Thiourea Bond Research Articles

Mannose-coupled AAV2: A second-generation AAV vector for increased retinal gene therapy efficiency

Inherited retinal diseases are a leading and untreatable cause of blindness and are therefore candidate diseases for gene therapy. Recombinant vectors derived from adeno-associated virus (rAAV) are currently the most promising vehicles for in vivo therapeutic gene delivery to the retina. However, there is a need for novel AAV-based vectors with greater efficacy for ophthalmic applications, as underscored by recent reports of dose-related inflammatory responses in clinical trials of rAAV-based ocular gene therapies. Improved therapeutic efficacy of vectors would allow for decreases in the dose delivered, with consequent reductions in inflammatory reactions. Here, we describe the development of new rAAV vectors using bioconjugation chemistry to modify the rAAV capsid, thereby improving the therapeutic index. Covalent coupling of a mannose ligand, via the formation of a thiourea bond, to the amino groups of the rAAV capsid significantly increases vector transduction efficiency of both rat and nonhuman primate retinas. These optimized rAAV vectors have important implications for the treatment of a wide range of retinal diseases.

Upcycling of dynamic thiourea thermoset polymers by intrinsic chemical strengthening

Thermoset polymers are indispensable but their environmental impact has been an ever-increasing concern given their typical intractability. Although concepts enabling their reprocessing have been demonstrated, their practical potential is limited by the deteriorated performance of the reprocessed materials. Here, we report a thiourea based thermoset elastomer that can be reprocessed with enhanced mechanical properties. We reveal that the thiourea bonds are dynamic which leads to the reprocessibility. More importantly, they can undergo selective oxidation during high temperature reprocessing, resulting in significant chemical strengthening within certain reprocessing cycles. This is opposite to most polymers for which reprocessing typically results in material deterioration. The possibility of having materials with inherent reprocessing induced performance enhancement points to a promising direction towards polymer recycling.

Robust and Reprocessable Artificial Muscles Based on Liquid Crystal Elastomers with Dynamic Thiourea Bonds

AbstractThis work reports a new class of liquid crystal elastomers (LCEs) cross‐linked with poly(ether‐thiourea) comprising a triethylene glycol spacer (LCE‐TUEG) wherein thiourea bonds impart a hydrogen bonding capability as well as permit dynamic covalent bond (DCB) exchange at elevated temperatures. While hydrogen bonding enhances the mechanical properties of LCE‐TUEG, the DCB allows the macromolecular network rearrangement of the LCEs, resulting in various useful properties that are not present in conventional LCEs, including the ability to undergo welding, melt and solution reprocessing, reprogrammable actuation, and self‐healing. By exploiting these dynamic features, electrically powered artificial muscles are fabricated that can be actuated by Joule heating using a resistive wire. In particular, an excellent specific work is demonstrated (≈65 J kg−1) for the artificial muscle, and full recyclability of both the LCE matrix and the metallic heating wire is achieved. Furthermore, a biomimetic artificial hand is created by welding and assembling multiple LCE‐TUEG films embedded with heating wires, followed by mechanical alignment. The integration of a microcontroller to the artificial hand enables the selective actuation of each finger, and various hand gestures are successfully demonstrated.

Bioinspired Carbohydrate-Decorated Long-Period Fiber Grating for Label-Free Bacteria Detection

Pathogenic bacteria cause thousands of human infections every year. Their effective detection can prevent diseases, decrease the cost of patient hospitalizations, and thus enhance the standard of people’s life. Here, we present a bioinspired sensor for bacteria detection in water, which is based on long-period fiber grating (LPFG) and $\alpha $ -mannoside receptor. Embedding of p-aminophenyl- $\alpha $ -D-mannopyranoside, sensitive to E. coli strain, into the biosensor, allows mimicking natural bacteria adhesion to the host cell. The receptor has been covalently immobilized by a thiourea bond to the LPFG platform to ensure stable and reproducible work. The lowest detectable concentration of bacteria was equal to 103 colony forming unit ml−1.

