Functionalized Pyrrolidines Inhibit α-Mannosidase Activity and Growth of Human Glioblastoma and Melanoma Cells

Highly stereocontrolled total synthesis of racemic codonopsinol B through isoxazolidine-4,5-diol vinylation

A new highly diastereoselective synthesis of the polyhydroxylated pyrrolidine alkaloid (±)-codonopsinol B and its N-nor-methyl analogue, starting from achiral materials, is presented. The strategy relies on the trans-stereoselective epoxidation of 2,3-dihydroisoxazole with in situ-generated DMDO, the syn-selective α-chelation-controlled addition of vinyl-MgBr/CeCl3 to the isoxazolidine-4,5-diol intermediate, and the substrate-directed epoxidation of the terminal double bond of the corresponding γ-amino-α,β-diol with aqueous hydrogen peroxide catalyzed by phosphotungstic heteropoly acid. Each of the key reactions proceeded with an excellent diastereoselectivity (dr > 95:5). (±)-Codonopsinol B was prepared in 10 steps with overall 8.4% yield. The antiproliferative effect of (±)-codonopsinol B and its N-nor-methyl analogue was evaluated using several cell line models.

Targeting cancer via Golgi α-mannosidase II inhibition: How far have we come in developing effective inhibitors?

Dysregulation of glycosylation pathways has been well documented in several types of cancer, where it often participates in cancer development and progression, especially cancer metastasis. Hence, inhibition of glycosidases such as mannosidases can disrupt the biosynthesis of glycans on cell surface glycoproteins and modify their role in carcinogenesis and metastasis. Several reviews have delineated the role of N-glycosylation in cancer, but the data regarding effective inhibitors remains sparse. Golgi α-mannosidase has been an attractive therapeutic target for preventing the formation of ß1,6-branched complex type N-glycans. However, due to its high structural similarity to the broadly specific lysosomal α-mannosidase, undesired co-inhibition occurs and this leads to serious side effects that complicates its potential role as a therapeutic agent. Even though extensive efforts have been geared towards the discovery of effective inhibitors, no breakthrough has been achieved thus far which could allow for their use in clinical settings. Improving the specificity of current inhibitors towards Golgi α-mannosidase is requisite in progressing this class of compounds in cancer chemotherapy. In this review, we highlight a few potent and selective inhibitors discovered up to the present to guide researchers for rational design of further effective inhibitors to overcome the issue of specificity.

Visible-Light-Induced Intermolecular Oxyimination of Alkenes

An intermolecular vicinal O-N difunctionalization reaction of olefins with oxime esters through energy transfer catalysis has been developed.

Selective Golgi α-mannosidase II inhibitors: N-alkyl substituted pyrrolidines with a basic functional group

Enzymatic assays, molecular modeling and NMR studies of novel 1,4-dideoxy-1,4-imino-l-lyxitols provided new information on the GH38 family enzyme inhibitors and their selectivity.

Nitro-Substituted Benzaldehydes in the Generation of Azomethine Ylides and Retro-1,3-Dipolar Cycloadditions

1,3-Dipolar cycloaddition of 2- and 3-nitrobenzaldehydes with 2-aminomethylpyridine and ethyl (2E)-2-cyano-3-(4-nitrophenyl)prop-2-enoate yielded endo-cycloadducts as the sole products under various reaction conditions. Fortuitously, 4-nitrobenzaldehyde behaved differently in three- and four-component cascades to produce a mixture of endo- and exo'-cycloadducts. This reaction is solvent- and temperature-dependent, and consequently, both the endo- and exo'-cycloadducts were synthesized in an excellent regio-, stereo-, and chemoselective fashion. Retro-1,3-dipolar cycloadditions of the endo-cycloadducts were conducted under mild reaction conditions, and the generated syn-dipoles were stereomutated into anti-dipoles which recycloadded with the dipolarophiles to provide the exo'-cycloadducts. Mechanistic studies were carried out to support the proposed mechanisms. Unprecedentedly, particular arylidene scaffolds participated as aldehyde or activated methylene precursors. Density functional theory calculations were performed to shed light on the importance of AcOH in the generation and isomerization of dipoles and to explain the high selectivity and the possibility of retro-cycloaddition.

