Two regioisomeric alpha-phenyl-beta-pyridylacrylic acids were hydrogenated with cinchonidine (CD)-modified Pd/C. The low ee obtained was attributed to the strong adsorption of the substrate, which caused desorption of CID from the catalyst surface. The ee was improved at the low substrate/CD ratio up to 82% for the 4-pyridyl isomer. The unmodified site in the CD-modified Pd catalyst was experimentally proved to be variable depending on the relative adsorption strength between the substrate and CD. At the low substrate/CD ratio, the ee with the 3-pyridyl isomer was also improved, but the highest ee was only 45%. The difference between the isomers suggests that the strong adsorption of the substrate on the metal surface may interrupt the interaction between CD and the substrate. (C) 2009 Elsevier B.V. All rights reserved.