SYNTHETIC STUDIES ON DITERPENOID QUINONES WITH INTERLEUKIN-1 INHIBITORY ACTIVITY - TOTAL SYNTHESIS OF (PLUS-OR-MINUS)- AND (+)-TRIPTOQUINONE-A

An efficient first total synthesis of (+/-)- and (+)-triptoquinone A (1), a novel diterpenoid quinone with significant inhibitory activity against interleukin-1 releases, has been completed. Birch reduction of tricyclic enone (+/-)-7, prepared from known 6-methoxy-2-isopropyl-1-naphthol (22), which is readily available in large quantities, was followed by immediate enolate trapping to provide silyl enol ether (+/-)-30. Compound 30 was converted into carboxylic acid (+/-)-4 via the corresponding enol triflate (+/-)-31 either by sequential palladium-catalyzed carbonylation and oxidation or by direct carboxylation. The total synthesis of (+/-)-1 was completed by oxidation of (+/-)-4 with CAN in 12 steps from 22 in 19% overall yield at best. A second, enantioselective total synthesis of (+)-1 was accomplished via (+/-)-7, which was prepared by (-)-N- [4-(trifluoromethyl)benzyl]cinchonidinium bromide (33) catalyzed asymmetric Michael reaction of 6 with ethyl vinyl ketone and a subsequent aldol condensation. The absolute structures of triptoquinone B (2) and C (3), which were isolated concomitantly with triptoquinone A from the same plant sources, were established by a series of chemical reactions based on (+)-7.