Polyhydroxylated alkaloids -- natural occurrence and therapeutic applications

Polyhydroxylated Quinolizidine Iminosugars as Nanomolar Selective Inhibitors of α-Glucosidases

Polyhydroxylated quinolizidines bearing a hydroxymethyl group at the ring junction were synthesized from a readily available l-sorbose-derived ketonitrone. Evaluated as glycoside hydrolase inhibitors, these quinolizidines revealed to be potent and selective α-glucosidase inhibitors. Quinolizidine 9a is the first quinolizidine-scaffolded iminosugar exhibiting nanomolar inhibition of a glycoenzyme.

Diastereoselective [3 + 2] vs [4 + 2] Cycloadditions of Nitroprolinates with α,β-Unsaturated Aldehydes and Electrophilic Alkenes: An Example of Total Periselectivity

Diastereoselective multicomponent reactions of enantioenriched 4-nitroprolinates, obtained by enantiocatalyzed 1,3-dipolar cycloaddition (1,3-DC) of imino esters and nitroalkenes, with α,β-unsaturated aldehydes and electrophilic alkenes proceed with total periselectivity depending on the structure of the aldehyde employed. This process evolves through a [3 + 2] 1,3-DC when cinnamaldehyde is used in the presence of an azomethine ylide, giving the corresponding highly substituted pyrrolizidines with endo selectivity. However, in the case of the α,β-unsaturated aldehyde, which contains a hydrogen atom at the γ position, an amine-aldehyde-dienophile (AAD) [4 + 2] cycloaddition takes place by formation of an intermediate 1-amino-1,3-diene, affording highly functionalized cyclohexenes with high endo diastereoselectivity. This AAD process only occurred when a nitro group is bonded to the 4-position of the initial enantiomerically enriched pyrrolidine ring. DFT calculations have been carried out with the aim of explaining this different behavior between pyrrolidines with or without a nitro group, demonstrating the strong nitro-group-dependent periselectivity. The results of these computational studies also support the experimentally obtained absolute configuration of the final adducts.

Fate of d-Fagomine after Oral Administration to Rats

d-Fagomine is an iminosugar found in buckwheat that is capable of inhibiting the adhesion of potentially pathogenic bacteria to epithelial mucosa and reducing the postprandial blood glucose concentration. This paper evaluates the excretion and metabolism of orally administered d-fagomine in rats and compares outcomes with the fate of 1-deoxynojirimycin. d-Fagomine and 1-deoxynojirimycin show similar absorption and excretion kinetics. d-Fagomine is partly absorbed (41-84%, dose of 2 mg/kg of body weight) and excreted in urine within 8 h, while the non-absorbed fraction is cleared in feces within 24 h. d-Fagomine is partially methylated (about 10% in urine and 3% in feces). The concentration of d-fagomine in urine from 1 to 6 h after administration is higher than 10 mg/L, the concentration that inhibits adhesion of Escherichia coli. Orally administered d-fagomine is partially absorbed and then rapidly excreted in urine, where it reaches a concentration that may be protective against urinary tract infections.

Palladium-Catalyzed Double Allylation of Sugar-Imines by Employing Tamaru-Kimura's Protocol: Access to Unnatural Iminosugars

Conversion of vinyl pyranosylamine and vinyl furanosylamines to 2,6- and 2,5-disubstituted pyrrolidine and piperidine iminosugars, respectively, in one pot was developed using Kimura and Tamaru's procedure, where a Pd salt in the presence of Et₂Zn was used for the domino reaction. In this procedure, double allylation, which involves nucleophilic allylation-heterocyclization, took place to give desired nitrogen heterocycles. This strategy was further elaborated to synthesize some unnatural deoxycalystegines, hydroxylated pyrrolidines, piperidines, and indolizidine analogues.

Enantioselective synthesis of an octahydroindolizine (indolizidine) alcohol using an enzymatic resolution

A homo-chiral synthesis of (7R,8aS)-octahydro-5,5-dimethylindolizin-7-amine 8 and (7S,8aS)-octahydro-5,5-dimethylindolizin-7-ol 9, amine building blocks which have found applications within the pharmaceutical industry, is presented.

Pharmacological effects of the phytochemicals of Anethum sowa L. root extracts

BACKGROUND

Anethum sowa L. is widely used as an important spice and traditional medicinal plants to treat various ailments. On the basis of scientific ethnobotanical information, this study was undertaken to evaluate the antioxidant, antimicrobial and cytotoxic activity of the crude extracts of Anethum sowa L. roots as well as to identify the classes of phytochemicals by chemical tests.

