Conjugates of catecholamines. VII. Synthesis and beta-adrenergic activity of peptide catecholamine conjugates

A series of novel catecholamine derivatives has been prepared in which one of the N-methyl substituents of isoproterenol has been extended by a spacer consisting of a chain of four methylenes which terminates with an amide linkage to a peptide, the point of attachment being via the aromatic amino group of p-aminophenylalanine. In one of the derivatives, two catecholamines are attached to the same peptide in this manner. The peptides, which range in size from three to eight amino acid residues and contain phenylalanine, glycine, and L-alpha-amino-delta-hydroxyvaleric acid, were synthesized via stepwise and fragment condensation techniques. The beta-adrenergic agonist activities of the derivatives were evaluated in vitro by measuring the intracellular accumulation of cyclic AMP in S49 mouse lymphoma cells.     

Sequential oligopeptides. Synthesis and characterization of the oligopeptides and a polypeptide with the repeating sequence L-norvalyl-glycyl-L-proline

The synthesis and characterization of a series of oligopeptides (from the tripeptide to the octadecapeptide) with the repeating sequence L -norvalyl-glycyl-L -proline and a polytripeptide with this sequence are reported. The oligomers were synthesized step by step using the mixed anhydride method. All the products were chemically and optically pure. The polymer was prepared by the active ester method, using the p-nitrophenyl ester as the polymerizable tripeptide derivative. Good yield of relatively high average molecular-weight polymer was obtained. In the accompanying paper conformational investigations, both in solution and in the solid state, on the oligomers and the polymer are described.     

Synthesis and characterization of digoxin-phospholipid conjugates

The preparation of immunoreactive derivatives of digoxin for analytical applications is most often carried out by periodate cleavage of the terminal sugar ring (digitoxose) followed by reaction with an enzyme, protein, carrier, or related biological molecules. Here we report an improved and more efficient synthesis which was developed to provide digoxin-phospholipid conjugates useful for liposome immunoassay. The approach used involved the linking of the cleaved digitoxose through a carboxymethyl oxime functionality, which provides much improved yields of readily purified products. The synthetic modification should be applicable to the preparation of analogous phospholipid conjugates involving linkage through a sugar ring (digitoxin, ouabain, and related cardiac glycosides) or to those involving steroids (i.e., 3-digoxigenone) which can be modified to form oxime derivatives remote from key functionalities important for immunorecognition by specific antibody. The characterization of the digoxin-phospholipid conjugates with high-resolution NMR and fast atom bombardment mass spectrophotometry will also be discussed.     

Synthesis and characterization of insulin-transferrin conjugates

Receptor-mediated endocytosis can be exploited for improving the transcellular delivery of therapeutic proteins. Insulin conjugated to transferrin by forming disulfide bonds has been shown to improve insulin oral bioavailability in diabetic rats. We are developing a combination strategy involving complexation hydrogels as delivery vehicles for insulin-transferrin conjugates. The complexation hydrogels developed in our laboratory have been shown to be promising carriers for oral delivery of proteins and peptides. Integrating the strategies based on the complexation hydrogels and insulin-transferrin conjugates may prove to be a novel approach for oral delivery of insulin and other therapeutic proteins. In this work, electrospray ionization mass spectrometry (ESI-MS) was used to study the modification of insulin during its reaction with transferrin. The stability of the conjugated insulin to enzymatic degradation was also studied. ESI-MS studies confirmed the site-specific modifications of insulin. The transferrin conjugation of insulin was also shown to increase the stability of insulin to enzymatic degradation.     

Synthesis and characterization of novel natural product-Gd(III) MRI contrast agent conjugates

Several novel gadolinium chelates conjugated with paclitaxel, colchicine and thyroxine have been prepared as MRI contrast agents targeted to tubulin and thyroxine-binding globulin, respectively.     

