Recent developments of transition-state analogue glycosidase inhibitors of non-natural product origin

A facile approach for the synthesis of 1,3-di- and 1,2,3-tri-substituted indolizines

A convenient synthesis of 1,3-di- and 1,2,3-tri-substituted indolizines involving the multicomponent reaction of pyridinium salt (or quinolinium salt), olefine acid, and 1,2-dichloroethane has been achieved. The process proceeds smoothly in moderate to high yields.

Direct synthesis of imino-C-nucleoside analogues and other biologically active iminosugars

Iminosugars have attracted increasing attention as chemical probes, chaperones and leads for drug discovery. Despite several clinical successes, their de novo synthesis remains a significant challenge that also limits their integration with modern high-throughput screening technologies. Herein, we describe a unique synthetic strategy that converts a wide range of acetaldehyde derivatives into iminosugars and imino-C-nucleoside analogues in two or three straightforward transformations. We also show that this strategy can be readily applied to the rapid production of indolizidine and pyrrolizidine iminosugars. The high levels of enantio- and diastereoselectivity, excellent overall yields, convenience and broad substrate scope make this an appealing process for diversity-oriented synthesis, and should enable drug discovery efforts.

Iminosugars are biologically and medicinally important compounds but methods for their synthesis are often laborious. Here, the authors report a simple, rapid route for the enantioselective synthesis of multiple biologically active iminosugars and C-nucleoside analogues.

Antidiabetic potential of polyoxotungstates: in vitro and in vivo studies

Diabetes mellitus is a chronic metabolic disorder continuously affecting people all over the world. A common way to treat diabetes mellitus is to limit the conversion of carbohydrates into glucose which is mediated by glucosidase enzymes. Diabetes mellitus is also famous for its life-threatening microvascular (retinopathy, neuropathy and nephropathy) and macrovascular (atherosclerosis) complications. Aldose reductases present in eye lens (ALR1) and kidney (ALR2) are responsible for microvascular complications. The production of advanced glycation end products (AGEs) is involved in the development of atherosclerosis. The present work was aimed at the synthesis and in vitro/in vivo evaluation of different polyoxotungstates against glucosidases (α- and β), aldose reductases (ALR1 and ALR2) and AGEs to discover a new treatment which may limit the complications associated with diabetes mellitus. The polyanion [P6W18O79](20-) was found to be the most potent inhibitor of α-glucosidase (IC50 = 1.33 ± 0.41 μM), ALR1 (IC50 = 0.4 ± 0.009 μM) and ALR2 (IC50 = 0.38 ± 0.02 μM). Animal studies showed that the polyanion [H2W12O40](6-) was very effective in reducing the blood glucose level to 84.25 ± 5.07 mg dL(-1) when compared with standard antidiabetic drug glibenclamide (150.62 ± 9.35 mg dL(-1)) measured after maximum 8 h of dose administration. The data obtained from in vitro and in vivo experiments confirm that [P6W18O79](20-) and [H2W12O40](6-) could be used as a new treatment of diabetes mellitus.

One-pot synthesis of indolizine via 1,3-dipolar cycloaddition using a sub-equivalent amount of K2Cr2O7 as an efficient oxidant under base free conditions

X = Cl or Br; EWG₁, EWG₂ = electron withdrow group, one-pot reaction, 29 examples, yields from moderate to high, gram scale-up potential confirmed.

Practical aqueous reactions leading to skeletally diverse carbohydrate-derived ketones

The reactions starting from aldosyl hemiacetals and methyl ketones catalyzed by cheap catalysts and mediated by water producing four types of ketones are reported.

Stable analogues of nojirimycin – synthesis and biological evaluation of nojiristegine and manno-nojiristegine

Two novel iminosugars called nojiristegines, being structural hybrids between nor-tropane alkaloid calystegine and nojirimycins, have been synthesised and the hemiaminal functionality found to be stable.

Diazaspiro-iminosugars and polyhydroxylated spiro-bislactams: synthesis, glycosidase inhibition and molecular docking studies

Synthesis of a new class of iminosugars 1–4 has been reported.

