β2,2-aminoxy acids: A new building block for turns and helices

The conformational properties of peptides 1-4 built from 3-aminoxy-2,2-dimethyl-propionic acid, a β2,2-aminoxy acid, were investigated by NMR spectroscopy and X-ray crystallography. A novel β N-O turn involving a nine-membered-ring intramolecular hydrogen bond between NHi+2 and COi was formed in diamides 1 and 2, which was further stabilized by another six-membered-ring intramolecular hydrogen bond between NHi+2 and NOi+1. Triamides 3 and 4 displayed a well-defined helical structure featuring two consecutive β N-O turns. The X-ray structure of 4 revealed that the amide carbonyl group at position i+2 was twisted +65.9° from that at i position, suggesting a novel 1.79 helix. Therefore, β2,2-aminoxy acid can be used as a new building block for turns and helices. Copyright © 2002 American Chemical Society.link_to_subscribed_fulltex