Plasmodium vivax CS peptides display conformational preferences for folded forms in solution.

Spectroscopic techniques have been used to study the conformations of several synthetic peptides with sequences corresponding to the repeat regions of the circumsporozoite proteins of Plasmodium vivax, variants vk-210 and vk-247. As has previously been shown for P. falciparum, turn-like folded conformations are observed, in rapid dynamic equilibrium with extended-chain forms. These results are consistent with the known similarity of the structural, biosynthetic and immunological properties of the circumsporozoite proteins of different plasmodial species. Additionally, the observation of folded conformers provides a rationale for the effectiveness of these peptides as immunogens and potential vaccines.

Design and optimization of 20-O-linked camptothecin glycoconjugates as anticancer agents.

To improve the biological profile of 20(S)-camptothecin, a novel class of 20-O-linked camptothecin glycoconjugates has been designed for preferential cellular uptake into tumor cells by an active transport mechanism. Such conjugates have been optimized for enhanced solubility, stabilization of the camptothecin lactone ring, sufficient hydrolytic and proteolytic stability, and for an overall improvement in tumor selectivity. The constitution of the peptide spacer has a major impact on stability and biological activity of the conjugates both in vitro and in vivo. Glycoconjugates 17-22 with valine residues at the linkage position to camptothecin are sufficiently stable and show good antitumor activity in vitro against HT29 and other tumor cell lines. Fluorescence microscopy and flow cytometry experiments indicate that glycoconjugates such as 19 are taken up into lysosomal compartments of the tumor cell line HT29 by an active transport mechanism. The steric configuration of the particular amino acid residues linked to the camptothecin moiety has a major impact on the in vivo activity of the corresponding glycoconjugates in the breast cancer xenograft MX-1 model. Inhibiting tumor growth by >96%, the glycoconjugates 19 and 21 show the best activity in this particular model and have been investigated more extensively. The glycoconjugate 19 compares favorably to topotecan 4 and glycoconjugate 21 with respect to toxicity against hematopoietic stem cells and hepatocytes. Based on its profile, 19 has been selected for clinical trials.

Discovery and evaluation of piperidinyl carboxylic acid derivatives as potent alpha(4)beta(1) integrin antagonists.

Piperidinyl carboxylic acid-based derivatives were prepared as antagonists of the leukocyte cell adhesion process that is mediated through the interaction of the alpha(4)beta(1) integrin (VLA-4, very late antigen 4) and the vascular cell adhesion molecule 1 (VCAM-1). Compounds 2a-h inhibited the adhesion in a cell-based assay in the low and sub micromolar range, a pharmacokinetic study of 2d is reported.

Photochemistry of 4'-benzophenone-substituted nucleoside derivatives as models for ribonucleotide reductases: competing generation of 3'-radicals and photoenols.

Ribonucleotide reductases (RNRs) catalyze the 2'-reduction of ribonucleotides, thus providing 2'-deoxyribonucleotides, the monomers for DNA-biosynthesis. The current mechanistic hypothesis for the catalysis effected by this class of enzymes involves a sequence of radical reactions. A 3'-hydrogen abstraction, effected by a radical at the enzyme's active site, is believed to initiate the catalytic cycle. As models for this substrate-enzyme interaction, the photochemically induced intramolecular hydrogen abstraction in a series of 4'-benzophenone-substituted nucleoside analogues was studied. Model compounds with hydroxy-, methoxy-, mesyloxy-groups or a cyclic carbonate in 2'- and 3'-positions were investigated. Depending on the substitution pattern, two different types of photoproducts were observed: Those which result from photoenol formation (gamma-H-abstraction) and those which result from abstraction of the 3'-H-atom (delta-H-abstraction). Photoenol formation was further supported by H/D-exchange experiments. Thus, the 3'-H-abstraction postulated as the initial step in RNR action was successfully modeled by photolysis of 4'-benzophenone-substituted nucleoside analogues. The regioselectivity of the photochemical H-abstraction and thus of the product distribution as a function of the 2'- and 3'-substituents was rationalized on the basis of a conformational analysis of the four model systems, utilizing molecular mechanics simulations.

Coordination chemistry of co(II)-bleomycin: its investigation through NMR and molecular dynamics.

Previous studies on the coordination chemistry of Co-bleomycin have suggested the secondary amine in beta-aminoalanine, the N5 and N1 nitrogens in the pyrimidine and imidazole rings, respectively, and the amide nitrogen in beta-hydroxyhistidine as equatorial ligands to the cobalt ion. The primary amine in beta-aminoalanine and the carbamoyl group of the mannose have been proposed alternatively as possible axial ligands. The first coordination sphere of Co(II) in Co(II)BLM has been investigated in the present study through the use of NMR and molecular dynamics calculations. The data collected from the NMR experiments are in agreement with the equatorial ligands previously proposed, and also support the participation of the primary amine as an axial ligand. The paramagnetic shifts of the gulose and mannose protons could suggest the latter as a second axial ligand. This possibility was investigated by way of molecular dynamics, with distance restraints derived from the relaxation times measured through NMR. The molecular dynamics results indicate that the most favorable structure is six-coordinate, with the primary amine and either the carbamoyl oxygen or a solvent molecule occupying the axial sites. The analysis of the structures previously derived for HOO-Co(III)-bleomycin and HOO-Co(III)-pepleomycin led us to propose the six-coordinate structure with only endogenous ligands, as the one held in solution by the Co(II) derivative of bleomycin.

NMR studies of the paramagnetic complex Fe(II)-bleomycin.

The coordination chemistry of the iron(II) complex of the antitumor drug bleomycin has been extensively investigated with a number of spectroscopic and chemical techniques. However, the actual structure of this complex is not established. In this report, we present NMR studies of the paramagnetic Fe(II)BLM and use one- and two-dimensional methods to assign the paramagnetically shifted features to particular protons. The data analysis points toward the primary and secondary amines of the beta-aminoalanine fragment, the pyrimidine and imidazole rings, and the amide nitrogen of the beta-hydroxyhistidine fragment as ligands to the metal center. Correlation of the T1 values with the metal-proton distances derived from the NMR-generated solution structure of HOO-Co(III)BLM [Wu, W., Vanderwall, D. E., Lui, S. M., Tang, X.-J., Turner, C. J., Kozarich, J. W., & Stubbe, J. (1996) J. Am. Chem. Soc. 118, 1268-1280] indicates that the two metallobleomycins share similar structures. The chemical shifts as well as the T1 values of the sugar protons indicate that these fragments are close but not bound to the metal in Fe(II)BLM.