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Reaction of [(Cp 2 TiCH 3 )(THF) + ][BPh 4 − ] with Tripeptide Derivatives: Formation of Cationic (Peptide)titanocene Complexes
Author(s) -
Harmsen Dirk,
Erker Gerhard,
Fröhlich Roland,
Kehr Gerald
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200212)2002:12<3156::aid-ejic3156>3.0.co;2-6
Subject(s) - chemistry , tripeptide , moiety , stereochemistry , cationic polymerization , chelation , amino acid , adduct , electrophile , medicinal chemistry , peptide , alanine , organic chemistry , catalysis , biochemistry
A series of Z‐ and Boc‐protected tripeptide methyl esters [Z‐/Boc‐ 5 to ‐ 12 (pept)] was prepared using the amino acids glycine, alanine and valine. In both the alanine and the valine series a single glycine unit was introduced and its position inside the tripeptide framework was systematically varied. Reaction of these 16 tripeptide derivatives with the organometallic reagent [Cp 2 TiCH 3 (THF) + ][BPh 4 − ] ( 13 ) resulted in the formation of methyl(peptide)titanocene cation complexes that contained the strongly electrophilic [Cp 2 TiCH 3 + ] cation moiety coordinated to a single carboxamide carbonyl oxygen atom. Mostly, the carbonyl oxygen atom of the central amino acid residue was specifically attached to yield the coordination products 5 − 12 (coord 7 ). In a few specific cases, formation of the κO‐adduct between the [Cp 2 TiCH 3 + ] cation and the N ‐terminal amino acid moiety was also observed, especially in the cases of the N ‐terminal glycine derivatives. In one case we observed the migration of the [Cp 2 TiCH 3 + ] group along the chain from the C4=O to the C7=O position. Subsequent thermally induced CH 4 elimination of the products 5 − 12 (coord) gave the cationic peptide chelate derivatives 5 − 12 (chel). These are characterized by the presence of a five‐membered κ O ,κ N ‐chelate with an anellated four‐membered κ N ,κ O ‐chelate. This is mostly centered around the central amino acid unit [products 5 − 12 (chel B )], but in some cases the N ‐terminal amino acid, together with the N ‐terminal protective group, also forms this type of a stable peptide titanocene cation chelate complex [products 5 − 12 (chel A )]. The selective formation of these series of (peptide)metallocene cation complexes was readily analyzed by means of their very characteristic 1 H and 13 C NMR spectra. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)