Morinda morindoides (Kongobololo or Nkongabululu) is one of the most popular medicinal plants used in the Democratic Republic of Congo. Ten of its constituent flavonoids were evaluated in the xanthine-xanthine oxidase enzymatic system. The compounds were identified by spectroscopic methods as quercetin (1), quercetin 7,4′ dimethylether (2), luteolin 7 glucoside (3), apigenin 7 glucoside (4), quercetin 3 rhamnoside (5), kaempferol 3 rhamnoside (6), quercetin 3 rutinoside (7), kaempferol 3 rutinoside (8), chrysoeriol 7 neohesperidoside (9) and kaempferol 7 rhamnosylsophoroside (10). The aglycones chrysoeriol (11), kaempferol (12), luteolin (13) and apigenin (14), obtained by acid hydrolysis of the corresponding glycosides, were also included.
Compound 5 exhibited only scavenging activity, 9 and 11 were devoid of any effect against xanthine oxidase and scavenging activity, and the remaining flavonoids exhibited xanthine oxidase inhibiting and superoxide scavenging activity to varying extent. Study of structure activity relationships demonstrated that the activity was not only dependent on the nature of substituents and the substitution site, but also on the nature of the aglycone.
These results partially explain and support the use of Morinda morindoides in the treatment of rheumatism.