Enantioselective synthesis of polyhydroxyindolizidinone and quinolizidinone derivatives from a common precursor

A concise asymmetric synthetic route to two new tetrahydroxyindolizidinone and quinolizidinone derivatives has been developed from a common intermediate which featured a highly selective dihydroxylation reaction and a RCM reaction as key steps.

A highly efficient catalyst for selective oxidative scission of olefins to aldehydes: abnormal-NHC-Ru(II) complex in oxidation chemistry

The utility and selectivity of the catalyst [Ru(COD)(L(1))Br2] (1) bearing a fused π-conjugated imidazo[1,2-a][1,8]naphthyridine-based abnormal N-heterocyclic carbene ligand L(1) is demonstrated toward selective oxidation of C═C bonds to aldehydes and C≡C bonds to α-diketones in an EtOAc/CH3CN/H2O solvent mixture at room temperature using a wide range of substrates, including highly functionalized sugar- and amino acid-derived compounds.

Synthesis of Novel Indolizine, Pyrrolo[1,2-A] Quinoline, and 4,5-Dihydrothiophene Derivatives Via Nitrogen Ylides and their Antimicrobial Evaluation

Treatment of 2-(2-bromoacetyl)-3 H-benzo[ f]chromen-3-one with pyridine, quinoline, and 2-methylquinoline afforded the corresponding pyridinium, quinolinium and 2-methylquinolinium bromides. The latter salts underwent [3 + 2] 1,3-dipolar cycloaddition with some electron deficient acetylene and ethylene derivatives to give the corresponding indolizine and pyrrolo[1,2- a]quinoline derivatives. Moreover, 2-(2-bromoacetyl)-3 H-benzo[ f]chromen-3-one reacted with arylidene cyanothioacetamides to afford the corresponding 2-amino-4,5-dihydrothiophene-3-carbonitriles. The synthesised compounds were characterised based on their elemental analysis and spectral data. Antimicrobial activity of some of the synthesised compounds was evaluated.

3-Hydroxypyrrolidine and (3,4)-dihydroxypyrrolidine derivatives: inhibition of rat intestinal α-glucosidase

Thirteen pyrrolidine-based iminosugar derivatives have been synthesized and evaluated for inhibition of α-glucosidase from rat intestine. The compounds studied were the non-hydroxy, mono-hydroxy and dihydroxypyrrolidines. All the compounds were N-benzylated apart from one. Four of the compounds had a carbonyl group in the 2,5-position of the pyrrolidine ring. The most promising iminosugar was the trans-3,4-dihydroxypyrrolidine 5 giving an IC50 of 2.97±0.046 and a KI of 1.18 mM. Kinetic studies showed that the inhibition was of the mixed type, but predominantly competitive for all the compounds tested. Toxicological assay results showed that the compounds have low toxicity. Docking studies showed that all the compounds occupy the same region as the DNJ inhibitor on the enzyme binding site with the most active compounds establishing similar interactions with key residues. Our studies suggest that a rotation of ∼90° of some compounds inside the binding pocket is responsible for the complete loss of inhibitory activity. Despite the fact that activity was found only in the mM range, these compounds have served as simple molecular tools for probing the structural features of the enzyme, so that inhibition can be improved in further studies.

Development of α-glucosidase inhibitors by room temperature C-C cross couplings of quinazolinones