New total synthesis and structure confirmation of putative (+)-hyacinthacine C3 and (+)-5-epi-hyacinthacine C3

A unique synthesis of polyhydroxylated pyrrolizidine alkaloids, namely (+)-hyacinthacine C₃ and (+)-5-epi-hyacinthacine C₃ is presented. The strategy relies on a 1,3-dipolar cycloaddition of an l-mannose derived nitrone, which owing to its great syn-stereoselectivity builds up the majority of the required stereocenters. The following key steps include Wittig olefination and iodine-mediated aminocyclisation, that provide two epimeric pyrrolizidines with the appropriate configuration. As a result, structure and steric arrangement of the first synthetically prepared (+)-hyacinthacine C₃ are proved to be correct, clearly confirming the inconsistency with the stereochemistry assigned to the natural sample. With respect to the previously proven glycosidase inhibitory activities, the antiproliferative effect of (+)-hyacinthacine C₃ and (+)-5-epi-hyacinthacine C₃ was evaluated using several cell line models.

A second total synthesis of (+)-hyacinthacine C₃ is reported. As a result, structure of the first synthetically prepared alkaloid is proved to be correct, clearly confirming the inconsistency with the stereochemistry assigned to the natural sample.

A class of low-cost alternatives to kifunensine for increasing high mannose N-linked glycosylation for monoclonal antibody production in Chinese hamster ovary cells

N-linked glycosylation of therapeutic monoclonal antibodies is an important product quality attribute for drug safety and efficacy. An increase in the percent of high mannose N-linked glycosylation may be required for drug efficacy or to match the glycosylation profile of the innovator drug during the development of a biosimilar. In this study, the addition of several chemical additives to a cell culture process resulted in high mannose N-glycans on monoclonal antibodies produced by Chinese hamster ovary (CHO) cells without impacting cell culture performance. The additives, which include known mannosidase inhibitors (kifunensine and deoxymannojirimycin) as well as novel inhibitors (tris, bis-tris, and 1-amino-1-methyl-1,3-propanediol), contain one similar molecular structure: 2-amino-1,3-propanediol, commonly referred to as serinol. The shared chemical structure provides insight into the binding and inhibition of mannosidase in CHO cells. One of the novel inhibitors, tris, is safer compared to kifunensine, 35x as cost-effective, and stable at room temperature. In addition, tris and bis-tris provide multiple low-cost alternatives to kifunensine for manipulating glycosylation in monoclonal antibody production in a cell culture process with minimal impact to productivity or cell health.

N-Nonyloxypentyl-l-Deoxynojirimycin Inhibits Growth, Biofilm Formation and Virulence Factors Expression of Staphylococcus aureus

Staphylococcus aureus is one of the major causes of hospital- and community-associated bacterial infections throughout the world, which are difficult to treat due to the rising number of drug-resistant strains. New molecules displaying potent activity against this bacterium are urgently needed. In this study, d- and l-deoxynojirimycin (DNJ) and a small library of their N-alkyl derivatives were screened against S. aureus ATCC 29213, with the aim to identify novel candidates with inhibitory potential. Among them, N-nonyloxypentyl-l-DNJ (l-NPDNJ) proved to be the most active compound against S. aureus ATCC 29213 and its clinical isolates, with the minimum inhibitory concentration (MIC) value of 128 μg/mL. l-NPDNJ also displayed an additive effect with gentamicin and oxacillin against the gentamicin- and methicillin-resistant S. aureus isolate 00717. Sub-MIC values of l-NPDNJ affected S. aureus biofilm development in a dose-dependent manner, inducing a strong reduction in biofilm biomass. Moreover, real-time reverse transcriptase PCR analysis revealed that l-NPDNJ effectively inhibited at sub-MIC values the transcription of the spa, hla, hlb and sea virulence genes, as well as the agrA and saeR response regulator genes.

