Reactivity Of Donors Research Articles

Mannopyranosyl Uronic Acid Donor Reactivity

The reactivity of a variety of mannopyranosyl uronic acid donors was assessed in a set of competition experiments, in which two (S)-tolyl mannosyl donors were made to compete for a limited amount of promoter (NIS/TfOH). These experiments revealed that the reactivity of mannuronic acid donors is significantly higher than expected based on the electron-withdrawing capacity of the C-5 carboxylic acid ester function. A 4-O-acetyl-β-(S)-tolyl mannuronic acid donor was found to have similar reactivity as per-O-benzyl-α-(S)-tolyl mannose.

Regulatory T cell therapy combined with donor-specific T cell deletion promotes long-term survival of islet allografts (169.32)

Abstract Although Tregs are vital for peripheral tolerance, adoptive transfer of Tregs is insufficient in inducing long-term allograft survival in lymphoreplete hosts without preconditioning or adjunct immunosuppression. We hypothesize that reducing donor-reactive T cells may create a therapeutic window for Tregs to induce allograft tolerance without additional immunosuppression. We preconditioned recipient mice using donor-specific transfusion followed by cyclophosphamide treatment to selectively kill proliferating donor-reactive cells. This approach deleted 70-90% donor-reactive T cells, but failed to prolong islet allograft survival. Addition of Tregs with direct donor reactivity prior to transplantation led to long-term survival of BALB/c islets in 70% of C57BL/6 recipients. Equal numbers of polyclonal Tregs significantly prolonged graft survival, but 90% of the recipients rejected their grafts by 100 days. Increasing the numbers of polyclonal Tregs was able to confer long-term graft protection. Similar strategy of combining donor-reactive T cell deletion and polyclonal Tregs did not protect C3H islets in autoimmune NOD recipients. Further addition of Tregs specific for islet autoantigen was required to prolong graft survival in NOD mice. Together, these results demonstrate a clinically viable approach to harness the tolerogenic property of Tregs for inducing long-term allograft acceptance without additional immunosuppression.

Ag(I)-Catalyzed Regioselective Ring-Opening ofN-Tosylaziridine andN-Tosylazetidine withS-,O-, andN-Nucleophiles and Tethered Dinucleophiles

[Ag(COD)(2)]PF(6) catalyzes the ring-opening of N-tosylaziridines and -azetidines with alcohols, amines, thiols, and related tethered 1,2-ethane dinucleophiles. Initial rate studies and DFT-based evaluation of stepwise energetics suggest an inverse relationship between the nucleophilic reactivity of a heteroatom donor and its binding affinity to cationic Ag(I).