Immobilization of polyoxometalate hybrid catalysts onto mesoporous silica supports using phenylene diisothiocyanate as a cross-linking agent

Abstract The hybrid derivative of heteropolytungstate bearing two aniline groups, namely (nBu4N)3[NaHPW9O34{As(O)C6H4NH2}2], was post-functionalized in the presence of 1,4-phenylene diisothiocyanate (PDITC). The resulting molecular moiety was characterized by IR, 1H and 31P NMR spectroscopy. In a second step, this post-functionalized hybrid of polyoxometalate was covalently grafted onto the surface of an amino-functionalized SBA-15 silica by means of the formation of thiourea bonds. This simple and efficient strategy of immobilization did not require the use of a coupling agent and was performed in mild reaction conditions. Various physicochemical techniques (13C and 31P CP MAS NMR spectroscopies, XPS, XRF, HR-TEM microscopy and N2 sorption) contributed to the full characterization of the supported catalyst. In addition HR-TEM was found to be an essential technique for the identification of the polyoxometalate units inside the pores of SBA-15. Finally, the catalytic performances of the supported polyoxometalates were evaluated in the epoxidation of cyclooctene with aqueous H2O2 in acetonitrile at 50 °C.

Modification of Oligopeptides on Aspartic Acid or Lysine Residues by Solid-Phase Synthesis through On-Resin Side-Chain Conjugation

On-resin side-chain conjugations of various moieties to oligo­peptides were performed through an orthogonal protecting protocol using side-chain-protecting groups for aspartic acid or lysine that could be selectively removed on-resin. Various types of modification, such as PEGylation, biotinylation, glycosylation, or fluorophore-labeling of peptides, were realized by using this strategy. The formation of ester, amide, hydrazide, and thiourea bonds was accomplished through the on-resin conjugation. Our work provides an improved and convenient solid-phase synthetic protocol for the modification of oligopeptides on their aspartic acid or lysine residues. This is a universal and practical method that is expected to increase the potential application of peptide-related drugs.

Fluorescent-fipronil: Design and synthesis of a stable conjugate

Fipronil is a phenyl pyrazole molecule widely used across the world as both insecticide and veterinary drug. The main goal of this work was to synthesize a fluorescently labeled fipronil derivative for cellular imaging without affecting its intrinsic properties. We selected fluorescein as fluorescent probe and we investigated different strategies for stable chemical ligation between both entities, such as thiourea and direct peptide bond. While thiourea bond displayed low stability, direct peptide bond was difficult to achieve due to problems of steric hindrance. The best result was obtained by conjugation using click chemistry, which allowed to obtain fipronil stably labeled with the fluorescent probe.

Cellular uptake of glucoheptoamidated poly(amidoamine) PAMAM G3 dendrimer with amide-conjugated biotin, a potential carrier of anticancer drugs

