Abstract
The identity of crystalline urobilin and stercobilin, as isolated from human urine and feces, was established previously.1-5 In confirmation of this the same crystalline hydrobromide has been prepared from each substance. The method of preparation is briefly as follows: The free urobilin is prepared from the hydrochloride as previously described. 2 It is not crystallized but is extracted from its chloroform solution with 25% hydrobromic acid. The latter is diluted with 3-4 volumes of distilled water, and the hydrobromide extracted with chloroform. The chloroform solution is dried over anhydrous Na2SO4, filtered, and concentrated to a small volume on the water bath. This is poured into at least 10 volumes of petroleum ether. After precipitation of the hydrobromide, the precipitate is collected on a small filter paper, and dissolved by repeated extraction with small amounts of hot ethyl acetate. After moderate concentration, the solution is allowed to cool and crystallization soon commences. The yields have varied between 40-50%. The crystals have a very remarkable shape resembling long, narrow boats with several compartments (transverse cleavage lines). The substance is readily recrystallized from ethyl acetate, and has a light yellow color with slight orange cast. M.P. 145-150° (Shrinking above 135°). The absorption spectrum is the same as that of the hydrochloride, and the green fluorescence with zinc acetate appears to be fully as intense. It was conceivable that this substance was a degradation product of urobilin, not simply a hydrobromide. This possibility was excluded by ready conversion to the hydrochloride which was identified by the character of its crystals, and by preparation of its characteristic iron chloride molecular compound. 6
Heilmeyer and Krebs 7 have recently stated that the hydrochloride of the urobilin which they isolated is a dihydrochloride. In this investigation stercobilin was also isolated by the method which they described. It was found to differ in no way from that isolated according to the method previously described by the writer. 5
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