Metal complexes of biologically important ligands, Part CXVIII. Metathesis of dehydro amino acids with Fischer carbene complexes: synthesis of complexes of amino acid- and peptide-#alpha#-carbenes and of isoindoles

摘要

Metathesis of N-protected dehydro alanine esters with Fischer carbene complexes affords #alpha#-amino acid metal carbenes O(CH_2CH_2)_2N-C[=M(CO)_5](CO_2Me) (3) and Ph_2C=N-C[=M(CO)_5](CO_2Et) (6) (M = Cr, Mo, W). The X-ray structural analysis of 6c shows the dominance of the zwitterionic form Ph_2C=N=C[M(CO)_5](CO_2Et) in these complexes. Labeling of peptides by the M(CO)_5 fragment is demonstrated by the synthesis of Ph_2C=N-C[=Cr(CO)_5]CONHCH(CH_2Ph)CO_2Me (9). The strongly fluorescent isoindole 7 was obtained from the carbene complexes 6 and was characterized by X-ray diffraction.