Pharmacological Study of Antimyeloma Agents on Hemostasis

AbstractAbstract 3175 Introduction:Patients with multiple myeloma (MM) have an increasing risk of developing venous thromboembolism (VTE). The use of thalidomide or lenalidomide, two antimyeloma agents has been associated with an increased risk of VTE especially when associated with dexamethasone or melphalan-prednisone. This increased risk in less pronounced with the proteasome inhibitor bortezomib. The pharmacological effects of thalidomide, lenalidomide and bortezomib have never been studied on platelet aggregation or coagulation. These preliminary data are necessary to understand the differential effects of these drugs on thrombotic events. Aims:The aim of our study is to investigate the pharmacological effects of these drugs on primary hemostasis by light transmission agregometry (LTA) and on secondary hemostasis using thrombin generation test (TGT). Methods:LTA was performed with a Chrono-Log aggregometer (Kordia). Platelet-rich plasma (PRP) of healthy blood donors (n=3 to 10) was adjusted to 300,000 platelets/μl. Platelet-poor plasma (PPP) and PRP were used respectively to adjust the photometric measurement to the minimum and maximum optical density. The platelet reactivity of the healthy donors was previously checked by LTA. Thalidomide (racemic, enantiomer (+) and enantiomer (-)), lenalidomide and bortezomib were spiked at final concentration of 200 μM in PRP except for studying the influence of thalidomide on ADP-induced platelet aggregation where the maximal concentration usable was 100 μM. LTA was performed without (spontaneous aggregation) and with addition of 5μM ADP, 190μg/ml collagen, 600μM arachidonic acid (AA) and 10 μM PAR1-AP (final concentrations). Negative controls (physiological saline and DMSO at concentrations used to dissolve the drugs) were also included. TGT was performed both on PPP (from normal pool plasma (NPP)) and on PRP. We first validated the method on NPP and PRP with two anticoagulants: a thrombin direct inhibitor (i.e. argatroban) and a FXa direct inhibitor (i.e. ZK-807834). Thalidomide ((+/−), (+) and (-)), lenalidomide and bortezomid were tested at the final concentrations of 5, 10, 50, 100 and 200 μM. For the experiments on NPP, PPP reagent (5 pM TF + 4 μM PL in the final assays), PPP reagent low (1 pM TF + 4 μM PL in the final assays) and MP reagent (4 μM PL in the final assays) were used whereas for the experiments on PRP, PRP reagent (1 pM TF in the final assays) was used. Results:LTA Both three drugs did not induce spontaneous aggregation until 200 μM. Lenalidomide and bortezomib showed no effect on induced platelet aggregation until 200 μM, whatever the agonist used. On the contrary, for racemic thalidomide, platelet aggregation was reduced at 50 and 100 μM with 5 μM ADP and at 150 and 200 μM with 600 μM AA. These effects were more pronounced with thalidomide (+) than with thalidomide (-). So, the half maximal inhibitory concentrations (IC50) for platelet aggregation induced by 600 μM AA were 127, 143 and 221 μM for racemic, enantiomer (+) and enantiomer (-), respectively. When 190μg/ml collagen or 10 μM PAR1-AP were used as agonists, no effect was observed on platelet aggregation until 200 μM thalidomide. TGT. With argatroban and ZK-807834, we observed a concentration-dependent decrease and delay of the thrombin activity profiles in PRP and NPP, whatever the inducer used. No significant effect on thrombin activity in NPP or PRP has been observed for antimyeloma drugs at all concentrations tested, whatever the inducer used. Conclusions:Lenalidomide, thalidomide and bortezomid do not induce spontaneous platelet aggregation and do not affect platelet aggregation induced by collagen or PAR1-AP. Conversely to lenalidomide and bortezomib, thalidomide, and especially its enantiomer (+), moderately inhibits platelet aggregation induced by ADP and AA. Moreover, these antimyeloma agents have no effect on thrombin generation. The increased risk of VTE by thalidomide or lenalidomide in patients with multiple myeloma is thus not mediated by a direct impact on primary or secondary hemostasis at therapeutic concentrations. Disclosures:No relevant conflicts of interest to declare.

Electrochemistry and Electrogenerated Chemiluminescence of Dithienylbenzothiadiazole Derivative. Differential Reactivity of Donor and Acceptor Groups and Simulations of Radical Cation−Anion and Dication−Radical Anion Annihilations

We report here the electrochemistry and electrogenerated chemiluminescence (ECL) of a red-emitting dithienylbenzothiadiazole-based molecular fluorophore (4,7-bis(4-(4-sec-butoxyphenyl)-5-(3,5-di(1-naphthyl)phenyl)thiophen-2-yl)-2,1,3-benzothiadiazole, 1b). 1b contains two substituted thiophene groups as strong electron donors at the ends connected directly to a strong electron acceptor, 2,1,3-benzothiadiazole, in the center. Each thiophene moiety is substituted in position 2 by 3,5-di(1-naphthyl)phenyl and in position 3 by 4-sec-butoxyphenyl. Cyclic voltammetry of 1b, with scan rate ranging from 0.05 to 0.75 V/s, shows a single one-electron reduction wave (E°(red) = -1.18 V vs SCE) and two nernstian one-electron oxidation waves (E°(1,ox) = 1.01 V, E°(2,ox) = 1.24 V vs SCE). Reduction of the unsubstituted 2,1,3-benzothiadiazole center shows nernstian behavior with E°(red) = -1.56 V vs SCE. By comparison to a digital simulation, the heterogeneous electron-transfer rate constant for reduction, k(r)° = 1.5 × 10(-3) cm/s, is significantly smaller than those for the oxidations, k(o)° > 0.1 cm/s, possibly indicating that the two substituted end groups have a blocking effect on the reduction of the benzothiadiazole center. The ECL spectrum, produced by electron-transfer annihilation of the reduced and oxidized forms, consists of a single peak with maximum emission at about 635 nm, consistent with the fluorescence of the parent molecule. Relative ECL intensities with respect to 9,10-diphenylanthracene are 330% and 470% for the radical anion-cation and radical anion-dication annihilation, respectively. Radical anion (A(-•))-cation (A(+•)) annihilation produced by potential steps shows symmetric ECL transients during anodic and cathodic pulses, while for anion (A(-•))-dication (A(2+•)) annihilation, transient ECL shows asymmetry in which the anodic pulse is narrower than the cathodic pulse. Digital simulation of the transient ECL experiments showed that the origin of the observed asymmetry is asymmetry in the amount of generated charges rather than instability of the electrogenerated species.