Synthesis and characterization of new porphyrazine-Gd(III) conjugates as multimodal MR contrast agents

Magnetic resonance imaging (MRI) has long been used clinically and experimentally as a diagnostic tool to obtain three-dimensional, high-resolution images of deep tissues. These images are enhanced by the administration of contrast agents such as paramagnetic Gd(III) complexes. Herein, we describe the preparation of a series of multimodal imaging agents in which paramagnetic Gd(III) complexes are conjugated to a fluorescent tetrapyrrole, namely, a porphyrazine (pz). Zinc metalated pzs conjugated to one, four, or eight paramagnetic Gd(III) complexes are reported. Among these conjugates, Zn-Pz-8Gd(III) exhibits an ionic relaxivity four times that of the monomeric Gd(III) agent, presumably because of increased molecular weight and a molecular relaxivity that is approximately thirty times larger, while retaining the intense electronic absorption and emission of the unmodified pz. Unlike current clinical MR agents, Zn-Pz-1Gd(III) is taken up by cells. This probe demonstrates intracellular fluorescence by confocal microscopy and provides significant contrast enhancement in MR images, as well as marked phototoxicity in assays of cellular viability. These results suggest that pz agents possess a new potential for use in cancer imaging by both MRI and near-infrared (NIR) fluorescence, while acting as a platform for photodynamic therapy.     

Synthesis and characterization of positively charged porphyrin-peptide conjugates

The total syntheses of 14 porphyrin conjugates containing one to four positively charged amino acids and two distinct linkers are described. All conjugates were fully characterized using spectroscopic methods, and the X-ray structure of a porphyrin isothiocyanate precursor was obtained. In vitro studies using HEp2 cells show that these conjugates have low cytotoxicity (IC50 > 250 microM) and that the extent of their cellular uptake depends significantly on the number, nature, and sequence of amino acids in the peptide, and on the presence of a centrally chelated metal ion. Metal-free conjugates bearing three consecutive arginine residues accumulated the most within cells. On the other hand, the preferential sites of subcellular localization were found to be independent from the number, nature, and sequence of amino acids in the conjugate, the linker, and coordinated metal ion; it is suggested, based on theoretical calculations, that the peptides in these conjugates fold over the porphyrin macrocycle in order to maximize intramolecular hydrophobic interactions.     

Synthesis and characterization of fluorescent Lucifer yellow-lipid conjugates

The syntheses of fluorescent lipid probes composed of Lucifer yellow dyes linked to either cholesterol or phospholipids are described. The spectral properties of these probes are characterized, and the probes are evaluated for use with model membranes and with live animal and plant cells. Of the probes synthesized, the cholesterol derivative is the easiest to prepare and appears to be the most useful because it readily labels the plasma membrane of live cells and maintains a high ratio of cell surface-to-cytoplasmic fluorescence.     

Synthesis and characterization of membrane-active GALA-OKT9 conjugates

Cellular processing of immunotoxins is inefficient, limiting the overall effectiveness of current immunotoxin therapies. Specifically, translocation of ribosome-inactivating toxins across intracellular membranes is agonizingly slow. In one strategy to improve immunotoxin efficacy, membrane-active peptides are attached to immunotoxins to facilitate transfer of the toxic moiety across a cellular membrane to the cytosol. pH-sensitive peptides are of particular interest, as the membrane activity can be localized to the endosomal/lysosomal pathway, reducing nonspecific interactions at the cell surface. In this study, GALA, a pH-sensitive peptide that forms multimeric pores in membranes, was chemically attached to OKT9, an anti-transferrin receptor mAb. Conjugates were tested by measuring release of encapsulated dyes from liposomes to determine the extent to which the membrane-lytic properties of GALA were retained. The most significant feature affecting the lytic properties of GALA-OKT9 conjugates was the number of attached GALA per OKT9. Conjugates with a single GALA per OKT9 caused almost no leakage while conjugates with two or three GALA per OKT9 caused significant leakage in a concentration-dependent manner. Invariably, GALA-OKT9 conjugates were significantly less active than unconjugated GALA, attributable to a decrease both in partitioning and in surface aggregation. No improvement in membrane-lytic activity was achieved by using a longer, more flexible poly(ethylene glycol) cross-linker. Attachment of GALA via C- versus N-terminal linkage had no effect on membrane-lytic properties. Size-selective release of high molecular weight dextrans was almost identical for conjugated and unconjugated GALA, suggesting that GALA forms the same pore structure regardless of conjugation state.     

Synthesis and characterization of two (111)In-labeled DTPA-peptide conjugates.

