Abstract:The efficient organocatalytic synthesis of heterocyclic systems of biological relevance is a subject of growing interest. We have found that the pyrrolidine/benzoic acid-catalyzed reaction of α-substituted propenals such as methacrolein, 2-benzylpropenal and 2-(n-hexyl)propenal with activated hydrazines takes place in very good yields (83%-99.6%) under very mild conditions to afford 4-substituted pyrazolidin-3-ols (as diastereomer mixtures); subsequent oxidation with PCC affords the corresponding-4-substituted-3-pyrazolidinones in essentially quantitative yields. In a similar way, 4-substituted isoxazolidinones are obtained with N-Cbz-hydroxylamine as a reagent. The use of chiral diarylprolinol trimethylsilyl ethers as catalysts allows the synthesis of several of these compounds in optically active form, in some cases with excellent enantioselectivity (up to 96:4 er). A preliminary evaluation of the biological activity shows that some of these compounds exhibit interesting antibacterial and antifungal activities.
In this study, the complexation of trans 3,5,3 0 ,4 0 -tetrahydroxystilbene, also known as piceatannol (PIC), with b-cyclodextrin (b-CD) was investigated using the semi-empirical PM3 method in vacuum. Two orientations were assessed for the encapsulation of piceatannol in the cavity of b-cyclodextrin. The orientation in which the A aromatic ring of PIC was directed toward the inner cavity of b-CD was named 'A' and that in which the B aromatic ring is located inside the b-CD cavity was named 'B'. The results indicated that both orientations were favorable for the complexation of PIC/b-CD. Indeed, the energy difference between the two orientations was less than 1 kcal/mol. Additionally, the negative interaction energies obtained for a 1:1 stoichiometry suggest that the complexation process is exothermic and indicate that the PIC/b-CD complex was highly stable and enthalpically driven. HOMO and LUMO investigations confirmed these results.
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