Gold-catalyzed glycosidations: unusual cleavage of the interglycosidic bond while studying the armed/disarmed effect of propargyl glycosides

Armed/disarmed effect of propargyl glycosides in the presence of AuBr 3 is studied. Observed that oxophilic AuBr 3 cleaves interglycosidic bond of an armed disaccharide resulting in the formation of a disaccharide and a 1,6-anhydro sugar. Trisaccharides were obtained after fine tuning the reactivity of the glycosyl donor with different protecting groups.

Renal Transplantation Across HLA and ABO Antibody Barriers: Integrating Paired Donation into Desensitization Protocols

The field of desensitization and incompatible transplantation has made great gains over the past decade. There are now several options and effective therapies for many patients who face antibody barriers. Kidney paired donation (KPD) and desensitization have traditionally been considered competing strategies and patients have been offered one or the other without regard for the probability of a successful outcome. It is now possible to predict which donor/recipient phenotypes will benefit from each of these modalities. KPD should be favored among patients with immunologic phenotypes that are likely to match without prolonged waiting times. However, as many as 50% of patients with incompatible donors will fail to find a match in a KPD pool and many of these patients could be desensitized to their donor. Positive crossmatch and ABO incompatible transplantation has been accomplished in selective cases without the need for heavy immunosuppression or B-cell ablative therapy. Patients who are both difficult-to-match due to broad sensitization and hard-to-desensitize because of strong donor reactivity can often be successfully transplanted through a combination of desensitization and KPD. Using these various modalities it is estimated that most patients with incompatible live donors can undergo successful renal transplantation.

Migration of reactive trace compounds from Novozym ® 435 into organic solvents and ionic liquids

The commercial form of immobilized Candida antarctica lipase B (CALB), known as Novozym ® 435, is a catalyst routinely used in enzymatic reactions. However, we observed a number of compounds migrated from this enzyme preparation into organic solvents and ionic liquids (ILs). These compounds were further identified by GC–MS analysis as a mixture of 17 substances, including 5 major components: glycerol, benzoic acid, 2-hydroxyethyl benzoate, 2-hydroxyethyl sorbate, and sorbic acid. The importance of this discovery is that all five major compounds are reactive in the presence of CALB, especially the last four compounds are potential acyl donors in enzymatic (trans)esterification reactions. We then quantified the migration of these acyl donors into various aqueous solutions, organic solvents and ILs, and observed that the migration into polar organic solvents and ILs was rapid (10–30 min). We also measured the reactivities of these acyl donors with 1-propanol in Novozym ® 435-catalyzed (trans)esterifications. Our data suggest that the initial reaction rates of sorbic acid and sorbate ester were very fast; although the initial rates of benzoic acid and benzoate were much slower, their conversions into propyl benzoate were significant within 24 h period. The presence of these compounds in Novozym ® 435 may not have considerable impact on fast reactions involving high substrate concentrations, however, it is important to realize that these trace compounds may affect the enzyme activity, and may cause confusion during the analysis of enzymatic reactions.

