title: Preparation and properties of crystalline biliverdin IX alpha. Simple methods for preparing isomerically homogeneous biliverdin and [14C[biliverdin by using 2,3-dichloro-5,6-dicyanobenzoquinone.
abstract: Amorphous isomerically pure biliverdin IX alpha is readily prepared in more than 70% yield by dehydrogenation of bilirubin with 2,3-dichloro-5,6-dicyanobenzoquinone in dimethyl sulphoxide under carefully controlled conditions. Crystalline biliverdin IX alpha and amorphous [14C]biliverdin can be obtained similarly in more than 40+ yield. The pure crystalline pigment was characterized by elemental analysis, methylation, chemical and enzymic reduction to bilirubin, i.r.- and u.v.-visible-absorption spectroscopy, n.m.r. spectroscopy and field-desorption mass spectrometry, and its solubility was determined. Under certain conditions, dehydrogenation, gave biliverdin contaminated with III alpha and XIII alpha isomers as a result of disproporationation of bilirubin. Formation of non-IX alpha isomers depends on the concentrations of the reagents and the order in which they are mixed, and occurs under neutral anaerobic conditions. Free-radical reactions probably are responsible, suggesting that the first step in the deydrogenation of bilirubin with 2,3-dichloro-5,6-dicyanobenzoquinone in dimethyl sulphoxide is formation of a bilirubin cation radical, rather than hydride ion abstraction.
mesh_terms: D016227:Benzoquinones; D001663:Bilirubin / Q000031:analogs & derivatives*; D001664:Biliverdine / Q000138:chemical synthesis* / Q000302:isolation & purification; D002250:Carbon Radioisotopes; D055598:Chemical Phenomena; D002621:Chemistry; D003460:Crystallization; D007536:Isomerism; D008722:Methods; D008956:Models, Chemical; D011809:Quinones; D013053:Spectrophotometry
chemical_list: D016227:Benzoquinones; D002250:Carbon Radioisotopes; D011809:Quinones; C000928:dichlorodicyanobenzoquinone; D001664:Biliverdine; D001663:Bilirubin