METHODS

The antioxidant potential of the extracts was ascertained with the stable organic free radical (2, 2-diphenyl-1-picryl-hydrazyl). The agar well diffusion method was used to determine the susceptibility of bacterial and fungal strains of the crude extracts. The minimum inhibitory concentration (MIC) and minimum bactericidal concentrations (MBC) were determined by the microdilution test. Cytotoxic activities were screened using brine shrimps (Artemia salina) lethality assay. Finally, phytochemicals were profiled using standard procedures.

RESULTS

A preliminary phytochemical screening of the different crude extracts by methanol, ethyl acetate and chloroform showed the presence of secondary metabolites such as flavonoids, alkaloids, saponin, cardiac glycosides and tannins while cyanogenetic glycosides were not detected. The methanol, ethyl acetate and chloroform extracts displayed high antioxidant activity (IC50 = 13.08 ± 0.03, 33.48 ± 0.16 and 36.42 ± 0.41 μg/mL, respectively) in the DPPH assay comparable to that of the standard ascorbic acid and BHT (IC50 = 3.74 ± 0.05 and 11.84 ± 0.29 μg/mL). The cytotoxic activity of the crude ethyl acetate and chloroform extracts possessed excellent activity (LC50 = 5.03 ± 0.08, 5.23 ± 0.11 and 17.22 ± 0.14 μg/mL, respectively) against brine shrimp larvae after 24 h of treatment and compared with standard vincristine sulphate (LC50 = 0.46 ± 0.05 μg/mL). The extracts also showed good antimicrobial activity against both Gram-positive and Gram-negative bacteria when compared with two standard antibiotics ciprofloxacin and tetracycline.

CONCLUSION

These results showed that the Anethum sowa root extracts are the important source of the antioxidant, antimicrobial and cytotoxic agent. So, further research is necessary to isolate and characterize of different phytoconstituents for pharmaceutical drug lead molecules and also to verify its traditional uses.

Six-Step Syntheses of (-)-1-Deoxyaltronojirimycin and (+)-1-Deoxymannonojirimycin from N-Z-O-TBDPS-l-serinal

Highly stereoselective six-step syntheses of (-)-1-deoxyaltronojirimycin (altro-DNJ) and (+)-1-deoxymannojirimycin (manno-DNJ) from N-Cbz-O-TBDPS-l-serinal are described. Key transformations involve a two-step preparation of a functionalized dihydropyridin-3-one as a common intermediate followed by Luche reduction and dihydroxylation (for altro-DNJ). The same sequence employing an epoxidation/epoxide opening in place of dihydroxylation furnishes manno-DNJ.

Identification of Novel Human Breast Carcinoma (MDA-MB-231) Cell Growth Modulators from a Carbohydrate-Based Diversity Oriented Synthesis Library

The application of a cell-based growth inhibition on a library of skeletally different glycomimetics allowed for the selection of a hexahydro-2H-furo[3,2-b][1,4]oxazine compound as candidate inhibitors of MDA-MB-231 cell growth. Subsequent synthesis of analogue compounds and preliminary biological studies validated the selection of a valuable hit compound with a novel polyhydroxylated structure for the modulation of the breast carcinoma cell cycle mechanism.

Carbohydrate-Processing Enzymes of the Lysosome: Diseases Caused by Misfolded Mutants and Sugar Mimetics as Correcting Pharmacological Chaperones

Lysosomal storage diseases are hereditary disorders caused by mutations on genes encoding for one of the more than fifty lysosomal enzymes involved in the highly ordered degradation cascades of glycans, glycoconjugates, and other complex biomolecules in the lysosome. Several of these metabolic disorders are associated with the absence or the lack of activity of carbohydrate-processing enzymes in this cell compartment. In a recently introduced therapy concept, for susceptible mutants, small substrate-related molecules (so-called pharmacological chaperones), such as reversible inhibitors of these enzymes, may serve as templates for the correct folding and transport of the respective protein mutant, thus improving its concentration and, consequently, its enzymatic activity in the lysosome. Carbohydrate-processing enzymes in the lysosome, related lysosomal diseases, and the scope and limitations of reported reversible inhibitors as pharmacological chaperones are discussed with a view to possibly extending and improving research efforts in this area of orphan diseases.

