A General Access to Taiwaniaquinoids Based on a Hypothetical Abietane C7−C8 Cleavage Biogenetic Pathway

Abstract

A new strategy for synthesizing taiwaniaquinoids, a group of terpenoids with an unusual rearranged 5(6→7) or 6-nor-5(6→7)abeo-abietane skeleton, which exhibit promising biological activities, is reported. The procedure, based on the cleavage of the C7−C8 double bond of abietane diterpenes, is the only one yet reported for synthesizing C20 taiwaniaquinoids bearing a carbon function on the cyclopentane B ring; it is also applicable to the synthesis of the wide variety of existing taiwaniaquinoids. Utilizing this, (−)-taiwaniaquinone A, F, G, and H, (−)-taiwaniaquinol B, and (−)-dichroanone have been synthesized from (+)-abietic acid. The versatility of this strategy allows us to propose the abietane C7−C8 cleavage as a possible biosynthetic pathway to this type of rearranged diterpenes; this proposal seems to be supported by phytochemical evidence.