Synthesis of alpha- and beta-linked tyvelose epitopes of the Trichinella spiralis glycan: 2-acetamido-2-deoxy-3-O-(3,6-dideoxy-D-arabino-hexopyranosyl)-beta -D-galactopyranosides

Synthesis of Salmonella enteritidis Antigenic Tetrasaccharide Repeating Unit by Employing Cationic Gold(I)-Catalyzed Glycosylation Involving Glycosyl N-1,1-Dimethylpropargyl Carbamate Donors

Synthesis of an antigenic tetrasaccharide repeating unit of the O-polysaccharide of Salmonella enteritidis lipopolysaccharide has been accomplished. Those four monosaccharides were assembled stereoselectively by employing our recently developed cationic gold(I)-catalyzed glycosylation methodology involving various glycosyl N-1,1-dimethylpropargyl carbamate donors. The newly formed α-anomeric stereochemical configuration was controlled by the axial C2-OBz of the glycosyl donors via anchimeric assistance.

Targeting the Epidermal Growth Factor Receptor with Molecular Degraders: State-of-the-Art and Future Opportunities

Epidermal growth factor receptor (EGFR) is an oncogenic drug target and plays a critical role in several cellular functions including cancer cell growth, survival, proliferation, differentiation, and motility. Several small-molecule tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs) have been approved for targeting intracellular and extracellular domains of EGFR, respectively. However, cancer heterogeneity, mutations in the catalytic domain of EGFR, and persistent drug resistance limited their use. Different novel modalities are gaining a position in the limelight of anti-EGFR therapeutics to overcome such limitations. The current perspective reflects upon newer modalities, importantly the molecular degraders such as PROTACs, LYTACs, AUTECs, and ATTECs, etc., beginning with a snapshot of traditional and existing anti-EGFR therapies including small molecule inhibitors, mAbs, and antibody drug conjugates (ADCs). Further, a special emphasis has been made on the design, synthesis, successful applications, state-of-the-art, and emerging future opportunities of each discussed modality.

LYTACs that engage the asialoglycoprotein receptor for targeted protein degradation

Selective protein degradation platforms have afforded new development opportunities for therapeutics and tools for biological inquiry. The first lysosome targeting chimeras (LYTACs) targeted extracellular and membrane proteins for degradation by bridging a target protein to the cation-independent mannose-6-phosphate receptor (CI-M6PR). Here, we developed LYTACs that engage the asialoglycoprotein receptor (ASGPR), a liver-specific lysosomal targeting receptor, to degrade extracellular proteins in a cell type-specific manner. We conjugated binders to a tri-GalNAc motif that engages ASGPR to drive downregulation of proteins. Degradation of EGFR by GalNAc-LYTAC attenuated EGFR signaling compared to inhibition with an antibody. Furthermore, we demonstrated that a LYTAC comprising a 3.4 kDa peptide binder linked to a tri-GalNAc ligand degrades integrins and reduces cancer cell proliferation. Degradation with a single tri-GalNAc ligand prompted site-specific conjugation on antibody scaffolds, which improved the pharmacokinetic profile of GalNAc-LYTACs in vivo. GalNAc-LYTACs thus represent an avenue for cell-type restricted protein degradation.

Zeolites and other silicon-based promoters in carbohydrate chemistry

Silicon-based materials, namely zeolites, clays, and silica gel have been widely used in organic synthesis, allowing mild reaction conditions and environmentally friendly methodologies. These heterogeneous catalysts are easy to handle, possess nontoxic and noncorrosive character and offer the possibility of recovery and reuse, thus contributing to clean and sustainable organic transformations. Moreover, they present shape-selective properties and provide stereo- and regiocontrol in chemical reactions. Herein, we survey the most significant applications of silicon-based materials as catalysts in carbohydrate chemistry, to mediate important transformations such as glycosylation, sugar protection and deprotection, and hydrolysis and dehydration. Emphasis is placed on their promising synthetic potential in comparison with conventional catalysts.

Base-Promoted Rearrangement of Sugar Epoxides to Unsaturated Sugars

[chemical reaction: see text]. A simple and efficient method for rearranging 2,3-anhydro carbohydrates to unsaturated sugars has been developed. The exceptionally mild reaction conditions and high stereoselectivity should make this an attractive method for the preparation of unsaturated carbohydrate derivatives.

