Regio- and Stereoselective Cycloadditions of Cyclic Nitrones to Maleic Diamide Forced in a Peptide:  Synthesis of Potent Ligands of Human NK-2 Receptor

The regioselectivity and the stereoselectivity induced by relatively small peptidomimetic maleic diamide 1 in cycloaddition reactions with cyclic nitrones 2−5 was studied. The high regio- and stereoselectivity observed, sensibly increased by nonpolar solvents, was the effect of a double-asymmetric induction produced by the nitrone substituent on the pseudopeptidic tether. A new class of potent human tachykinin NK-2 receptor ligands was synthesized.