A method for stabilizing the cis prolyl peptide bond: influence of an unusual n→π∗ interaction in 1,3-oxazine and 1,3-thiazine containing peptidomimetics
                                
                                    
                                        作者:Damodara N. Reddy、Ravula Thirupathi、Shama Tumminakatti、Erode N. Prabhakaran                                    
                                    
                                        DOI:10.1016/j.tetlet.2012.06.031
                                    
                                    
                                        日期:2012.8
                                    
                                    The cis/trans isomer ratios of the Xaa-Pyr (Pyr = pyrrolidine) 3 degrees amide bonds are significantly high (similar to 90% cis) in the novel peptidomimetics where Pyr contains 1,3-oxazine (Oxa) or 1,3-thiazine (Thi) at its 2 position. We find that an unusual n -> pi(i-1)* interaction, selectively stabilizes the cis conformer and the n X n repulsion destabilizes the trans conformer of these molecules. Both these electronic effects oppose the steric effects in the 3 degrees amide bond. The structural requirements for manifestation of these electronic effects are determined. (c) 2012 Elsevier Ltd. All rights reserved.