1. P. Flesch, J. invest. Derm.51, 337 (1968) and references cited therein.
2. G. Prota andR. A. Nicolaus, inAdvances in Biology of Skin (Eds.W. Montagna andF. Hu; Pergamon Press, New York 1967), vol. 8, p. 323.
3. R. A. Nicolaus, G. Prota, C. Santacroce, G. Scherillo andD. Sica, Gazz. chim. ital.99, 323 (1969).
4. G. Prota, G. Scherillo, O. Petrillo andR. A. Nicolaus, Gazz. chim. ital.99, 1193 (1969).
5. The stereochemistry of theΔ 2,2′-bibenzothiazine skeleton in I, II and III has not yet been defined. However, studies of model compounds (F. Giordano, L. Mazzarella, G. Prota, C. Santacroce andD. Sica, J. chem. Soc., in press) have shown that the interconvention of geometrical isomers in this series occurs rather readily and the isolated pigments may well be equilibrium mixtures of the 2 forms.