Chemical studies on antioxidant mechanism of garcinol: analysis of radical reaction products of garcinol and their antitumor activities

Garcinol (1), a polyisoprenylated benzophenone, purified from Garcinia indica fruit rind, displays antioxidant properties and is thought to act as an antioxidant in biological systems. However, the mechanisms of its antioxidant reactions remain unknown. The objective of this study was to characterize the reaction products of garcinol with a stable radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH). Structural elucidation of these products can provide insights into specific mechanisms of antioxidant reactions. Two major reaction products, GDPPH-1 (2) and GDPPH-2 (3), were isolated and identified for the first time. Their structures were determined on the basis of detailed high field 1D and 2D spectral analysis. The identification of these products provides the first unambiguous proof that the principal sites of antioxidant reactions are on the 1,3-diketone and the phenolic ring part of 1. The induction of apoptosis in human leukemia HL-60 cells, the inhibition of NO generation, the effects on the activity of MMP, and the inhibitory effects on H2O2 production of TPA-stimulate HL-60 cells by 1 and its two oxidant products (2 and 3) were investigated and would also be discussed in this paper.