Discovery of structurally diverse natural product antagonists of chemokine receptor CXCR3

The chemokines (CXCL9, CXCL10 and CXCL11) and associated CXCR3 receptor are expressed during the inflammatory process from multiple sclerosis, atherosclerosis or organ transplantation resulting in the recruitment of lymphocytes leading to tissue damage. It is hypothesized that blocking of the ligand/CXCR3 receptor interaction has potential to provide opportunity for development of agents that would block tissue rejection. In this paper, four classes of natural product inhibitors (IC₅₀ ranging 0.1–41 M) have been described that block the CXCR3 receptor interaction of IP-10 ligand. These include a cyclic thiopeptide (duramycin), polyketide glycosides (roselipins), steroidal glycosides (hypoglausin A and dioscin) and a novel alkyl pyridinium alkaloid that were isolated by bioassay-guided fractionation of the organic extracts derived from actinomycete, fungal, plant and marine sources and discovered using ¹²⁵ I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC₅₀ of 0.1 M. Roselipins 2A, 2B and 1A showed IC₅₀ values of 14.6, 23.5, and 41 M, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC₅₀ values of 2.1, 0.47 and 3 M, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC₅₀ of 0.67 M.     

Synthesis of pentafluorophenylmethylamines via silicon Mannich reaction

[reaction: see text] The three-component coupling of aldehydes, secondary amines, and methoxytris(pentafluorophenyl)silane, MeOSi(C(6)F(5))(3), affording pentafluorophenylmethylamines has been described. The generation of the five-coordinate silicate intermediate is believed to be the key feature responsible for the efficiency of the reaction.     

Long-lived nuclear spin states in high-field solution NMR

Nuclear spin order may be stored in a liquid for a much longer time than the longitudinal relaxation time T1, by using rf fields to isolate states of different symmetry. The method is demonstrated on a sample containing AX spin systems.     

Bioactivation of self-immolative dendritic prodrugs by catalytic antibody 38C2

Self-immolative dendrimers have recently been developed and introduced as a potential platform for a multi-prodrug. These unique structural dendrimers can release all of their tail units, through a self-immolative chain fragmentation, which is initiated by a single cleavage at the dendrimer's core. Incorporation of drug molecules as the tail units and an enzyme substrate as the trigger can generate a multi-prodrug unit that will be activated with a single enzymatic cleavage. We have synthesized the first generation of dendritic prodrugs with doxorubicin and camptothecin as tail units and a retro-aldol retro-Michael focal trigger, which can be cleaved by catalytic antibody 38C2. The bioactivation of the dendritic prodrugs was evaluated in cell-growth inhibition assay with the Molt-3 leukemia cell line in the presence and the absence of antibody 38C2. The dendritic unit was applied as a platform for a heterodimeric prodrug, which achieved a remarkable increase in toxicity with its bioactivation.     

Some conjectures for cogwheel phase cycling

Cogwheel phase cycles are often significantly shorter than traditional nested phase cycles. However, optimal solutions for cogwheel cycles are often difficult to find. This paper presents techniques and conjectures which the authors have found useful for generating cogwheel phase cycles either without the need for computer searches or with significantly smaller searches than would otherwise be necessary. The conjectures presently lack proofs but have been tested successfully for a large number of cases.     

Defining the antigenic structure of human GM-CSF and its implications for receptor interaction and therapeutic treatments

Three epitopes of human Granulocyte-Macrophage Colony-Stimulating Factor (hGM-CSF) recognised by neutralising and non-neutralising monoclonal antibodies (mAbs) were characterised using competitive binding assays, dissociation constant measurements with glycosylated and non-glycosylated rhGM-CSF, bioactivity inhibition studies, and synthetic peptide arrays. Based on the first approach, two different binding sites were identified: an area referred to as A, recognised by mAbs M1B8 and CC5B5, and an area referred to as B, recognised by mAbs CC1H7 and CC3C12. These binding sites on hGM-CSF were accurately delineated using cytokine-derived overlapping peptide scans and combinatorial hexapeptide libraries prepared by SPOT synthesis on cellulose membranes. We assigned the identical linear epitope A₁P₂A₃R₄ to both non-neutralising mAbs CC1H7 and CC3C12. The conformational epitopes A₁₈E₂₁R₂₃R₂₄F₁₁₉ and R₂₃E₂₁N₁₇W₁₃ recognised by mAb CC5B5, and P₁₁₈F₁₁₉EW₁₃E₁₄ recognised by mAb M1B8, were delineated by dual-positional scanning and subsequent iterative searches with two interrogating positions. Competitive binding assays with mAbs M1B8 and CC5B5 revealed the overlapping nature of the cytokine recognition. However, peptide library screening confirmed their binding to different epitopes of which the essential amino acids were found very closely located on the native protein surface. Inhibition of hGM-CSF biological activity by these mAbs demonstrated that these epitopes are located within or very near the receptor binding site of hGM-CSF. Finally, this work supports the importance of residues from helix A and residues from the C-terminal region of the cytokine, composing a common area that is indispensable for the cytokine's biological activity.     

Dynamics of alkoxy-oligothiophene ground and excited states in nanochannels

Two oligothiophenes, 4,4'-dipentoxy-2,2'-dithiophene and 4,4"-dipentoxy-2,2':5',2":5",2' '-tetrathiophene, have been included in the nanochannels of the autoassembling host TPP (tris-o-phenylenedioxycyclotriphosphazene). The effect of the confinement on the structure and properties of the two dyes, as conformational arrangements, dynamics, and photophysical behavior, was addressed by the combination of high spinning speed solid-state NMR and time-resolved EPR spectroscopy. We compared the conformations of the dyes in their ground and photoexcited triplet states and described in detail the dynamics of the supramolecular adducts from 4 K to room temperature. Above 200 K surprisingly fast spinning rates of the dithiophene core were discovered, while the side chains show far slower reorientation motion, being in bulky gauche-rich conformations. These lateral plugs keep the planar core as appended in the space like a nanoscale gyroscope, allowing a reorientation in the motion regime of liquids and a long triplet lifetime at unusually high temperature. The nuclear magnetic properties of the guest dyes are also largely affected by the aromatic rings of the neighboring host, imparting an impressive magnetic susceptibility effect (2 ppm proton shift). The high mobility is due to the formation of a nanocage in a channel where aliphatic and aromatic functions isolate the thiophene moieties. Instead, two conformers of the tetrathiophene twisted on the central bond are stabilized by interaction with the host. They interconvert fast enough to be averaged in the NMR time scale.     

A note on the nucleolus and the kernel of the assignment game

There exist coalitional games with transferable utility which have the same core but different nucleoli. We show that this cannot happen in the case of assignment games. Whenever two assignment games have the same core, their nucleoli also coincide. To show this, we prove that the nucleolus of an assignment game coincides with that of its buyer–seller exact representative.I am grateful to C. Rafels and to the referees for their comments. Institutional support from research grants BEC 2002-00642 and SGR2001–0029 is also acknowledged.     

A priori inequalities for solutions of mixed boundary-value problems in unbounded domains

We prove some a priori inequalities for solutions of mixed boundary-value problems for a class of divergence form elliptic equations with discontinuous and unbounded coefficients in unbounded domains. Mathematics Subject Classification (2000) 35J25