Inhibition of Porcine Pancreas α-Amylase by Chlorogenic Acids from Green Coffee Beans and Cinnamic Acid Derivatives

α-Amylase inhibitors appear helpful in the prevention and medical treatment of metabolic syndromes such as type 2 diabetes and obesity. Here, we focus on the inhibitory effects on porcine pancreas α-amylase by nine types of chlorogenic acids (CGAs) from green coffee beans: three subgroups of caffeoylquinic acids (CQAs), feruloylquinic acids (FQAs), and dicaffeoylquinic acids. The inhibition modes of six types of CQAs and FQAs were mixed-type, suggesting that the inhibitor-binding site (I-site) for CGAs exists separately from the substrate-binding site on the enzyme surface. CQAs (esters of caffeic acid (CA) and quinic acid (QA)) and FQAs (esters of ferulic acid (FA)) and QA bound to the same I-site, which was separated into two subsites (i.e., CA/FA subsite and QA subsite), thereby accommodating the CA or FA substructures and QA substructure of CQA or FQA, respectively, based on a comparison of the inhibitor constants for each CGA.