Gene discovery in the adenophorean nematode Trichinella spiralis: an analysis of transcription from three life cycle stages

Expressed sequence tags (ESTs) were produced from cDNA libraries for immature L1, mature muscle larva and adult stages of the adenophorean nematode Trichinella spiralis. 10,130 ESTs were grouped into 3454 gene clusters. The clusters represent a conservative estimate of 3262 unique genes. Interspecific comparisons of the predicted proteins support an ancient divergence of clade I nematodes from other nematodes in the phylum Nematoda. Furthermore, apparent clade I or Trichocephalida-specific proteins were identified, which may include molecular determinants important in the evolution of these species. Similarity matches identified 463 C. elegans genes homologs that confer phenotypes by RNA interference. Classification of predicted proteins suggested diverse cellular, metabolic and extracellular functions, significantly expanding the dataset of T. spiralis proteins with prospective, and potentially critical, functions. Several lines of evidence suggested stage-specific expression of certain genes beyond those previously identified. Evidence was obtained for the existence of large gene families encoding isoforms of known secreted proteins, such as p43 and TspE1. Unexpectedly, diverse isoforms of the muscle larva p43 gene appear to be expressed by immature L1. Proteinases, kinases, antioxidant proteins and enzymes involved in glycan synthesis are implicated in T. spiralis interactions with its hosts. Numerous genes were identified that encode predicted proteins in these categories. The genes discovered, when put into context of functional classification, stage of expression, and biology of the parasite, should substantially enhance experimental potential for research on this parasite.

Comparison of synthetic tyvelose antigen with excretory-secretory antigen for the detection of trichinellosis in swine using enzyme-linked immunosorbent assay

Two enzyme-linked immunosorbent assay (ELISA) systems, one using natural excretory-secretory (ES) antigens and the other a synthetic glycan antigen (3,6-dideoxy-D-arabinohexose [tyvelose, TY]), were evaluated for the serological diagnosis of trichinellosis in swine. Sensitivity was estimated using samples (n = 113) collected 3-21 wk PI from 15 experimentally infected pigs, and specificity was estimated using samples (n = 397) from a population of Trichinella spp.-free pigs. Results were analyzed using 2 cutoff values recommended in international guidelines (Office Internationale des Epizooties [OIE]) and by the optimal cutoff level as determined by receiver-operator characteristic (ROC) analysis. The ROC-optimized TY-ELISA consistently performed better than all other combinations. None of the combinations of test and cut-off detected infected pigs sooner than 35 days; however, the ROC-optimized TY-ELISA identified 8 of 15 pigs earlier than the ES-ELISA and detected 2 pigs missed by all other tests. At 49 days PI the sensitivity and specificity of the ROC-optimized TY-ELISA were 94.3 and 96.7%, respectively, as compared with the ROC-optimized ES-ELISA at 84.9 and 96.0%, respectively. The ROC-optimized TY-ELISA was 100% specific at OIE-recommended cut-offs. This study indicates that the TY-ELISA is as good or better than the ES-ELISA for the detection of trichinellosis in swine.

Antigenic glycans in parasitic infections: implications for vaccines and diagnostics

Infections by parasitic protozoans and helminths are a major world-wide health concern, but no vaccines exist to the major human parasitic diseases, such as malaria, African trypanosomiasis, amebiasis, leishmaniasis, schistosomiasis, and lymphatic filariasis. Recent studies on a number of parasites indicate that immune responses to parasites in infected animals and humans are directed to glycan determinants within cell surface and secreted glycoconjugates and that glycoconjugates are important in host-parasite interactions. Because of the tremendous success achieved recently in generating carbohydrate-protein conjugate vaccines toward microbial infections, such as Haemophilus influenzae type b, there is renewed interest in defining parasite-derived glycans in the prospect of developing conjugate vaccines and new diagnostics for parasitic infections. Parasite-derived glycans are compelling vaccine targets because they have structural features that distinguish them from mammalian glycans. There have been exciting new developments in techniques for glycan analysis and the methods for synthesizing oligosaccharides by chemical or combined chemo-enzymatic approaches that now make it feasible to generate parasite glycans to test as vaccine candidates. Here, we highlight recent progress made in elucidating the immunogenicity of glycans from some of the major human and animal parasites, the potential for developing conjugate vaccines for parasitic infections, and the possible utilization of these novel glycans in diagnostics.