Developments in Carbohydrate-Based Cancer Therapeutics

Cancer cells of diverse origins express extracellular tumor-specific carbohydrate antigens (TACAs) because of aberrant glycosylation. Overexpressed TACAs on the surface of tumor cells are considered biomarkers for cancer detection and have always been prioritized for the development of novel carbohydrate-based anti-cancer vaccines. In recent years, progress has been made in developing synthetic, carbohydrate-based antitumor vaccines to improve immune responses associated with targeting these specific antigens. Tumor cells also exhaust more energy for proliferation than normal cells, by consuming excessive amounts of glucose via overexpressed sugar binding or transporting receptors located in the cellular membrane. Furthermore, inspired by the Warburg effect, glycoconjugation strategies of anticancer drugs have gained considerable attention from the scientific community. This review highlights a small cohort of recent efforts which have been made in carbohydrate-based cancer treatments, including vaccine design and the development of glycoconjugate prodrugs, glycosidase inhibiting iminosugars, and early cancer diagnosis.

Exploring the divalent effect in fucosidase inhibition with stereoisomeric pyrrolidine dimers

Multi-valent inhibitors offer promise for the enhancement of therapeutic compounds across a range of chemical and biological processes. Here, a significant increase in enzyme-inhibition potencies was observed with a dimeric iminosugar-templated fucosidase inhibitor (IC50 = 0.108 μM) when compared to its monovalent equivalent (IC50 = 2.0 μM). Such a gain in binding is often attributed to a "multivalent effect" rising from alternative recapture of the scaffolded binding epitopes. The use of control molecules such as the meso analogue (IC50 = 0.365 μM) or the enantiomer (IC50 = 569 μM), as well as structural analysis of the fucosidase-inhibitor complex, allowed a detailed analysis of the possible mechanism of action, at the molecular level. Here, the enhanced binding affinity of the dimer over the monomer can be attributed to additional interactions in non-catalytic sites as also revealed in the 3-D structure of a bacterial fucosidase inhibitor complex.

N-Benzyl Substitution of Polyhydroxypyrrolidines: The Way to Selective Inhibitors of Golgi α-Mannosidase II

Inhibition of the biosynthesis of complex N-glycans in the Golgi apparatus influences progress of tumor growth and metastasis. Golgi α-mannosidase II (GMII) has become a therapeutic target for drugs with anticancer activities. One critical task for successful application of GMII drugs in medical treatments is to decrease their unwanted co-inhibition of lysosomal α-mannosidase (LMan), a weakness of all known potent GMII inhibitors. A series of novel N-substituted polyhydroxypyrrolidines was synthesized and tested with modeled GH38 α-mannosidases from Drosophila melanogaster (GMIIb and LManII). The most potent structures inhibited GMIIb (K_i =50-76 μm, as determined by enzyme assays) with a significant selectivity index of IC₅₀ (LManII)/IC₅₀ (GMIIb) >100. These compounds also showed inhibitory activities in in vitro assays with cancer cell lines (leukemia, IC₅₀ =92-200 μm) and low cytotoxic activities in normal fibroblast cell lines (IC₅₀ >200 μm). In addition, they did not show any significant inhibitory activity toward GH47 Aspergillus saitoiα1,2-mannosidase. An appropriate stereo configuration of hydroxymethyl and benzyl functional groups on the pyrrolidine ring of the inhibitor may lead to an inhibitor with the required selectivity for the active site of a target α-mannosidase.

