The isolation of crystalline d-urobilinogen.

Until recently there have been only two well recognized members of the urobilinogen group, mesobilirubinogen, the chromogen of i-urobilin,’ and stercobilinogen, the leuco compound of urobilin or stercobilin. While mesobilirubinogen is readily obtained in crystalline form following amalgam reduction of bilirubin or i-urobilin, stercobilinogen has never been crystallized. Stercobilin, however, was first isolated in 1932 (1) and has been studied in considerable detail (2). As pointed out in the preceding paper (3), a third urobilin, d-urobilin, was isolated from infected fistula bile in 1942 (4). At that time the probable existence of a chromogen of d-urobilin was recognized and this was designated as d-urobilinogen, although it was not isolated. The occurrence of d-urobilin in the feces of patients treated with Aureomycin was reported in 1951 (5). Recently, while crystallizing isotopically labeled bilirubin from this source (6), it was found possible for the first time to isolate d-urobilinogen in crystalline form. The purpose of the present communication is to describe methods of isolation as well as some of the properties of this chromogen.