Antiproliferative Activity of Amathaspiramide Alkaloids and Analogs.

Assisted by the total syntheses of all the amathaspiramides, six natural products and four synthetic intermediates with partially fluctuating structures were prepared and subjected to a growth inhibition assay in four human cancer cell lines. The results showed amathaspiramides A, C, and E had moderate antiproliferative activity. Examination of the structure-activity relationship revealed the importance of the amine or imine substructure on the pyrrolidine moiety and the 8R stereochemistry on the N-acyl hemiaminal moiety for the antiproliferative activity of amathaspiramide alkaloids.

Enantioselective synthesis of α-quaternary Mannich adducts by palladium-catalyzed allylic alkylation: total synthesis of (+)-sibirinine.

A catalytic enantioselective method for the synthesis of α-quaternary Mannich-type products is reported. The two-step sequence of (1) Mannich reaction followed by (2) decarboxylative enantioselective allylic alkylation serves as a novel strategy to in effect access asymmetric Mannich-type products of "thermodynamic" enolates of substrates possessing additional enolizable positions and acidic protons. Palladium-catalyzed decarboxylative allylic alkylation enables the enantioselective synthesis of five-, six-, and seven-membered ketone, lactam, and other heterocyclic systems. The mild reaction conditions are notable given the acidic free N-H groups and high functional group tolerance in each of the substrates. The utility of this method is highlighted in the first total synthesis of (+)-sibirinine.

Structures of two haptotropic isomers generated by the sliding of 1,3,5-triene ligands on a Pd-Pd-Pd chain.

Two haptotropic isomers of [Pd3(micro3-DMVC)2(CH3CN)2][BF4]2 (DMVC=1,2-di-(E)-carbomethoxyvinylcyclopentene) were structurally determined by X-ray crystallographic analyses; a monoclinic crystal contained a symmetric sandwich complex (micro3-eta2:eta2:eta2-coordination of DMVC ligands) and a triclinic crystal contained an unsymmetric sandwich complex (micro3-eta2:eta3:eta1-coordination of DMVC ligands), where the latter are connected to each other by C-HO hydrogen bonds.

Reductive coupling of metal triangles in sandwich complexes.

The one-electron reduction of [Pd3(C7H7)2(CH3CN)3][BF4]2 in acetonitrile resulted in the formation of the dimer dication [Pd6(C7H7)4(CH3CN)4][BF4]2, whose structure containing a novel bitriangle hexapalladium skeleton was determined by X-ray crystallographic analysis. The dimer is stable in CD3CN at ambient temperature for several days but is highly air-sensitive. Similarly, the cycloheptatriene tripalladium complex [Pd3(C7H7R)2(CH3CN)3][BF4]2 (R = H, t-Bu) dimerized upon one-electron reduction. Both monomer and dimer of cycloheptatriene complexes were structurally determined by X-ray crystallographic analyses.