active phenoxazines. 

Polarographic,35 chromatographic, and electrophoretic 36 investigations on phenoxazine derivatives have been reported for naturally occurring phenoxazones (actinomycins). 

Mention should be made of oxazine dyes, used also as biological stains, which are oxidized phenoxazine derivatives containing suitable auxochromic groups. A detailed treatment of these dyes, however, is beyond the scope of this review. Most of the industrial phenoxazine dyes are derived from benzophenoxazines (e.g., Meldola s blue) or from more complex ring systems containing the phenoxazine residue (triphendioxazine dyes).3,118 The long-known dyestuffs orcein and litmus which are prepared by the action of ammonia on certain lichens, and may also occur accidentally in nature, are both based on the oxidized phenoxazine ring system as shown by Musso and co-workers.119... 

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