Propolis Components from Stingless Bees Collected on South Sulawesi, Indonesia, and Their Xanthine Oxidase Inhibitory Activity

Three new compounds, namely, 4-(4'-hydroxy-3'-methoxyphenyl)-3,5,7-trihydroxycoumarin (1) and sulawesins A (2) and B (3), were isolated from the propolis of stingless bees ( Tetragonula aff. biroi) collected on South Sulawesi, Indonesia. In addition, five known compounds, glyasperin A, broussoflavonol F, (2 S)-5,7-dihydroxy-4'-methoxy-8-prenylflavanone, (1' S)-2- trans,4- trans-abscisic acid, and (1' S)-2- cis,4- trans-abscisic acid, were identified. The structures of the new compounds were determined by a combination of methods that included mass spectrometry and NMR spectroscopy. The absolute configuration of sulawesin A (2), a new podophyllotoxin derivative, was determined by X-ray crystallography. The absolute configuration of sulawesin B (3) was also determined by the ECD calculation. 4-(4'-Hydroxy-3'-methoxyphenyl)-3,5,7-trihydroxycoumarin (1) and sulawesin A (2) were examined for Xanthine Oxidase (XO) inhibitory activity; 1 exhibited XO inhibitory activity, with an IC₅₀ value of 3.9 μM.