The Genome of Undifilum oxytropis Provides Insights into Swainsonine Biosynthesis and Locoism

Undifilum oxytropis is a fungal endophyte of locoweeds. It produces swainsonine, which is the principal toxic ingredient of locoweeds. However, the genes, pathways and mechanisms of swainsonine biosynthesis are not known. In this study, the genome of U. oxytropis was firstly sequenced and assembled into a 70.05 megabases (Mb) draft genome, which encoded 11,057 protein-coding genes, and 54% of them were similar to current publicly available sequences. U. oxytropis genes were annotated and 164 putative genes were annotated into enzymes, such as Saccharopine dehydrogenase, Saccharopine oxidase, and Pyrroline-5-carboxylate reductase, hypothesized to be involved in the biosynthesis pathway of swainsonine. The genome sequence and gene annotation of U. oxytropis will provide new insights into functional analyses. The characterization of genes in swainsonine biosynthesis will greatly facilitate locoweed poisoning research and help direct locoism management.

Evaluation of antidiabetic effect of total calystegines extracted from Hyoscyamus albus

BACKGROUND

Hyoscyamus albus L. (Solanaceae) an old medicinal plant is a rich source of tropane and nortropane alkaloids which confers to this plant a number of very interesting and beneficial therapeutic effects.

PURPOSE

Calystegines that are polyhydroxylated alkaloids and imino-sugars poccess significant glycosidases inhibitory activities and are therefore good candidats for the treatment of diabetes mellitus.

STUDY DESIGN

Calystegines extracted from Hyoscyamys albus seeds were tested for teir acute oral toxicity and investigated for their in-vivo antidiabetic effect on Streptozotocine induced diabetes in mice.

METHODES

Calystegines were extracted from the seeds plant using an Ion exchange column; the remaining extract was then administrated orally to mice at several single doses for acute toxicity assay. A dose of 130mg/kg streptozotocine was injected to mice to induce diabetes mellitus, and diabetic mice were treated orally during 20days with 10mg/kg and 20mg/kg calystegines and 20mg/kg glibenclamide as the reference drug.

RESULTS

Acute oral toxicity showed that calystegines are not toxic up to a dose of 2000mg/kg with absence of any signs of intoxication and damages in Liver and kidney tissues. The nortropane alkaloids markedly reduced blood glucose levels and lipid parameters of diabetic mice to normal concentrations after 20days of treatment at 10mg/kg and 20mg/kg (p<0.05). Histopathological study of diabetic mice pancreas indicated that calystegines of Hyoscyamus albus have minimized streptozotocine damages on β-cells of islets of langerhans, stimulated β-cells regeneration and improved with this insulin secretion.

CONCLUSION

The findings of this study suggest that calystegines are potent antidiabetic agents with antihyperglicemic and hypolipidemic effects, and a protective fonction on pancreas in streptozotocin induced diabetes in mice.

Blackpatch of Clover, Cause of Slobbers Syndrome: A Review of the Disease and the Pathogen, Rhizoctonia leguminicola

Rhizoctonia leguminicola Gough and Elliott is a widely used name for the causal agent of blackpatch disease of red clover (Trifolium pratense L.). This fungal pathogen produces alkaloids (slaframine and swainsonine) that affect grazing mammals. Slaframine causes livestock to salivate profusely, and swainsonine causes neurological problems. Although the blackpatch fungus was classified as a Rhizoctonia species (phylum Basidiomycota), morphological studies have indicated that it is in the phylum Ascomycota, and sequencing data have indicated that it may be a new genus of ascomycete. The effects of the alkaloids on grazing mammals and their biosynthetic pathways have been extensively studied. In contrast, few studies have been done on management of the disease, which requires a greater understanding of the pathogen. Methods of disease management have included seed treatments and fungicides, but these have not been investigated since the 1950s. Searches for resistant cultivars have been limited. This review summarizes the biological effects and biosynthetic precursors of slaframine and swainsonine. Emphasis is placed on current knowledge about the epidemiology of blackpatch disease and the ecology and taxonomy of the pathogen. Possibilities for future research and disease management efforts are suggested.

(±)-Homocrepidine A, a Pair of Anti-inflammatory Enantiomeric Octahydroindolizine Alkaloid Dimers from Dendrobium crepidatum

A pair of racemic indolizidine enantiomers, (±)-homocrepidine A (1), and a piperidine derivative, homocrepidine B (2), were isolated from Dendrobium crepidatum along with the known alkaloid crepidine (3). The racemic mixture of 1 was separated into a pair of enantiomers, (+)-1 and (-)-1, by HPLC using a chiral chromatographic substrate, which represents the first successful example of resolving indolizidine racemic mixtures. The absolute configurations of (+)-1 and (-)-1 were assigned from single-crystal X-ray diffraction data. The evaluation of anti-inflammatory activity with LPS-induced RAW 264.7 macrophages revealed that (+)-1 strongly inhibited the production of nitric oxide (IC50, 3.6 μM) and significantly decreased the expression of inducible nitric oxide synthase, while (-)-1 and (±)-1 only had moderate inhibitory effects (IC50, 22.8 and 14.7 μM). Compound 2 showed moderate anti-inflammatory activity (IC50, 27.6 μM).

