Isolation and characterization of an antimicrobial compound from the traditional medicinal plant Pittosporum tetraspermum Wight & Arn.

Pittosporum tetraspermum Wight & Arn. belongs to the family Pittosporaceae of the order Polygalineae. It is used for treating chronic bronchitis and as an antidote for snake poisoning. The root bark is a remedy for rheumatic swelling. The bioactive principle present in the leaves of Pittosporum tetraspermum was isolated and characterized in the present study. Repeated extraction of powdered leaves of Pittosporum tetraspermum with petroleum ether resulted in defatted leaves, which was further extracted with methanol to yield crude methanol extract. The n-butanol fraction of methanol extract was passed through celite and obtained a mixture of crude saponins. The crude saponin mixture upon separation through silica gel column chromatography yielded 9 fractions. The structure of the bioactive fraction IX was determined by analyzing the peaks in IR, 1H NMR, 13C NMR, and ESI Mass Spectra. Fraction IX showed the highest zone of inhibition against fungal growth (13.3 mm in diameter) and it was higher than the zone of inhibition of the reference drug Nystatin. The IR spectrum of the bioactive fraction IX showed a broad signal at 3413 cm-1 due to the symmetrical stretching of –OH group in the molecule. The bioactive component responsible for the biological activity of Pittosporum tetraspermum is identified as trihydroxyoleanolic acid glycoside, whose aglycone part is characterized as trihydroxyoleanolic acid and the glycone part as sugars glucose and glucuronic acid.