In search for soluble derivatives of PAMAM dendrimers as potential carriers for hydrophobic drugs, the conjugates of PAMAM G3 with biotin, further converted into glycodendrimer with d-glucoheptono-1,4-lactone, were prepared. Polyamidoamine dendrimer (PAMAM) of third generation, G3 was functionalized with four biotin equivalents covalently attached to terminal amine nitrogens via amide bond G34B. The remaining 28 amine groups were blocked by glucoheptoamide substituents (gh) to give G34B28gh or with one fluorescein equivalent (attached by reaction of G34B with fluorescein isothiocyanate, FITC) via thiourea bond as FITC followed by exhaustive glucoheptoamidation to get G34B27gh1F. As a control the G3 substituted totally with 32 glucoheptoamide residues, G3gh and its fluorescein labeled analogue G331gh1F were synthesized.The glucoheptoamidation of PAMAM G0 dendrimer with glucoheptono-1,4-lactone was performed in order to fully characterize the 1H NMR spectra of glucoheptoamidated PAMAM dendrimers and to control the derivatization of G3 with glucoheptono-1,4-lactone. Another two derivatives of G3, namely G34B28gh1F′ and G332ghF′, with ester bonded fluorescein were also obtained.Biological properties of obtained dendrimer conjugates were estimated in vitro with human cell lines: normal fibroblast (BJ) and two cancer glioblastoma (U-118 MG) and squamous carcinoma (SCC-15), including cytotoxicity by reduction of XTT and neutral red (NR) assays. Cellular uptake of dendrimer conjugates was evaluated with confocal microscopy.Obtained results confirmed, that biotinylated bioconjugates have always lower cytotoxicity and 3–4 times higher cellular uptake than non-biotinylated dendrimer conjugates in all cell lines. Comparison of various cell lines revealed different dose-dependent cell responses and the lower cytotoxicity of examined dendrimer conjugates for normal fibroblasts and squamous carcinoma, as compared with much higher cytotoxic effects seen in glioblastoma cell line. Synthetized multi-functional conjugate (G34B27gh1F) is a promising candidate as biocompatible vehicle for hydrophobic molecules used in anticancer therapy.

Si-HPMC and Si-chitosan hydrogel for tissue engineering

Event Abstract Back to Event Si-HPMC and Si-chitosan hydrogel for tissue engineering Gildas Rethore1, Cécile Boyer1, Fabienne Jordana1, Olivier Gauth1, 2, Jérome Guicheux1 and Pierre Weiss1 1 Université de Nantes - INSERM - Centre Hospitalier Universitaire de Nantes, LIOAD - UMRS 791, France 2 ONIRIS - École Vétérinaire, LIOAD - UMRS 791, France Introduction: It was believed that biomaterial selection was performed based on its macroporosity, biocompatibility and degradability properties but recently its ability to withstand biomechanical stress has also been considered. Discher et al[1]. have indeed shown that material stiffness induces critical effects on cell behaviour and differentiation. Therefore, we have recently embarked on the development of mechanically-competent hydrogels for bone and cartilage tissue engineering. We prepared a cellulose based polymer capable of self cross-linkage (Si-HPMC) to avoid any toxicity issues resulting from using cross-linking chemicals or photo cross-linking. Therefore, LIOAD has been working on the development of hydrogels as ECM for bone and cartilage regeneration. The objectives of the present work are to modulate the physico-chemical and biological properties of our hydrogels by mixing two silated polysaccharides Si-HPMC and Si-Chitosan. Experimental Methods: The self cross-linkable polymer (Si-HPMC) was prepared according to an already published method developed in LIOAD[2]. Silanol groups were linked to amine moieties of the chitosan via thio-urea bond. Hydrogel characterizations: Hydrogels and reinforced hydrogels were characterized physico chemically to determine their elastic moduli using MARS rheometer (G’), Dynamic Mechanical Analysis (E’) and microscopy. Biological investigations have been done with human nasal chondrocytes by determining the cell viability in 2D using MTS, 3D by confocal microscopy after Live&Dead staining. In vivo investigations have been performed in subcutaneous sockets in nude mice and in focal defects in rabbit. Results and Discussion: The characterizations showed that adding Si-Chitosan within Si-HPMC hydrogels increases the elastic moduli without interfering with the biocompatibility. Indeed, all the constructs that we used in this study showed no toxicity both in 2D and 3D (as shown in figure 1). Culturing cells in 3D within our hydrogel containing Si-Chitosan also induces cell adhesion onto the matrice as I can be observed on confocal micrograph in figure 2. It is worth noted that after 5 weeks of implantation, the chondrocytes showed a good viability and still express a chondrocyte phenotype. Moreover, during the surgery, due to the presence of chitosan, our constructs showed good adhesion behaviour onto the cartilage focal defect. Fig 1: left : 2D hASCs viability in contact with Si-HPMC/Si-Chitosan hydrogels (Positive control : cell alone, control for cell death: actinomycin). Right : Confocal micrograph showing living cells (green) and dead cells (red) after 7 days of culture inside hydrogels. Fig 2 : Confocal micrographs showing cell adhesions after 7 days culture in Si-HPMC/Si-Chitosan hydrogel. Conclusion: The study demonstrates the feasibility of our approach to modulate our self-setting hydrogel while keeping them biocompatible. ANR (HYCAR); Région Pays de la Loire (BIOREGOS)

