Synthesis of dipyrrinone esters using carbodiimide reagents

Article abstract of DOI:10.1016/S0040-4020(01)96106-X

The esters of xanthobilirubic acid (XBR) with rac-(±)-, (R)-(+)-, and (S)-(-)-alpha-methylbenzyl alcohol (1, 2 and 3 respectively), with rac-(±)-, (R)-(+)-, and (S)-(-)-sec-butyl alcohol (4, 5 and 6 respectively), with rac-(±)-, (R)-(+)-, and (S)-(-)-2-octanol (7, 8 and 9 respectively) have been synthesized in good to excellent yields using as condensing agent the mixture dicyclohexylcarbodiimide/dimethylaminopyridine W(DCCI/DMAP). These esters are models for the study of exciton coupling in hydrogen-bonded dimers. The esters of XBR with monomethoxypolyethyleneglycol (MPEG) of FW=1900, and with polyethyleneglycol (PEG) of FW=2000 (10 and 11 respectively) have been quantitatively prepared by the same procedure. These water-soluble dipyrrinone esters are models for the study of Z ? E photoisomerization in rats. Attempts to extrapolate the procedure to the synthesis of the same esters of bilirubin (BR) have always led to difficult-to-separate mixtures of products.