The synthesis of some deoxygenated analogues of early intermediates in the biosynthesis of glycosylphosphatidylinositol (GPI) membrane anchors

Syntheses are described of 2-azido-4,6-di-O-benzyl-2,3-dideoxy-d-ribo-hexopyranosyl fluoride, 6-O-acetyl-2-azido-3-O-benzyl-2,4-dideoxy-d-xylo-hexopyranosyl fluoride and 2-azido-3,4-di-O-benzyl-2,6-dideoxy-d-glucopyranosyl fluoride. These glycosyl donors were coupled with the acceptor 1d-2,3,4,5-tetra-O-benzyl-1-O-(4-methoxybenzyl)-myo-inositol and the alpha-coupled products were transformed into alpha-d-3dGlcpN-PI, alpha-d-4dGlcpN-PI and alpha-d-6dGlcpN-PI by way of the H-phosphonate route. Brief mention is made of the biological evaluation of these deoxy-sugar analogues and their N-acetylated forms as candidate substrate/inhibitors of the N-deacetylase and alpha-(1-->4)-d-mannosyltransferase activities present in trypanosomal and HeLa (human) cell-free system.

Synthesis of a typical N-acetylglucosamine-containing saponin, oleanolic acid 3-yl alpha-L-arabinopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6)-2-acetamido-2-deoxy-beta-D-glucopyranoside

Oleanolic acid 3-yl alpha-L-arabinopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->6)-2-acetamido-2-deoxy-beta-D-glucopyranoside, a cytotoxic saponin isolated from Acacia tenuifolia and Albizia subdimidiata with a typical structure of the N-acetylglucosamine-containing plant saponins, was synthesized. The synthesis adopted a stepwise glycosylation fashion employing glycosyl trifluoroacetimidates 5 and 9 and thioglycoside 12 as donors.

Synthesis of threeSalmonellaepitopes for biosensor studies of carbohydrate–antibody interactions

Disaccharides 1-3 corresponding to the antigenic determinants of Salmonella serotypes A, B, and D1were synthesized in a form suited for use in biosensors. The disaccharide determinants each contain a unique 3,6-dideoxyhexose, namely abequose (3,6-dideoxy-D-xylo-hexose), paratose (3,6-dideoxy-D-ribohexose), and tyvelose (3,6-dideoxy-D-arabino-hexose), are α-linked to the 3-position of D-mannopyranose. The disaccharides were further derivatized with a linear aglycon that has a terminal amino group, and can be readily coupled to pertinent chains carrying a terminal thiol for the construction of self-assembled monolayers (SAMs). Efficient routes that employed a single 3,6-dideoxygenation step were developed for the synthesis of paratoside 15 and tyveloside 22.Key words: Salmonella O-antigens, lipopolysaccharide, abequose, paratose, tyvelose, 3,6-dideoxyhexose, deoxygenation, glycoside tethers, immobilization via pentenyl glycosides.

Synthesis of disaccharide congeners of the Trichinella spiralis glycan and binding site mapping of two monoclonal antibodies

The tetrasaccharide epitope, β-D-Tyvp(1[Formula: see text]3)β-D-GalNAcp(1[Formula: see text]4)[α-L-Fucp(1[Formula: see text]3)]β-D-GlcNAcp (1) is the major constituent of the N-glycan expressed on the cell surface of the parasite Trichinella spiralis. Two monoclonal antibodies (Mabs 9D4 and 18H1) that protect rats against infection by T. spiralis bind the terminal disaccharide epitope β-D-Tyvp(1[Formula: see text]3)β-D-GalNAcp conjugated to BSA. The syntheses of disaccharide congeners containing mono-deoxy, mono-methyl, as well as modifications to replace the acetamido group are reported. These target disaccharides were assayed for binding to the protective MAbs. For each antibody different clusters of three hydroxyl groups, that include C-2 and C-4 of tyvelose and for 18H1, the GalNAc acetamido group, provide the key polar interactions with the antibody binding sites. Mapping of the sites by functional group replacement revealed a similar pattern of recognition for the dideoxyhexose by the two MAbs while each recognizes distinct surfaces of the GalNAc residue. Consequently although both antibodies bury the 4-OH of tyvelose, the principal contact surface occurs on opposite sides of the 3,6-dideoxyhexose.Key words: β-tyveloside, 3,6-dideoxy-D-arabino-hexose, Trichinella carbohydrate antigen, antibody mapping, Trichinella spiralis, N-glycans, molecular recognition of carbohydrates, antigen topology, functional group replacement.

