Total synthesis of 3,3-difluorinated 1-deoxynojirimycin analogues

Aza-Heterocyclic Building Blocks with In-Ring CF2 -Fragment

Modern organic chemistry is a titan supporting and reinforcing pharmaceutical, agricultural, food and material science products. Over the past decades, the organic compounds market has been evolving to meet all the research demands. In this regard, medicinal chemistry is especially dependent on available chemical space as subtle tuning of the molecule structure is required to create a drug with relevant physicochemical properties and a remarkable activity profile. The recent rapid evolution of synthetic methodology to deploy fluorine has brought fluorinated compounds to the spotlight of MedChem community. And now unique properties of fluorine still keep fascinating more and more as its justified installation into a molecular framework has a beneficial impact on membrane permeability, lipophilicity, metabolic stability, pharmacokinetic properties, conformation, pKa , etc. The backward influence of medicinal chemistry on organic synthesis has also changed the landscape of the latter towards new fluorinated topologies as well. Such complex relationships create a flexible and ever-changing ecosystem. Given that MedChem investigations strongly lean on the ability to reach suitable building blocks and the existence of reliable synthetic methods in this review we collected advances in the chemistry of respectful, but still enigmatic gem-difluorinated aza-heterocyclic building blocks.

Quantitative Analysis of 2D EXSY NMR Spectra of Strongly Coupled Spin Systems in Transmembrane Exchange

Solute translocation by membrane transport proteins is a vital biological process that can be tracked, on the sub-second timescale, using nuclear magnetic resonance (NMR). Fluorinated substrate analogues facilitate such studies because of high sensitivity of 19 F NMR and absence of background signals. Accurate extraction of translocation rate constants requires precise quantification of NMR signal intensities. This becomes complicated in the presence of J-couplings, cross-correlations, and nuclear Overhauser effects (NOE) that alter signal integrals through mechanisms unrelated to translocation. Geminal difluorinated motifs introduce strong and hard-to-quantify contributions from non-exchange effects, the nuanced nature of which makes them hard to integrate into data analysis methodologies. With analytical expressions not being available, numerical least squares fitting of theoretical models to 2D spectra emerges as the preferred quantification approach. For large spin systems with simultaneous coherent evolution, cross-relaxation, cross-correlation, conformational exchange, and membrane translocation between compartments with different viscosities, the only available simulation framework is Spinach. In this study, we demonstrate GLUT-1 dependent membrane transport of two model sugars featuring CF2 and CF2 CF2 fluorination motifs, with precise determination of translocation rate constants enabled by numerical fitting of 2D EXSY spectra. For spin systems and kinetic networks of this complexity, this was not previously tractable.

Unified Strategy toward Stereocontrolled Assembly of Various Glucans Based on Bimodal Glycosyl Donors

Polymers of glucose, the most abundant and one of the biologically important natural products, named glucans are widely present in fungi, bacteria, mammals, and plants with various anomeric configurations and glycosidic linkages. Because of their structural diversity, the unified strategy for the assembly of pure glucans is yet to be developed. Herein, we describe a general strategy that is applicable to construction of all types of glucans by exploiting a bimodal glycosyl donor equipped with C2-o-TsNHbenzyl ether (TAB), which enables stereocontrolled synthesis of both α- and β-glycosides by switching reaction conditions.

CuAAC click chemistry with N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol provides access to triazole-linked piperidine and azepane pseudo-disaccharide iminosugars displaying glycosidase inhibitory properties

Protecting group-free synthesis of 1,2:5,6-di-anhydro-D-mannitol, followed by ring opening with propargylamine and subsequent ring closure produced a separable mix of piperidine N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and azepane N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol. In O-acetylated form, these two building blocks were subjected to CuAAC click chemistry with a panel of three differently azide-substituted glucose building blocks, producing iminosugar pseudo-disaccharides in good yield. The overall panel of eight compounds, plus 1-deoxynojirimycin (DNJ) as a benchmark, was evaluated as prospective inhibitors of almond β-glucosidase, yeast α-glucosidase and barley β-amylase. The iminosugar pseudo-disaccharides showed no inhibitory activity against almond β-glucosidase, while the parent N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol likewise proved to be inactive against yeast α-glucosidase. Inhibitory activity could be reinstated in the former series by appropriate substitution on nitrogen. The greater activity of the piperidine could be rationalized based on docking studies. Further, potent inhibition of β-amylase was observed with compounds from both the piperidine and azepane series.

Stereoselective access to fluorinated and non-fluorinated quaternary piperidines: synthesis of pipecolic acid and iminosugar derivatives

The preparation of optically pure quaternary piperidines, both fluorinated and non-fluorinated, has been achieved from a chiral imino lactone derived from (R)-phenylglycinol. In the case of the fluorinated derivatives, the addition of (trifluoromethyl)trimethylsilane (TMSCF(3)) followed by iodoamination and migration of the CF(3) group allowed access to four derivatives of α-(trifluoromethyl)pipecolic acid. A theoretical study of the CF(3)-group rearrangement has been carried out to help establish the reaction mechanism of this uncommon transformation. Moreover, a route to trifluoromethyl-substituted iminosugars was also developed through the diastereoselective dihydroxylation of suitable synthetic intermediates. Conversely, alkylation of the starting substrate and subsequent cross-metathesis and aza-Michael reactions led to α-alkyl derivatives of the target compounds.

Imino sugars and glycosyl hydrolases: historical context, current aspects, emerging trends

Forty years of discoveries and research on imino sugars, which are carbohydrate analogues having a basic nitrogen atom instead of oxygen in the sugar ring and, acting as potent glycosidase inhibitors, have made considerable impact on our contemporary understanding of glycosidases. Imino sugars have helped to elucidate the catalytic machinery of glycosidases and have refined our methods and concepts of utilizing them. A number of new aspects have emerged for employing imino sugars as pharmaceutical compounds, based on their profound effects on metabolic activities in which glycosidases are involved. From the digestion of starch to the fight against viral infections, from research into malignant diseases to potential improvements in hereditary storage disorders, glycosidase action and inhibition are essential issues. This account aims at combining general developments with a focus on some niches where imino sugars have become useful tools for glycochemistry and glycobiology.