| Abstract
| - Two new dipeptide isosteres derived from l-leucine and meso-tartaric acid derivatives, named6-endo-BTL and 6-endo-BtL, were inserted in a small peptide by means of SPPS, and theconformational features of the resulting peptides 3 and 4 were studied by NMR, IR, and molecularmodeling techniques. The presence of a reverse turn conformation was observed in all the structures,suggesting the key role of the scaffolds as reverse turn promoters. Peptides 3 and 4 did not adopta preferred conformation as indicated by the presence of equilibria between open turn andintramolecular hydrogen-bonded structures. 6-endo-BTL-peptide 3 showed a 3:1 mixture ofconformers. The major conformer adopted mainly an open turn structure in equilibrium withhydrogen-bonded structures. The minor conformer displayed a better organized structure with a14-membered ring hydrogen-bond typical of a β-hairpin-like structure, in equilibrium with a γ-turn,too. 6-endo-BtL-peptide 4 showed a unique conformer, and did not adopt as good a conformation as3, due to the bulky equatorial substituent at C-2. Thus, marked structural differences betweenpeptides containing 6-endo-BTL and 6-endo-BtL scaffolds as reverse turn inducers exist.
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