Reactivity Of Donors Research Articles

Organo- and Organometallic-Catalytic Intramolecular [1,5]-Hydride Transfer/Cyclization Process through C(sp(3) )-H Bond Activation.

The direct functionalization of C(sp(3) )-H bonds is one of the most synthetically powerful research areas in current organic synthesis. Organocatalytic C(sp(3) )-H bond activation reactions have recently been developed in addition to the traditional metal-catalyzed C(sp(3) )-H activation reactions. In this review, we aim to give a brief overview of organo- and organometallic internal redox cascade reactions with respect to the mechanism, the reactivity of hydrogen donors and acceptors, and the migration modes of hydrogen.

Variability of the IFN-γ ELISpot assay in the context of proficiency testing and bridging studies

Assays that assess cellular mediated immune responses performed under Good Clinical Laboratory Practice (GCLP) guidelines are required to provide specific and reproducible results. Defined validation procedures are required to establish the Standard Operating Procedure (SOP), include pass and fail criteria, as well as implement positivity criteria. However, little to no guidance is provided on how to perform longitudinal assessment of the key reagents utilized in the assay. Through the External Quality Assurance Program Oversight Laboratory (EQAPOL), an Interferon-gamma (IFN-γ) Enzyme-linked immunosorbent spot (ELISpot) assay proficiency testing program is administered. A limit of acceptable within site variability was estimated after six rounds of proficiency testing (PT). Previously, a PT send-out specific within site variability limit was calculated based on the dispersion (variance/mean) of the nine replicate wells of data. Now an overall ‘dispersion limit’ for the ELISpot PT program within site variability has been calculated as a dispersion of 3.3. The utility of this metric was assessed using a control sample to calculate the within (precision) and between (accuracy) experiment variability to determine if the dispersion limit could be applied to bridging studies (studies that assess lot-to-lot variations of key reagents) for comparing the accuracy of results with new lots to results with old lots. Finally, simulations were conducted to explore how this dispersion limit could provide guidance in the number of replicate wells needed for within and between experiment variability and the appropriate donor reactivity (number of antigen-specific cells) to be used for the evaluation of new reagents. Our bridging study simulations indicate using a minimum of six replicate wells of a control donor sample with reactivity of at least 150 spot forming cells per well is optimal. To determine significant lot-to-lot variations use the 3.3 dispersion limit for between and within experiment variability.

From Umpolung to Alternation: Modified Reactivity of Donor-Acceptor Cyclopropanes Towards Nucleophiles in Reaction with Nitroalkanes.

A conceptually new type of donor-acceptor cyclopropane reactivity towards nucleophiles has been disclosed. An essential characteristic of the process is an unusual nucleophilic attack on the C(3)-position of a cyclopropane, combined with typical small ring-opening by cleavage of the C(1)-C(2) bond between the acceptor and the donor. Based on this new reaction between cyclopropane-1,1-diesters and nitroalkanes, we developed a convenient approach to γ-nitroesters that can be efficiently transformed to the substituted pyrrolidones, structural analogues of racetame family drugs (rolipram, phenylpiracetam, etc.).

Sialylation with systematically protected allyl galactoside acceptors using sialyl phosphate donors

Various N-protected sialyl donors were synthesized and utilized in sialylation to investigate the reactivity and stereoselectivity of sialyl phosphate donors. Furthermore, in order to understand the effects of protecting groups and hydroxyl group positions on galactosyl acceptors, the sialylation efficiencies of all of the hydroxy groups on galactoses, which were protected with benzyl or benzoyl groups, were investigated. Consequently, the sialylation of N-acetyl-5-N,4-O-oxazolidinone-protected sialyl phosphate donors with allyl galactosides was accomplished and gave the GM4 regioisomers.

Carbohydrate reactivity: Glycosyl cations out on parole.

The reactivity of glycosyl donors is often explained by invoking putative glycosyl cation intermediates but, until now, they have not been observed in the condensed phase.

Donor Cell Composition and Reactivity Predict Risk of Acute Graft-versus-Host Disease after Allogeneic Hematopoietic Stem Cell Transplantation.

