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Total synthesis and structural revision of biyouyanagin B.

Plants of the Hypericum genus (Clusiaceae) have been known around the world for centuries for their medicinal properties. While H. perforatum (St. John’s wort), used to treat moderate depression,[1] is perhaps the most famous of these species, H. Chinense is the most recent member of this family of plants to receive notoriety as the source of biyouyanagin A. A potent anti-HIV agent and a lipopolysaccharide-induced cytokine production inhibitor, this novel natural product was first reported by Tanaka and co-workers in 2005 as possessing structure 1′ (Figure 1a).[2] Following our total synthesis of biyouyanagin A (1) from ent-zingiberene (ent-3) and hyperolactone C (4), through a [2+2] photocycloaddition, and revision of its structure from 1′ to 1 (Figure 1a),[3,4] a second biyouyanagin (B) was isolated from the same species and reported by the same group as possessing structure 2′ (Figure 1b) on the basis of spectroscopic and mass spectrometric analysis.[5] We now report the total synthesis and structural revision of biyouyanagin B (from 2′ to 2, Figure 1b) as well as the synthesis of several new biyouyanagins not yet discovered in nature, despite their possible existence based on biosynthetic considerations.