METAL-COMPLEXES OF BIOLOGICALLY IMPORTANT LIGANDS .88. ORGANOMETALLICHALF-SANDWICH COMPLEXES PROMOTE THE FORMATION OF LINEAR OLIGOPEPTIDESFROM AMINO-ACID ESTERS
R. Kramer et al., METAL-COMPLEXES OF BIOLOGICALLY IMPORTANT LIGANDS .88. ORGANOMETALLICHALF-SANDWICH COMPLEXES PROMOTE THE FORMATION OF LINEAR OLIGOPEPTIDESFROM AMINO-ACID ESTERS, Chemistry, 2(12), 1996, pp. 1518-1526
Organometallic dipeptide ester complexes of the general formula [(L)M(
Cl)(kappa(2)-NH(2)CH(2)CONCH(2)CO(2)R)] (1: L = Cp, M = Rh, 2: L = Cp
, M = Ir, 3: L = eta(6)-C(6)Me(6), M = Ru) react smoothly with variou
s alpha-L-amino acid esters in the presence of NEt(3) to yield the tri
peptide ester complexes )M(Cl)(kappa(2)-NH(2)CHR'CONCH(2)CONHCH(2)CO(2
)R)] (5-7). In the same fashion chloro kappa(2)-tetrapeptide ester com
plexes 10 and 11 are obtained either from tripeptide ester complexes o
r by subsequent addition of two equivalents of amino acid ester to a d
ipeptide ester complex. When the strong base NaOMe is used in the reac
tion of the diglycine ester compounds with amino acid esters, kappa(3)
-tripeptide ester complexes 12 and 13 are produced, in which one of th
e two coordinated peptide nitrogen atoms is pyramidal. The hexamethylb
enzene ruthenium complexes 13 with tripeptide ligands are formed with
very high diastereoselectivity. A plausible reaction mechanism for the
metal-promoted peptide synthesis is presented. Synthesis and isolatio
n of the peptide esters proceeds without racemization.