SYNTHESIS AND PROPERTIES OF A LIPID BILIRUBIN ANALOG

A new synthesis of dipyrrinone acids is described from the known dipyr rinone, 3-ethyl-2,7,9-trimethyl-(10H)-dipyrrin-1-one (11) with a free beta-position. In six steps, 11 was convened to 5 with a C-20 eicosano ic acid chain, and 5 was converted to a lipid analog (1) of bilirubin with eicosanoic acids replacing propionic at carbons C(8) and C(12). U nlike bilirubins with short acid chains, 1 behaves much like its dimet hyl ester (2) and probably adopts a helical rather than the characteri stic ridge-tile conformation. Circular dichroism of 1 complexed with q uinine in CHCl3 gives a bilirubin-like bisignate Cotton effect: Delta epsilon max/438 +18, Delta epsilon max/390 -24.