Synthesis of 2‐C‐Branched Oligo(glyco–amino acid)s (OGAAs) by Ring Opening of 1,2‐Cyclopropanecarboxylated Sugar Donors

Carbohydrates decorated with amino acids are becoming an important area of glyco-chemistry research. Possessing the architecture of a sugar and an amino acid in a single molecule, these glyco–amino acids (GAAs) are expected to exhibit the characteristics of both carbohydrates and amino acids, which are both biological polymer precursors. C-branched glyco–a-amino acid moieties are found in a ACHTUNGTRENNUNGvariety of nucleoside antibiotics, such as polyoxins, miharamycins, nikkomycin and amipuramycin. Very few methods are available in the literature for the synthesis of monosaccharide-derived C-branched GAA derivatives. Linking an a-amino acid at C-2 or C-4 through a C C bond has been found to be very difficult. For this reason, the biological importance of these GAAs is not yet fully understood. It has been shown that unnatural 2-C-acetonylsugars serve as metabolic substrates for cell surface engineering by mimicking 2-N-acetylsugars. Similarly, a 2-C-N-hydroxy ACHTUNGTRENNUNGacetamide mimic of GlcNAc was synthesised and shown to be an inhibitor of the biosynthesis of lipid A. Herein, we report the first stereoselective synthesis of 2-C-branched oligo(glyco– amino acid)s (OGAAs) by ring opening of 1,2-cyclopropanecarboxylated sugar donors. The high reactivity and regioselectivity of donor–acceptor cyclopropanes has been well documented in the literature. 1,2-cyclopropanecarboxylated sugars have been used as donor–acceptor cyclopropanes in the synthesis of 2-Cbranched monosaccharides through electrophilic C1–C7 ACHTUNGTRENNUNGcyclopropane ring opening or by transition-metal-catalysed glycosylation. Recently, a four-component Pavarov reaction and a transition-metal-mediated radical reaction were developed for the direct synthesis of 2-C-branched carbohydrate derivatives from glucals. These branched glycosides were further derivatised to bicyclic carbohydrate 1,2lactones. Glucal-derived donor–acceptor cyclopropanes have also been used as 1,3-dipoles under acidic conditions, which result in (3+2) cycloaddition reactions in presence of dipolarophiles. By using the ability of 1,2-cyclopropanecarboxylated sugars to undergo electrophilic ring opening assisted by the adjacent oxygen in presence of an electrophile, we herein present the N-iodosuccinimide (NIS)mediated ring opening of 1,2-cyclopropanecarboxylated glycosyl donors with carbohydrate O-nucleophilic glycosyl bond acceptors. To achieve this novel glycosylation reaction, we began by using 1,5-anhydro-2,6-dideoxy-1,2-C-(exo-carbomethoxymethylene)-3,4-di-O-benzyl-a-l-rhamnal 1 as the donor and 1,2-3,4-diisopropylidine-a-d-galactose 2 as the acceptor with NIS as the electrophile at 0 8C in acetonitrile. However, no expected disaccharide was observed under these reaction conditions, even with an excess of acceptor 2 (>3 equiv). Similar reaction conditions with dichloromethane as the

A Multiplex Bead Array Analysis to Monitor Donor-Specific Cytokine Responses After Withdrawal of Immunosuppression in HLA-Identical living Related Kidney Transplant Patients

Immune reactivity after HLA-identical living related (LR) kidney transplantation can be caused by minor histocompatibility antigen and non-HLA antigen mismatches between donor and recipient. In our center, HLA-identical LR kidney transplant recipients receive azathioprine (AZA) or mycophenolate mofetil (MMF) in combination with corticosteroids for 1 year after transplantation. Thereafter, AZA or MMF was withdrawn, and the patients were treated with steroid monotherapy as maintenance therapy. We questioned whether withdrawal of AZA or MMF affected the donor-specific lymphocyte proliferation and cytokine production. Donor and third-party T-cell reactivities were determined by mixed lymphocyte reactions and by cytokine production using multiplex bead array technique. The donor and third-party proliferative capacities were not affected after withdrawal of AZA or MMF. Thirteen of 17 cytokines were detected by the multiplex bead array technique. No differences were observed after third-party induced cytokine production after withdrawal of AZA or MMF. However, production of donor-specific interferon-γ and macrophage inflammatory protein-1β increased after discontinuation of AZA or MMF, but no clinically relevant acute rejection was observed. In conclusion, after HLA-identical LR kidney transplantation, donor-specific cytokine responses can be found when AZA or MMF therapy is discontinued. The clinical relevance of this phenomenon is still not evident.

