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J Nat Prod. 2011 Mar 25;74(3):402-10. doi: 10.1021/np100798q. Epub 2011 Jan 7.

Unraveling the bastarane and isobastarane oximo amide configurations and associated macrocycle conformations: implications of their influence on bioactivities.

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  • 1Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, United States. winman@ucsc.edu


Our rigorous re-examination of the conformational properties of bastadins that comprise the isobastarane and bastarane-type macrocycle has generated some interesting new insights. We determined that these macrocycles are flexible and possess a surprising degree of reflection symmetry that generates enantiomeric conformations. The macrocycle symmetry arises from its ability to twist in a disrotatory fashion, providing one set of conformers, and then twists with the opposite disrotation to generate a corresponding set of enantiomers. Overall, the isobastarane conformations for (E,E)-bastadin 19 (1a) are complex and can access several distinct ring conformations. In contrast, the bastarane macrocycle in bastadin 5 (2) and bastadin 6 (3) maintains a similar overall shape. We postulate that the short-term stability of the (Z)-oximo amide, an uncommon configuration found in bastadins and psammaplins, is due to the existence of conformers with intramolecular hydrogen bonds involving the (Z)-oxime, and hydrogen bonding impedes oxime isomerization to the more stable (E)-oximo amide in solution. Finally, the modeling results provided insights toward understanding the different antiproliferative activity against endothelial cells as well as Ca(2+) channel modulation activities attributed to bastaranes 2 and 3 versus isobastarane 1a.

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