Synthesis and anti-HCV activity of a series of ß-d-2'-deoxy-2'-dibromo nucleosides and their corresponding phosphoramidate prodrugs.

Several ß-d-2'-deoxy-2'-substituted nucleoside analogs have displayed potent and selective anti-HCV activities and some of them have reached human clinical trials. In that regard, we report herein the synthesis of a series of 2'-deoxy,2'-dibromo substituted U, C, G and A nucleosides 10a-d and their corresponding phosphoramidate prodrugs 13a-d. The synthesized nucleosides 10a-d and prodrugs 13a-d were evaluated for their inhibitory activity against HCV as well as cellular toxicity. The results showed that the most potent compound was prodrug 13a, which exhibited micromolar inhibitory activity (EC50 = 1.5 ±â€¯0.8 µM) with no observed toxicity. In addition, molecular modeling and free energy perturbation calculations for the 5'-triphosphate formed from 13a and related 2'-modified nucleotides are discussed.

Organometallic enantiomeric scaffolding: a strategy for the enantiocontrolled construction of regio- and stereodivergent trisubstituted piperidines from a common precursor.

Reported herein is a general and efficient method to construct 2,3,6-trisubstituted piperidines in a substituent-independent fashion. From the high enantiopurity organometallic scaffold (-)-Tp(CO)(2)[(η-2,3,4)-(1S,2S)-1-benzyloxycarbonyl-5-oxo-5,6-dihydro-2H-pyridin-2-yl)molybdenum (Tp = hydridotrispyrazolylborato), a variety of TpMo(CO)(2)-based 2,3,6-trifunctionalized complexes of the (η-3,4,5-dihydropyridinyl) ligand were easily obtained in 5 steps through a sequence of highly regio- and stereospecific metal-influenced transformations (15 examples). From the 2,3,6-trifunctionalized molybdenum complexes, either 2,6-cis-3-trans or 2,3,6-cis systems were selectively obtained through the choice of an appropriate stereodivergent demetalation protocol. The potential of this strategy in synthetic chemistry was demonstrated by the short total synthesis of four natural and one non-natural alkaloids: indolizidines (±)-209I and (±)-8-epi-219F in the racemic series, and enantiocontrolled syntheses of (-)-indolizidine 251N, (-)-quinolizidine 251AA, and (-)-dehydroindolizidine 233E.

Organometallic enantiomeric scaffolding. Sequential semipinacol/1,5-"Michael-like" reactions as a strategic approach to bridgehead-quaternary center aza[3.3.1]bicyclics: application to the total synthesis of (-)-adaline.

A nontraditional approach to the enantiocontrolled construction of quaternary center-bearing heteroatom-bridged bicyclo[3.3.1]nonanes (homotropanes) is reported that is based on organometallic enantiomeric scaffolding. This strategy takes advantage of the unique reactivity profiles of TpMo(CO)(2)(5-oxo-eta(3)-pyranyl) and TpMo(CO)(2)(5-oxo-eta(3)-pyridinyl) scaffolds, and features a molybdenum-mediated semipinacol/1,5-"Michael-like" reaction sequence to establish the quaternary center and synthesize the bridged bicyclic structure. An asymmetric total synthesis of (-)-adaline highlights this methodology.

Structural insights into competitive antagonism in NMDA receptors.

There has been a great level of enthusiasm to downregulate overactive N-methyl-D-aspartate (NMDA) receptors to protect neurons from excitotoxicity. NMDA receptors play pivotal roles in basic brain development and functions as well as in neurological disorders and diseases. However, mechanistic understanding of antagonism in NMDA receptors is limited due to complete lack of antagonist-bound structures for the L-glutamate-binding GluN2 subunits. Here, we report the crystal structures of GluN1/GluN2A NMDA receptor ligand-binding domain (LBD) heterodimers in complex with GluN1- and GluN2-targeting antagonists. The crystal structures reveal that the antagonists, D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5) and 1-(phenanthrene-2-carbonyl)piperazine-2,3-dicarboxylic acid (PPDA), have discrete binding modes and mechanisms for opening of the bilobed architecture of GluN2A LBD compared to the agonist-bound form. The current study shows distinct ways by which the conformations of NMDA receptor LBDs may be controlled and coupled to receptor inhibition and provides possible strategies to develop therapeutic compounds with higher subtype-specificity.

Design, synthesis, and structure-activity relationship of a novel series of GluN2C-selective potentiators.

NMDA receptors are tetrameric complexes composed of GluN1 and GluN2A-D subunits that mediate a slow Ca(2+)-permeable component of excitatory synaptic transmission. NMDA receptors have been implicated in a wide range of neurological diseases and thus represent an important therapeutic target. We herein describe a novel series of pyrrolidinones that selectively potentiate only NMDA receptors that contain the GluN2C subunit. The most active analogues tested were over 100-fold selective for recombinant GluN2C-containing receptors over GluN2A/B/D-containing NMDA receptors as well as AMPA and kainate receptors. This series represents the first class of allosteric potentiators that are selective for diheteromeric GluN2C-containing NMDA receptors.

Chutes and ladders in hepatitis C nucleoside drug development.