Active-site Mapping of a Populus Xyloglucan endo-Transglycosylase with a Library of Xylogluco-oligosaccharides

Restructuring the network of xyloglucan (XG) and cellulose during plant cell wall morphogenesis involves the action of xyloglucan endo-transglycosylases (XETs). They cleave the XG chains and transfer the enzyme-bound XG fragment to another XG molecule, thus allowing transient loosening of the cell wall and also incorporation of nascent XG during expansion. The substrate specificity of a XET from Populus (PttXET16-34) has been analyzed by mapping the enzyme binding site with a library of xylogluco-oligosaccharides as donor substrates using a labeled heptasaccharide as acceptor. The extended binding cleft of the enzyme is composed of four negative and three positive subsites (with the catalytic residues between subsites -1 and +1). Donor binding is dominated by the higher affinity of the XXXG moiety (G=Glcbeta(1-->4) and X=Xylalpha(1-->6)Glcbeta(1-->4)) of the substrate for positive subsites, whereas negative subsites have a more relaxed specificity, able to bind (and transfer to the acceptor) a cello-oligosaccharyl moiety of hybrid substrates such as GGGGXXXG. Subsite mapping with k(cat)/K(m) values for the donor substrates showed that a GG-unit on negative and -XXG on positive subsites are the minimal requirements for activity. Subsites -2 and -3 (for backbone Glc residues) and +2' (for Xyl substitution at Glc in subsite +2) have the largest contribution to transition state stabilization. GalGXXXGXXXG (Gal=Galbeta(1-->4)) is the best donor substrate with a "blocked" nonreducing end that prevents polymerization reactions and yields a single transglycosylation product. Its kinetics have unambiguously established that the enzyme operates by a ping-pong mechanism with competitive inhibition by the acceptor.

Donor-reactive cytokine profiles after HLA-identical living-related kidney transplantation

After HLA-identical living-related (LR) kidney transplantation, only non-HLA antigen mismatches between donor and recipient may exist. We questioned whether donor-reactive responses against non-HLA antigens could be found after HLA-identical LR kidney transplantation, and wondered whether donor reactivity in the HLA-identical setting was different from the HLA-mismatched setting during immunological quiescence. Healthy individuals served as controls. Elispot assays were performed to determine the number of alloreactive IFN-gamma-producing cells (pc), IL-10 pc, granzyme B (GrB) pc and IL-13 pc from peripheral blood mononuclear cells (PBMC) of HLA-identical, HLA-mismatched LR kidney transplant recipients and healthy individuals. The frequency of alloreactive IFN-gamma pc, IL-13 pc and GrB pc was higher in healthy individuals compared to both transplant patient groups. In the HLA-identical group, significantly higher numbers of donor-reactive IL-10 pc were found compared to their autologous control. These frequencies were also higher compared to the HLA-mismatched and healthy control group. The number of donor-reactive GrB pc was higher in the HLA-mismatched group than in the HLA-identical group. Donor-reactive IFN-gamma pc and IL-13 pc were comparable in both transplant groups. In recipients of HLA-identical LR kidney transplant, high donor-reactive IL-10 pc, in combination with low donor-reactive IFN-gamma pc, IL-13 pc and GrB pc, suggests active downregulation of reactivity against non-HLA molecules.

Synthesis of N,N‐Ac,Boc Laurylthio Sialoside and Its Application to O‐Sialylation.

