REACTIONS OF KETEN ACETALS .6. TOTAL SYNTHESES OF ANTHRAQUINONES (+--)-NALGIOVENSIN, (+/-)-ISORHODOPTILOMETRIN, AND (+/-)-RHODOPTILOMETRIN

The 3 title compounds were synthesized and compared with the natural products. Emodin trimethyl ether (11) was brominated and converted into the propenyl derivative (15). The latter could then be transformed into the 3-(2-hydroxypropyl) compound either by oxymercuration-demercuration or by epoxidation and reduction. (.+-.)-Nalgiovensin [1,8-dihydroxy-3-(2-hydroxypropyl)-6-methoxyanthraquinone, isolated from Penicillium nalgiovensis] was then obtained by partial demethylation. The completely demethylated (.+-.)-isorhodoptilometrin [isolated from the crinoid Ptilometra australis] was prepared analogously from the propenylanthraquinone (15) after demethylation and acetylation. For the synthesis of (.+-.)-rhodoptilometrin [1,3,8-trihydroxy-6-(1-hydroxypropyl)anthraquinone, isolated from the crinoids P. australis, Heterometra savignii, Lamprometra klunzingeri and Comanthus bennetti] the propenyl derivative (15) was hydrogenated, demethylated, and brominated; substitution of the bromide by acetate and saponification gave the desired product. Conditions for the preparation of the starting material (11) were further investigated.