✍ Scribed by Bernd Kayser; Janina Altman; Heinrich Nöth; Jörg Knizek; Wolfgang Beck
No coin nor oath required. For personal study only.
amino acids / N,O-Chelate complexes / Ferrocenes / Schiff bases / Platinum / Gold
The palladium-mediated coupling of p-ethynylphen-complexes of the types Ph 3 PAu-CϵC-R and (Et 3 P) 2 Pt-(CϵCR) 2 . The benzene-bridged di-, tri-, tetra-and hexa-p-ylalanine (p-epa) with different halogenated benzenes yielded alkyne-bridged α-amino acids. A series of cationic ethynylphenylalanine methyl esters form Schiff bases with ferrocene aldehyde and a tripodal ligand was obtained from mono-to hexanuclear (Ph 3 P) 2 Pt complexes with the anions of p-ethynylphenylalanine and alkynyl-or benzene-bridged Ph 2 PCH 2 CH 2 CH 2 NH 2 and the benzene-bridged triethynylphenyl-alanine. The structure of (Ph 3 P) 2 Pt[NH 2 C(H)-di-, tri-, tetra-and hexa-ethynyl phenylalanines as N,Ochelate ligands was prepared. N-t-Boc-p-ethynylphenyl-(CH 2 C 6 H 4 CϵCH)CO 2 ] + BF 4 -was determined by X-ray diffraction. alanine methyl ester was metal-substituted to give
Non-proteinogenic amino acids influence the biological properties of peptides and are useful for the synthesis of Chloro-bridged metal complexes have proven to be ideal peptidomimetics [3] . The synthesis of unnatural amino acids starting materials for the synthesis of N,O-α-aminocarboxis based either on electrophilic [4] or nucleophilic [5] equivaylate metal compounds [16] . We have chosen the chlorolents. A valuable building block for the derivatization of bridged complexes [(Ph 3 P) 2 Pt(µ-Cl) 2 Pt(PPh 3 ) 2 ] 2ϩ , (Et 3 P)phenylalanines has been developed by Schwabacher et al. [6] .
(Cl)Pd(µ-Cl)Pd(Cl)(PEt 3 ) and Cp*(Cl)Rh(µ-Cl) 2 Rh(Cl)Cp* p-Iodophenylalanine was used as starting material to build, from which N,O-chelates with natural α-amino acids have under palladium catalysis, amino acids which are bridged been obtained in our group. [16] [17] [18] [19] by a heteroatom [6] or the iodo substituent was replaced by sulfur-containing fragments or trimethyltin [7] . The pal-
The reaction of the chloro-bridged cationic complex {[(Ph 3 P) 2 Pt(µ-Cl)] 2 }{BF 4 } 2 with the anion of p-ethynyl-ladium-mediated coupling of terminal acetylides with piodophenylalanine afforded fluorescent marker mol-phenylalanine yielded the cationic N,O-chelate 1. ecules [8a] , which find growing attention in organometallic chemistry [8b-e] . Undheim et al. and Savi et al. reported the Pd-catalyzed synthesis of a series of α,αЈ-hydrocarbon bis(α-amino acids), including α,αЈ-alkynyl-bridged bis(glycines) and of alkyneϪbridged oxazolidines [9] . By means of the Heck [10] , especially the Sonogashira reaction [11] , we were able to synthesize various acetylidebridged phenylalanines [12a] . p-Ethynylphenylalanine was proven to be a potent inhibitor of the enzyme tryptophan-Suitable crystals for structure determination by X-ray difhydroxylase [13] ; therefore structural details of this comfraction of 1 were obtained by liquid-liquid diffusion of dipound appear of interest. The bis-, tris-, tetra-and hexaethyl ether into an methanolic solution of 1 at room tempodal [12b] amino acids should be useful starting compounds perature. By this means the structure of the new non-proin peptide chemistry, for the synthesis of organic as well as teinogenic amino acid p-ethynylphenylalanine (p-epa) [12a] metallo-dendrimers [14] , and for linearly-bridged metal comhas been established. The PtϪligand atom distances are plexes with unusual optical or electrical properties [15] . The close to those of similar complexes, e.g. (nBu 3 P)(Cl)scope of organometallic complexes of α-amino acids and Pt(O 2 CCH 2 NϭC(H)NMe 2 ) [20a] , (dppe)Pt[N(COMe)CH 2peptides has been recently reviewed [16] .
CO 2 ] [20b] and (Ph 3 P(Cl)Pt(NH 2 CMe 2 CO 2 ) [20c] . In this paper we wish to present the coordination chemis-The bond angle C11ϪC10ϪC7 is not exactly linear. try of the new amino acid derivatives.
The analogous reactions of bis-, tris-, tetra-and hexaethynylphenylalanine derivatives gave the cationic com- [᭛] For part CVII see ref. [1] .
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