Total Synthesis of Natural Enantiomers of Heliespirones A and C <i>via</i> the Diastereoselective Intramolecular Hosomi-Sakurai Reaction

A full account of the development of a novel type of the intramolecular Hosomi-Sakurai reactions of the substrates with a <i>p</i>-benzoquinone and an allylsilane moieties connected by an ether linkage is described. This transformation proceeds <i>via</i> an addition–elimination sequence and provides the products with two stereogenic centers through a 1,3­(or 1,4)-asymmetric induction in good to excellent diastereoselectivities. A reasonable mechanistic possibility for the reaction, determination of the stereochemistry for the product, and scope and limitation of the transformation are also discussed. The methodology developed here can successfully be applied to the enantiocontrolled total synthesis of the natural enantiomers of (−)-heliespirone A and (+)-heliespirone C, which have been isolated from sunflower <i>Helianthus annuus</i> L. as allelochemicals

Total Synthesis of Natural Enantiomers of Heliespirones A and C <i>via</i> the Diastereoselective Intramolecular Hosomi-Sakurai Reaction

A full account of the development of a novel type of the intramolecular Hosomi-Sakurai reactions of the substrates with a <i>p</i>-benzoquinone and an allylsilane moieties connected by an ether linkage is described. This transformation proceeds <i>via</i> an addition–elimination sequence and provides the products with two stereogenic centers through a 1,3­(or 1,4)-asymmetric induction in good to excellent diastereoselectivities. A reasonable mechanistic possibility for the reaction, determination of the stereochemistry for the product, and scope and limitation of the transformation are also discussed. The methodology developed here can successfully be applied to the enantiocontrolled total synthesis of the natural enantiomers of (−)-heliespirone A and (+)-heliespirone C, which have been isolated from sunflower <i>Helianthus annuus</i> L. as allelochemicals

Catecholamine-associated cytotoxicity of α-syn and methionine mutant α-syn in PC12 cells.

<p>(A) Western blotting of wildtype (wild), and mutant (M116A, M127A, and M116A/M127A) α-syn expression in Tet-Off-α-syn cells. Withdrawal of Dox from the medium induced α-syn expression 3–7 days after Dox withdrawal. β-actin expression was used as an internal control. (B–E) Cell viability using the MTT assay (B: wildtype α-syn, C: M116A α-syn, D: M127A α-syn, E: M116A/M127A α-syn). (B) The expression of wildtype α-syn following withdrawal of Dox (OFF) reduced cell viability compared to the α-syn-suppressed condition (ON), while inhibition of catecholamine metabolism by aMT (100μM) dramatically blocked this cytotoxicity. *p<0.01 vs. ON, **p<0.01 vs. OFF. (C) The expression of M116A α-syn following withdrawal of Dox (OFF) also reduced cell viability compared to the α-syn-suppressed condition (ON), but to a lesser degree than wildtype α-syn, and aMT (100 μM) blocked this cytotoxicity. *p<0.01 vs. ON, **p<0.01 vs. OFF). (D,E) By contrast, expression of the M127A mutant (D) or the combined M116A/M127A (E) mutant α-syn did not reduce cell viability compared to the respective α-syn-suppressed condition (ON), and aMT (100 μM) also had no effect on either.</p

Concentrations of H₂O₂ produced by DA alone and with various peptides from the C-terminal sequence of α-syn 15 min (light gray), 30 min (dark gray), and 60 min (black) after incubation.

<p>DA alone (no peptide) produced increasing amounts of H₂O₂ over time. Co-incubation of DA with the YEMPS peptide enhanced H₂O₂ production, while the Y127- (EMPSEEGY) and S129- (NEAYEMP) lacking peptides produced less H₂O₂ than DA alone or with the YEMPS peptide. Moreover, co-incubation of DA with the methionine-mutated peptide (YEAPS) produced the highest amounts of H₂O₂ among all conditions. *p<0.01 vs. no peptide, **p<0.01 vs. no peptide and YEMPS (ANOVA).</p

Detection of Met(O) in α-syn. (A) Western blots of α-syn immunoprecipitated (IP) from wildtype α-syn-expressing PC12 cells and immunostained with antibodies against Met(O).

<p>Met(O)-labeling was detected in the α-syn from PC12 cells with normal CA metabolism (left lane), but not in the α-syn from those treated with the tyrosine hydroxylase inhibitor aMT (100 μM) (middle lane). By contrast, Met(O) levels were enhanced by treatment with reserpine, an inhibitor of monoamine transport from cytosol to synaptic vesicles (right lane). (B) Met(O)-labeling in lines of PC12 cells expressing methionine mutants of α-syn. Lower levels of Met(O) were detected in the α-syn proteins with methionine mutations (M116A, M127A, M116A/M127A), especially in the M127A or M116A/M127A mutants of α-syn, even though catecholamine metabolism was not suppressed. (C) Met(O)-labeling in lines of PC12 cells expressing various mutants of α-syn. Lower levels of Met(O) were detected in the α-syn proteins with tyrosine (Y125D) and serine (S129A) mutations, compared with wildtype α-syn even though catecholamine metabolism was not suppressed. The lane for IgG control is also exhibited in order to prove the oligomer band is specific for α-syn.</p

Catecholamine-associated cytotoxicity of α-syn in PC12 cells.

<p><b> </b> (A) Western blotting for α-syn expression in Tet-Off-α-syn cells. Withdrawal of Dox (OFF days) from the medium induced the expression of α-syn at day 3, which increased by day 7 after Dox withdrawal. β-actin expression was used as an internal control. (B) Western blotting for β-syn expression in Tet-Off-β-syn cells. Withdrawal of Dox from the medium induced the expression of β-syn 3 and 7 days after Dox withdrawal. β-actin expression was used as an internal control. (C-F) Cell viability measured using the MTT assay (C: wildtype α-syn, D: Y125D-mutant α-syn, E: S129A-mutant α-syn, F: wildtype β-syn). (C) The expression of α-syn following withdrawal of Dox (OFF) significantly reduced cell viability compared with the α-syn-suppressed condition (ON). The inhibition of catecholamine metabolism by aMT (100 μM) dramatically raised cell viability even when α-syn expression was induced. *p<0.01 vs. ON, **p<0.01 vs. OFF (ANOVA). (D–F) The induction of Y125D α-syn- (D), S129A α-syn- (E) and β-syn- (F) expression by withdrawal of Dox (OFF) did not significantly alter cell viability compared to the respective α- or β-syn-suppressed conditions (ON). The inhibition of catecholamine metabolism by aMT (100 μM) also had no effect.</p