(ETA(6)-ARENE)RUTHENIUM(II) LABELING OF AMINO-ACIDS AND PEPTIDES WITHAROMATIC SIDE-CHAINS

Bis(arene)ruthenium(II) complexes of the type [(eta(6) -cymene)Ru(eta( 6)-aa)](CF3SO3)(n) (2-9) containing L-tyrosine and L-tryptophan deriva tives may be prepared by treatment of [(eta(6)-cymene)Ru{(CH3)(2)CO}(3 )](CF3SO3)(2) with the appropriate bioligand in CH2Cl2 for fully prote cted compounds and CF3COOH for alpha-amino acids (aa) with unprotected amine or carboxylic acid groups. Whereas the tyrosine and tryptophan methyl ester complexes [(eta(6)-cymene)Ru(eta(6)-H(2)tyrOMe)](CF3SO3)( 3) (4) and [(eta(6)-cymene)Ru(eta(6)-H(2)trpOMe)](CF3SO3)(3) (8) conta in trications with protonated amino functions, the remaining compounds all exhibit dications. The crystal structure analysis of [(eta(6)-cym ene)Ru(eta(6)-HtyrOH)](CF3SO3)(2) (5) confirms a marked distortion tow ards an eta(5)-oxohexadienyl coordination with deprotonation of the ar omatic side chain. Although facial isomers are formed in an effectivel y 1:1 ratio for all tryptophan derivatives fractional crystallization allowed an X-ray structural characterization of the beta isomer of [(e ta(6)-cymene)Ru(eta(6)-ActrpOMe)](CF3SO3)(2) (6). Chemo-specific label ing of the tryptophan side chain was established for the mixed dipepti de phenylalanyltryptophan.