This report describes the synthesis and characterization of two (111)In-labeled DTPA-peptide conjugates (DTPA-MA and DTPA-BA). It is surprising to find that (111)In(DTPA-MA) and (111)In(DTPA-BA) are more hydrophilic than their corresponding (90)Y analogues, suggesting a different coordination sphere in (111)In and(90)Y complexes of the same DTPA-peptide conjugate. By a reversed phase HPLC method, both (111)In(DTPA-MA) and (111)In(DTPA-BA) showed only one radiometric peak in their respective HPLC chromatogram due to a rapid interconversion of different isomers (particularly cis and trans isomers for (111)In(DTPA-MA); cis-cis, cis-trans, trans-cis, and trans-trans isomers for (111)In(DTPA-BA)). The interconversion of different isomers involves the "wagging" of the diethylenetriamine backbone, "shuffling" of the NO or NO(2) donor sets, and a rapid inversion at the terminal amine-nitrogen atoms.     

Synthesis and characterization of oligonucleotide conjugates bearing electroactive labels

Oxime bond formation has been applied to the preparation of oligonucleotides labeled with electrochemical ferrocene and viologen labels. Aminooxy functionalized ferrocene and viologen derivatives were prepared by a straightforward route and efficiently conjugated with aldehyde containing oligonucleotides either at 3′ or 5′ end. Both labels were found to not disturb the recognition properties of the oligonucleotide. The versatility of the method was further demonstrated by preparing bi-functionalized conjugates with a disulfide at 3′ end and an electrochemical label at 5′ end.     

Synthesis, characterization and antitumor activity of quinolone-platinum(II) conjugates.

A new series of quinolone-platinum(II) conjugates, [Pt(Q'-NH2)(dmso)X2] and cis-[Pt(Q"-en)X2], where Q' and Q" are quinolones (flumequine, nalidixic acid or oxolinic acid) linked to monodentate and bidentate amine ligands, respectively, and X2 is Cl2 or 1,1-cyclobutanedicarboxylate, have been synthesized with the aim of examining the synergetic antitumor activity of quinolone intercalation and platinum(II) chelation. The complexes were characterized by elemental analyses and IR and multinuclear (1H and 195Pt) NMR spectroscopies, and then subjected to in vitro and in vivo bioassays using the leukemia L1210 cell line.     

Synthesis and structural characterization of bioactive peptide conjugates using thioether linkage approaches.

Applications of cysteine-insertion and thioether linkage approaches to the preparation of a number of bioactive peptide conjugates are reported. Peptides containing epitopes from (i) herpes simplex virus type 1 glycoprotein D, (ii) a specific N-terminal beta-amyloid epitope recognized by therapeutically active antibodies, and (iii) a GnRH-III peptide from sea lamprey with antitumour activity, were elongated with Cys residues and attached to a chloroacetylated tetratuftsin derivative carrier via a thioether linkage either directly, or by insertion of a spacer. The structures and molecular homogeneity of all the peptide conjugates were ascertained by HPLC, MALDI and electrospray mass spectrometry. The use of a spacer such as an oligoglycine or GFLG-tetrapeptide gave an increased yield in the conjugation reaction and enhanced reaction rates. In the formation of cysteinyl-thioether linkages, it was found that the position of flanking Cys residues markedly influenced the conjugation reaction and the formation of intermolecular epitope disulfide-dimers. C-terminal Cys residues gave thioether conjugates with significantly diminished epitope-dimerization, while Cys at the N-terminal caused rapid disulfide-dimerization, thereby preventing efficient conjugation.     

Synthesis and functional characterization of novel derivatives related to oxotremorine and oxotremorine-M.

Two subseries of nonquaternized (5a-10a) and quaternized derivatives (5b-10b) related to oxotremorine and oxotremorine-M were synthesized and tested. The agonist potency at the muscarinic receptor subtypes of the new compounds was estimated in three classical in vitro functional assays: M1 rabbit vas deferens, M2 guinea pig left atrium and M3 guinea pig ileum. In addition, the occurrence of central muscarinic effects was evaluated as tremorigenic activity after intraperitoneal administration in mice. In in vitro tests a nonselective muscarinic activity was exhibited by all the derivatives with potencies values that, in some instances, surpassed those of the reference compounds (i.e. 8b). Functional selectivity was evidenced only for the oxotremorine-like derivative 9a, which behaved as a mixed M3-agonist/M1-antagonist (pD2 = 5.85; pA2 = 4.76, respectively). In in vivo tests non-quaternary compounds were able to evoke central muscarinic effects, with a potency order parallel to that observed in vitro.     

