Bile pigment studies-VI. Syntheses of model systems
The synthesis of various mammalian and algal bile pigment models from monopyrroles and by ring cleavage of intact metalloporphyrins and metallochlorins is discussed. A previously reported synthesis of etiobiliverdin IVγ (6) from the self-condensation of a 5-bromo-5'-bromomethyldipyrrylmethene hydrobromide (5) is modified to afford a new, efficient and general route to biliverdins through 1,19-di-t-butoxycarbonyl-a, c-biladienes or -b-bilenes. Owing to symmetry limitations inherent in the a,c-biladiene route, that through b-bilenes is shown to be more generally effective for the synthesis of biliverdins. The key step in the transformation of the biladiene or bilene into biliverdin involves treatment with bromine in trifluoroacetic acid, and this affords biliverdin in high yield. The route is proposed to proceed through a 1,19-dibromo-a,b,c-bilitriene and then a 1,19-di-(trifluoroacetoxy)-a,b,c-bilitriene, though these intermediates are not isolated. © 1983.
Publication Source (Journal or Book title)
Smith, K., & Kishore, D. (1983). Bile pigment studies-VI. Syntheses of model systems. Tetrahedron, 39 (11), 1841-1847. https://doi.org/10.1016/S0040-4020(01)88697-X