Using DFT methodology for more reliable predictive models: Design of inhibitors of Golgi α-Mannosidase II

Human Golgi α-mannosidase II (GMII), a zinc ion co-factor dependent glycoside hydrolase (E.C.3.2.1.114), is a pharmaceutical target for the design of inhibitors with anti-cancer activity. The discovery of an effective inhibitor is complicated by the fact that all known potent inhibitors of GMII are involved in unwanted co-inhibition with lysosomal α-mannosidase (LMan, E.C.3.2.1.24), a relative to GMII. Routine empirical QSAR models for both GMII and LMan did not work with a required accuracy. Therefore, we have developed a fast computational protocol to build predictive models combining interaction energy descriptors from an empirical docking scoring function (Glide-Schrödinger), Linear Interaction Energy (LIE) method, and quantum mechanical density functional theory (QM-DFT) calculations. The QSAR models were built and validated with a library of structurally diverse GMII and LMan inhibitors and non-active compounds. A critical role of QM-DFT descriptors for the more accurate prediction abilities of the models is demonstrated. The predictive ability of the models was significantly improved when going from the empirical docking scoring function to mixed empirical-QM-DFT QSAR models (Q(2)=0.78-0.86 when cross-validation procedures were carried out; and R(2)=0.81-0.83 for a testing set). The average error for the predicted ΔGbind decreased to 0.8-1.1kcalmol(-1). Also, 76-80% of non-active compounds were successfully filtered out from GMII and LMan inhibitors. The QSAR models with the fragmented QM-DFT descriptors may find a useful application in structure-based drug design where pure empirical and force field methods reached their limits and where quantum mechanics effects are critical for ligand-receptor interactions. The optimized models will apply in lead optimization processes for GMII drug developments.

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.

Amino-functionalized iminocyclitols: synthetic glycomimetics of medicinal interest

A review on the syntheses and biological activities of unnatural glycomimetics highlighting the effect of replacement of hydroxyl groups of natural iminosugars by amino functionalities is presented.

Cell cycle arrest, apoptosis and autophagy induced by iminosugars on K562 cells

Iminosugars have gained a remarkable importance as new therapeutic agents since 1966. In this study, compounds A and B, two iminosugar analogs synthesized previously, showed an inhibition of the growth of K562 cells. They allowed cell cycle arrested at the G0/G1 phase, promoted apoptotic activities and also lowered the mitochondrial membrane potential. Further exploration of the apoptosis mechanism revealed that compound B significantly suppressed the expression of Hsp70, which is a major anti-apoptotic molecular chaperone. Significant decrease was also found in the expression of Akt, a serine/threonine-specific protein kinase with anti-apoptosis activities also known as protein kinase B (PKB). At mitochondria level in comparison with compound A, compound B brought a better promotion in the expression of pro-apoptotic protein Bad in Bcl-2 family. As a result of the promotion, the expression of anti-apoptotic protein Bcl-xL was down-regulated. Cytochrome c was released, activating the intrinsic signaling pathways of caspase and resulting in the occurrence of cascade reaction. In addition, compound B stimulated autophagy effectively by up-regulating Beclin 1, thus causing the conversion of LC3-I to LC3-II through Akt/mTOR signaling pathway. In summary, these results indicated that compounds A and B induced cell death through multiple pathways. The disclosed results not only provide an evidence of antitumor activity of iminosugars as a foundation for further studies, but also may find potential applications in chronic myeloid leukemia therapy as new heat shock protein inhibitors and autophagy inducer.

Jack bean α-mannosidase: amino acid sequencing and N-glycosylation analysis of a valuable glycomics tool

Jack bean (Canavalia ensiformis) seeds contain several biologically important proteins among which α-mannosidase (EC 3.2.1.24) has been purified, its biochemical properties studied and widely used in glycan analysis. In the present study, we have used the purified enzyme and derived its amino acid sequence covering both the known subunits (molecular mass of ∼66,000 and ∼44,000 Da) hitherto not known in its entirety. Peptide de novo sequencing and structural elucidation of N-glycopeptides obtained either directly from proteolytic digestion or after zwitterionic hydrophilic interaction liquid chromatography solid phase extraction-based separation were performed by use of nanoelectrospray ionization quadrupole time-of-flight mass spectrometry and low-energy collision-induced dissociation experiments. De novo sequencing provided new insights into the disulfide linkage organization, intersection of subunits and complete N-glycan structures along with site specificities. The primary sequence suggests that the enzyme belongs to glycosyl hydrolase family 38 and the N-glycan sequence analysis revealed high-mannose oligosaccharides, which were found to be heterogeneous with varying number of hexoses viz, Man8-9GlcNAc2 and Glc1Man9GlcNAc2 in an evolutionarily conserved N-glycosylation site. This site with two proximal cysteines is present in all the acidic α-mannosidases reported so far in eukaryotes. Further, a truncated paucimannose type was identified to be lacking terminal two mannose, Man1(Xyl)GlcNAc2 (Fuc).

