Polykondensationen mit α-aminocarbonsäureestern. II. SnCl4-katalysierte kondensation des Glycinäthylesters

During the SnCl₄ catalyzed polycondensation of glycin ethylester at 0–80°C., the yield of total condensation products is passing a maximum and becomes constant after 24 hrs. Under these pseudo-equilibrium conditions the DP is enhanced strongly for SnCl₄ concentrations above 4 mole-%, the yield at condensation temperatures above 80°C. The polycondensation is catalyzed by a complex of SnCl₄ and glycin ethyl ester. The yield of 2,5-dioxopiperazine is passing a maximum with time too, but is always low and in the order of 5%. Dioxopiperazine will not be polymerized by SnCl₄ alone, however under the conditions the polyreaction takes place. The formation of the dioxopiperazine is caused by the glycine ethylester hydrochloride, which is formed by ethanolysis of SnCl₄.     

Polykondensationen mit α-aminocarbonsäureestern. I. Orientierende papierchromatographische untersuchungen

Glycine esters undergo polycondensation under the action of different catalysts at temperatures between 0 and 80°C, whereas esters of substituted amino acids need higher reaction temperatures. High catalytic activity is exhibited by acids like HOHC as well as by compounds like SnCl₄, PCl₅, and BiCl₃. The R_f-values of some amino acid derivatives in different media are reported.     

Polykondensationen mit α-aminocarbonsäureestern. III. Analytische bestimmung der dioxopiperazine des glycins und des L-leucins in polykondensaten

The dioxopiperazines (DOP) of glycine and L-Leucine can be sublimed quantitatively from mixture of the DOP with the corresponding oligomer and polymer peptide esters at 180°C. The lower homolog of L-Leucine must be eluated with 0.5 N HCl before sublimation. During the eluation, a part of the leucine-DOP is transformed into the dileucine up to the corresponding solubility limit. The leucine-DOP can be determined by infrared spectroscopy in mixture with other condensation products, which is not possible with the glycine-DOP.     

Polykondensationen mit α-aminocarbonsäureestern. IV. Komplexe des zinntetrachlorids mit den äthylestern und dioxopiperazinen des glycins und des L-leucins

Tin tetrachloride forms a 1:2 complex with glycine ethylester, 1:1 complexes with L-leucine ethylester, 2,5-dioxopiperazine resp. 3,6-diisobutyl-2,5-dioxopiperazine. Complex formation takes place via the amine groups as well as via the ester carbonyl groups as could be shown by IR spectroscopy. The relative amount of each type of bonding depends on temperature (+22 to ?80°C.) and solvent (n-hexane and benzene) from which the complexes were precipitated. A coordination number of 5 seems to be probable for the 1:1 complexes.     

Polymere und Copolymere mit p-Vinyl-α.α-diphenyläthylen-Grundbausteinen

p-Vinyl-α.α-diphenylethylene (pNDPÄ) was polymerized radically in bulk at 80°C and copolymerized with styrene. The resulting polymers and copolymers had relatively low degrees of polymerization (ranging from 10 to 100). The polymerization took place primarily via the vinyl group and to a lower extend via the vinyliden group. The unsaturated side group enabled subsequent crosslinking reactions with these polymers. Copolymers with pVDPÄ-groups having higher molecular weights were obtained by GRIGNARD reaction of p-vinyl benzophenone/styrene copolymers with methyl magnesium iodide. These copolymers yielded the corresponding macromolecular polyanions upon treatment with naphthalene sodium in tetrahydrofuran; the latter were able to start graft-copolymerization of acrylonitrile, methylmethacrylate, and styrene; when using styrene, living side chains were formed. It was shown by dissolution experiments that no ungrafted backbone polymer and no free homopolymers were present in the graft-copolymers with acrylonitrile and methylmethacrylate.     

