TOTAL SYNTHESIS OF (+/-)-AMAROLIDE, A QUASSINOID BITTER PRINCIPLE

The first total synthesis of amarolide (1), a bitter tasting quassinoid having a picrasane skeleton with 10 chiral centers, is described in racemic form. The synthesis of (+/-)-1 was accomplished stereoselectively in 35 steps and 0.5% overall yield from a known tricyclic compound 7. An orthoester Claisen rearrangement and a lead tetraacetate oxidation were utilized as key reactions to prepare hydroxy ketone 14 with a complete picrasane skeleton. This hydroxy ketone was transformed into 1 in 18 steps that included 1,3-carbonyl transposition, introduction of hydroxyl groups at C-2 and C-11 positions, and oxidation of an ether to afford a delta-lactone.