Noncovalent interaction-driven stereoselectivity of copper(II) complexes with cyclodextrin derivatives of L- and D-carnosine

L-Carnosine (?-alanyl-L-histidine, LCar) is the most widely and abundantly distributed copper(II)-coordinating endogenous dipeptide. Though its physiological role has not been completely understood yet, many functions have been proposed for this compound. LCar might be crucial in the potential reduction or prevention of several pathologies in which the metal ions are thought to be involved. The potential therapeutic applications of LCar are drastically limited because of hydrolysis by specific dipeptidases (carnosinases). D-Carnosine (DCar), the enantiomer of the naturally occurring dipeptide, shows the same properties as those of LCar, but it is not hydrolyzed by carnosinases. Chemical modification of LCar has been proposed as a promising strategy to reduce its enzymatic hydrolysis; conjugation of a carbohydrate moiety may also improve site-specific transport to different tissues, which would enhance the peptide bioavailability. On this basis, we have functionalized DCar with ?-cyclodextrin (CDDCar) and characterized the compound via NMR. The copper(II) binding properties of the new DCar derivative were investigated by spectroscopic techniques (UV-vis, circular dichroism, electron paramagnetic resonance) and potentiometric measurements. The results surprisingly revealed a pronounced difference from the analogous LCar derivative (CDLCar), especially concerning the dimeric species. The spectroscopic data show that this stereoselectivity is driven by noncovalent interactions, namely, hydrogen bonds, CH-? interactions, and steric and hydrophobic effects of the cyclodextrin cavity. © 2011 American Chemical Society.