Kinetik der radikalischen copolymerisation α-substituierter styrole mit styrol. 1. Teil. Copolymerisation von α-methylstyrol mit styrol oberhalb der ceiling-temperatur von α-methylstyrol

The radical copolymerization of α-methylstyrene with styrene in the temperature range from 60 to 150°C can be described according to the equations derived by WITTMER with the assumption, that the addition steps of α-methylstyrene may be reversibel. For the temperature range from 60 to 110°C it could be demonstrated that it would be sufficient to consider only the reversibility of the addition steps of α-methylstyrene to a radical end with α-methylstyrene as the terminal unit. At a reaction temperature of 150°C the addition of α-methylstyrene to a styryl chain end is also reversible, the equilibrium constant being only 1/30 of the α-methylstyrene homopolymerization. The retardation of the polymerization rate by admixture of small amounts of α-methylstyrene to styrene was measured. The results allow an estimation of the rate constants and activation energies of the chain propagation and depolymerization steps.     

Zur Taktizität von Poly(α-methylstyrol), 6. Zum stereoregulierenden Mechanismus der Polyreaktion des α-Methylstyrols mit Butyllithium in Tetrahydrofuran

Some models of the stereoregulating mechanism of the polymerisation of α-methylstyrene with butyllithium in tetrahydrofuran are discussed. A mechanism is proposed, in which the depolymerisation of the polymer chain and an isomerisation reaction of the active site change the tacticity generated by each propagation step. The isomerisation reaction is interpreted as a dissociation of the active lithiumorganic compound occurring with racemisation. The quantitative calculation of the tacticity based on the mechanism without depolymerisation using kinetic data agrees well with the experimental dependence of the tacticity on reaction temperature and initial monomer concentration. The activation parameters of the isomerisation reaction used in this treatment are (index r = racemic, m = meso):      

Über Derivate des Poly-α-chloracroleins. II. Dehydrochlorierung von Poly(α-chloracroleindimethylacetal-co-vinylchlorid) und Poly-α-chloracroleindiacetat mit Basen

Dehydrochlorination of poly(vinylchloride-co-α-chloroacroleindimethylacetale) by sodium amide in ammonia or tetrahydrofuran leads to insoluble products below chlorine contents of 36.5% Soluble products down to chlorine contents of 10% were found by applying potassium tert-butylate. The rate of dehydrochlorination is practically independent of the copolymer composition. At high concentrations of the base, the rate is a function of chlorine concentration only at low degrees of dehydrochlorination, but of base concentration only at high conversion. The unusual exponents of 3.3 for chlorine concentration and 4.3 for base concentration resp. were found for these limiting cases. Below chlorine contents of 34%, the heptaene-sequence was found to have the highest absorption. No influence of reaction temperature on sequence distribution could be detected. Diene and triene, sequences are present in the highest mole concentrations at all stages of the reaction.     

Spaltung des α-L-Arabinofuranosids, β-D-Glucopyranosids und β-Cellobiosids von 4-Nitrophenol durch Enzyme verschiedener Pilze — ein Beitrag in Verbindung mit Versuchen zur Steigerung der Selektivität der Tumortherapie

To carry out long-term experiments as part of a therapy concept of malignant tumours using inactive transport forms of cancerostatic substances and their specific cleavage in the acidic pH region of the tumours by application of extraneous enzymes, we require enzymes with similar catalytic and pharmacokinetic properties which differ from each other in immunological respect. In the search for such enzymes, the α-L-arabinofuranosidases from 12 different fungi, among them 9 basidiomycetes, were studied. The enzymes mentioned were demonstrable in all fungi. Optimum pH values ranged between 2.5 and 5.5. The Km values for the cleavage of α-L-arabinofuranoside were, in most cases, 0.5 to 1.8 moles · liter^?1 · 10^?3. With regard to pH dependence, the α-L-arabino-furanosidases of most of the fungi investigated proved adequate for the long-term trials envisaged. 4-nitrophenyl-β-D-glucopyranoside and -β-cellobioside were also cleaved by enzyme preparations of all the 11 fungi investigated. The β-D-glucopyranosidases showed a less favourable pH dependence than the α-L-arabinofuranosidases. The cleavage of 4-nitrophenyl-β-cellobioside, on the contrary, showed mostly a comparatively favourable pH dependence. On the basis of the coinciding optimal pH values and the occurrence of 4-nitrophenyl-β-D-glucopyranoside as an intermediate product in the cleavage of the corresponding cellobioside, we assume that both substrates are cleaved by β-glucosidase. Because the occurrence of the glucoside during the cleavage of cellobioside is undesirable for the therapeutic trial, a method is proposed for selection of an appropriate cellobioside splitting enzyme basing on the present studies and the relevant literature.     

