Cystic fibrosis and diabetes: isoLAB and isoDAB, enantiomeric carbon-branched pyrrolidine iminosugars

Acetonides are the only protecting groups used in the syntheses of isoDAB from d-ribose and of isoLAB from d-tagatose. isoDAB is a potent and highly specific competitive α-glucosidase inhibitor (for rice α-glucosidase, Ki = 4 μM for isoDAB compared to Ki 14 μM for DAB). isoDAB is not an—whereas DAB is a potent—inhibitor of glycogen phosphorylase. This is the first example of any potent inhibition of glycosidases by a carbon-branched iminosugar pyrrolidine. Although isoLAB shows no inhibition of any glycosidase, preliminary experiments suggest that isoLAB partially rescues the defective F508del-CFTR function and so may have a role in the study of cystic fibrosis.