Chutes and Ladders is an exciting up-and-down-again game in which players race to be the first to the top of the board. Along the way, they will find ladders to help them advance, and chutes that will cause them to move backwards. The development of nucleoside analogs for clinical treatment of hepatitis C presents a similar scenario in which taking shortcuts may help quickly advance a program, but there is always a tremendous risk of being sent backwards as one competes for the finish line. In recent years the treatment options for chronic hepatitis C virus (HCV) infection have expand due to the development of a replicon based in vitro evaluation system, allowing for the identification of multiple drugable viral targets along with a concerted and substantial drug discovery effort. Three major drug targets have reached clinical study for chronic HCV infection: the NS3/4A serine protease, the large phosphoprotein NS5A, and the NS5B RNA-dependent RNA polymerase. Recently, two oral HCV protease inhibitors were approved by the FDA and were the first direct acting anti-HCV agents to result from the substantial research in this area. There are currently many new chemical entities from several different target classes that are being evaluated worldwide in clinical trials for their effectiveness at achieving a sustained virologic response (SVR) (Pham et al., 2004; Radkowski et al., 2005). Clearly the goal is to develop therapies leading to a cure that are safe, widely accessible and available, and effective against all HCV genotypes (GT), and all stages of the disease. Nucleoside analogs that target the HCV NS5B polymerase that have reached human clinical trials is the focus of this review as they have demonstrated significant advantages in the clinic with broader activity against the various HCV GT and a higher barrier to the development of resistant viruses when compared to all other classes of HCV inhibitors.

Novel synthesis and biological evaluation of enigmols as therapeutic agents for treating prostate cancer.

Enigmol is a synthetic, orally active 1-deoxysphingoid base analogue that has demonstrated promising activity against prostate cancer. In these studies, the pharmacologic roles of stereochemistry and N-methylation in the structure of enigmols were examined. A novel enantioselective synthesis of all four possible 2S-diastereoisomers of enigmol (2-aminooctadecane-3,5-diols) from l-alanine is reported, which features a Liebeskind-Srogl cross-coupling reaction between l-alanine thiol ester and (E)-pentadec-1-enylboronic acid as the key step. In vitro biological evaluation of the four enigmol diastereoisomers and 2S,3S,5S-N-methylenigmol against two prostate cancer cell lines (PC-3 and LNCaP) indicates that all but one diastereomer demonstrate potent oncolytic activity. In nude mouse xenograft models of human prostate cancer, enigmol was equally effective as standard prostate cancer therapies (androgen deprivation or docetaxel), and two of the enigmol diastereomers, 2S,3S,5R-enigmol and 2S,3R,5S-enigmol, also caused statistically significant inhibition of tumor growth. A pharmacokinetic profile of enigmol and N-methylenigmol is also presented.

Novel Substitutions of 1-Alkoxy- and 1-Arylsulfonyloxy-η-Allylmolybdenum Complexes. A Case for η-Alkenyl Carbene Complexes as Intermediates.

A series of acyclic and cyclic 1-alkoxy- and 1-arylsulfonyloxy-substituted TpMo(CO)(2)(η(3)-allyl) complexes was synthesized and characterized, and exchange of the oxygenated substituent was investigated under a variety of reaction conditions. 1-Alkoxy-substituted η(3)-allyl and η(3)-butenyl complexes participated in direct, uncatalyzed exchange of the alkoxy substituent with benzylamine, but required a Lewis acid for exchange with alcohols. The 1-alkoxy-substituted η(3)-cyclohexenyl complex was unreactive towards exchange under all conditions investigated. The corresponding acyclic arylsulfonyloxy-substituted complexes underwent direct, uncatalyzed exchange with both benzylamine and alcohols, while the arylsulfonyloxy-substituted cyclohexenyl compounds participated in direct substitution with benzylamine, but not alcohols. High enantiopurity acyclic and cyclic alkoxy- and arylsulfonyloxy-substituted complexes provided exchange products with predominant, but incomplete, losses in enantiomeric excess in all cases examined. Mechanisms accounting for the observed reactivity trends and for the losses in enantiomeric excess are discussed. Reaction of alkoxy-substituted complexes through an associative mechanism and of arylsulfonyloxy-substituted compounds through a dissociative mechanism is suggested.

Ceramide synthase inhibition by fumonisin B1 causes accumulation of 1-deoxysphinganine: a novel category of bioactive 1-deoxysphingoid bases and 1-deoxydihydroceramides biosynthesized by mammalian cell lines and animals.

Fumonisin B(1) (FB(1)) is a mycotoxin that inhibits ceramide synthases (CerS) and causes kidney and liver toxicity and other disease. Inhibition of CerS by FB(1) increases sphinganine (Sa), Sa 1-phosphate, and a previously unidentified metabolite. Analysis of the latter by quadrupole-time-of-flight mass spectrometry assigned an m/z = 286.3123 in positive ionization mode, consistent with the molecular formula for deoxysphinganine (C(18)H(40)NO). Comparison with a synthetic standard using liquid chromatography, electrospray tandem mass spectrometry identified the metabolite as 1-deoxysphinganine (1-deoxySa) based on LC mobility and production of a distinctive fragment ion (m/z 44, CH(3)CH=NH (+)(2)) upon collision-induced dissociation. This novel sphingoid base arises from condensation of alanine with palmitoyl-CoA via serine palmitoyltransferase (SPT), as indicated by incorporation of l-[U-(13)C]alanine into 1-deoxySa by Vero cells; inhibition of its production in LLC-PK(1) cells by myriocin, an SPT inhibitor; and the absence of incorporation of [U-(13)C]palmitate into 1-[(13)C]deoxySa in LY-B cells, which lack SPT activity. LY-B-LCB1 cells, in which SPT has been restored by stable transfection, however, produce large amounts of 1-[(13)C]deoxySa. 1-DeoxySa was elevated in FB(1)-treated cells and mouse liver and kidney, and its cytotoxicity was greater than or equal to that of Sa for LLC-PK(1) and DU-145 cells. Therefore, this compound is likely to contribute to pathologies associated with fumonisins. In the absence of FB(1), substantial amounts of 1-deoxySa are made and acylated to N-acyl-1-deoxySa (i.e. 1-deoxydihydroceramides). Thus, these compounds are an underappreciated category of bioactive sphingoid bases and "ceramides" that might play important roles in cell regulation.