Activity-guided discovery of antioxidative compounds in bark extract of Garcinia buchananii

Reactive oxygen species (ROS) are well-known to be generated as byproducts of the normal cell aerobic respiration that is essential to life and play a crucial role in cell signaling and homeostasis. However, overproduction of ROS causes undesirable oxidative stress which is associated with degenerative and chronic diseases such as, e.g. cardiovascular disease, cancer, diabetes, neurodegeneration and is involved in the process of aging.

About 400 species are known of the genus Garcinia, familiy Guttiferae, in which extracts and pure compounds from Garcinia species exhibited forms of biological activity such as anticancer, antimicrobial, anti-inflammatory and antioxidant properties. In order to identify antioxidant components in the stem bark extract of G. buchananii tree, were performed activity-guided fractionation using in vitro tests like H₂O₂ scavenging, oxygen radical absorbance capacity (ORAC) as well as trolox equivalent antioxidant capacity (TEAC) assays. The most active principles were identified by means of UPLC-TOF-MS^e analysis, 1D- and 2D-NMR and CD spectroscopy as a series of 3,8''-linked biflavanones and flavanone-C-glycosides (Figure). The H₂O₂ scavenging, TEAC and ORAC assays demonstrated that these natural products have an extraordinarily high antioxidative power compared to common antioxidants like (epi)catechin, rutin, quercetin, naringenin or ascorbic acid. Finally, reconstitution experiments were done to evaluate additive and/or synergistic effects of the antioxidative compounds identified. These findings demonstrate that G. buchananii bark extract is a rich natural source of biflavanone and flavanone glycoside antioxidants.