Chiral Bipyridine and Terpyridine Ligands Grafted with l-Tyrosine Fragments

Abstract

The synthesis of stable terpyridine and bipyridine frames substituted with l-tyrosine fragments is reported. These highly functionalized compounds have been prepared from the corresponding iodo, and ethynyl substituted analogs by a reaction catalyzed by low valent palladium(0), itself generated in situ from palladium(II) and CuI. A tertiary amine is required to quench the nascent acid. Complexation of the chelating part of the molecule with ruthenium(II) metal afforded redox and photoactive complexes. With the terpy-Ru complex carrying a genuine tyrosine fragment an efficient quenching reaction (k_q = 2.2 × 10⁹ s^-1) due to electron transfer is observed in DMF and in the presence of K₂CO₃. The blank experiment performed under the same conditions with the tyrosine-protected benzoyl ester proved that this process is inhibited. The synthetic methods reported herein provide a practical methodology to the rational design of transition metal complexes bearing different kinds of bioactive functionalities.

Key words

bipyridine - terpyridine - palladium - alkyne - tyrosine - electron transfer

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