ANTIOXIDANT ACTIVITY OF QUINONES EXTRACTED FROM TANSHEN (SALVIA-MILTIORRHIZA BUNGE)

Six compounds have been solvent extracted from tanshen and separated by column and thin-layer chromatography. The structures have been identified by spectroscopic methods as rosmariquinone, dehydrorosmariquinone, miltirone I, tanshinone II(A), cryptotanshinone, and dihydrotanshinone. The antioxidant activity of these quinones in lard at 100-degrees-C was determined with a Rancimat. The following structural features are associated with increased activity: (1) additional conjugated double bonds in the A ring; (2) a dihydrofuran ring rather than a furan ring; (3) an isopropyl substituent ortho to a quinone carbonyl rather than a dihydrofuran ring. An addition product has been isolated from the reaction between 9,10-phenanthrenedione and methyl oleate, and it is proposed that the quinones act as primary antioxidants by addition of the lipid radical to the quinone to form a stabilized radical which interrupts the autoxidation chain reaction.