Two Antioxidative Diterpenes from Rosemary (<i>Rosmarinus officinalis</i> L.) and a Revised Structure for Rosmanol^†

Two new antioxidative compounds, named epirosmanol (4a) and isorosmanol (6a), were isolated from the leaves of rosemary (Rosmarinus officinalis L.). The structures have been determined to be 7β,11,12-trihydroxy-6,10-(epoxymethano)abieta-8,l 1,13-trien-20-one and 6α,ll,12-trihydroxy-7,10-(epoxymethano)abieta-8,ll,13-trien-20-one, respectively, on the basis of chemical and spectroscopic evidence. Both are isomers of rosmanol (1a), whose structure was revised to be 7α,ll,12-trihydroxy-6,10-(epoxymethano)abieta-8,ll,13-trien-20-one by the NOE experiment and X-ray analysis. These two antioxidants showed high activity in both lard and linoleic acid and, particularly in lard, were about four times more active than such synthetic antioxidants, as BHA and BHT.

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