A NEW METHOD OF INTERPRETATION OF FERRIC CHLORIDE OXIDATION PATTERNS OF UROBILINOIDS

A new and more definitive interpretation of the results of a standard method of FeCl3 oxidation of the urobilinoids is presented. This interpretation is based on the actual yields of mesobiliviolin, glaucobilin, or unchanged urobilinoid. The yields are used to calculate the two distinctive ratios characteristic of urobilinoid type. Correction is made for the effects due to overlapping of spectra and the method has been programmed for a digital computer. Blind analyses of appropriate known mixtures of l-stercobilin, mesobiliviolin, and glaucobilin have given satisfactory results. Comparison of the ratios following FeCl3 oxidation of binary mixtures of representative urobilinoids permits analysis of their composition. Evidence is presented that the FeCl3 method involves two types of oxidation: (a) Dehydrogenation to mesobiliviolin and glaucobilin, the extent of oxidation depending on saturation or unsaturation of the end rings. Stercobilin, with both end rings saturated, yields neither mesobiliviolin or glaucobilin; half-stercobilin with one end ring saturated yields stable mesobiliviolin and unreacted urobilinoid; and the urobilins proper, with both end rings unsaturated, are converted first to labile mesobiliviolin then to glaucobilin. (b) All three types also undergo some degradative oxidation as indicated by the presence of ethylmethylmaleimide from unsaturated, and ethylmethylsuceinimide from saturated end rings. © 1969.