Background. Graft-versus-host disease (GVHD) is a serious complication after allogeneic hematopoietic stem cell transplantation (HSCT). We designed a functional assay for assessment of individual risk for acute GVHD. Study Design and Methods. Blood samples were collected from patients and donors before HSCT. Two groups of seven patients each were selected, one in which individuals developed acute GVHD grades II–IV and one in which none showed any clinical signs of GVHD. Peripheral blood mononuclear cells (PBMCs) isolated from donors were incubated in mixed lymphocyte cultures (MLCs) with recipient PBMCs. The cells were characterized by flow cytometry before and after MLC. Results. Samples from donors in the GVHD group contained significantly lower frequencies of naïve γδ T-cells and T-cells expressing NK-cell markers CD56 and CD94. Donor samples in this group also exhibited lower frequencies of naïve CD95+ T-cells compared to controls. After MLC, there were dissimilarities in the CD4/CD8 T-cell ratio and frequency of CD69+ T-cells between the two patient groups, with the non-GVHD group showing higher frequencies of CD8+ and CD69+ T-cells. Conclusion. We conclude that a thorough flow cytometric analysis of donor cells for phenotype and allogeneic reactivity may be of value when assessing pretransplant risk for severe acute GVHD.

Nucleic acid testing: Is it the only answer for safe Blood in India?

Background:With the implementation of NAT in countries around the world, there is a growing pressure on the transfusion services in India to adopt NAT testing. India has about 2545 licensed Blood Centres. The Transfusion Services in India are fragmented, poorly regulated and the quality standards are poorly implemented. Blood Centres are still dependent on replacement/family donors and in most places laboratory testing for Transfusion transmitted infections is not quality assured, laboratory equipment are not calibrated and maintained, and validation of results is not carried out. Against the current scenario introducing NAT for screening of blood donors in India would pose a challenge.Aim:To study the prudence of universal NAT testing in India.Materials and Methods:A retrospective study of 5 years from 2008-2012 was undertaken to study the true reactivity of donors using WHO strategy II and III and therefore the true seroprevalence of TTI infections in the donor populations.Results:The true reactivity of the donors was much less as compared to the initially reactive donors due to the use of a well designed testing algorithm. In addition having a total voluntary blood collection along with good pre-donation counseling program also reduces the transmission of infections.Conclusions:What India essentially needs to do is religiously implement the strategies outlined in the WHO Aide-memoire. The blood should be collected only from voluntary non remunerative and repeat donors, there should be stringent donor selection with pre-donation counseling instituted. Strict implementation of quality management system, development of well defined testing startegies and strong haemovigilance system could take us a step in the right direction.

Use of CMV Unselected Blood Products Does Not Increase the Risk of CMV Reactivation in Patients Undergoing Hematopoetic Stem Cell Transplant (HSCT)

Introduction: Conventionally patients receiving allogeneic HSCT (AlloHSCT) have received CMV negative blood products to obviate the risk of transfusion related CMV transmission. In the era of leucodepletion with more than log 4 reduction in blood product WBC content, the utility of this practice has been questioned and, in line with SABTO (Safety of Blood, Tissues and Organs) guidance, most UK transplant centers have adopted the policy of using unselected blood products for this patient cohort. At this center, our policy was changed to conform to recommended national practice in April 2013. This analysis was carried out to evaluate if this change has resulted in an increased incidence of CMV reactivation.Methods: 868 (M: 561; median age: F: 307; median age:) patients who received HSCT from January 1998 to November 2014 were included in analysis. Transplant types included AutoHSCT (n=384), AlloHSCT-Sibling (n=217) and AlloHSCT-MUD (n=267). Diagnosis was Ac Leukaemia (n=313), Chr Leukaemia (n=36), Myeloma (n=216), Lymphoma (n=261) or other malignancies (n=42). Commonest indication for AutoHSCT was myeloma or lymphoma. TBI based condition was used in 225 AlloHSCT and 50 AutoHSCT cases. RIC was used in 268 cases and full intensity in 215 cases (unknown in 1). Alemtuzumab or ATG was used in conditioning for 274 cases. Source of stem cell was PBSC (AutoHSCT: 363, AlloHSCT: 382), BM (AutoHSCT: 7, AlloHSCT: 97), both (AutoHSCT: 2, AlloHSCT: 9) and 8 AlloHSCT were UCB grafts.Results: 26, 345 blood PCR results were evaluated. 3100 tests were requested in AutoHSCT patients and 109 (3.6%) were positive. There were no differences in the incidence of positive CMV PCR results before and after use of CMV unselected blood products. Further analysis was limited to AlloHSCT patients. AlloHSCT patients were divided in two groups, GrpA: 1998 to 2013 and GrpB: 2013 to 2014 to evaluate the effect of using CMV unselected blood products. In AlloHSCT group, 9.1% of 23278 samples tested for CMV PCR were positive (Median log: 2.7, range: 0.3-7.3). Incidence of CMV reactivation was not different in GrpB as compared to GrpA (47.7% vs. 48.1%, p=0.93). There was no difference with gender (M: 45.8% vs. F: 53.1%, p=0.13), type of donor (Sibling: 48.6% vs. MUD: 47.9%, p=0.98), use of Alemtuzumab/ATG (50.6% vs. 45.4%, p=0.51), source of stem cells (BM: 36.4% vs. PBSC: 51.3%, p=0.07), use of TBI (43.8% vs. 52.3%, p=0.06). Higher incidence was observed with use of RIC transplant (53.2% vs. 42.3%, p=0.02) and donor-recipient CMV mismatch (NP: 24.5%, PN: 80%, PP: 90.8%, p<0.0001).Conclusion: This analysis suggests that the risk of CMV reactivation is related to the donor-recipient CMV mis-match and the transplant intensity. Use of CMV unselected blood products does not increase the risk of CMV reactivation and careful selection of donors using CMV sero-status is the key factor to reduce the risk of CMV reactivation post AlloHSCT. DisclosuresCavet:Janssen: Consultancy, Research Funding, Speakers Bureau; Celgene: Consultancy, Research Funding, Speakers Bureau. Somervaille:Novartis Pharmaceuticals Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Chemical Synthesis of a Glycopeptide Derived from Skp1 for Probing Protein Specific Glycosylation.

