27 抗生物質TAN-1085の不斉全合成(口頭発表の部)

抄録

TAN-1085 (1) is an antibiotic produced by Streptomyces sp. S-11106. This compound has attracted considerable synthetic interest not only from its important biological activities, e.g., angiogenesis and aromatase inhibitory activitities, but also from its unique structural features composed of a benzo[a]anthraquinone chromophore with a vicinal diol at the B -ring, one of which is glycosylated with a rhodinose. We recently completed the first total synthesis of this compound, clarifying unknown the relative and absolute stereochemistries, and therefore the remaining problem was the asymmetric synthesis of the aglycon portion. Herein, we report a promising method to construct the axially chiral biaryl structure and asymmetric total synthesis of target molecule. The key point of our strategy was that a new class of axially chiral compounds, "axially chiral styrenes" was used as a chiral building blocks. It is the styrene derivatives whose rotation around the C-C bond that connects aryl and ethenyl moieties is restricted by having large subsutituents on their skeleton. In planning the effective access to the target structure, we envisaged a consecutive chiral transfer approach starting from the axially chial styrene. Through a series of model experiments, we were able to design chiral styryl sulfoxide 25. After connection with a benzocyclobutenone 3 followed by pericyclic ring enlargement to the biaryl 5, the "styryl tereochemistry" was cleanly transferred into the axial stereochemistry, which in turn was transferred into the central stereochemistries of the vicinal diol via pinacol cyclization. The overall process provided the targeted aglycon 6 in highly enantio-enriched form, and introduction of the sugar moiety 7 accomplished the asymmetric total synthesis of 1.