Total Synthesis and Absolute Stereochemistry of Plakortone E.

Abstract

Total Synthesis and Absolute Stereochemistry of Plakortone E. -(AKIYAMA, M.; ISODA, Y.; NISHIMOTO, M.; NARAZAKI, M.; OKA, H.; KUBOKI, A.; OHIRA, S.; Tetrahedron Lett. 47 (2006) 14, 2287-2290; Dep. Biol.

Plakilactones from the Marine SpongePlakinastrella mamillaris. Discovery of a New Class of Marine Ligands of Peroxisome Proliferator-Activated Receptor γ

“…The stereochemistry at C-6 and C-8 of methyl ester (2) and at C-4 and C-6 of γ-lactone 3 and plakilactone A (7) was determined as shown in Figure 3. The 6R,8R absolute stereochemistry of methyl ester 1, [α] D 25 −281.8 (c 0.40, CHCl 3 ), has been unambiguously established by chemical degradation, 30 enantioselective synthesis, 31,32 and optical rotation values. 32 As expected by chemical shift and optical rotation considerations (see Supporting Information for NMR data), when subjected to reductive ozonolysis, compounds 1 and 3 gave the same aldehyde 14, 33 thus allowing us to establish the absolute configuration for γ-lactone 3.…”

“…The 6R,8R absolute stereochemistry of methyl ester 1, [α] D 25 −281.8 (c 0.40, CHCl 3 ), has been unambiguously established by chemical degradation, 30 enantioselective synthesis, 31,32 and optical rotation values. 32 As expected by chemical shift and optical rotation considerations (see Supporting Information for NMR data), when subjected to reductive ozonolysis, compounds 1 and 3 gave the same aldehyde 14, 33 thus allowing us to establish the absolute configuration for γ-lactone 3. Mild hydrogenation of methyl ester 1 afforded the synthetic methyl ester 2 whose NMR and optical rotation data were identical to those of the natural sample 2.…”

Dual Lewis Acid/Photoredox-Catalyzed Addition of Ketyl Radicals to Vinylogous Carbonates in the Synthesis of 2,6-Dioxabicyclo[3.3.0]octan-3-ones

“…The most common method for the synthesis of these bicyclic structures is by conjugate addition of a pendant alcohol to an already constructed unsaturated γ-lactone. 4−11 Other assemblies of this moiety include palladium-catalyzed carbonylative oxidation, 12−16 iodolactonization of a dihydrofuran, 17 and by ionic rearrangement cascades. 18,19 These methods focus primarily on the formation of C-O bonds in the core structure; methods that center around C-C bond formation remain lacking.…”

Chemistry and Selective Tumor Cell Growth Inhibitory Activity of Polyketides from the South China Sea Sponge Plakortis sp.

“…Polyketides with lactone fragment, i.e., plakortones A-G, are the second most prominent metabolites in these sponge-derived polyketides, exhibiting cardiac SR-Ca 2+ -pumping ATPase activating and in vitro cytotoxic activities [ 7 , 8 , 9 ]. The intrigoing structures and broad spectrum of bioactivities of the metabolites attracted attention on the chemical synthesis of such a cluster of molecules [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Also, the high flexibility of aliphatic chains or rings of these polyketides leads to a challenge in the absolute configuration identification.…”

“…Also, the high flexibility of aliphatic chains or rings of these polyketides leads to a challenge in the absolute configuration identification. The absolute configurations were determined at an early stage mainly by chemical methods, such as chemical degradation [ 30 ] and total synthesis [ 29 , 31 , 32 ]. In recent years, the calculating of NMR parameters provided a strong and convenient approach for the assignment of relative or absolute configuration of these highly flexible systems [ 33 , 34 , 35 ].…”