Isolation of eleven phenolic compounds from propolis (bee glue) collected in Alexandria, Egypt

The total polyphenol content (mg rutin equivalent/g propolis) of 70% ethanol extracts of 7 different propolis samples, applying a validated Folin-Ciocaltau method, were determined and compared with that of green tea [Camellia sinensis] as positive control. The two samples collected in October and May from Abees Apiculture Unit, Agricultural Research Farm, University of Alexandria, showed higher values (482.3 ± 14.9 and 523.2 ± 7.3) than that of green tea (271.7647 ± 4.56). Thus, one of the two samples was extracted with 70% alcohol and subjected to silica gel Column Chromatography. Eleven phenolic compounds were isolated and examined by HPTLC, UV, 1D- and 2D-NMR, and ESI MS. These were identified as 5-hydroxy-7-methoxyflavanone (pinostrobin); 5-hydroxy-7-methoxyflavonol (galangin-7-O-methyl ether or izalpinin); 5-hydroxy-7-methoxyflavone (chrysin-7-O-methyl ether or tectochrysin); 5,7-dihydroxyflavanone (pinocembrin), 5,7-dihydroxyflavonol (galangin); 5,7-dihydroxyflavone (chrysin); 3,3'-dimethoxy-5,7,4'-trihydroxyflavone (quercetin-3,3'-di-O-methyl ether); 3-methoxy-5,7,4'-trihydroxyflavone (kaempferol-3-O-methyl ether); quercetin-3,7-di-O-methyl ether; 3-hydroxy-4-methoxycinnamic acid (isoferulic acid); and galangin-5-O-methyl ether. These 11 compounds are isolated for the first time from an Egyptian propolis sample.