Transendothelial chemotaxis of human αβ and γδ T lymphocytes to chemokines

Two subpopulations of human T lymphocytes expressing different antigen receptors, α / β and γ / δ, emigrate into inflamed tissues in distinctive patterns. We compared the transmigration of α / β and γ / δ T cells to C-C and C-X-C chemokines using an in vitro transendothelial chemotaxis assay. The C-C chemokines monocyte chemoattractant protein (MCP)-1, RANTES, macrophage inflammatory protein (MIP)-1α and MIP-1β stimulated similar, dose-dependent chemotaxis of purified γ / δ T cells, whereas MCP-1, RANTES, and MIP-1α pro duced greater chemotaxis of purified α / β T cells than MIP-1β. In contrast, the C-X-C chemokines interleukin (IL)-8 and interferon-γ inducible protein-10 (IP-10) did not promote chemotaxis of either α / β or γ / δ T cells. Three γ / δ T cell clones with differing CD4 and CD8 phenotypes also migrated exclusively to C-C chemokines. Phenotypic analysis of mononuclear cells that transmigrated from an input population of unfractionated peripheral blood mono nuclear cells confirmed the results with purified γ / δ T cells. Our data demonstrate that human peripheral blood α / β and γ / δ T cells can transmigrate to MCP-1, RANTES, MIP-1α, and MIP-1β, and suggest that both T lymphocyte subpopulations share the capacity to emigrate in response to C-C chemokines during inflammation.     

The α4β1 integrin in sickle cell disease

The α4β1 integrin is an adhesion receptor expressed on reticulocytes in sickle cell disease (SCD) and mediates the adhesion of these cells to sub-endothelial matrix proteins and the endothelium. In this review, we describe the mechanism of activation of the α4β1 integrin on sickle reticulocytes and discuss novel roles for this integrin in SCD as a result of this activation. We also illustrate novel therapies in SCD that may target the integrin and alleviate vaso-occlusion.     

Zur copolymerisation von α-methylstyrol und butadien III. Das NMR-spektrum der sequenzen mit zentraler α-methylstyroleinheit

220 MHz proton resonance spectra of copolymers from α-methylstyrene and butadiene have been investigated. Model compounds have been prepared by a lithiumbutyl initiated copolymerisation in tetrahydrofurane at ?75°C. The NMR spectra of the phenyl and α-methyl group are interpreted by signals from configurational and compositional triads with a central χ-methylstyrene unit. The chemical shift of the triads, possessing a central α-methyl styrene unit, takes place to lower field in the α-methyl region to such an extend that no strong overlapping with the signals of the configurational triads takes place. In the region of the phenyl protons configurational and compositional triads are overlapping each other. Using 3,4,5-trideuterio-α-methylstyrene it is possible to assign configurational and compositional triads in the resonance spectrum of the ortho-phenylprotons.     