Synthesis and characterization of covalently linked single-stranded DNA oligonucleotide-dendron conjugates

A solution-phase synthesis and characterization of covalent DNA-dendron conjugates is presented. Thiol-terminated 12-base oligonucleotides were added to second- and third-generation triazine-based dendrons via thiol/disulfide exchange chemistry. Single-stranded DNA oligonucleotides were successfully attached to dendrons at the core, the periphery, and both. Proof of structure for these architectures is derived primarily from mass spectrometry and polyacrylamide gel electrophoresis and complemented by labeling analysis using Ellman's reagent and degradation analysis using a reducing agent.     

Fully synthetic immunogens. Part III. Synthesis of hinge-peptide/gastrin conjugates and their immunological properties.

As core molecule for the multiple attachment of antigenic peptides we have selected the human IgG1 hinge fragment 225-232/225'-232'. Two types of conjugates of this double-chain bis-cystinyl hinge-peptide were prepared i) by linking its C-termini to [NIe15]-human-little-gastrin-[2,17] and ii) by elongating the resulting hinge-peptide/[NIe15]-little-gastrin-[2-17] conjugate at the two N-termini with the human big-gastrin sequence 1-14 to produce the big-gastrin-[1-14]/hinge-peptide/little-gastrin-[2-17] conjugate. For the synthesis of these peptide structures both the route via the preformed double-chain bis-cystinyl peptide and the route via suitably protected monomeric bis-cysteinyl peptides were used. For the latter approach advantage was taken of the previous observation about the preferred oxidation of the bis-cysteinyl hinge-peptide 225-232 to the dimer in parallel alignment. Both synthetic routes led to identical products. Immunization experiments in guinea pigs with the synthetic hybrids led to surprisingly strong immune responses with anti-little-gastrin antibody titers comparable to those induced by the iso-1-cytochrome c/little-gastrin-[2-17] conjugate as carrier-hapten system. These findings show that the two gastrin constructs are fully competent immunogens. Additionally, the gastrin receptor-like specificity of the antibodies indicates that both the synthetic hybrids and the cytochrome c conjugate allow for expression of a little-gastrin-specific conformational epitope similar to the bioactive structure of this hormone. The usefulness of such synthetic hybrids is further confirmed by the observation that the bivalent immunogen, containing both the little-gastrin 2-17 and the big-gastrin 1-14 sequence, is capable of inducing an immune response against both antigenic sequences, although with different efficiency. These results fully confirm our expectations.     

Synthesis and characterization of poly(ethylene glycol)-insulin conjugates

Human insulin was modified by covalent attachment of short-chain (750 and 2000 Da) methoxypoly (ethylene glycol) (mPEG) to the amino groups of either residue PheB1 or LysB29, resulting in four distinct conjugates: mPEG(750)-PheB1-insulin, mPEG(2000)-PheB1-insulin, mPEG(750)-LysB29-insulin, and mPEG(2000)-LysB29-insulin. Characterization of the conjugates by MALDI-TOF mass spectrometry and N-terminal protein sequence analyses verified that only a single polymer chain (750 or 2000 Da) was attached to the selected residue of interest (PheB1 or LysB29). Equilibrium sedimentation experiments were performed using analytical ultracentrifugation to quantitatively determine the association state(s) of insulin derivatives. In the concentration range studied, all four of the conjugates and Zn-free insulin exist as stable dimers while Zn(2+)-insulin was exclusively hexameric and Lispro was monomeric. In addition, insulin (conjugate) self-association was evaluated by circular dichroism in the near-ultraviolet wavelength range (320-250 nm). This independent method qualitatively suggests that mPEG-insulin conjugates behave similarly to Zn-free insulin in the concentration range studied and complements results from ultracentrifugation studies. The physical stability/resistance to fibrillation of mPEG-insulin conjugates in aqueous solution were assessed. The data proves that mPEG(750 and 2000)-PheB1-insulin conjugates are substantially more stable than controls but the mPEG(750 and 2000)-LysB29-insulin conjugates were only slightly more stable than commercially available preparations. Circular dichroism studies done in the far ultraviolet region confirm insulin's tertiary structure in aqueous solution is essentially conserved after mPEG conjugation. In vivo pharmacodynamic assays reveal that there is no loss in biological activity after conjugation of mPEG(750) to either position on the insulin B-chain. However, attachment of mPEG(2000) decreased the bioactivity of the conjugates to about 85% of Lilly's HumulinR formulation. The characterization presented in this paper provides strong testimony to the fact that attachment of mPEG to specific amino acid residues of insulin's B-chain improves the conjugates' physical stability without appreciable perturbations to its tertiary structure, self-association behavior, or in vivo biological activity.     

