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In continuation of our studies on ferrocene amino acids [1, 2] we have prepared and characterized several derived peptides, which were partially described in ref. [3]. tert-Butyl 1-carboxyferrocene-1-carbamate (Boc-Fca, 1) was coupled with a series of the natural and other amino acids (AA) using EDC/ HOBt method to give oligopeptides of the type I Boc-(AA)nFca(AA)n-OMe. Dipeptides (m = 0 ; n = 1 ; AA = L-Ala, D-Ala and _-Ala), tripeptide (m = 0 ; n = 2 ; AA = L-Ala) and (m, n = 1 ; AA = L-Ala), tetrapeptide (m = 1 ; n = 2 ; AA = L-Ala) and pentapeptide (m = 2 ; n = 2 ; AA = L-Ala) were obtained in the CH2Cl2 solutions using the same method. In such a way the Fca-containing oligopeptides with the antiparallel peptide strands (which can serve as turn mimetics) were prepared for the very first time. The crystallographic analysis shows that dipeptides are helical enantiomers whose conformations are stabilized by intramolecular 9-membered hydrogen bond and the similar helical chirality is confirmed for tetrapeptide (10- and 12-membered hydrogen bonds). This chirality is retained in solution (CD-spectra) and the intramolecular hydrogen bonds involved are additionaly characterized by IR- and 1H-NMR-analysis. [1] L. Barišić, V. Rapić, V. Kovač, Croat. Chem. Acta 75 (1) (2002) 199-210. [2] L. Barišić, V. Rapić, H. Pritzkow, G. Pavlović, I. Nemet, J. Organomet. Chem. 682 (2003) 131-142. [3] L. Barišić, M. Dropučić, V. Rapić, H. Pritzkow, S. I. Kirin, N. Metzler-Nolte, Chem. Commun. 17 (2004) 2004-2005. |
