Peptidostarands: valence tautomers of cyclic peptides

Ab initio molecular orbital calculations, at the HF/6-31G* and MP2//HF/6-31 G* levels of theory, have been performed on a hypothetical class of organic compound which we call peptidostarands. These molecules are valence tautom ers of cyclic peptides. Calculations predict that cyclohexaglycine lies 76 kcal/mol lower in energy than its peptidostarand isomer, but when both mole cules are derivatised with electron-withdrawing CFO groups on the nitrogen atoms, the peptidostarand becomes the more stable valence tautomer, by 19 k cal/mol. Strategies for synthesising peptidostarands are discussed. (C) 199 9 Elsevier Science Ltd. All rights reserved.