One-Pot Synthesis of Substituted Piperidinones and 3,4-Dihydropyrimidinones Using a Highly Active and Recyclable Supported Ionic Liquid Phase Organocatalyst

1-Ethyl-3-methylimidazolium ethyl sulfate was synthesized and its supported ionic liquid phase form was prepared and used as an organocatalyst for the synthesis of substituted piperidinones and 3,4-dihydropyrimidinones. The ionic liquid was characterized by 1H NMR, 13C NMR, and mass spectrometry. The catalyst is novel, stable, completely heterogeneous, and recyclable for several times and can be easily recovered by filtration. It was characterized with scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and energy-dispersive X-ray spectroscopy techniques. The workup procedures are very simple, and products were obtained in good-to-excellent yields with reasonable purities without the need for further chromatographic purification.

Gem-difluoromethylated and trifluoromethylated derivatives of DMDP-related iminosugars: synthesis and glycosidase inhibition

Gem-difluoromethylated and trifluoromethylated derivatives of DMDP-related iminosugars have been synthesized from cyclic nitrones and assayed against various glycosidases.

Synthesis, spectroscopic (FT-IR, FT-Raman, UV and NMR) and computational studies on 3t-pentyl-2r,6c-diphenylpiperidin-4-one semicarbazone

The structural and spectroscopic studies of 3t-pentyl-2r,6c-diphenylpiperidin-4-one semicarbazone (PDPOSC) were made by adopting B3LYP/HF levels theory using 6-311++G(d,p) basis set. The FT-IR and Raman spectra were recorded in solid phase, the fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. DFT method indicates that B3LYP is superior to HF method for molecular vibrational analysis. UV-vis spectrum of the compound was recorded in different solvents in the region of 200-800 nm and the electronic properties such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies were evaluated by time-dependent DFT (TD-DFT) approach. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The hyperconjugative interaction energy (E((2))) and electron densities of donor (i) and acceptor (j) bonds were calculated using NBO analysis. In addition, MEP and atomic charges of carbon, nitrogen and oxygen were calculated using B3LYP/6-311++G(d,p) level theory. Moreover, thermodynamic properties of the title compound were calculated by B3LYP/HF, levels using 6-311++G(d,p) basis set. The (1)H and (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results.

Re-exploring promising α-glucosidase inhibitors for potential development into oral anti-diabetic drugs: Finding needle in the haystack

Treatment of diabetes mellitus by oral α-glucosidase inhibitors is currently confined to acarbose, miglitol and voglibose marred by efficacy problems and unwanted side effects. Since the discovery of the drugs more than three decades ago, no significant progress has been made in the drug development area of anti-diabetic α-glucosidase inhibitors. Despite existence of a wide chemical diversity of α-glucosidase inhibitors identified to date, majority of them are simply piled up in publications and reports thus creating a haystack destined to be forgotten in the scientific literature without given consideration for further development into drugs. This review finds those "needles" in that haystack and lays groundwork for highlighting promising α-glucosidase inhibitors from the literature that may potentially become suitable candidates for pre-clinical or clinical trials while drawing attention of the drug development community to consider and take already-identified promising α-glucosidase inhibitors into the next stage of drug development.

Monomethyl ethers of 4,5-dihydroxypipecolic acid from Petaladenium urceoliferum: Enigmatic chemistry of an enigmatic legume

Leaves of Petaladenium (Leguminosae), an Amazonian monospecific genus recently revealed as a member of the Amburaneae clade among the earliest-diverging papilionoid legumes, were found to accumulate three monomethyl ethers of 4,5-dihydroxypipecolic acids. These were characterised by spectroscopic means as the (2S,4S,5R) and (2S,4R,5S) epimers of 5-hydroxy-4-methoxypipecolic acid and (2S,4R,5R)-4-hydroxy-5-methoxypipecolic acid. These compounds were not detected in any other genera in the Amburaneae clade or the wider Angylocalyceae-Dipterygeae-Amburaneae (ADA) clade of papilionoid legumes. Hydroxypipecolic acids, however, were detected in leaves of Myrocarpus and Myroxylon (sister genera in the Amburaneae clade), Angylocalyx and Xanthocercis (sister genera in the Angylocalyceae clade) and Monopteryx (Dipterygeae clade), and were also present in Petaladenium. Iminosugars, known to be accumulated by all four genera in the Angylocalyceae clade (Alexa, Angylocalyx, Castanospermum and Xanthocercis), were found to be characteristic of this group within the ADA clade.