Isolation and identification of novel tocotrienols from rice bran with hypocholesterolemic, antioxidant, and antitumor properties

Two novel tocotrienols were isolated from stabilized and heated rice bran, apart from the known alpha-, beta-, gamma-, and delta-tocopherols and tocotrienols. These new tocotrienols were separated by HPLC, using a normal phase silica column. Their structures were determined by ultraviolet, infrared, nuclear magnetic resonance, circular dichroism, and high-resolution mass spectroscopies and established as desmethyl tocotrienol [3,4-dihydro-2-methyl-2-(4,8,12-trimethyltrideca-3'(E),7'(E),11'-trienyl)-2H-1-benzopyran-6-ol] and didesmethy tocotrienol [3,4-dihydro-2-(4,8,12-trimethyltrideca-3'(E),7'(E),11'-trienyl)-2H-1-benzopyran-6-ol]. These tocotrienols significantly lowered serum total and LDL cholesterol levels and inhibited HMG-CoA reductase activity in chickens. They had much greater in vitro antioxidant activities and greater suppression of B16 melanoma cell proliferation than alpha-tocopherol and known tocotrienols. Results indicated that the number and position of methyl substituents in tocotrienols affect their hypocholesterolemic, antioxidant, and antitumor properties.