SYNTHETIC CAROTENOIDS, NOVEL POLYENE POLYKETONES AND NEW CAPSORUBIN ISOMERS AS EFFICIENT QUENCHERS OF SINGLET MOLECULAR-OXYGEN

Novel synthetic polyene polyketones and new synthetic capsorubin isomers were examined for their ability to quench singlet molecular oxygen (1O2) generated by the thermodissociation of the endoperoxide of 3,3'-(1,4-naphthylene) dipropionate (NDPO2). C28-polyene-tetrone (1) exhibits the highest physical quenching rate constant with 1O2 (k(q) = 16 x 10(9) M-1 s-1 and that constant for the most efficient biological carotenoid, lycopene (3) is k(q) = 9 x 10(9) M-1 s-1 and that of beta-carotene (5) k(q) = 5 x 10(9) M-1 s-1. The presence of two oxalyl chromophores at the ends of the polyene chain seems to enhance the 1O2 quenching ability in the C28-polyene-tetrone (1). C28-polyenetetrone-diacetal (2) (k(q) = 9 x 10(9) M-1 s-1) and C40-epiisocapsorubin (4) (k(q) = 8 x 10(9) M-1 s-1) also have high 1O2 quenching abilities. Two carotenoids from plants, phytoene and phytofluene, were much less efficient, k(q) values being below 10(7) M-1 s-1. Due to the very high singlet oxygen quenching abilities, C28-polyene-tetrone (1), C28-polyene-tetrone-diacetal (2) and C40-epiisocapsorubin (4) may have potential use in preventing 1O2-induced damage in biological and non-biological systems.