Skp1 is a cytoplasmic and nuclear protein, best known as an adaptor of the SCF family of E3-ubiquitin ligases that label proteins for their degradation. Skp1 in Dictyostelium is posttranslationally modified on a specific hydroxyproline (Hyp) residue by a pentasaccharide, which consists of a Fucα1,2-Galβ-1,3-GlcNAcα core, decorated with two α-linked Gal residues. A glycopeptide derived form Skp1 was prepared to characterize the α-galactosyltransferase (AgtA) that mediates the addition of the α-Gal moieties, and to develop antibodies suitable for tracking the trisaccharide isoform of Skp1 in cells. A strategy was developed for the synthesis of the core trisaccharide-Hyp based on the use of 2-naphthylmethyl (Nap) ethers as permanent protecting groups to allow late stage installation of the Hyp moiety. Tuning of glycosyl donor and acceptor reactivities was critical for achieving high yields and anomeric selectivities of glycosylations. The trisaccharide-Hyp moiety was employed for the preparation of the glycopeptide using microwave-assisted solid phase peptide synthesis. Enzyme kinetic studies revealed that trisaccharide-Hyp and trisaccharide-peptide are poorly recognized by AgtA, indicating the importance of context provided by the native Skp1 protein for engagement with the active site. The trisaccharide-peptide was a potent immunogen capable of generating a rabbit antiserum that was highly selective toward the trisaccharide isoform of full-length Skp1.

Halobenzoyl groups in glycosylation: effect on stereoselectivity and reactivity of glycosyl donors

Described herein is the synthesis and evaluation of a series of glycosyl donors equipped with halobenzoyl substituents at O(4) and O(6) to study their properties in glycosylations. Among possible effects that may include carbonyl participation or H-bond mediated aglycone delivery, our results indicate that halobenzoyls act via a different mode.

CTLA4-CD28 chimeric gene modification of T cells enhances therapeutic efficacy of donor lymphocyte infusion for hematological malignancy (VAC5P.1122)

Abstract Donor lymphocyte infusion (DLI) has been used as an effective therapeutic regimen for the relapsed hematologic malignancies, such as chronic myelocytic leukemia, after allogenic bone marrow transplantation. However, therapeutic efficacy of DLI for other types of leukemia including acute lymphocytic leukemia (ALL) has been limited so far. Thus, we tested if increasing the reactivity of donor T cells by gene modification could enhance therapeutic effect of DLI in a murine model of ALL. For this purpose, we introduced CTLA4-CD28 chimeric gene (CTC28), in which the intracellular signaling domain of CTLA4 was replaced with the CD28 signaling domain, into donor T cells and evaluated the graft-versus-tumor (GVT) effect in an EL4 tumor-bearing mixed bone marrow chimera model. The modification significantly enhanced GVT effect of donor T cells. This effect was correlated with increased expansion of CD8 T cells and elimination of CD8 T cells abolished this effect. GVT effect and CD8 T cell expansion were dependent on the CTC28-modification of CD4 T cells, emphasizing the role of CD4 help in this therapeutic effect. Modified CD4 T cells not only expanded more, but also showed enhanced functional responsiveness. Modified T cell-derived IL-2 was indispensable for the GVT effect, although not required for expansion of the T cells. Thus, combined genetic modification of CD4 and CD8 donor T cells with CTC28 can be a promising strategy for enhancing therapeutic efficacy of DLI for ALL.

