Antimicrobial activity of flavonoids glycosides and pyrrolizidine alkaloids from propolis of Scaptotrigona aff. postica

Abstract

Stingless bees, or simply meliponines, are a large group of bees (about 550 described species), comprising the tribe Meliponini. They belong in the family Apidae, and are closely related to Apis mellifera. Scaptotrigona affinis postica Latreille, 1807 from northeast of Brazil is popularly known as “tubi” in Maranhão State. Flavones di-C-glycosides, and the pyrrolizidine alkaloid 3-methoxy-7-(2-methylbutyryl)-9-echimidinyl retronecine (7) were reported previously in propolis from S. postica and detected only in samples collected in October, November and December. The presence of pyrrolizidine alkaloids and their N-oxides were reported in honey and pollen. In the present study, the preparative liquid chromatography in reversed-phase column from ethanolic extract of propolis allowed the separation of fractions 40AEP and 40 MEP, which were analyzed by LC-MS. Many pyrrolizidine alkaloids, among them, lithosenine (14), lithosenine arabinoside (19), 7-angeloyl-9-(2,3- dihydroxybutyryl) retronecine (1), 7-(2- methylbutyryl) retronecine (3), 9-sarracinoyl retronecine (13) and viridinatine (8), besides the flavonoids schaftoside (15), aromadendrin-7-O-methyl ether (12), 7- methoxy-5,6,3’,4’,5’,6’-hexahydroxy-flavone-3-O-glucuronide (11), mangiferin (10) and mangiferin-O-methyl ether (17) were detected in these fractions. Fraction 40MEP showed antibacterial effect against gram positive and gram negative bacterial pathogens with MIC ranging from 62.5 μg/mL to 200 μg/mL, while fractions 40AEP and 40MEP showed antimicrobial activity against gram negative bacteria, including Escherichia coli D31- streptomycin resistant. The cells were treated with 40MEP and 40AEP at a concentration of 200 μg/mL and were not observed statistical difference between treated and untreated cells. HIGHLIGHTS Propolis from Scaptotrigona aff. postica bees exhibited antimicrobial activity against Escherichia coli D31- streptomycin resistant. Preparative liquid chromatography in reversed-phase column allowed the separation of fractions rich in alkaloids and flavonoids. Pyrrolizidine alkaloids and flavonoids were detected as the main constituents. Flavones di-C-glycosides and flavones C-glycosides were reported in propolis. Cell viability demonstrated that pyrrolizidine alkaloids did not cause cytotoxicity in epithelial cells.