Identification of alkylidene hydrazides as glucagon receptor antagonists.

High throughput screening of our small molecule combinatorial library identified a class of benzoylnaphthalenehydrazones with modest affinity for the human glucagon receptor. Optimization of this initial hit through a series of targeted libraries and traditional medicinal chemistry led to ligands with nanomolar affinities. Pharmacological evaluation demonstrated that these ligands were competitive glucagon receptor antagonists. Intravenous administration of a representative benzoylnaphthalenehydrazone into rats attenuated glucagon-stimulated glucose levels.

Combichem and chemoinformatics.

New developments in cheminformatics are reviewed in the perspective of combinatorial chemistry and drug discovery. One of the most important trends is the realization that the ability to generate compounds in large numbers may not, in isolation, be helpful. It is more important to enrich combinatorial libraries with compounds which, if found to be active, can be quickly developed into viable drug candidates. Library design tools are being created that incorporate an accumulated medicinal chemistry experience necessary to produce compounds with desirable pharmacological properties. The development of methods to ensure chemical accessibility of designed libraries has also become important because of the need to integrate all steps of library generation, from design to synthesis, into one automated high-throughput process.

A polycation causes migration of negatively charged phospholipids from the inner to outer leaflet of the liposomal membrane.

Aggregation of the negatively charged liposomes caused by the addition of the linear polycation, poly-N-ethyl-4-vinylpyridine bromide, was studied. At the point of maximal size and zero electrophoretic mobility of aggregates, the concentration of positive charges brought in by the adsorbed polycation was found to be equal to the total concentration of negative charges both on the outer and inner surface of the lipid bilayer. Since polycation saturation of the liposomal negative charges was found to occur without disruption of the membrane, it was concluded that the polycation induced migration of negatively charged phospholipid molecules from the inner to outer leaflet of the bilayer.

Synthesis and conformational properties of the lanthionine-bridged opioid peptide [D-AlaL2,AlaL5]enkephalin as determined by NMR and computer simulations.

We report the synthesis and conformational analysis by means of NMR and computer simulations of a novel opioid peptide with the sequence [formula: see text], which we write as [formula: see text], abbreviated [D-AlaL2,L-AlaL5]EA, where AlaL denotes each of the lanthionine amino acid ends linked by a monosulfide bridge and EA indicates enkephalinamide. Data from 2D NMR (HOHAHA and ROESY) provide short-range NOEs that are used as constraints in molecular modeling; measurement of coupling constants shows that chi 1 (D-AlaL2) is predominantly in either the t or g- conformation, and temperature coefficient data suggest the participation of the AlaL5 amide proton in an intramolecular hydrogen bond. The use of NOE and hydrogen-bond constraints in a distance-geometry program yields a large number of initial conformations compatible with the data. Energy minimization of these structures using CHARMM results in three families of backbone ring conformations, labled A1, A2, and B. The torsion chi 1 in D-AlaL2 remains close to trans for all three conformations. Molecular dynamics in vacuo at 300 K show that these three families of conformers interconvert, with concerted shifts in two of the three torsions psi(Phe), phi(AlaL5), and chi(AlaL5). The [D-AlaL2,L-AlaL5]EA is superactive in the guinea pig ileum (GPI) and mouse vas deferens (MVD) in vitro tests and also in the rat hot plate test in vivo. At the same time, this analog with a constrained 13-membered ring shows virtually no selectivity with a ratio IC50 (MVD)/IC50 (GPI) of 0.882.

Minimum energy conformations of proline-containing helices.

Proline occurs frequently in transmembrane alpha-helices of transport and receptor proteins even though statistical surveys demonstrate the overwhelming preference of this residue for a non-alpha-helical, hydrophilic environment. As a result, membrane-buried proline has been proposed to be functionally important, with function arising from structural discontinuity or destabilization of the helix. Destabilization may occur by Pro-mediated conformational transitions between discrete states, and may be manifested in membrane protein systems through reversible processes such as channel opening and closing or signal transduction. In this study, computer modeling of a model transmembrane alpha-helix, (Ala)8-Leu-Pro-Phe-(Ala)8, in a medium of low polarity (dielectric = 2), is used to examine the occurrence and energetic accessibility of Pro-mediated conformational interconversions. Leu psi and chi 1, Pro psi, and Phe phi and chi 1 torsion angles were assigned random values so that a data base of 200 conformations for each of the cis and trans states was generated. The conformations were minimized and low-energy structures organized into families. This analysis demonstrated that the most populated lowest energy family is the Trans-I conformation, corresponding to proline in a kinked alpha-helix. Two additional trans structures, Trans-II and Trans-III, as well as a cis conformation, Cis-I, are also energetically competitive. Interconversions between the trans states could thus be mediated by changes at a single torsion angle, accompanied by minor local hydrogen-bonding rearrangements. This work substantiates that membrane-buried proline can provide the basis for conformational transitions between discrete alpha-helix-based structures in a nonpolar environment.

A simple gas chromatographic method for the analysis of trace organics in ambient air.

A simple method using adsorption, heat desorption, and F.I.D. gas chromatography to determine ppb quantities of various organic vapors in air is described. Laboratory results with chemicals such as bischloromethyl ether, vinyl chloride monomer and volatile ketones are discussed.