engleski

Preparation and Conformational Analysis of N-(Ferrocenoyl)dipeptide Esters and Their 1’-Acetyl Derivatives

Ferrocene-containing dipeptides X-Fn-CO-AA-AA-OMe(3/4, X = H, AA = Gly/Ala ; 5/6, X = Ac, AA = Gly/Ala, Fn = ferrocene-1, 1-diyl) were prepared in 51-67 % yields from the starting appropriate ferrocenecarboxylic acid and dipeptide ester by the HOBt/EDC protocol. Conformation analysis of these bioconjugates was performed by spectroscopic methods (IR, 1H and 13C NMR, CD) and by X-ray crystal structure analysis, as well as by molecular modelling (DFT). Crystallographic analysis showed that self-assembly processes prevailed in compound 5, and almost exclusively hydrogen-bonded species were also detected in all the compounds studied in the solid state by IR spectroscopy (KBr). Spectroscopic studies of conjugates 3-6 undertaken in solution in nonpolar solvents demonstrated formation of intra- and interchain weak to medium hydrogen bonds spanning NHAA2 with 1-FcCO, 1-FcCO and/or NAA1 (Fc = ferrocenyl). The same experiments revealed that NHAA1 is not involved in hydrogen bonds. The interchain hydrogen bond in conjugate 6 caused a (P)-helical arrangement of the ferrocene moiety exhibiting a positive Cotton effect at 495 nm (246 deg M-1 cm-1). All of the experimental findings were corroborated by DFT calculations, which furthermore showed conformation preferences in respect to the natural amino acid side chain of conjugates 3-6.

bioorganometallic chemistry / ferrocene / peptides / hydrogen bonds / Pi- interactions / Density functional calculations

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