Stereoselective Synthesis of 1,4,5-Tri-cis-guaiane Sesquiterpene: First Total Synthesis of (-)-Dendroside C Aglycon

A unified strategy for the total syntheses of eribulin and a macrolactam analogue of halichondrin B

A unified synthetic route for the total syntheses of eribulin and a macrolactam analog of halichondrin B is described. The key to the success of the current synthetic approach includes the employment of our reverse approach for the construction of cyclic ether structural motifs and a modified intramolecular cyclization reaction between alkyl iodide and aldehyde functionalities to establish the all-carbon macrocyclic framework of eribulin. These syntheses, together with our previous work on the total syntheses of halichondrin B and norhalichondrin B, demonstrate and validate the powerful reverse approach in the construction of cyclic ether structural motifs. On the other hand, the unified synthetic strategy for the synthesis of the related macrolactam analog provides inspiration and opportunities in the halichondrin field and related polycyclic ether areas.

Effect of Tethered, Axially Coordinated Ligands (TACLs) on Dirhodium(II,II) Catalyzed Cyclopropanation: A Linear Free Energy Relationship Study

Hammett correlation experiments were used to determine the influence of dirhodium(II,II) paddlewheel complexes with tethered, axially coordinated ligands (TACLs) on the selectivity of rhodium carbenoids in competitive cyclopropanation reactions. The results suggest that dirhodium(II,II) paddlewheel complexes with TACLs are less sensitive to changes in electronics and reduce selectivity in cyclopropanation reactions with acceptor-substituted rhodium carbenoids. Also, Hammett plots with aryl diazoacetates resulted in a nonlinear downward curvature, suggesting a change in the rate-limiting step of the carbene transfer reaction.

Collective Syntheses of Guaiane Sesquiterpenes: Stereoselective Syntheses of (+)-Dysodensiol F, (+)-10β,14-Dihydroxy-allo-aromadendrane, and (-)-Dendroside C Aglycon

A collective synthetic route for tricyclic guaiane sesquiterpenes and total syntheses of (+)-dysodensiol F, (+)-10β,14-dihydroxy-allo-aromadendrane, and (-)-dendroside C aglycon starting from a versatile hydroazulene intermediate were accomplished. The key features of these syntheses involve late-stage carbene-mediated diastereoselective cyclopropanation, construction of an unusual cis-fused-hydroazulene skeleton via intramolecular Dieckmann condensation, and highly stereoselective tandem conjugate addition/intramolecular allylic alkylation to afford a 5/7/3 tricyclic skeleton of guaiane natural products. The synthesis of (-)-dendroside C aglycon and the first total synthesis of (+)-dysodensiol F and (+)-10β,14-dihydroxy-allo-aromadendrane are described in detail. Activation of the Nrf2/ARE signaling pathway by (-)-dendroside C aglycon is also disclosed via our synthesis.

Guaiane-Type Sesquiterpenoids from the Roots of Daphne genkwa and Evaluation of Their Neuroprotective Effects

Chromatographic purification of the roots of Daphne genkwa led to 11 new guaiane-type sesquiterpenoids (1-11), named genkwanoids A-K, and six known analogues (12-17). A comprehensive set of spectroscopic methods including IR, UV, HRESIMS, and 1D/2D NMR were used to elucidate the structures and relative configurations of 1-11. The absolute configurations were determined by the optical rotation calculations and the modified Mosher's method. The possible biosynthetic pathways for 1-11 are proposed. Furthermore, the neuroprotective effects of 1-17 on H₂O₂-induced damage in human neuroblastoma SH-SY5Y cells were screened using an MTT assay. Compounds 9, 10, and 16 exhibited moderate neuroprotective effects, with survival rates of 79.34%, 79.94%, and 75.64% after treatment with 12.5 μM, values that were comparable to the positive control, Trolox (78.65%). Furthermore, annexin V-FITC/PI staining of cells treated with 9, 10, and 16 showed that the neuroprotective effects of these compounds may arise from inhibiting cell apoptosis.