Bicyclic isoureas derived from 1-deoxynojirimycin are potent inhibitors of β-glucocerebrosidase

GCase Enhancers: A Potential Therapeutic Option for Gaucher Disease and Other Neurological Disorders

Pharmaceutical chaperones (PCs) are small compounds able to bind and stabilize misfolded proteins, allowing them to recover their native folding and thus their biological activity. In particular, lysosomal storage disorders (LSDs), a class of metabolic disorders due to genetic mutations that result in misfolded lysosomal enzymes, can strongly benefit from the use of PCs able to facilitate their translocation to the lysosomes. This results in a recovery of their catalytic activity. No PC for the GCase enzyme (lysosomal acid-β-glucosidase, or glucocerebrosidase) has reached the market yet, despite the importance of this enzyme not only for Gaucher disease, the most common LSD, but also for neurological disorders, such as Parkinson’s disease. This review aims to describe the efforts made by the scientific community in the last 7 years (since 2015) in order to identify new PCs for the GCase enzyme, which have been mainly identified among glycomimetic-based compounds.

sp2-Iminosugars targeting human lysosomal β-hexosaminidase as pharmacological chaperone candidates for late-onset Tay-Sachs disease

The late-onset form of Tay-Sachs disease displays when the activity levels of human β-hexosaminidase A (HexA) fall below 10% of normal, due to mutations that destabilise the native folded form of the enzyme and impair its trafficking to the lysosome. Competitive inhibitors of HexA can rescue disease-causative mutant HexA, bearing potential as pharmacological chaperones, but often also inhibit the enzyme O-glucosaminidase (GlcNAcase; OGA), a serious drawback for translation into the clinic. We have designed sp²-iminosugar glycomimetics related to GalNAc that feature a neutral piperidine-derived thiourea or a basic piperidine-thiazolidine bicyclic core and behave as selective nanomolar competitive inhibitors of human Hex A at pH 7 with a ten-fold lower inhibitory potency at pH 5, a good indication for pharmacological chaperoning. They increased the levels of lysosomal HexA activity in Tay-Sachs patient fibroblasts having the G269S mutation, the highest prevalent in late-onset Tay-Sachs disease.

Remodeling of N-Heterocyclic Iminato Ligand Frameworks for the Facile Synthesis of Isoureas from Alcohols and Carbodiimides Promoted by Organoactinide (Th, U) Complexes

A new class of actinide complexes [(L)An(N{SiMe₃}₂)₃] (An = Th or U) (Th1-Th3 and U1-U3) supported by highly nucleophilic seven-membered N-heterocyclic iminato ligands were synthesized and fully characterized by single-crystal X-ray diffraction. These complexes were successfully exploited as powerful catalysts for the addition of alcohols to carbodiimides to yield the corresponding desirable isourea products at room temperature with short reaction times and excellent yields. Thorough stoichiometric, thermodynamic, and kinetic studies were carried out, allowing us to propose a plausible mechanism for the catalytic reaction.

Synthesis of novel seven-membered carbasugars and evaluation of their glycosidase inhibition potentials

Here, we report the synthesis of five novel seven-membered carbasugar analogs. We adopted a chiral-pool strategy starting from the cheap and readily available d-mannitol to synthesize these ring-expanded carbasugars. Apart from several regioselective protecting group manipulations, these syntheses involved Wittig olefination and ring-closing metathesis as the key steps. We observed an unprecedented deoxygenation reaction of an allylic benzyl ether upon treatment with H₂/Pd during the synthesis. Preliminary biological evaluation of the carbasugars revealed that these ring expanded carbasugars act as inhibitors of various glycosidases. This study highlights the importance of the synthesis of novel ring expanded carbasugars and their biological exploration.

Here, we report the synthesis of five novel seven-membered carbasugar analogs.

Thiol-ene "Click" Synthesis and Pharmacological Evaluation of C-Glycoside sp2-Iminosugar Glycolipids