Isosteric substitutions of urea to thiourea and selenourea in aliphatic oligourea foldamers: site-specific perturbation of the helix geometry.

Nearly isosteric oxo to thioxo substitution was employed to interrogate the structure of foldamers with a urea backbone and explore the relationship between helical folding and hydrogen-bonding interactions. A series of oligomers with urea bonds substituted by thiourea bonds at discrete or all positions in the sequence have been prepared and their folding propensity was studied by using a combination of spectroscopic methods and X-ray diffraction. The outcome of oxo to thioxo replacements on the helical folding was found to depend on whether central or terminal ureas were modified. The canonical helix geometry was not affected upon insertion of thioureas close to the negative end of the helix dipole, whereas thioureas close to the positive pole were found to increase the terminal flexibility and cause helix fraying. Perturbation was amplified when a selenourea was incorporated instead, leading to a structure that is only partly folded.

Anticancer effects of a novel class rosin-derivatives with different mechanisms

In this Letter, the anticancer activity of novel rosin-derivatives introducing indicated side chains at position C18 of dehydroabietic acid (DHAA) was reported. Gratifyingly, all of these derivatives showed significantly cytotoxicity toward diverse human carcinoma cell lines. We found the compound 4 could induce cell membrane damage at high concentration as well as cell apoptosis at low concentration. However, compound 5, attachment of quinidine to dehydroabietic acid via thiourea bond, only induced apoptotic cell death. In addition, all these active compounds induced apoptosis mainly through mitochondrial-dependent pathway. Interestingly, compound 5 exhibited the highest anticancer activity and little toxicity to normal cells compared with the other derivatives. Therefore, 5 merits further investigation as a potential agent for future anticancer treatment.

Development of a bifunctional chelating agent containing isothiocyanate residue for one step F-18 labeling of peptides and application for RGD labeling

We report herein a novel isothiocyanate active ligand for fluorine-18 labeling prepared by four step synthesis. It can be conjugated to a target molecule containing an amino functional group under weak basic conditions by way of thiourea bond formation. We explored the application of synthesized ligand by conjugating to well known αvβ3 integrin targeting peptide, c(RGDyK). The conjugated peptide showed good radiochemical yield and efficiency with an excellent radiochemical purity (97.1±1.2%) in a short reaction time (10min). Labeled peptide showed excellent in vitro and in vivo stability (>95%). αvβ3 integrin specific tumor uptake was observed both in biodistribution and small animal microPET studies on αvβ3-positive U87MG (human glioma cells) xenograft bearing mice. In general, successful application of synthesized ligand for labeling of RGD peptide could facilitate the possibility of using this ligand for labeling peptides containing an amino functional group.

Comparison of 64Cu-Complexing Bifunctional Chelators for Radioimmunoconjugation: Labeling Efficiency, Specific Activity, and in Vitro/in Vivo Stability

