Search

Highly stereoselective formal [3 + 3] cycloaddition reactions of chiral vinylogous amides with α,β-unsaturated iminiums are described. A mechanistic model is proposed to rationalize the observed stereoselectivity. The 6π-electron electrocyclic ring closure appears to be reversible, and a preferred rotation of the alkenyl group, one of the three 2π-components, during the ring closure step provides the thermodynamically favored diastereomer as the major product.

4-Hydroxypyrones belong to an important class of compounds not only because of their medicinal significance, but also because they represent a common structural feature among natural products that are biologically relevant. We describe here preparations of a small library of 6-aryl-4-hydroxy-pyrones which represent structural analogs of the DE-ring of arisugacin, a potent and selective inhibitor against acetylcholinesterasc. Given the structural significance of the DE-ring in the inhibitory activity of arisugacin chemical shifts of relevant protons on the pyrone ring are compared and distinct features in UV absorptions of these 6-aryl-4-hydroxy-pyrones are described.

A general approach to synthesis of dihydroxanthone derivatives is described here. In vitro evaluation of these dihydroxanthones demonstrated that some derivatives possess moderate anti-cholinesterase activities and better selectivities than tacrine for acetylcholinesterase over butyrylcholinesterase. Structural effects on anti-cholinesterase activities were also examined, and docking experiments were carried out to provide preliminary understandings of these experimental observations.