Structure revision of disaccharidic conjugates of bilirubin-IX α in human bile and identification of phenylazo derivatives B4, B5, and B6 as 2-, 3- and 4-O-acylglucuronides

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Abstract
Aniline azopigments B4, B5 and B6, derived from conjugates of bilirubin-IX.alpha. in human bile, and previously characterized as disaccharidic esters, were analyzed by using TLC and mass spectrometry. The compounds were identified as partially separated mixtures of 2-, 3- and 4-O-acylglucuronide positional isomers. The 1-O-acylglucuronide was not detected in the mixtures and was the only compound hydrolyzed with .beta.-glucuronidase. Further scrutiny of structural assignments led to identification of the lactone and hexuronic acid derivatives that were obtained from azopigment B5 along with glucuronolactone and glucuronic acid. A branched-chain structure, i.e., 3-C-hydroxymethyl-D-riburonic acid, was assigned previously, but the derivatives have now been identified as various incompletely silylated forms of glucuronolactone and glucuronic acid. Several trimethysilyl derivatives of glucuronolactone were isolated and characterized by NMR and mass spectrometry.

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