A specific inhibitor of class I α-1,2-mannosidase (IC50 = 20 mM), a key enzyme for N-glycan processing in the endoplasmic reticulum and Golgi; inhibiting α-1,2-mannosidase with 1-Deoxymannojirimycin generates N-linked oligosaccharides with high mannose content, preventing proteasomal degradation of misfolded proteins.