DL4‐mediated Notch signaling is required for the development of fetal αβ and γδ T cells

T‐cell development depends upon interactions between thymocytes and thymic epithelial cells (TECs). The engagement of delta‐like 4 (DL4) on TECs by Notch1 expressed by blood‐borne BM‐derived precursors is essential for T‐cell commitment in the adult thymus. In contrast to the adult, the earliest T‐cell progenitors in the embryo originate in the fetal liver and migrate to the nonvascularized fetal thymus via chemokine signals. Within the fetal thymus, some T‐cell precursors undergo programmed TCRγ and TCRδ rearrangement and selection, giving rise to unique γδ T cells. Despite these fundamental differences between fetal and adult T‐cell lymphopoiesis, we show here that DL4‐mediated Notch signaling is essential for the development of both αβ and γδ T‐cell lineages in the embryo. Deletion of the DL4 gene in fetal TECs results in an early block in αβ T‐cell development and a dramatic reduction of all γδ T‐cell subsets in the fetal thymus. In contrast to the adult, no dramatic deviation of T‐cell precursors to alternative fates was observed in the fetal thymus in the absence of Notch signaling. Taken together, our data reveal a common requirement for DL4‐mediated Notch signaling in fetal and adult thymopoiesis.     

Feldionen- und Elektronenstoß-Massenspektrometrie von Polymeren und Copolymeren, 3. Copolymere des α-Methylstyrols mit Methylmethacrylat und Acrylnitril

Pyro-field ion mass spectrometry was used to study the primary fragments as well as the depolymerization behaviour of some α-methylstyrene (α-MS) copolymers. α-MS-methyl methacrylate (MMA) copolymers, when pyrolyzed, decompose mainly into the two monomers. The zip-depolymerization usually proceeds through the whole chain, disregarding the hetero-links between different monomeric units. Hetero-fragments are formed only with a small probability; still lower is the concentration of homo-dimers in the pyrolysate. Primary fragments of poly(acrylonitrile) (PAN) are acrylonitrile (AN), (AN)₂, (AN)₃, HCN, C₃H₅CN, C₄H₇CN, C₅H₉CN and higher nitriles. During pyrolysis of α-MS-AN copolymers, α-MS sequences zipdepolymerize with formation of the monomer. This retropolymerization stops at heterolinks, and fragments of the type α-MS-AN or α-MS-(AN)₂ are formed. Long AN sequences in the copolymer cause, as PAN itself, formation of AN oligomeres as well as higher alkene cyanides. Isolated AN units lead to the formation of monomeric AN.     

Functional and molecular characterization of B cell-responsive Vδ1+ γδ T cells

Cells expressing the Vδ1⁺ gene segment are a minor γδ T cell population in human peripheral blood but predominate in epithelia and (inflamed) tissues. The characteristic dendritic-like morphology of these γδ T cells is consistent with their putative immune surveillance role in epithelia. Their function, however, remains unknown. We and others previously reported that a subset of Vδ1⁺ γδ T cells proliferates after stimulation with Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (LCL), but not with fresh peripheral blood-derived B cells. These responses were independent of the type of T cell receptor (TcR) γ chain co-expressed with the Vδ1 chain. The in vivo relevance of this LCL-mediated activation as well as the nature of the stimulatory ligand on the LCL is not well established. In this study, we tested the proliferative response of Vδ1⁺ LCL-responsive T cells against non-EBV-transformed B cells, activated through CD40 by murine EL4 B5 cells, and to a panel of B cell lines differing in the expression of EBV nuclear antigen proteins and adhesion/co-stimulatory molecules. The role of the Epstein-Barr virus-derived antigen in the induction of this response could be excluded as the activated (non-EBV-transformed) peripheral blood B cells were also able to induce a proliferative response in the LCL-responsive Vδ1⁺ T cells. Therefore, the stimulatory ligand on B cells is of cellular rather than of viral origin, and its expression is up-regulated upon activation of B cells. The expression of B7 and CD39 molecules on the surface of activated B cells appeared to be crucial since antibodies to these structures could block the induction of proliferation of the Vδ1⁺ T cells. Finally, we investigated the diversity of the responding Vδ1⁺ γδ T cell clones by sequence analysis of the TcRδ junctional regions. No restricted V-D-J sequences were found among the LCL-responsive Vδ1⁺ T cell clones, arguing strongly against a mono- or oligoclonal Vδ1⁺ γδ T cell response to LCL. These findings may explain the presence of polyclonally activated Vδ1⁺ T cells in inflamed tissues where activated B cells are often present.     