High radiolabeling efficiency, preferably to high specific activity, and good stability of the radioimmunoconjugate are essential features for a successful immunoconjugate for imaging or therapy. In this study, the radiolabeling efficiency, in vitro stability, and biodistribution of immunoconjugates with eight different bifunctional chelators labeled with (64)Cu were compared. The anti-CD20 antibody, rituximab, was conjugated to four macrocyclic bifunctional chelators (p-SCN-Bn-DOTA, p-SCN-Bn-Oxo-DO3A, p-SCN-NOTA, and p-SCN-PCTA), three DTPA derivatives (p-SCN-Bn-DTPA, p-SCN-CHX-A″-DTPA, and ITC-2B3M-DTPA), and a macrobicyclic hexamine (sarcophagine) chelator (sar-CO2H) = (1-NH2-8-NHCO(CH2)3CO2H)sar where sar = sarcophagine = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane). Radiolabeling efficiency under various conditions, in vitro stability in serum at 37 °C, and in vivo biodistribution and imaging in normal mice over 48 h were studied. All chelators except sar-CO2H were conjugated to rituximab by thiourea bond formation with an average of 4.9 ± 0.9 chelators per antibody molecule. Sar-CO2H was conjugated to rituximab by amide bond formation with 0.5 chelators per antibody molecule. Efficiencies of (64)Cu radiolabeling were dependent on the concentration of immunoconjugate. Notably, the (64)Cu-NOTA-rituximab conjugate demonstrated the highest radiochemical yield (95%) under very dilute conditions (31 nM NOTA-rituximab conjugate). Similarly, sar-CO-rituximab, containing 1/10th the number of chelators per antibody compared to that of other conjugates, retained high labeling efficiency (98%) at an antibody concentration of 250 nM. In contrast to the radioimmunoconjugates containing DTPA derivatives, which demonstrated poor serum stability, all macrocyclic radioimmunoconjugates were very stable in serum with <6% dissociation of (64)Cu over 48 h. In vivo biodistribution profiles in normal female Balb/C mice were similar for all the macrocyclic radioimmunoconjugates with most of the activity remaining in the blood pool up to 48 h. While all the macrocyclic bifunctional chelators are suitable for molecular imaging using (64)Cu-labeled antibody conjugates, NOTA and sar-CO2H show significant advantages over the others in that they can be radiolabeled rapidly at room temperature, under dilute conditions, resulting in high specific activity.

Synthesis of 68Ga-labeled DOTA-nitroimidazole derivatives and their feasibilities as hypoxia imaging PET tracers

The imaging of hypoxia is important for therapeutic decision making in various diseases. 68Ga is an important radionuclide for positron emission tomography (PET), and its usage is increasing, due to the development of the 68Ge/ 68Ga-generator. In the present study, the authors synthesized two nitroimidazole derivatives by conjugating nitroimidazole and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) via an amide bond ( 4) and a thiourea bond ( 5). Both derivatives were labeled with 68Ga with high labeling efficiency and were stable after labeling. The low partition coefficients (log P) of 68Ga- 4 (−4.6) and 68Ga- 5 (−4.5) demonstrated the hydrophilic natures of the derivatives, and both showed higher uptake in cancer cell lines cultured under hypoxic condition than under normoxic condition. However, 68Ga- 5 showed higher liver uptake than 68Ga- 4 in a biodistribution study due to higher lipophilicity. In an animal PET study, 68Ga- 4 showed higher standard uptake values (SUV) in tumors than 68Ga- 5 in mice xenografted with CT-26 mouse colon cancer cells.

Synthesis and Characterization of Nitroimidazole Derivatives for 68Ga-Labeling and Testing in Tumor Xenografted Mice

Radiolabeled nitroimidazole (NI) derivatives have been used for imaging hypoxic tissues. We synthesized NI derivatives conjugated with bifunctional chelating agents such as 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and isothiocyanatobenzyl-NOTA (SCN-NOTA) via ethyleneamine bridge by formation of amide and thiourea bond, respectively. We proved that amide oxygen of Ga-NOTA-NI contributes to the formation of metal complex by X-ray crystallography. We labeled them with (68)Ga and found that both (68)Ga-NOTA-NI and (68)Ga- SCN-NOTA-NI were labeled in high efficiency (>96%) and were stable at room temperature in the prepared medium and at 37 degrees C in human serum. In vitro cell uptake experiments using CHO and CT-26 cell lines showed significantly increased uptakes of both of the agents in hypoxic condition. Biodistribution study in CT-26 xenografted mice showed increasing tumor to muscle ratios. (68)Ga-NOTA-NI showed lower intestine uptake than (68)Ga-NOTA-SCN-NI due to hydrophilicity. Also, (68)Ga-NOTA-NI showed higher tumor uptake than (68)Ga-NOTA-SCN-NI in an animal PET study. In conclusion, we successfully developed (68)Ga labeled NI derivatives for hypoxic tissue imaging.

