Illuminating the binding interactions of galactonoamidines during the inhibition of β-galactosidase (E. coli)

Borane-Trimethylamine Complex: A Versatile Reagent in Organic Synthesis

Borane-trimethylamine complex (Me3N·BH3; BTM) is the most stable of the amine-borane complexes that are commercially available, and it is cost-effective. It is a valuable reagent in organic chemistry with applications in the reduction of carbonyl groups and carbon-nitrogen double bond reduction, with considerable examples in the reduction of oximes, hydrazones and azines. The transfer hydrogenation of aromatic N-heterocycles and the selective N-monomethylation of primary anilines are further examples of recent applications, whereas the reduction of nitrobenzenes to anilines and the reductive deprotection of N-tritylamines are useful tools in the organic synthesis. Moreover, BTM is the main reagent in the regioselective cleavage of cyclic acetals, a reaction of great importance for carbohydrate chemistry. Recent innovative applications of BTM, such as CO2 utilization as feedstock and radical chemistry by photocatalysis, have extended their usefulness in new reactions. The present review is focused on the applications of borane-trimethylamine complex as a reagent in organic synthesis and has not been covered in previous reviews regarding amine-borane complexes.

Glycal mediated synthesis of piperidine alkaloids: fagomine, 4-epi-fagomine, 2-deoxynojirimycin, and an advanced intermediate, iminoglycal

Glucal and galactal are transformed into 2-deoxyglycolactams, which are important building blocks in the synthesis of biologically active piperidine alkaloids, fagomine and 4-epi-fagomine. In one of the strategies, reduction of 2-deoxyglycolactam-N-Boc carbonyl by lithium triethylborohydride (Super-Hydride®) has been exploited to generate lactamol whereas reduction followed by dehydration was utilized as the other strategy to functionalize the C1-C2 bond in the iminosugar substrate. The strategies provide the formal synthesis of 2-deoxynojirimycin, nojirimycin and nojirimycin B. DFT studies were carried out to determine the reason for the failure of the formation of the 2-deoxygalactonojirimycin derivative. Further, DFT studies suggest that phenyl moieties of protecting groups and lone pairs of oxygen in carbamate group plays a vital role in deciphering the conformational space of the reaction intermediates and transition-state structures through cation-π or cation-lone pair interactions. The influence of these interactions is more pronounced at low temperature when the entropy factor is small.

Picomolar inhibition of β-galactosidase (bovine liver) attributed to loop closure

In an effort to examine similarities in the active sites of glycosidases within the GH35 family, we performed a structure-activity-relationship study using our recently described library of galactonoamidines. The kinetic evaluation based on UV/Vis spectroscopy disclosed inhibition of β-galactosidase (bovine liver) in the picomolar concentration range indicating significantly higher inhibitor affinity than previously determined for β-galactosidase (A. oryzae). Possible alterations in the secondary protein structure or folding were excluded after further examination of the inhibitor binding using CD spectroscopy. Molecular dynamics studies suggested loop closing interactions as a rationale for the disparity of the active sites in the β-galactosidases under investigation.

Binuclear copper(II) complexes discriminating epimeric glycosides and α- and β-glycosidic bonds in aqueous solution

Two chiral binuclear copper(II) complexes were synthesized and characterized for the first time as efficient chemoselective catalysts for the hydrolysis of aryl glycosides and disaccharides in aqueous solution at near neutral pH. Under these conditions, discrimination of epimeric aryl α-glycopyranosides was observed both by 29-fold different reaction rates and 3-fold different proficiency of the catalyst. Additionally, large differentiation of the nature of α- and β- glycosidic bond in aryl glycosides as model compounds is apparent, but also noted in selected disaccharides. The influence of the chirality of the complexes and the role of the configuration of the carbohydrate upon interaction with the catalyst is discussed in detail. Lastly, a putative mechanism for the metal complex-catalyzed hydrolysis is derived from the experimental evidence pointing at deprotonation of the hydroxyl group at C-2 as a pre-requisite for glycoside hydrolysis.

Arabinoamidine synthesis and its inhibition toward β-glucosidase (sweet almonds) in comparison to a library of galactonoamidines

Aiming at the development of potent inhibitors of β-glucosidases, a small library of galactonoamidines and one arabinoamidine derived in analogy were studied as inhibitors of sweet almond β-glucosidase. The five-membered glycon in arabinoamidine was shown to interact with the proton donor in the active site of the retaining enzyme, but not with the nucleophile. By contrast, the corresponding galactonoamidine with a six-membered glycon and identical aglycon interacts with both hydrolysis-promoting amino acids in the active site and inhibits the enzymatic hydrolysis of β-glucosides in the low nanomolar concentration range. While both inhibitors are competitive, their inhibition ability is more than 37,000-fold different.

Discrimination of chiral copper(ii) complexes upon binding of galactonoamidine ligands

Chiral binuclear Cu(ii) complexes are differentiated upon binding top-methylbenzyl-d-galactonoamidine. A sequential binding model is elaborated reflecting the altered coordination sites.