Glucagon is a 29-amino acid peptide that is an important counter-regulatory hormone in the control of glucose homeostasis (1). Glucagon secretion from the endocrine pancreas induces an increase in hepatic glycogenolysis and gluconeogenesis, and it attenuates the ability of insulin to inhibit these processes. As such, the overall rates of hepatic glucose synthesis and glycogen metabolism are controlled by the systemic ratio of insulin and glucagon (2, 3). Therefore, glucagon antagonists have the potential to improve hepatic insulin sensitivity and to be effective hypoglycemic agents.Peptidyl glucagon antagonists and their hypoglycemic activity were first described over 15 years ago, and an extensive exploration of the structure/activity relationships of these glucagon analogs has been reported (4 -6). The hepatic receptor for glucagon was cloned recently (7,8), confirming that it is a member of the seven-transmembrane domain, G-protein-coupled receptor superfamily. This receptor superfamily has a binding pocket for small-molecule ligands within the transmembrane domain that has made it possible to identify nonpeptidyl antagonists for many receptor families in which the endogenous ligands are small peptides or proteins (9). Thus, we initiated an effort to identify non-peptidyl, orally active antagonists for the human glucagon receptor.Collins et al. (10) have described a dichloroquinoxaline glucagon antagonist with weak affinity (IC 50 ϭ 4 M) for the rat glucagon receptor. However, there have been no subsequent reports in the patent or scientific literature describing the development of potent antagonists from this series. Our initial screening efforts identified a series of triarylimidazole and triarylpyrrole compounds with significant binding affinity for the human glucagon receptor, and efforts to evaluate the structure-activity relationships of this series have lead to the identification of potent glucagon antagonists (11). In the present article, we describe the identification and characterization of a potent glucagon antagonist from this series. MATERIALS AND METHODSCharacterization of Binding Affinity and Functional Activity-Stable CHO 1 cell lines or COS cells transiently expressing the human glucagon receptor were prepared as described previously (8, 12). Antagonist binding affinity was assessed by measuring inhibition of radiolabeled glucagon binding to CHO cell membranes. Briefly, 125 I-glucagon (58 pM) binding to the membrane preparation was measured in 20 mM Tris, pH 7.4, containing 1 mM dithiothreitol, 5 g/ml leupeptin, 10 g/ml benzamidine, 40 g/ml bacitracin, 5 g/ml soybean trypsin inhibitor, and 3 M o-phenanthroline Ϯ 1 M glucagon for 1 h at room temperature. Bound cpm were recovered by filtration using a Tomtec harvester and quantified in a ␥-scintillation counter.The ability of compound to inhibit glucagon-stimulated adenylyl cyclase was assessed as described previously (12). Briefly, cells were harvested from monolayers with enzyme-free cell dissociation solution (Specialty Media, Inc.) and were...

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QuinoxapeptmA and B are novel chromodepsipeptides which were isolated from a nocardioform actinomycete with indeterminant morphology. Quinoxapeptins A and B are potent inhibitors of HIV-1and HIV-2reverse transcriptase and almost equally active against two single mutants forms as well as a double mutant form of HIV-1 reverse transcriptase. Qumoxapeptin A and B are specific inhibitors of HIV-1 and HIV-2 reverse transcriptase because they did not inhibit human DNA polymerase a, /?, y and S. Quinoxapeptin A and B are structurally similar to luzopeptin A which was also active against HIV-landHIV-2reverse transcriptase.

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 microM) 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 125I IP-10/CXCR3 binding assay. Duramycin was the most potent with an IC50 of 0.1 microM. Roselipins 2A, 2B and 1A showed IC50 values of 14.6, 23.5, and 41 microM, respectively. Diosgenin glycosides dioscin, hypoglaucin A and kallstroemin D exhibited IC50 values of 2.1, 0.47 and 3 microM, respectively. A novel cyclic 3-alkyl pyridinium salt isolated from a sponge displayed a binding IC50 of 0.67 microM.