The unique stereoelectronic properties of sp2-iminosugars enable their participation in glycosylation reactions, thereby behaving as true carbohydrate chemical mimics. Among sp2-iminosugar conjugates, the sp2-iminosugar glycolipids (sp2-IGLs) have shown a variety of interesting pharmacological properties ranging from glycosidase inhibition to antiproliferative, antiparasitic, and anti-inflammatory activities. Developing strategies compatible with molecular diversity-oriented strategies for structure-activity relationship studies was therefore highly wanted. Here we show that a reaction sequence consisting in stereoselective C-allylation followed by thiol-ene "click" coupling provides a very convenient access to α-C-glycoside sp2-IGLs. Both the glycone moiety and the aglycone tail can be modified by using sp2-iminosugar precursors with different configurational profiles (d-gluco or d-galacto in this work) and varied thiols, as well as by oxidation of the sulfide adducts (to the corresponding sulfones in this work). A series of derivatives was prepared in this manner and their glycosidase inhibitory, antiproliferative and antileishmanial activities were evaluated in different settings. The results confirm that the inhibition of glycosidases, particularly α-glucosidase, and the antitumor/leishmanicidal activities are unrelated. The data are also consistent with the two later activities arising from the ability of the sp2-IGLs to interfere in the immune system response in a cell line and cell context dependent manner.

Rhodium-Catalyzed Tandem Reaction of Isocyanides with Azides and Oxygen Nucleophiles: Synthesis of Isoureas

A novel rhodium-catalyzed tandem reaction of isocyanides with azides and various oxygen nucleophiles has been developed. The reaction provides a simple and highly efficient one-pot synthesis of various N-sulfonyl/acylisoureas with broad substrate scope in an atom-economical manner from readily available starting materials in a highly stereoselective manner.

Probing the Inhibitor versus Chaperone Properties of sp²-Iminosugars towards Human β-Glucocerebrosidase: A Picomolar Chaperone for Gaucher Disease

A series of sp²-iminosugar glycomimetics differing in the reducing or nonreducing character, the configurational pattern (d-gluco or l-ido), the architecture of the glycone skeleton, and the nature of the nonglycone substituent has been synthesized and assayed for their inhibition properties towards commercial glycosidases. On the basis of their affinity and selectivity towards GH1 β-glucosidases, reducing and nonreducing bicyclic derivatives having a hydroxylation profile of structural complementarity with d-glucose and incorporating an N′-octyl-isourea or -isothiourea segment were selected for further evaluation of their inhibitory/chaperoning potential against human glucocerebrosidase (GCase). The 1-deoxynojirimycin (DNJ)-related nonreducing conjugates behaved as stronger GCase inhibitors than the reducing counterparts and exhibited potent chaperoning capabilities in Gaucher fibroblasts hosting the neuronopathic G188S/G183W mutation, the isothiourea derivative being indeed one of the most efficient chaperone candidates reported up to date (70% activity enhancement at 20 pM). At their optimal concentration, the four selected compounds promoted mutant GCase activity enhancements over 3-fold; yet, the inhibitor/chaperoning balance became unfavorable at much lower concentration for nonreducing as compared to reducing derivatives.

Orthoester functionalized N-guanidino derivatives of 1,5-dideoxy-1,5-imino-d-xylitol as pH-responsive inhibitors of β-glucocerebrosidase

Alkylated guanidino derivatives of 1,5-dideoxy-1,5-imino-d-xylitol bearing an orthoester moiety were prepared using a concise synthetic protocol. Inhibition assays with a panel of glycosidases revealed that one of the compounds prepared displays potent inhibition against human β-glucocerebrosidase (GBA) at pH 7.0 with IC50 values in the low nanomolar range. Notably, a significant drop in inhibitory activity is observed when the same compound is tested at pH 5.2. This pH sensitive activity is due to degradation of the orthoester functionality at lower pH accompanied by loss of the alkyl group. This approach provides a degree of control in tuning enzyme inhibition based on the local pH. Compounds like those here described may serve as tools for studying various lysosomal storage disorders such as Gaucher disease. In this regard, the most active compound was also evaluated as a potential pharmacological chaperone by assessing its effect on GBA activity in an assay employing fibroblasts from Gaucher patients.

N-Guanidino Derivatives of 1,5-Dideoxy-1,5-imino-d-xylitol are Potent, Selective, and Stable Inhibitors of β-Glucocerebrosidase

A series of lipidated guanidino and urea derivatives of 1,5-dideoxy-1,5-imino-d-xylitol were prepared from d-xylose using a concise synthetic protocol. Inhibition assays with a panel of glycosidases revealed that the guanidino analogues display potent inhibition against human recombinant β-glucocerebrosidase with IC₅₀ values in the low nanomolar range. Related urea analogues of 1,5-dideoxy-1,5-imino-d-xylitol were also synthesized and evaluated in the same fashion and found to be selective for β-galactosidase from bovine liver. No inhibition of human recombinant β-glucocerebrosidase was observed for the urea analogues. Computational studies provided insight into the potent activity of analogues bearing the substituted guanidine moiety in the inhibition of lysosomal glucocerebrosidase (GBA).