Total Synthesis of Talatisamine.

Talatisamine (1) is a member of the C19 -diterpenoid alkaloid family, and exhibits K+ channel inhibitory and antiarrhythmic activities. The formidable synthetic challenge that 1 presents is due to its highly oxidized and intricately fused hexacyclic 6/7/5/6/6/5-membered-ring structure (ABCDEF-ring) with 12 contiguous stereocenters. Here we report an efficient synthetic route to 1 by the assembly of two structurally simple fragments, chiral 6/6-membered AE-ring 7 and aromatic 6-membered D-ring 6. AE-ring 7 was constructed from 2-cyclohexenone (8) through fusing an N-ethylpiperidine ring by a double Mannich reaction. After coupling 6 with 7, an oxidative dearomatization/Diels-Alder reaction sequence generated fused pentacycle 4 b. The newly formed 6/6-membered ring system was then stereospecifically reorganized into the 7/5-membered BC-ring of 3 via a Wagner-Meerwein rearrangement. Finally, Hg(OAc)2 induced an oxidative aza-Prins cyclization of 2, thereby forging the remaining 5-membered F-ring. The total synthesis of 1 was thus accomplished by optimizing and orchestrating 33 transformations from 8.

Total synthesis of (-)-4-hydroxyzinowol.

(-)-4-Hydroxyzinowol (1) is a potent inhibitor of P-glycoprotein, which has been implicated in multi-drug resistance in the treatment of cancer. The highly oxygenated structure of 1 comprises a trans-decalin (AB-ring) and a tetrahydrofuran (C-ring) and possesses six acyloxy, one hydroxy, and one alkoxy groups. The challenge of synthesizing 1 is particularly heightened by the nine consecutive stereogenic centers on the 10-carbon decalin skeleton. The total synthesis of this extremely complex structure was achieved in 36 steps from 5-acetoxynaphthalen-1-ol by the judicious application of powerful chemo- and stereoselective reactions. The rhodium-catalyzed asymmetric 1,4-addition of the isopropenyl group set the C7-stereocenter, and the remaining three cis-oriented hydroxy groups (C6, 8, and 9) of the B-ring were stereoselectively constructed in a stepwise fashion. The C5-tetra-substituted and C10-quaternary carbons at the juncture of the AB-ring were then introduced by oxidative dearomatization and Diels-Alder reaction, respectively. After acid-promoted formation of the C-ring ether, the C1-, 2-, 4- and 6-oxygen-based functional groups were stereoselectively installed to deliver the fully functionalized tricycle. Finally, the polyhydroxylated structure was converted to the polyacylated target molecule 1 via regioselective acetylation and benzoylation.

Stereochemical assignment and anti-inflammatory properties of the omega-3 lipid mediator resolvin E3.

Uncontrolled inflammation is now considered to be a link between many widely occurring diseases. Thus, controlling the innate inflammatory response and its local chemical mediators has been receiving increasing attention. We recently identified a novel family of eicosapentaenoic acid (EPA)-derived mediators produced by eosinophils, denoted as resolvin E3 (RvE3), that possess potent anti-inflammatory actions both in vitro and in vivo. Carbons at 17 and 18 positions are asymmetric and thus the molecule has a total of four potential stereoisomers. Here, we assigned the stereochemistry of the conjugated double bonds and chirality of alcohols present in two natural isomers of RvE3 with four different stereoisomers prepared by total organic synthesis. The complete structures of two natural isomers of RvE3 were determined to be 17R,18S- and 17R,18R-dihydroxy-5Z,8Z,11Z,13E,15E-EPA, respectively. These natural isomers prepared by total organic synthesis displayed a potent anti-inflammatory action by limiting neutrophil infiltrations both in vitro and in vivo. The unnatural stereoisomers were much less active compared with the natural isomers, demonstrating the stereoselective action of RvE3.