Improved treatments for chronic hepatitis C virus (HCV) infection are needed due to the suboptimal response rates and deleterious side effects associated with current treatment options. The triphosphates of 2-C-methyl-adenosine and 2-C-methyl-guanosine were previously shown to be potent inhibitors of the HCV RNA-dependent RNA polymerase (RdRp) that is responsible for the replication of viral RNA in cells. Here we demonstrate that the inclusion of a 7-deaza modification in a series of purine nucleoside triphosphates results in an increase in inhibitory potency against the HCV RdRp and improved pharmacokinetic properties. Notably, incorporation of the 7-deaza modification into 2-C-methyl-adenosine results in an inhibitor with a 20-fold-increased potency as the 5-triphosphate in HCV RdRp assays while maintaining the inhibitory potency of the nucleoside in the bicistronic HCV replicon and with reduced cellular toxicity. In contrast, while 7-deaza-2-C-methyl-GTP also displays enhanced inhibitory potency in enzyme assays, due to poor cellular penetration and/or metabolism, the nucleoside does not inhibit replication of a bicistronic HCV replicon in cell culture. 7-Deaza-2-C-methyl-adenosine displays promising in vivo pharmacokinetics in three animal species, as well as an acute oral lethal dose in excess of 2,000 mg/kg of body weight in mice. Taken together, these data demonstrate that 7-deaza-2-C-methyl-adenosine is an attractive candidate for further investigation as a potential treatment for HCV infection.

Calcitonin gene-related peptide (CGRP) is a potent neuropeptide that plays a key role in the pathophysiology of migraine headache. CGRP levels in the cranial circulation are increased during a migraine attack, and CGRP itself has been shown to trigger migraine-like headache. The correlation between CGRP release and migraine headache points to the potential utility of CGRP receptor antagonists as novel therapeutics in the treatment of migraine. Indeed, clinical proof-of-concept in the acute treatment of migraine was demonstrated with an intravenous formulation of the CGRP receptor antagonist BIBN4096BS (olcegepant). Here we report on the pharmacological characterization of the first orally bioavailable CGRP receptor antagonist in clinical development, MK-MK-0974 is a potent antagonist of the human (K i ϭ 0.77 nM) and rhesus (K i ϭ 1.2 nM) CGRP receptors but displays Ͼ1500-fold lower affinity for the canine and rat receptors as determined via 125 I-human CGRP competition binding assays. A rhesus pharmacodynamic assay measuring capsaicin-induced changes in forearm dermal blood flow via laser Doppler imaging was utilized to determine the in vivo activity of CGRP receptor antagonism. MK-0974 produced a concentration-dependent inhibition of dermal vasodilation, generated by capsaicininduced release of endogenous CGRP, with plasma concentrations of 127 and 994 nM required to block 50 and 90% of the blood flow increase, respectively. In conclusion, MK-0974 is a highly potent, selective, and orally bioavailable CGRP receptor antagonist, which may be valuable in the acute treatment of migraine.CGRP is a 37 amino acid neuropeptide produced by tissuespecific alternative mRNA splicing of the calcitonin gene (Amara et al., 1982) and is a member of the calcitonin family of peptides, which includes calcitonin, amylin, and adrenomedullin. CGRP activity is mediated by the coexpression of a G-protein-coupled receptor, calcitonin receptor-like receptor, a single transmembrane-spanning protein designated receptor activity-modifying protein (RAMP) 1 (McLatchie et al., 1998), and an intracellular protein, receptor component proArticle, publication date, and citation information can be found at

Hepatitis C virus infection constitutes a significant health problem in need of more effective therapies. We have recently identified 2'-C-methyladenosine and 2'-C-methylguanosine as potent nucleoside inhibitors of HCV RNA replication in vitro. However, both of these compounds suffered from significant limitations. 2'-C-Methyladenosine was found to be susceptible to enzymatic conversions by adenosine deaminase and purine nucleoside phosphorylase, and it displayed limited oral bioavailability in the rat. 2'-C-Methylguanosine, on the other hand, was neither efficiently taken up in cells nor phosphorylated well. As part of an attempt to address these limitations, we now report upon the synthesis and evaluation of a series of heterobase-modified 2'-C-methyl ribonucleosides. The structure-activity relationship within this series of nucleosides reveals 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine as potent and noncytotoxic inhibitors of HCV RNA replication. Both 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine display improved enzymatic stability profiles as compared to that of 2'-C-methyladenosine. Consistent with these observations, the most potent compound, 4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine ribonucleoside, is orally bioavailable in the rat. Together, the potency of the 2'-C-methyl-4-amino-pyrrolo[2,3-d]pyrimidine ribonucleosides and their improved pharmacokinetic properties relative to that of 2'-C-methyladenosine suggests that this class of compounds may have clinical utility.

ABSTRACT, with a t 1/2 value of 59 min. In vitro autoradiography studies on rhesus monkey brain slices identified the highest level of binding in the cerebellum, brainstem, and meninges. Finally, as an index of central nervous system penetrability, the in vivo cerebrospinal fluid/plasma ratio was determined to be 2 to 3% in cisterna magna-ported rhesus monkeys.Migraine is one of the most prevalent and disabling neurological disorders, with characteristic symptoms that can last for several days. Despite its severity and high prevalence, migraine is not generally recognized as a serious medical condition and the societal burden is not fully appreciated. Migraine often affects people during their most productive years, which in turn burdens families and employers and ultimately affects the quality of life of the migraine sufferer. Migraine is generally agreed to be underdiagnosed and many migraineurs do not receive appropriate therapy, indicating there is significant room for improvement in the diagnosis and management of migraine.An overall improvement in migraine treatment occurred Article, publication date, and citation information can be found at