γδ cells regulate autoimmunity

γδ cells are attractive candidates for mediators of autoimmune disease. They can expand in germ-free mice, probably through recognition of autoantigens, and γδ-cell-deficient mice, unlike mice deficient in αβ T cells or B cells, show no severe defects in the immune response to foreign antigen challenge. A capacity of γδ cells to effect or regulate tissue damage is also plausible, given their ready localization to tissues, and their myriad of effector functions. Added to this, attempts to reconstruct the physiological course of autoimmune diseases with only autoreactive αβ T cells seem invariably to fall short for lack of other unidentified players. γδ cells and their putative ligands have been linked to autoimmune conditions, and recent experiments confirm that γδ cells play a significant role in autoimmune disease in vivo.     

Developmental expression of the αIELβ7 integrin on T cell receptor γδ and T cell receptor αβ T cells

A novel monoclonal antibody, 2E7, was shown by immunoprecipitation to be reactive with the α_IELβ7 integrin and was employed to analyze the expression of this integrin in lymphocyte subsets and during T cell ontogeny. In adult lymph nodes, α_IEL was expressed at low levels by 40–70% of CD8⁺ T cells and < 5% of CD4⁺ T cells. However, virtually all intestinal intraepithelial lymphocytes and ?20% of lamina propria CD4⁺ T cells were 2E7⁺, indicating a preferential expression of this integrin on mucosal T cells. Examination of α_IEL integrin expression during thymus ontogeny revealed that ?3–5% of fetal or adult thymocytes were 2E7⁺. Interestingly, early in fetal thymus ontogeny, ?40% of 2E7⁺ cells expressed T cell receptor (TcR)-γδ and this subset persisted through birth. A developmental switch occurred such that 2E7⁺ TcR^? CD4^?8⁺ cells detected on fetal day 19 were followed by 2E7⁺ TcR-αβ CD4^?8⁺ cells in the neonatal thymus. The latter population persisted throughout thymus ontogeny into adulthood. Interestingly, a subset of TcR-γδ Vγ3⁺ day 16 fetal thymocyte dendritic epidermal cell (DEC) precursors were 2E7⁺, but all mature DEC expressed high levels of α_IEL integrin, suggesting that the α_IEL integrin was acquired late in DEC maturation. This possibility was strenghthened by immunohistochemical localization of the majority of 2E7⁺ γδ and αβ T cells to the medullary regions of the thymus. Overall, the results demonstrate a developmentally ordered expression pattern of the α_IELβ₇ integrin that suggests a common function for this integrin during TcR-γδ and -αβ CD4^?8⁺ T cell thymocyte development or perhaps in effector functions for these subsets.     

A TCR α chain transgene induces maturation of CD4− CD8− α β+ T cells from γ δ T cell precursors

The proportion of CD4⁻ CD8⁻ double-negative (DN) α β T cells is increased both in the thymus and in peripheral lymphoid organs of TCR α chain-transgenic mice. In this report we have characterized this T cell population to elucidate its relationship to α β and γ δ T cells. We show that the transgenic DN cells are phenotypically similar to γ δ T cells but distinct from DN NK T cells. The precursors of DN cells have neither rearranged endogenous TCRα genes nor been negatively selected by the Mls^a antigen, suggesting that they originate from a differentiation stage before the onset of TCR α chain rearrangements and CD4/CD8 gene expression. Neither in-frame VδDδJδ nor VγJγ rearrangements are over-represented in this population. However, since peripheral γ δ T cells with functional TCRβ gene rearrangements have been depleted in the transgenics, we propose that the transgenic DN population, at least partially, originates from the precursors of those cells. The present data lend support to the view that maturation signals to γ δ lineage-committed precursors can be delivered via TCR α β heterodimers.