A potent and selective inhibitor of class I α-mannosidases and serves as a key inhibitor of glycoprotein biosynthesis; inhibits both human ER α-1,2-mannosidase I and Golgi class I mannosidases (Golgi α-mannosidase IA, IB, and IC) exhibiting Ki values of 130 and 23 nM, respectively; inhibits mung bean α-1,2-mannosidase I with an IC50 value of 20-50 nM