Predicting the reactivity of hydride donors in water: thermodynamic constants for hydrogen.

The chemical reactivity of hydride complexes can be predicted using bond strengths for homolytic and heterolytic cleavage of bonds to hydrogen. To determine these bond strengths, thermodynamic constants describing the stability of H(+), H˙, H(-), and H2 are essential and need to be used uniformly to enable the prediction of reactivity and equilibria. Due to discrepancies in the literature for the constants used in water, we propose the use of a set of self-consistent constants with convenient standard states.

Influence of silyl protections on the anomeric reactivity of galactofuranosyl thioglycosides and application of the silylated thiogalactofuranosides to one-pot synthesis of diverse β-D-oligogalactofuranosides.

We describe in this paper the tuning effect of silyl protecting groups on the donor reactivity of galactofuranosyl phenyl thioglycosides. Silyl ethers on the galactofuranose ring are found to have an arming effect on the glycosylation reactivity, but the cyclic 3,5-acetal protecting group decreases the reactivity. The reactive phenyl 2,6-di-O-Bz-3,5-di-O-TBS-1-thio-β-d-galactofuranoside 3 is proved to be a useful glycosyl building block. By taking advantage of this donor, we achieved the highly efficient one-pot solution-phase assembly of a panel of β-d-galactofuranosyl tri- and tetrasaccharides possessing diverse glycosidic linkages.

Endogenous Memory CD8 T Cells Exhibit Increased Early Proliferation in Cardiac Allografts Subjected to Prolonged Ischemia.

Introduction: Memory T cells induced to microbial infections provide protection to subsequent exposures but can have cross-reactivity with other antigens including allogeneic MHC molecules. High numbers of memory T cells with donor reactivity in human and non-human primate recipients prior to transplant are associated with poorer allograft survival and resistance to costimulatory blockade strategies given to induce long-term graft survival. Rodent transplant models have failed to replicate the detrimental impact of endogenous memory T cells on allograft survival and tolerance induction, raising questions about the sufficiency of these models to study this component of alloimmunity. Methods: A/J (H-2a) hearts were subjected to 0.5 or 8 h of cold ischemic storage in UW solution before being heterotopically transplanted to C57BL/6 (H-2b) recipients. BrdU (1 mg) was injected intraperitoneally on days 0 and +1 and graft infiltrating T cell proliferation was assessed on day 2 by flow cytometry. Results: We have recently shown a direct association between increasing duration of cold ischemic storage and numbers of early graft infiltrating memory CD8 T cells that markedly up-regulate effector functions and directly mediate costimulatory blockade resistant rejection of cardiac allografts in a mouse transplant model. Here we show that endogenous memory CD8 T cells exhibit increased early proliferation in grafts subjected to prolonged ischemia that is supported by memory CD4 T cells. Recipient depletion of CD4 T cells or treatment with MR1 (anti-CD40L) at transplant significantly decreased early memory CD8 T cell proliferation and extended survival of grafts subjected to prolonged cold ischemia. Conclusion: These studies provide novel insights into mechanisms underlying endogenous memory CD8 T cell mediated graft injury and the poor outcomes associated with cadaver donor grafts.

Glycosyl alkoxythioimidates as building blocks for glycosylation: a reactivity study

Structural modifications of the leaving group of S-glycosyl O-methyl phenylcarbamothioates (SNea) involving change of substituents that express different electronic effects led to a better understanding of how the reactivity of these glycosyl donors can be modified by changing the structure of their leaving groups. Mechanistic studies involving the isolation of departed aglycones were indicative of the direct activation of both p-methoxy-SNea and p-nitro-SNea leaving groups via the anomeric sulfur rather than the remote nitrogen atom. The presence of an electron donating substituent (p-methoxy) has a strong effect on the nucleophilicity of the sulfur atom that becomes more susceptible toward the attack of thiophilic reagents, in particular. This key observation allowed to differentiate the reactivity levels of p-methoxy-SNea versus p-nitro-SNea and even unmodified SNea leaving groups. The reactivity difference observed in the series of SNea leaving groups is sufficient to be exploited in expeditious oligosaccharide synthesis via selective activation strategies.

Organoboron-catalyzed regio- and stereoselective formation of β-2-deoxyglycosidic linkages.

