| Abstract
| - The MoCp(η-C3H5)(CO)2 moiety is introduced as a new labeling group in bioorganometallic chemistry. Starting from the acid derivative Mo(C5H4-CO2H)(η-C3H5)(CO)2, a variety of amino acid and a peptide derivative are prepared by standard peptide synthesis methods. The conjugates show excellent chemical stability and favorable spectroscopic properties. A single-crystal X-ray analysis of the phenylalanine derivative Mo(C5H4-CO-Phe-OCH3)(η-C3H5)(CO)2 shows some unusual features, and the origin of fluxionality in the allyl group is elucidated by NMR spectroscopy.
- The MoCp(η-C3H5)(CO)2 (Cp = η-cyclopentadienyl) moiety is introduced as a new labelinggroup in bioorganometallic chemistry. The acid Mo(C5H4-CO2H)(η-C3H5)(CO)2 (2) wasobtained from the reaction of MoCp(η-C3H5)(CO)2 (1) with BuLi and solid CO2 followed byaqueous workup. Coupling of 2 to amino acids with various complexity and C-terminalfunctionality by standard peptide chemistry methods yielded the amino acid derivativesMo(C5H4-CO-AA-R)(η-C3H5)(CO)2, 3 (3a, AA = Phe, R = OCH3; 3b, AA = Leu, R = NH2; 3c,AA = Gly, R = OCH3). In addition, the dipeptide derivative Mo(C5H4-CO-Leu-Phe-OCH3)(η-C3H5)(CO)2 (4) was synthesized by reacting 2 with H-Leu-Phe-OCH3. All new compoundsare characterized by elemental analysis, IR, MS, and NMR spectroscopy. X-ray analysis on3a shows the unit cell to contain two independent molecules, A and B, which differ mainlyby the orientation of the allyl and carbonyl groups with respect to the amino acid substituenton the Cp ring. Furthermore, an allyl-endo conformation for both A and B is observed. Thisis the first example of such a conformation in the crystal structure of a MoCp(C3H5)(CO)2derivative. In solution, both the exo and endo isomer are present, as concluded from 1H NMRspectroscopy approximately in a 4:1 ratio. The activation barriers of interconversion weredetermined to be 62.7 ± 0.5 kJ mol-1 (3a) and 60.5 ± 0.5 kJ mol-1 (3c).
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