Pentacarbonyl(methoxyorganylcarben)-Komplexe des Chroms und Wolfram (Organyl
Pentacarbonyl(orga6yIcarbene)chromium and -tungsten as Amino-Protecting Groups in Peptide SynthesesPentacarbonyl(methoxyorgany1carbene) complexes of chromium and tungsten (organyl = CH,, CsH5) react with amino acid esters to give aminocarbene complexes, in which the pentacarbonyl-(organylcarbenyl) groups act as amino-protecting groups (1 -15). The alkaline hydrolysis of the esters yields derivatives with free carboxyl groups (16-U), at which peptide coupling reactions are carried out by means of the dicyclohexylcarbodiimide/N-hydroxysuccinimide (DCCD/HOSU) method. The carbene complex protective groups can be cleaved off with trifluoroacetic acid (TFE). In the case of pentacarbonyl(organyIcarbeny1)tungsten groups side reactions are observed. The cleavage of the carbene complex protecting group may also be achieved with 80% acetic acid.The pentacarbonyl(phenylcarbenyl)tungsten group of Wpc-Gly-OMe (8) can be cleaved off by BBrs at -25°C. I140 (1976).
Praparative Ergebnisse