A borinic acid derived catalyst enables regioselective and β-selective reactions of 2-deoxy- and 2,6-dideoxyglycosyl chloride donors with pyranoside-derived acceptors having unprotected cis-1,2- and 1,3-diol groups. The use of catalysis to promote a β-selective pathway by enhancement of acceptor nucleophilicity constitutes a distinct approach from previous work, which has been aimed at modulating donor reactivity by variation of protective and/or leaving groups.

The use of O-trifluoroacetyl protection and profound influence of the nature of glycosyl acceptor in benzyl-free arabinofuranosylation

The influence of O-trifluoroacetyl (TFA) groups at different positions of thioglycoside glycosyl donors on stereoselectivity of α-arabinofuranosylation leading to corresponding disaccharides was studied. It was shown that TFA group in thioglycoside glycosyl donors, when combined with 2-O-(triisopropylsilyl) (TIPS) non-participating group, may be regarded as an electron-withdrawing protecting group that may enhance 1,2-cis-selectivity in arabinofuranosylation, the results strongly depending on the nature of glycosyl acceptor. The reactivities of the glycosyl donors were compared with those of a similar thioglycoside with O-pentafluoropropionyl groups and the known phenyl 3,5-O-(di-tert-butylsilylene)-1-thio-α-d-arabinofuranosides with 2-O-TIPS and 2-O-benzyl groups. The ‘matching’ in the donor–acceptor combination was found to be critical for achieving both high reactivity of glycosyl donor and β-stereoselectivity of arabinofuranosylation. The use of glycosyl donors with TFA and silyl protection may be useful in the realization of the benzyl-free approach to oligoarabinofuranosides with azido group in aglycon—convenient building blocks for the preparation of neoglycoconjugates.

Endogenous memory CD8 T cells exhibit increased early proliferation in cardiac allografts subjected to prolonged ischemia (TRAN3P.880)

Abstract Memory T cells induced to microbial infections provide protection to subsequent exposures but can have cross-reactivity with allogeneic MHC molecules. High numbers of memory T cells with donor reactivity in human and non-human primate recipients prior to transplant are associated with poorer allograft survival and resistance to costimulatory blockade strategies given to induce long-term graft survival. Rodent transplant models have failed to replicate the detrimental impact of endogenous memory T cells on allograft survival and tolerance induction, raising questions about the sufficiency of these models to study this component of alloimmunity. We have recently shown a direct association between increasing duration of cold ischemic storage and numbers of early graft infiltrating memory CD8 T cells that markedly up-regulate effector functions and directly mediate costimulatory blockade resistant rejection of cardiac allografts in a mouse model. Here we show that endogenous memory CD8 T cells exhibit increased early proliferation in grafts subjected to prolonged ischemia that is supported by memory CD4 T cells. Recipient depletion of CD4 T cells or treatment with MR1 (anti-CD40L) at transplant significantly decreased early memory CD8 T cell proliferation and extended survival of grafts subjected to prolonged cold ischemia. These studies provide novel insights into endogenous memory CD8 T cell mediated graft injury and the poor outcomes associated with cadaver donor grafts.

ChemInform Abstract: Intramolecular Donor—Acceptor Cyclopropane Ring‐Opening Cyclizations

AbstractReview: 50 refs.

Endogenous Memory CD8 T Cells Directly Mediate Cardiac Allograft Rejection

Differences in levels of environmentally induced memory T cells that cross-react with donor MHC molecules are postulated to account for the efficacy of allograft tolerance-inducing strategies in rodents versus their failure in nonhuman primates and human transplant patients. Strategies to study the impact of donor-reactive memory T cells on allografts in rodents have relied on the pretransplant induction of memory T cells cross-reactive with donor allogeneic MHC molecules through recipient viral infection, priming directly with donor antigen or adoptive transfer of donor antigen primed memory T cells. Each approach accelerates allograft rejection and confers resistance to tolerance induction, but also biases the T cell repertoire to strong donor reactivity. The ability of endogenous memory T cells within unprimed mice to directly reject an allograft is unknown. Here, we show a direct association between increased duration of cold ischemic allograft storage and numbers and enhanced functions of early graft infiltrating endogenous CD8 memory T cells. These T cells directly mediate rejection of allografts subjected to prolonged ischemia and this rejection is resistant to costimulatory blockade. These findings recapitulate the clinically significant impact of endogenous memory T cells with donor reactivity in a mouse transplant model in the absence of prior recipient priming.