The human secretome atlas initiative: implications in health and disease conditions

Proteomic analysis of human body fluids is highly challenging, therefore many researchers are redirecting efforts toward secretome profiling. The goal is to define potential biomarkers and therapeutic targets in the secretome that can be traced back in accessible human body fluids. However, currently there is a lack of secretome profiles of normal human primary cells making it difficult to assess the biological meaning of current findings. In this study we sought to establish secretome profiles of human primary cells obtained from healthy donors with the goal of building a human secretome atlas. Such an atlas can be used as a reference for discovery of potential disease associated biomarkers and eventually novel therapeutic targets. As a preliminary study, secretome profiles were established for six different types of human primary cell cultures and checked for overlaps with the three major human body fluids including plasma, cerebrospinal fluid and urine. About 67% of the 1054 identified proteins in the secretome of these primary cells occurred in at least one body fluid. Furthermore, comparison of the secretome profiles of two human glioblastoma cell lines to this new human secretome atlas enabled unambiguous identification of potential brain tumor biomarkers. These biomarkers can be easily monitored in different body fluids using stable isotope labeled standard proteins. The long term goal of this study is to establish a comprehensive online human secretome atlas for future use as a reference for any disease related secretome study. This article is part of a Special Issue entitled: An Updated Secretome.

Chemo-enzymatic synthesis and glycosidase inhibitory properties of DAB and LAB derivatives

A chemo-enzymatic strategy for the preparation of 2-aminomethyl derivatives of (2R,3R,4R)-2-(hydroxymethyl)pyrrolidine-3,4-diol (also called 1,4-dideoxy-1,4-imino-D-arabinitol, DAB) and its enantiomer LAB is presented. The synthesis is based on the enzymatic preparation of DAB and LAB followed by the chemical modification of their hydroxymethyl functionality to afford diverse 2-aminomethyl derivatives. This strategy leads to novel aromatic, aminoalcohol and 2-oxopiperazine DAB and LAB derivatives. The compounds were preliminarily explored as inhibitors of a panel of commercial glycosidases, rat intestinal disaccharidases and against Mycobacterium tuberculosis, the causative agent of tuberculosis. It was found that the inhibitory profile of the new products differed considerably from the parent DAB and LAB. Furthermore, some of them were active inhibiting the growth of M. tuberculosis.

Functionalization of microstructured open-porous bioceramic scaffolds with human fetal bone cells

Bone substitute materials allowing trans-scaffold migration and in-scaffold survival of human bone-derived cells are mandatory for development of cell-engineered permanent implants to repair bone defects. In this study, we evaluated the influence on human bone-derived cells of the material composition and microstructure of foam scaffolds of calcium aluminate. The scaffolds were prepared using a direct foaming method allowing wide-range tailoring of the microstructure for pore size and pore openings. Human fetal osteoblasts (osteo-progenitors) attached to the scaffolds, migrated across the entire bioceramic depending on the scaffold pore size, colonized, and survived in the porous material for at least 6 weeks. The long-term biocompatibility of the scaffold material for human bone-derived cells was evidenced by in-scaffold determination of cell metabolic activity using a modified MTT assay, a repeated WST-1 assay, and scanning electron microscopy. Finally, we demonstrated that the osteo-progenitors can be covalently bound to the scaffolds using biocompatible click chemistry, thus enhancing the rapid adhesion of the cells to the scaffolds. Therefore, the different microstructures of the foams influenced the migratory potential of the cells, but not cell viability. Scaffolds allow covalent biocompatible chemical binding of the cells to the materials, either localized or widespread integration of the scaffolds for cell-engineered implants.