Synthesis, characterization, and in vitro activity of dendrimer-streptokinase conjugates

Dendrimer conjugation with low molecular weight drugs has been of increasing interest recently for improving pharmacokinetics, targeting drugs to specific sites, and facilitating cellular uptake. Opportunities for increasing the performance of relatively large therapeutic proteins such as streptokinase (SK) using dendrimers are being explored in this study. Using the active ester method, a series of streptokinase-poly(amido amine) (PAMAM) G3.5 conjugates were synthesized with varying amounts of dendrimer-to-protein molar ratios. Characterization of these conjugates by GPC, IEC, and native-PAGE suggested that the conjugation reaction was successful, resulting in relatively pure SK-dendrimer conjugates. The conjugate made with an equimolar ratio of dendrimer to streptokinase (1:1) exhibited the highest enzymatic activity retention ( approximately 80% retained) that has been reported so far for conjugated streptokinase with macromolecules such as PEG or dextran. SK conjugates with higher streptokinase-to-dendrimer molar ratios (1:10 and 1:20) exhibited lower initial enzymatic activities. However, these conjugates showed sustained thrombolytic activity in plasma, perhaps due to the release of SK from the conjugate. All of the SK conjugates displayed significantly improved stability in phosphate buffer solution, compared to free SK. The high coupling reaction efficiencies and the resulting high enzymatic activity retention achieved in this study could enable a desirable way for modifying many bioactive macromolecules with dendrimers.     

Synthesis and characterization of water-soluble free-base, zinc and copper porphyrin-oligonucleotide conjugates

We describe the synthesis and characterization of a series of water-soluble free-base, zinc, and copper porphyrin-oligonucleotide (ODN) conjugates. A non-charged tetraarylporphyrin was directly attached to the 5'-position of thymine via a short amide linker. Such a linker should allow for rigid connection to the adjacent nucleobases, thus increasing the sensitivity for monitoring conformational changes of the ODNs by electronic circular dichroism due to capping effects or ligand binding. Two complementary synthetic approaches have been used to incorporate porphyrin chromophores into the DNA. In the first approach a porphyrin carboxylic acid is conjugated to 5'-amino-ODN. In the second approach the phosphoramidite of the porphyrin-amido-thymidine is coupled to 5'-hydroxy-ODN using standard automated phosphoramidite chemistry. In both cases a spontaneous metallation of the free-base porphyrin in porphyrin-DNA conjugates was observed during the porphyrin-DNA conjugate cleavage from the solid support and its consequent deprotection using concentrated aqueous ammonia. Zinc and copper porphyrin-DNA conjugates were isolated by HPLC and characterized together with the anticipated free-base porphyrin-DNA conjugate. Authentic zinc and copper porphyrin-DNA conjugates were intentionally prepared from intentionally metallated porphyrins to compare their spectroscopic and HPLC characteristics with isolated metallospecies and to confirm the spontaneous metallation.     

薯蓣皂甙元ELISA定量分析方法的建立Ⅰ-薯蓣皂甙元全抗原的合成

建立薯蓣皂甙元的ELISA定量分析方法必须先合成薯蓣皂甙元的全抗原。试验利用薯蓣皂甙元3位上的-OH,在DMAP的催化下,薯蓣皂甙元与丁二酸酐反应,生成薯蓣皂甙元丁二酸单酯,用MSI、R1、H NMR1、3CNMR等方法对产物结构进行了表征。用混合酸酐法制备薯蓣皂甙元与牛血清白蛋白的结合物(DG-HS-BSA),碳二亚胺法制备薯蓣皂甙元与卵清蛋白的结合物(DG-HS-OVA),经TNBS测定,每分子结合物连接的薯蓣皂甙元分子数分别为28.0和8.8。