Novel quinazolinone based α-glucosidase inhibitors have been developed. For this purpose a virtual screening model has been generated and validated utilizing acarbose as a α-glucosidase inhibitor. Homology modeling, docking, and virtual screening were successfully employed to discover a set of structurally diverse compounds active against α-glucosidase. A search of a 3D database containing 22,500 small molecules using the structure based virtual model yielded ten possible candidates. All ten candidates were N-3-pyridyl-2-cyclopropyl quinazolinone-4-one derivatives, varying at the 6 position. This position was modified by Suzuki-Miyaura cross coupling with aryl, heteroaryl, and alkyl boronic acids. A catalyst screen was performed, and using the best optimal conditions, a series of twenty five compounds was synthesized. Notably, the C-C cross coupling reactions of the 6-bromo-2-cyclopropyl-3-(pyridyl-3-ylmethyl)quinazolin-4(3H)-one precursor have been accomplished at room temperature. A comparison of the relative reactivities of 6-bromo and 6-chloro-2,3-disubstituted quinazolinones with phenyl boronic acid was conducted. An investigation of pre-catalyst loading for the reaction of the 6-bromo-2-cyclopropyl-3-(pyridyl-3-ylmethyl)quinazolin-4(3H)-one substrate was also carried out. Finally, we submitted our compounds to biological assays against α-glucosidase inhibitors. Of these, three hits (compounds 4a, 4t and 4r) were potentially active as α-glucosidase inhibitors and showed activity with IC50 values <20 μM. Based on structural novelty and desirable drug-like properties, 4a was selected for structure-activity relationship study, and thirteen analogs were synthesized. Nine out of thirteen analogs acted as α-glucosidase inhibitors with IC50 values <10 μM. These lead compounds have desirable physicochemical properties and are excellent candidates for further optimization.

Molecular dynamic simulations reveal the mechanism of binding between xanthine inhibitors and DPP-4

We apply molecular docking, molecular dynamics (MD) simulation, and binding free energy calculation to investigate and reveal the binding mechanism between five xanthine inhibitors and DPP-4. The electrostatic and van der Waals interactions of the five inhibitors with DPP-4 are analyzed and discussed. The computed binding free energies using MM-PBSA method are in qualitatively agreement with experimental inhibitory potency of five inhibitors. The hydrogen bonds of inhibitors with Ser630 and Asp663 can stabilize the inhibitors in binding sites. The van der Waals interactions, especially the key contacts with His740, Asn710, Trp629, and Tyr666 have larger contributions to the binding free energy and play important roles in distinguishing the variant bioactivity of five inhibitors.

Cyclodidepsipeptides with a promising scaffold in medicinal chemistry

Among the large family of cyclodepsipeptides, the simplest members are the cyclodidepsipeptides which have an ester group and an amide group in the same six-membered ring. To point out the pharmacological potential of this class of compounds, the present article reviews structure, isolation, synthesis and biological properties of the known cyclodidepsipeptides. Synthesis of cyclodidepsipeptides is achieved by two general approaches--by initial formation of the amide bond, or initial formation of the ester bond; and subsequent intermolecular cyclization to cyclodidepsipeptide structure. It is closely related to the condensation and ring-closure strategies applied in the preparation of the larger members of the cyclodepsipeptide family. However, due to synthesis of the smaller heretocycles it allows for the use of more versatile building blocks. There are data on antimicrobial, antioxidant and immunomodulatory activities of cyclodidepsipeptides as well as their inhibitory activities toward α-glucosidase, acyl-CoA:cholesterol acyltransferase, xanthine oxidase and platelet aggregation. Because we have recently found that two 6-(propan-2-yl)-4-methyl-morpholine-2,5-diones, as novel non-purine xanthine oxidase inhibitors, may give promise to be used in the treatment of gout, in this review we have included a study of molecular interactions of the selected cyclodidepsipeptides with xanthine oxidase using idTarget web server. Cyclodidepsipeptides showed promising pharmacological activities and meet all criteria for good solubility and permeability. However, further research of their medical application is necessary. In addition to this, the diversity of natural cyclodidepsipeptides, simplicity for synthesis and convenience for rational drug design indicate the cyclodidepsipeptide as promising scaffold in medicinal chemistry.

Iminosugar-based glycopolypeptides: glycosidase inhibition with bioinspired glycoprotein analogue micellar self-assemblies

Glycosidase inhibition with bioinspired glycoprotein analogue micellar self-assemblies.

Stereoselectively fluorinated N-heterocycles: a brief survey

The stereoselective incorporation of fluorine atoms into N-heterocycles can lead to dramatic changes in the molecules’ physical and chemical properties. These changes can be rationally exploited for the benefit of diverse fields such as medicinal chemistry and organocatalysis. This brief review will examine some of the effects that fluorine substitution can have in N-heterocycles, including changes to the molecules’ stability, their conformational behaviour, their hydrogen bonding ability, and their basicity. Finally, some methods for the synthesis of stereoselectively fluorinated N-heterocycles will also be reviewed.