Glycogen debranching enzyme 6 (AGL), enolase 1 (ENOSF1), ectonucleotide pyrophosphatase 2 (ENPP2_1), glutathione S-transferase 3 (GSTM3_3) and mannosidase (MAN2B2) metabolism computational network analysis between chimpanzee and human left cerebrum

We identified significantly higher expression of the genes glycogen debranching enzyme 6 (AGL), enolase 1 (ENOSF1), ectonucleotide pyrophosphatase 2 (ENPP2_1), glutathione S-transferase 3 (GSTM3_3) and mannosidase (MAN2B2) from human left cerebrums versus chimpanzees. Yet the distinct low- and high-expression AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism networks between chimpanzee and human left cerebrum remain to be elucidated. Here, we constructed low- and high-expression activated and inhibited upstream and downstream AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network between chimpanzee and human left cerebrum in GEO data set by gene regulatory network inference method based on linear programming and decomposition procedure, under covering AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 pathway and matching metabolism enrichment analysis by CapitalBio MAS 3.0 integration of public databases, including Gene Ontology, KEGG, BioCarta, GenMapp, Intact, UniGene, OMIM, etc. Our results show that the AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network has more activated and less inhibited molecules in chimpanzee, but less activated and more inhibited in the human left cerebrum. We inferred stronger carbohydrate, glutathione and proteoglycan metabolism, ATPase activity, but weaker base excision repair, arachidonic acid and drug metabolism as a result of inducing cell growth in low-expression AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network of chimpanzee left cerebrum; whereas stronger lipid metabolism, amino acid catabolism, DNA repair but weaker inflammatory response, cell proliferation, glutathione and carbohydrate metabolism as a result of inducing cell differentiation in high-expression AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network of human left cerebrum. Our inferences are consistent with recent reports and computational activation and inhibition gene number patterns, respectively.

Anti-cancer activity of 5-O-alkyl 1,4-imino-1,4-dideoxyribitols

New derivatives of 1,4-dideoxy-1,4-imino-D-ribitol have been prepared and evaluated for their cytotoxicity on solid and haematological malignancies. 1,4-Dideoxy-5-O-[(9Z)-octadec-9-en-1-yl]-1,4-imino-D-ribitol (13, IC(50) ∼2 μM) and its C(18)-analogues (IC(50) <10 μM) are cytotoxic toward SKBR3 (breast cancer) cells. 13 also inhibits (IC(50) ∼8 μM) growth of JURKAT cells.

Towards a stable noeuromycin analog with a D-manno configuration: synthesis and glycosidase inhibition of D-manno-like tri- and tetrahydroxylated azepanes

Noeuromycin is a highly potent albeit unstable glycosidase inhibitor due to its hemiaminal function. While stable D-gluco-like analogs have been reported, no data are available for D-manno-like structures. A series of tri- and tetrahydroxylated seven-membered iminosugars displaying either a D-manno-or a L-gulo-like configuration, were synthesized from methyl α-D-mannopyranoside using a reductive amination-mediated ring expansion as the key step. Screening towards a range of commercial glycosidases demonstrated their potency as competitive glycosidase inhibitors while cellular assay showed selective albeit weak glycoprotein processing mannosidase inactivation.

Synthesis and glycosidase inhibitory activity of 1-amino-3,6-anhydro-1-deoxy-D-sorbitol derivatives

3,6-Anhydro-1-(aryl or alkylamino)-1-deoxy-D-sorbitol derivatives have been prepared in four steps from isosorbide, a by-product from the starch industry. The inhibitory activities of these new compounds have been evaluated towards 13 glycosidases. A first lead-compound was identified, which inhibited beta-N-acetylglucosaminidase from bovine kidney (82% inhibition at 1mM).