AbstractEngineering bioactive iminosugars with pH‐responsive groups is an emerging approach to develop pharmacological chaperones (PCs) able to improve lysosomal trafficking and enzymatic activity rescue of mutated enzymes. The use of inexpensive l‐malic acid allowed introduction of orthoester units into the lipophilic chain of an enantiomerically pure iminosugar affording only two diastereoisomers contrary to previous related studies. The iminosugar was prepared stereoselectively from the chiral pool (d‐mannose) and chosen as the lead bioactive compound, to develop novel candidates for restoring the lysosomal enzyme glucocerebrosidase (GCase) activity. The stability of orthoester‐appended iminosugars was studied by 1H NMR spectroscopy both in neutral and acidic environments, and the loss of inhibitory activity with time in acid medium was demonstrated on cell lysates. Moreover, the ability to rescue GCase activity in the lysosomes as the result of a chaperoning effect was explored. A remarkable pharmacological chaperone activity was measured in fibroblasts hosting the homozygous L444P/L444P mutation, a cell line resistant to most PCs, besides the more commonly responding N370S mutation.