Preparation of a Promising Angiogenesis PET Imaging Agent: 68Ga-Labeled c(RGDyK)–Isothiocyanatobenzyl-1,4,7-Triazacyclononane-1,4,7-Triacetic Acid and Feasibility Studies in Mice

Arg-Gly-Asp (RGD) derivatives have been labeled with various radioisotopes for the imaging of angiogenesis in ischemic tissue, in which alpha(v)beta(3) integrin plays an important role. In this study, cyclic Arg-Gly-Asp-D-Tyr-Lys [c(RGDyK)] was conjugated with 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bz-NOTA) and then labeled with (68)Ga. The labeled RGD so produced was subjected to an in vitro binding assay and in vivo biodistribution and PET studies. A mixture of SCN-Bz-NOTA (660 nmol) and c(RGDyK) (600 nmol) in 0.1 M sodium carbonate buffer (pH 9.5) was allowed to react for 20 h at room temperature in the dark for thiourea bond formation. The conjugate obtained was purified by semipreparative high-performance liquid chromatography (HPLC). The purified c(RGDyK)-SCN-Bz-NOTA (NOTA-RGD) was then labeled with (68)Ga from a (68)Ge/(68)Ga generator and purified by semipreparative HPLC. A competitive binding assay for c(RGDyK) and NOTA-RGD was performed with (125)I-c(RGDyK) as a radioligand and alpha(v)beta(3) integrin-coated plates as a solid phase. (68)Ga-NOTA-RGD (0.222 MBq/100 microL) was injected, through a tail vein, into mice with hind limb ischemia and into mice bearing human colon cancer SNU-C4 xenografts. Biodistribution and imaging studies were performed at 1 and 2 h after injection. The labeling of NOTA-RGD with (68)Ga was straightforward. The K(i) values of c(RGDyK) and NOTA-RGD were 1.3 and 1.9 nM, respectively. In the biodistribution study, the mean +/- SD uptake of (68)Ga-NOTA-RGD by ischemic muscles was 1.6+/-0.2 percentage injected dose per gram (%ID/g); this uptake was significantly blocked by cold c(RGDyK) to 0.6+/-0.3 %ID/g (P<0.01). Tumor uptake was 5.1+/-1.0 %ID/g, and the tumor-to-blood ratio was 10.3+/-4.8. Small-animal PET revealed rapid excretion through the urine and high levels of tumor and kidney uptake. Stable (68)Ga-NOTA-RGD was obtained in a straightforward manner at a high yield and showed a high affinity for alpha(v)beta(3) integrin, specific uptake by angiogenic muscles, a high level of uptake by tumors, and rapid renal excretion. (68)Ga-NOTA-RGD was found to be a promising radioligand for the imaging of angiogenesis.

