1,4-Benzothiazine chromophore

Phenylsulfonyl)furo[2,3- ]quinoline and its parent unsubstituted heterocycle were found to have very similar absorption maxima hence, the sulfone group does not provide an additional conjugative effect <83JOC774>. In addition, furo[2,3-/ quinoline and its isomeric furo[3,2-< ] counterpart were found to exhibit UV absorption maxima that are almost identical. An absorption maximum at 435 nm consistent with the presence of a 2H-1,4-benzothiazine chromophore was one of the key pieces of data that enabled the structure determination of compounds based upon the new 1,2-dihydro-3//,8//-pyrrolo[2,3-/z][l,4]benzothiazine skeleton <87T5357>. The UV spectrum of l,4-benzodioxano[6,7-c]furoxan was found to exhibit four characteristic band maxima in the 350-480 nm region <88JHC803>. 

Chemical investigation of the trichochromes which are much smaller molecules has not been so hampered and several of these have been identified indeed, they are the only group of "melanin" pigments of well-defined structure, characterized by an unique pH-dependent 1,4-benzothiazine chromophore. Typical examples are the yellow... 

H- 1,4-Thiazines and benzothiazines undergo oxidation to dehydro dimers (83) and (84) which are of considerable interest as they are the parent chromophores of the trichosiderin (trichochrome) pigments which occur in mammalian red hair and in the feathers of some birds (74T2781). In the case of monocyclic thiazines, reagents such as nitrobenzene or picric acid are required, but air oxidation is sufficient in the bicyclic series. It is curious that whereas aerial oxidation of the ester (85) gives both the dehydro dimers (86) and (87), ethyl azodicarboxylate only yields the tautomer (87) <70AC(R)35l). 

Trichochromes E and F are based on the 2H-1,4-benzothiazine ring, while trichochromes B and C are mixed systems, with both 1,4-benzothiazine and l,4-benzothiazin-3-one fragments. These may be extracted from red hair and feathers under alkaline conditions.31,32 Apparently33 only trichochromes B and C occur in red feathers, and trichochromes E and F, reportedly isolated from this source, arise as artifacts. The chromophore in the trichochrome... 

Kaul synthesized the chromophore based on l,4-benzothiazin-3-one to obtain the skeleton 19 for trichochromes B and C.33... 

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