Lewis acid mediated substitution reactions using [D]triethylsilane as a nucleophile at the anomeric center of the four pentofuranoses, ribose, arabinose, xylose, and lyxose, all proceed with good to excellent stereoselectivity to provide the 1,2-cis adducts. To unravel the stereoelectronic effects underlying the striking stereoselectivity in these reactions we have mapped the energy landscapes of the complete conformational space of the oxocarbenium ions of the four pentofuranoses. The potential energy surface maps provide a detailed picture of the influence of the differently oriented substituents and their mutual interactions on the stability of the oxocarbenium ions and the maps can be used to account for the observed stereoselectivities of the addition reactions.

Lysosomal degradation of glycosphingolipids is mediated by the consecutive action of several glycosidases. Malfunctioning of one of these hydrolases can lead to a lysosomal storage disorder such as Fabry disease, which is caused by a deficiency in α-galactosidase A. Herein we describe the development of potent and selective activity-based probes that target retaining α-galactosidases. The fluorescently labeled aziridine-based probes 3 and 4 inhibit the two human retaining α-galactosidases αGal A and αGal B covalently and with high affinity. Moreover, they enable the visualization of the endogenous activity of both α-galactosidases in cell extracts, thereby providing a means to study the presence and location of active enzyme levels in different cell types, such as healthy cells versus those derived from Fabry patients.

The Lewis acid mediated reduction of ribose-, arabinose-, xylose-, and lyxose-derived methyl and phenyl ketofuranoses with triethylsilane as nucleophile was found to proceed with good to excellent stereoselectivity to provide the 1,2-cis addition products. The methyl ketoses reacted in a more stereoselective manner than their phenyl counterparts. The stereochemical outcome of the reactions parallels the relative stability of the oxocarbenium ion conformers involved, as assessed by calculating the free energy surface maps of their complete conformational space. The Lewis acid mediated reduction allows for a direct synthesis of C-glycosides with predictable stereochemistry.

Cyclophellitol and cyclophellitol aziridine are potent and irreversible mechanism‐based inhibitors of retaining β‐glucosidases. Alterations in the configuration of these compounds can lead to irreversible inhibition of different classes of retaining glycosidases. We have recently reported on the design of a set of α‐galactopyranose‐configured cyclophellitol and cyclophellitol aziridine derivatives that inhibit human retaining α‐galactosidases. Moreover, we have shown that fluorescently labeled derivatives enable the activity‐based profiling of these enzymes in vitro. In this report we describe in detail the synthetic strategies that were used to obtain these epoxide‐ and aziridine‐based probes. In addition, we describe the parallel synthesis of a set of β‐galactopyranose‐configured cyclophellitol isomers as putative inhibitors of retaining β‐galactosidases.

Golgi mannosidase II (GMII) catalyzes the sequential hydrolysis of two mannosyl residues from GlcNAc-Man 5 GlcNAc 2 to produce GlcNAcMan 3 GlcNAc 2 , the precursor for all complex N-glycans, including the branched N-glycans associated with cancer. Inhibitors of GMII are potential cancer therapeutics, but their usefulness is limited by off-target effects, which produce α-mannosidosis-like symptoms. Despite many structural and mechanistic studies of GMII, we still lack a potent and selective inhibitor of this enzyme. Here, we synthesized manno-epicyclophellitol epoxide and aziridines and demonstrate their covalent modification and time-dependent inhibition of GMII. Application of fluorescent manno-epi-cyclophellitol aziridine derivatives enabled activity-based protein profiling of α-mannosidases from both human cell lysate and mouse tissue extracts. Synthesized probes also facilitated a fluorescence polarization-based screen for dGMII inhibitors. We identified seven previously unknown inhibitors of GMII from a library of over 350 iminosugars and investigated their binding modalities through X-ray crystallography. Our results reveal previously unobserved inhibitor binding modes and promising scaffolds for the generation of selective GMII inhibitors.