Über Mesobilivioline. I. Mitteilung. Konstitution des Mesobiliviolins, Synthesen des Mesobiliviolins-IX,αund Mesobiliviolins-XIII,αsowie überψ-Mesobiliviolin und „Oxo“-urobilin
Mesobiliviolin XIII [alpha] dimethyl ester (l[image],8[image]-dihydroxy-l,3,6,8-tetramethyl-2,7-diethylbilidiene-(2[image] [alpha], ms, 5[image])-4.5-di-propionic acid dimethyl ester, C35H44O6N4) was prepared by condensation of formylneoxanthobilirubinic acid and neobilirubinic acid in the presence of HBr in MeOH. The pigment was purified by chromatographic adsorption on AI2O3. The pigment was isolated as red, oblique truncated prisms with a golden surface luster, m. 164[degree]. It formed a mono-HCl salt, m. 170[degree]. When the pigment was dissolved in absolute alc., in the presence of Zn(OAc)2, it formed a Zn complex salt, with magnificent red fluorescence, and having a characteristic spectrum. The Cu complex salt did not fluoresce, but its spectrum was similar to that of the Zn salt. Hydrogenation with Na-Hg gave a leuco compound, mesobilirubinogen XIII [alpha], m. 205[degree]. Attempts to prepare mesobiliviolin IX [alpha] (l[image],8[image]-dihydroxy-l,3,6,7-tetramethyl-2,8-diethylbilidiene-(2[image] [alpha], ms-5[image])-4,5-dipropionic acid dimethyl ester) from formylneoxanthodilirubinic acid and isoneo-bilirubinic acid in a similar manner gave an unstable product. The mono-HCl salt of this compound melted at about 165[degree]. Reduction withNa-Hg gave mesobilirubinogen IX [alpha]. Mesobiliviolin IX [alpha] dimethyl ester was also prepared by heating mesobilirubinogen with FeCl3 and HC1 in MeOH. The product could not be obtained in crystalline form, but its mono-HCl salt melted at about 160[degree]. Oxourebilin was obtained by oxidation of mesobiliviolin XIII [alpha] with Br2 or Pb(OAc)4. When stored for some mos., mesobiliviolin changed into "pseudomesobiliviolin" ([PSI]-mesobiliviolin). The new substance had a somewhat different color from mesobiliviolin, but its reactions were similar.