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O-2 Substituted pyranosyl oxacarbenium ions are C-2–O-2 2-fold rotors with a strong syn preference

The substituent at O-2 of glycopyranosides is known to have a pronounced effect on both the formation and the cleavage of glycosides at C-1. This is primarily attributed to stereoelectronic effects on the formation and stability of the related glycopyranosyl oxacarbenium ions. Previous QM studies of 2- O-methyl substituted manno and gluco configured pyranosyl oxacarbenium ions found a preference for the methyl carbon to be syn to the CH-2 methine. This study examines the conformational preference of variously substituted O-2 tetrahydropyranosyl oxacarbenium ions and confirms this syn preference. Neutral analogues are shown to have the expected 3-fold rotation whereas the charged species exhibit 2-fold rotation about C-2–O-2. Natural bond order (NBO) calculations suggest that the dominant stabilizing interaction is a unimodal O-2 lone pair to C-1–O-5 π-bond hyperconjugative interaction. This syn conformational preference has important implications for mimics of glycopyranosyl oxacarbenium ion transition states. It also suggests a conformational based mechanism that can be exploited to tune the reactivity of glycopyranosyl donors in the glycosylation reaction.

Going to Extremes: “Super” Armed Glycosyl Donors in Glycosylation Chemistry

This concept article gives an overview of stereoelectronic effects in monosaccharide systems and how these can be used to dramatically enhance the reactivity of glycosyl donors in oligosaccharide synthesis.

8165 POSTER Health-related quality of life among postmenopausal women with breast cancer during adjuvant treatment: symptom experience and predictors for global health/quality of life

An expedient synthesis and the reactivity of donor substituted cyanoketenes 7 (captodative substitution) are described. 3-Cyano β-lactams are formed from 7 and imines.

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An expedient synthesis and the reactivity of donor substituted cyanoketenes 7 (captodative substitution) are described. 3-Cyano β-lactams are formed from 7 and imines.

Synthesis of N, N-Ac,Boc laurylthio sialoside and its application to O-sialylation

The combination of the 5- N- tert-butoxycarbonyl (Boc) group of laurylthio sialoside and cyclopentyl methyl ether (CPME) as a solvent enhanced the reactivity and α-selectivity of the sialyl donor during sialylation. Selective deprotection of the N-Boc group of sialoside, including an acid-sensitive isopropylidene function, was successfully achieved by Yb(OTf) 3–SiO 2. Transformation of N, N-Ac,Boc into an N-acetylglycolyl group of sialoglycoside was easily performed via selective N-deacylation of the mixed Ac- N-Boc carbamate, subsequent Boc group removal, and acylation.

Differential O-3/O-4 regioselectivity in the glycosylation of α and β anomers of 6-O-substituted N-dimethylmaleoyl-protected d-glucosamine acceptors

An assessment of the relative O-3/O-4 reactivities of both methyl α- and β- d-glycosides of N-dimethylmaleoyl (DMM) d-glucosamine acceptors protected at O-6 with benzoyl (Bz), benzyl (Bn), and tert-butyldiphenylsilyl (TBDPS) groups is presented using per-O-benzoylated β- d-galactofuranosyl and per-O-acetylated α- d-galactopyranosyl trichloroacetimidates as glycosyl donors. Using the former donor, the α anomer of the 6-O-benzoylated compound gave exclusive substitution at O-3, whereas the other two compounds with α-configuration kept this site as preferential. The β anomer of the 6-O-benzoylated compound gave the same amounts of reaction products on O-3 and O-4, whereas the other β analogs carried a more reactive O-4. The same reactions were carried out using as donor the less-reactive per-O-acetylated α- d-galactopyranosyl trichloroacetimidate. Although the same trend was found to occur, the O-4 was always relatively more reactive with the pyranosyl donor than with the furanosyl donor, when keeping the remaining factors constant. Furthermore, the β anomers of the acceptor gave almost exclusive substitution at O-4. These observations confirm and extend the utility of these ‘matching’ donor and acceptor reactivities.

A Highly Convergent Chemical Synthesis of Conformational Epitopes of Rhamnogalacturonan II

Upon careful tuning of the reactivity of glycosyl donors and acceptors, tetra- and hexasaccharide fragments (see structure) of the B chain of rhamnogalacturonan II (RGII) were prepared in a convergent and stereoselective manner. The conformation of the central arabinopyranosyl ring (red) was found to depend on the saccharide substitution pattern. This conformational epitope may influence the biological functions of RGII.