Antioxidant Activities of Pentacyclic Triterpenes From Melipona beecheii Propolis and Their Semisynthetic Derivatives.

Four principal fractions (I-IV) were obtained from the Melipona beecheii propolis. GC-MS analysis of these fractions allowed us to recognize 11 pentacyclic triterpenes (PTs), fraction I [β-amyrin acetate (1), germanicol acetate (2), moretenol acetate (3) and 24-methylencycloartan-3-ol acetate (4)]; fraction II [marsformosanone (5), β-amyrenone (6), germanicone (7) and lupenone (8)]; fraction III [β-amyrin (9) and, glutinol (10)]; and fraction IV [9 and α-amyrin (11)]. This is the first time that triterpenes 7 and 10 are reported in the propolis of M. beecheii. Three semisynthetic derivatives were prepared: the reduction of fraction II and the acetylation and oxidation of fraction IV. The ethanolic extract of propolis and fraction III presented the highest free DPPH radical scavenging capacity at 53.89 ± 8.39% and 47.77 ± 0.91%, respectively, using a concentration of 10 mg/mL. In contrast, the reducing power of Fe (III) analysis showed a strong reducing power of Fe(III) for all fractions and their derivatives with an EC50 = 0.8-1.0 mg/mL.