Total synthesis of angucyclines, part 14 - Biomimetic synthesis of the racemic angucyclinones of the aquayamycin and WP 3688-2 types

The first synthesis of the racemic 8-deoxy WP3688-2 angucycline antibiotic (3), with characteristic cis-hydroxy groups at C-4a and C-12b, is reported. Key steps involve the coupling, mediated by samarium diiodide, of the bicy clic trione 37 to the tricyclic cis-diol 39. Biomimetic aldol cyclization o f the corresponding dione 41 gave a mixture of the tetracyclic cis- and tra ns-3,4a-diols 42 and 43, which were oxidized by cerium ammonium nitrate to the quinones 45 and 3. The synthetic compounds 45 and 3 corresponded in con figuration to the angucycline antibiotics aquayamicin (1) and WP 3688-2 (2) , respectively.