Synthesis and structural characterization of N-para-ferrocenyl benzoyl amino acid ethyl esters and the X-ray crystal structures of the glycyl and (±)-2-aminobutyric acid derivative Fc-C 6 H 4 CONHCH(C 2 H 5 )CO 2 Et David Savage a , Gwen Malone a , John F. Gallagher a,b, * , Yoshiteru Ida c , Peter T.M. Kenny a,b, * a School of Chemical Sciences, Dublin City University, Dublin 9, Ireland b National Institute of Cellular Biotechnology, Dublin City University, Dublin 9, Ireland c School of Pharmaceutical Sciences, Showa University, Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan Received 1 August 2004; accepted 1 August 2004 Available online 22 October 2004 Abstract A series of N-para-ferrocenyl benzoyl amino acid ethyl esters 1–8 have been prepared by coupling para-ferrocenyl benzoic acid with the amino acid esters using the conventional 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol. The amino acids employed in the synthesis were glycine, L-alanine, L-leucine, L-phenylalanine, b-alanine, 4-aminobutyric acid, (±)- 2-aminobutyric acid and 2-aminoisobutyric acid. The compounds were fully characterized by a range of spectroscopic techniques such as NMR and mass spectrometry. In addition the X-ray crystal structures of the glycyl 1 and (±)-2-aminobutyrate 7 derivatives have been determined. Analysis of relevant fragments in crystal structures on the Cambridge Structural Database indicates a relative paucity of common fragments such as the a-aminobutyrate group in comparison to the glycyl moiety. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Ferrocene; Bioorganometallic chemistry; Amino acid esters; X-ray crystal structures; Database analysis; Systematics 1. Introduction The organometallic compound ferrocene is a promis- ing candidate for incorporation in novel materials due to its stability, spectroscopic, electrochemical properties and ease of use [1]. As a direct consequence of these properties, research in the area of ferrocenyl derivatives has seen a dramatic increase in attention over the past decade, primarily for the ultimate goals of achieving no- vel sensor compounds, peptide mimetic models and unnatural drugs [2–10]. The synthesis and structural characterization of a variety of N-ferrocenoyl and N-ferrocenyl amino acid and peptide derivatives has been reported [11–25]. We now report the synthesis of a series of para-ferrocenyl benzoyl amino acid ethyl es- ters 1–8. The ferrocenyl moiety is linked to the amino acid residues through a para-benzoyl group. The com- pounds were fully characterized by 1 H NMR, 13 C NMR spectroscopy and mass spectrometry. In addition the X-ray crystal structures of compounds 1 and 7 are reported and compared with a related structure [22]. The compounds are composed of three key moieties, namely (i) an electroactive core, (ii) a conjugated linker that can act as a chromophore and (iii) an amino acid derivative that can interact with other molecules via hydrogen bonding. 0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2004.08.047 * Corresponding authors. Tel.: +353 1 7005689; fax: +353 1 7005503. E-mail addresses: john.gallagher@dcu.ie (J.F. Gallagher), peter. kenny@dcu.ie (P.T.M. Kenny). Journal of Organometallic Chemistry 690 (2005) 383–393 www.elsevier.com/locate/jorganchem