(m.n)-Homorubins: syntheses and structures

Five new homorubin analogs of bilirubin with their two dipyrrinone components conjoined to (CH2)2, (CH2)3, and (CH2)4 units were synthesized with propionic acid chains shortened to acetic and elongated to butyric, and examined by spectroscopy and molecular mechanics computations for an ability to form conformation-determining hydrogen bonds. With m designating the number of conjoining CH2 units and n indicating the number of CH2 units of the alkanoic acid chains of (m.n)-homorubins, (2.1), (3.2), (4.2), and (4.3) homorubins were prepared and compared with previously synthesized (2.2) and (2.3), which adopt intramolecularly hydrogen bonded conformations in CHCl3.