E~E~ER Binding Ability of a-Ketoamide Unit in Amino Acid Derivatives Tatiana Yu. Sliva, Anna M. Duda, Vladimir M. Amirkbanov, Igor Fritski, Tadeusz Ghrwiak, and Henryk Koztowski TYuS, VMA, IF. Faculty of Chemistry, University of Kiev, Kiev, Ukraine.--AMD, TG, HK. Faculty of Chemistry, University of Wrodaw, Y0383 Wroctaw, Poland Abstract An X-ray study of pyruvyl-L-methionine has shown that in the a-ketoamide group, the CO-CO bond is in trans orientation. Potentiometric and spectroscopic (EPR, CD, UV-VIS) studies of this ligand with Cu 2 + indicated that a-ketoamides of amino acids are efficient chelating agents for cupric ions able to involve their amide nitrogen in metal ion binding witbont tbe need for an anchoring site, e.g., in peptides. The likely modification of pyruvic moiety in basic solution (hydration) may have a distinct effect on the binding ability of the title ligands. © 1997 Elsevier Science Inc. Journal of Inorganic Biochemistry 6 Y, 67-71 (1997) to amide nitrogen may potentially efficiendy stabilize the Cu 2 + species and allow us to deprotonate and coordinate the neighboring nitrogen atom [6]. Experimental Ligand Synthesis Pyruvyl-L-methionine (pyr-Met) was synthesized in two steps according to the procedure given by Bergrnan and Grafe [7]. See Scheme I. Ligand was crystallized from aqueous solution and used for further studies. Purity was checked by potentiometry. I H NMR, and elemental anal- ysis [CHN%, cal. (found), C-43.82, (43.65), H-5.98, (6.10), N-6.39, (6.20)]. Introduction The ct-ketoamide unit (-NH-CO-CO-) is a key struc- tural element involved in the binding of powerful im- munosuppressants (e.g., rapamycin) to protein immuno- phylins and in inhibiting their m-tram isomerase [1-2]. The major interaction of the a-ketoamide unit with protein is the hydrogen bond system with amino acid side chains of protein. The preferred structure of the ot-keto- amide group is not well understood, although closely related oxalamide moiety in retro-bispeptides (-NH-CO-CO-NH-) assumes planar or nearly planar tram conformation, even with bulky substituents on the nitrogen atoms, except when the nitrogen atom is part of a cyclic system as a prolyl residue [3]. The a-ketoamide group has three potential metal bind- ing sites, including strongly basic amide nitrogen and two weakly coordinating carbonyl oxygens. In the case of a peptide bond CO-NH, both types of donors could be involved in metal ion binding, but usually an anchoring site is necessary to protect against metal ion hydrolysis [4, 5]. In the case of peptides, the anchoring group for metal ions like Cu 2+ is usually the N-terminal amine nitrogen or side-chain donor, e.g., imidazole nitrogen. The carboxylate is a very poor binding group, and in the case of peptides, is unable to efficiently anchor Cu 2+ ions. However, the presence of two carbonyl groups close Addresscorrespondence to: Prof. Hi Kozlowski,Faculty of Chemistry, University of Wrodaw, F.Joliot-Curie 14, 50383 Wrochw,Poland. X-Ray Structure of pyr-Met Colorless crystals were grown by slow evaporation from aqueous solution. Crystal data and the details of data collection and refinement procedure are given in Table 1. Selected bond lengths and torsion angles are given in Tables 2 and 3. Intensity data were collected with a KM4 computer-controlled four-circle diffractometer [8]. The ligand structure was solved by direct methods using the SHELXS-86 set of programs [9], and refined by full- matrix least-squares with anisotropic parameters for all nonhydrogen atoms. All hydrogen atoms were placed at computed positions, as determined from the successive Fourier difference maps. Computations were performed with a PC/AT computer using the Syntex XTL/XTLE computational package [10]. Sources of neutral atomic scattering factors for all atoms are given in [11]. O II //o H C--C--C--NH--CH--C.~ 3 II I --OH O CH I 2 CH 12 S I CH 3 Scheme I. © 1997 Elsevier Science Inc. 0162-01341971517.00 655 Avenue of the Americas, New York, NY 10010 PII S0162-0134(96)00081-5