The tripeptide ester complexes 2 and 3 are obtained from the diglycine ester complex [RuCl(N,NЈ-glyglyOMe-H + )(η 6 -C 6 Me 6 )] and the amino acid esters H 2 N(CH 2 ) n CO 2 Me (n = 2, 3). The reaction of the N,O-glycinato complex [RuCl(NH 2 CH 2 CO 2 )(η 6 -C 6 Me 6 )] with the β-, γand δ-amino acid methyl esters H 2 N(CH 2 ) n CO 2 Me (n = 2,3,4) in CH 3 OH and in the presence of NaOMe affords the η 3 -N,NЈO-dipep-The formation of peptides from nonactivated α-amino acid esters, [2] α-amino acids [3] or from cyclopentadienyltitanium, -zirconium and -tantalum α-aminocarboxylates [4] at the metal centres has been reported by several groups. We have shown that half-sandwich complexes of Ru, Rh and Ir promote the formation of linear oligopeptides from amino acid esters [5a] and that the continuous addition of glycine or alanine esters to [RuCl(glyglyglyOMe-H ϩ )(p-cymene)] leads to complexes of higher peptides. [5b] Previously we have used di-or tripeptide ester complexes and α-amino acid esters for the elongation of the peptide chain with a defined amino acid sequence. In view of the recent high interest in β-amino acids, [6] which stems from the significant developments in β-peptide chemistry by Seebach [7] and Gellman [8] and their co-workers, we wanted to see whether βor γamino acid esters could be used for peptide synthesis at half-sandwich complexes. We have also found that the condensation of amino acid esters even occurs with an N,Ochelate glycinate complex to give dipeptide complexes.
Formation of η 3 -N,NЈ,NЈЈ-Tripeptide Ester Ruthenium Complexes with N-terminal β-Alanine and γ-Amino Valeric AcidThe η 2 -N,NЈ-diglycine ester complex 1 [9] was found to insert the amino acid esters H 2 N(CH 2 ) n CO 2 Me (n ϭ 2,3) in the presence of NaOMe giving the tripeptide complexes 2 and 3 in high yields (ca. 90%; Scheme 1). The reactions were carried out at low temperatures in order to avoid side [ ‡] Metal Complexes of Biologically Important Ligands, CXXXVI.Ϫ Part CXXXV: see ref.[1] [a] 2485 tide complexes [Ru{H 2 N(CH 2 ) n CONCH 2 CO 2 }(η 6 -C 6 Me 6 )] 5−7 in good yields. These complexes are also obtained in a one pot reaction from [RuCl(µ-Cl)(η 6 -C 6 Me 6 )] 2 , glycine and the amino acid ester. The formation of small peptides at the metal represents a facile procedure which does not require either a protecting/activating group or a coupling agent.reactions, especially cyclisation [10] of the tripeptide ester at the ruthenium centre.
Scheme 1Compounds 2 and 3 showed the molecular ions in the FAB-MS spectra. The new complexes contain a six-or seven-membered chelate ring as well as a five-membered ring. Other examples of bis(chelate) complexes with a fiveand a seven-membered ring are half-sandwich complexes of Ru, Rh and Ir with -methionylglycinate; [11] those containing a five-and a six-membered ring are, for example,