Modeling of deoxy- and dideoxyaldohexopyranosyl ring puckering with MM3(92)

Extensive variations of the ring structures of three deoxyaldohexopyranoses, L-fucose, D-quinovose, and L-rhamnose, and four dideoxyaldohexopyranoses, D-digitoxose, abequose, paratose, and tyvelose, were studied by energy minimization with the molecular mechanics algorithm MM3(92). Chair conformers, 4C(1) in D-quinovose and the equivalent 1C(4) in L-fucose and L-rhamnose, overwhelmingly dominate in the three deoxyhexoses; in the D-dideoxyhexoses, 4C(1) is again dominant, but with increased amounts of 1C(4) forms in the alpha anomers of the three 3,6-dideoxyhexoses, abequose, paratose, and tyvelose and in both alpha and beta anomers of the 2,6-dideoxyhexose D-digitoxose. In general, modeled proton-proton coupling constants agreed well with experimental values. Computed anomeric ratios strongly favor the beta configuration except for D-digitoxose, which is almost equally divided between alpha and beta configurations, and L-rhamnose, where the beta configuration is somewhat favored. MM3(92) appears to overstate the prevalence of the equatorial beta anomer in all three deoxyhexoses, as earlier found with fully oxygenated aldohexopyranoses.

Sensitive and rapid immunoassays for Salmonella enteritidis

In order to develop more sensitive, specific, and rapid immunoassays to detect Salmonella enteritidis in food supplies, we have applied various approaches by using several different antibody preparations. Utilizing ELISA in both a plate and immunodot assay, we employed (i) a polycolonal rabbit antiserum to a boiled suspension of the organism; (ii) a monoclonal antibody to the cell surface of the bacterium; and (iii) mouse antisera to two oligosaccharides each containing the rare sugar tyvelose, and exhibited by S. enteritidis, a member of the group D salmonellae. We showed that the polyclonal antiserum and monoclonal antibody IG-10 to the cell surface could specifically detect from 10(2) to 10(3) organisms in a 10-microl sample in the plate and immunodot assay. Both assays are read in 4-5 hr. Further, in the mice immunized to the trisaccharide, (alpha-D-galactose-alpha-tyvelose-alpha-D-mannose), as well as those mice immunized to the tetrasaccharide, (alpha-D-galactose-alpha-tyvelose-alpha-D-mannose-alpha-L-rhamnose), specificity to tyvelose was determined by inhibition studies. The inhibitors of the antisera to the trisaccharide included the single sugar tyvelose conjugated to bovine serum albumin (BSA), a tetrasaccharide in which tyvelose is excluded, but contains alpha-D-galactose, alpha-ascarose, alpha-D-mannose, and alpha-L-rhamnose (conjugated to BSA), and others. The inhibition studies suggest that the mouse antisera are specific for tyvelose and also contain antibodies for mannose and rhamnose. The antibodies that have been made to the unique sugar tyvelose should improve the specificity in assays for S. enteritidis.

Efficient synthesis of 3, 6-dideoxy-beta-D-arabino-hexopyranosyl-terminated LacdiNac glycan chains of the Trichinella spiralis parasite

The synthesis of a linear trisaccharide epitope of the Trichinella spiralis N-linked glycan, in a form amenable to glycoconjugate formation, is reported. The trisaccharide contains the synthetically challenging LacdiNAc [beta-GalpNAc(1-->4)-beta-GlcpNAc] element, as well as a terminal 3,6-dideoxy-beta-D-arabino-hexopyranose (tyvelose) residue. An orthogonal protection strategy is described, which permits the protection and manipulation of three amino groups present in the disaccharide beta-GalNAc(1-->4)-beta-GlcNAc and the tether used to prepare neoglycoconjugates. The beta-linked dideoxyhexose was generated in excellent yield by the introduction of the dideoxyhexose unit as a beta-D-ribo-hexopyranoside (paratose) followed by an oxidation-reduction sequence to generate the beta-D-arabino configuration in high diastereomeric excess. The required dideoxyhexose donor was synthesized in a series of high-yielding steps from glucose utilizing the p-methoxyphenyl glycoside.