Recent developments of polar piezoelectric polymers

Following the extensive studies on the piezoelectric, pyroelectric and ferroelectric properties of polyvinylidene fluoride and its copolymers, a vast number of polymers were investigated for these properties. Piezoelectric thin films of polyurea were prepared by vapor deposition polymerization in vacuum and stable up to 200 degC. Piezoelectric odd nylon was characterized by the field induced rotation of amide dipoles in the molecular sheet crystalline structure. Completely amorphous vinylidene cyanide copolymers produced a remanent polarization proportional to the large dielectric relaxation strength during poling. Drawn films of polylactic acid exhibited the large shear piezoelectricity due to the crystalline structure of helical molecules, however, a remnant polarization was also produced by poling at high temperatures. Various polymers containing dipolar groups of carbonyl, urethane, urea and thiourea bonds were poled and their ferroelectric hysteresis was observed. Application of magnetic field as high as 10 Tesla to the liquid crystalline state of helical molecules of poly-y-benzyl-L-glutamate during film formation resulted in a very high shear piezoelectric constant 26 pC/N. Unprecedented high piezoelectric constant such as 1000 pC/N was found in the highly hydrated cornea membrane consisting of collagen fibrils

Studies which indicate that thiourea bonds interfere with radioiodination reactions

Studies which indicate that thiourea bonds interfere with radioiodination reactions

Biotin reagents for antibody pretargeting. 4. Selection of biotin conjugates for in vivo application based on their dissociation rate from avidin and streptavidin.

An investigation was conducted to determine the affect of structural variation of biotin conjugates on their dissociation rates from Av and SAv. This information was sought to help identify optimal biotin derivatives for in vivo applications. Fifteen biotin derivatives were conjugated with a cyanocobalamin (CN-Cbl) derivative for evaluation of their "relative" dissociation rates by size exclusion HPLC analysis. Two biotin-CN-Cbl conjugates, one containing unaltered biotin and the other containing iminobiotin, were prepared as reference compounds for comparison purposes. The first structural variations studied involved modification of the biotinamide bond with a N-methyl moiety (i.e., sarcosine conjugate), lengthening the valeric acid side chain by a methylene unit (i.e., homobiotin), and replacing the biotinamide bond with thiourea bonds in two conjugates. The rate of dissociation of the biotin-CN-Cbl derivative from Av and SAv was significantly increased for biotin derivatives containing those structural features. Nine additional biotin conjugates were obtained by coupling amino acids or functional group protected amino acids to the biotin moiety. In the conjugates, the biotin moiety and biotinamide bond were not altered, but substituents of various sizes were introduced alpha to the biotinamide bond. The results obtained from HPLC analyses indicated that the rate of dissociation from Av or SAv was not affected by small substituents alpha to the biotinamide (e.g., methyl, hydroxymethyl, and carboxylate groups), but was significantly increased when larger functional groups were present. On the basis of the results obtained, it appears that biotin conjugates which retain an unmodified biotin moiety and have a linker molecule conjugated to it that has a small functional group (e.g., hydroxymethylene or carboxylate) alpha to the biotinamide bond are excellent candidates for in vivo applications. These structural features are obtained in the biotin amino acid conjugates: biotin-serine, biotin-aspartate, biotin-lysine, and biotin-cysteine. Importantly, these biotin derivatives can be readily conjugated with other molecules for specific in vivo applications. In our studies, these derivatives will be used in the design of new biotin conjugates to carry radionuclides for cancer therapy using the pretargeting approach.

Multivalent ligands for the mannose-specific lectin on type 1 fimbriae of Escherichia coli : syntheses and testing of trivalent α-D-mannoside clusters

The syntheses of the triantennary cluster α-D-mannosides 16, 19, 23 and 24 and their capacities to inhibit mannose-dependent binding of E. coli HB 101 (pPKl4) are described. The cluster glycosides are formed by glycosylation of tris-(3-hydroxypropyl)nitromethane 13, and by linking of suitable mannoside derivatives via amide and thiourea bonds to tris-(2-carboxyethyl)nitromethane 17 and tris-(2-aminoethyl)amine 20. Functionalized mannosides are attached to the core molecules at the 6-position of the sugar ring to allow variation of the introduced aglycone moieties in order to compare their effects on the inhibitory potencies of the derived mannoside clusters. The 6-peptide-bridged cluster mannoside 19 displays the highest binding potency towards the type 1 fimbrial lectin of E. coli as tested by inhibition agglutination tests and ELISA.