The new cytotoxic agents rakicidins A and B were isolated from cultured broth of a Micromonospora sp. Spectroscopic and amino acid analysis has shown that rakicidin A is a new cyclic lipopeptide, consisting of 4-amino-penta-2,4-dienoic acid, 3-hydroxy-2,4,16-trimethylheptadecanoic acid, sarcosine, and 3-hydroxyasparagine. Rakicidin B differs by one methylene group in the lipid side chain. These compounds exhibited cytotoxicity against the Ml09 cell line. In our continuing search for newantitumor agents from microorganisms, an isolate of Micromonospora was selected for further evaluation. This research led to the discovery of two newcytotoxic lipopeptides, rakicidins A and B (Fig. 1). This paper describes the fermentation, biological evaluation, purification, physico-chemical characterization, and structure elucidation of these compounds. Fermentation Microorganism The producing organism was isolated from a soil sample collected at Andhra Pradesh, India and was identified as a Micromonospora sp., strain No. R385-2. Media and Culture Conditions Micromonospora strain No. R385-2 was grown on slants of modified Bennett's mediumwhich contained the following: 0.5% Japanese potato starch (Generichem DEC. 1995 Corp. Acadama Dextrin No. 3), 0.5% glucose, 0.1% fish meat extract (Mikuni Chem. Industry), 0.1% yeast extract (Difco), 0.2% N-Z Case (Sheffield Products), 0.2% NaCl, 0.1% CaCO3, 1.5% agar. The medium was sterilized at 121°C for 20 minutes. The culture was transferred from the slant into 100ml of GERmedium in a 500ml flask. The medium contained the following: 2.4% Japanese potato starch, 0.1% dextrose, 0.3% beef extract (BBL), 0.5% tryptone (Difco), 0.5% yeast extract (BBL), 0.2% CaCO3 and was adjusted to pH 7.6 before autoclaving. The mediumwas sterilized at 121°C for 20

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Nocathiacin I (BMS-249524) is a highly cross-linked thiazolyl peptide that displays potent activity against Gram-positive bacteria, including a number of antibiotic-resistant strains. This natural product contains 10 chiral centers. NMR studies have been performed to characterize the solution structure of nocathiacin I. A uniformly 13C,15N-labeled sample was used to obtain NMR assignments. Restrained simulated annealing calculations were performed by using accurately determined NOE distance restraints. All of the chiral centers were allowed to float during the simulated annealing protocol. Two clusters of structures were obtained that satisfy the NOE restraints very well and that are reasonably consistent with vicinal J-coupling constants. Within each cluster, all 10 chiral centers are uniquely defined. The two clusters are effectively mirror images of each other: all chiral centers that have the R(S) configuration in one cluster have the S(R) configuration in the other. The single threonine residue in nocathiacin I was subsequently determined to be l-threonine by chiral capillary electrophoresis, allowing the absolute configurations of all 10 chiral centers to be defined.

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The exceptional in vitro potency of the hepatitis C virus (HCV) NS5A inhibitor BMS-790052 has translated into an in vivo effect in proof-of-concept clinical trials. Although the 50% effective concentration (EC 50 ) of the initial lead, the thiazolidinone BMS-824, was ϳ10 nM in the replicon assay, it underwent transformation to other inhibitory species after incubation in cell culture medium. The biological profile of BMS-824, including the EC 50 , the drug concentration required to reduce cell growth by 50% (CC 50 ), and the resistance profile, however, remained unchanged, triggering an investigation to identify the biologically active species. Highperformance liquid chromatography (HPLC) biogram fractionation of a sample of BMS-824 incubated in medium revealed that the most active fractions could readily be separated from the parental compound and retained the biological profile of BMS-824. From mass spectral and nuclear magnetic resonance data, the active species was determined to be a dimer of BMS-824 derived from an intermolecular radical-mediated reaction of the parent compound. Based upon an analysis of the structural elements of the dimer deemed necessary for anti-HCV activity, the stilbene derivative BMS-346 was synthesized. This compound exhibited excellent anti-HCV activity and showed a resistance profile similar to that of BMS-824, with changes in compound sensitivity mapped to the N terminus of NS5A. The N terminus of NS5A has been crystallized as a dimer, complementing the symmetry of BMS-346 and allowing a potential mode of inhibition of NS5A to be discussed. Identification of the stable, active pharmacophore associated with these NS5A inhibitors provided the foundation for the design of more potent inhibitors with broad genotype inhibition. This culminated in the identification of BMS-790052, a compound that preserves the symmetry discovered with BMS-346.Hepatitis C virus (HCV) is the major causative agent of non-A, non-B hepatitis worldwide, which affects more than 3% of the world's population. Of those infected with HCV, ϳ70% proceed to a chronic state which can lead to severe liver diseases, including fibrosis, cirrhosis, or hepatocellular carcinoma (1, 7). There is currently no vaccine against HCV and no generally effective therapy for all HCV genotypes. The current optimal therapy is pegylated alpha interferon in combination with ribavirin, a regimen associated with significant side effects and limited efficacy in the most prevalent patient population, consisting of genotype 1 (4). Therefore, there is an urgent need for the development of more effective, HCV-specific antiviral therapies with fewer side effects.In the search for more efficacious, safer HCV therapies, the most actively pursued antiviral targets have been the NS3 protease and NS5B RNA-dependent RNA polymerase, both essential enzymes for the replication of HCV (2,11,12). Exciting progress has been demonstrated in clinical trials with multiple HCV NS3 serine protease inhibitors, as well as with both nucleoside and nonnucleoside po...

ABSTRACT:The iminothiazolidinone BMS-858 (2) was identified as a specific inhibitor of HCV repli cation in a genotype 1b replicon assay via a high-throughput screening campaign. A more potent analogue, BMS-824 (18), was used in resistance mapping studies, which revealed that inhibitory activity was related to disrupting the function of the HCV nonstructural protein 5A. Despite the development of coherent and interpretable SAR, it was subsequently discovered that in DMSO 18 underwent an oxidation and structural rearrangement to afford the thiohydantoin 47, a compound with reduced HCV inhibitory activity. However, HPLC bioassay fractionation studies performed after incubation of 18 in assay media led to the identification of fractions containing a dimeric species 48 that exhibited potent antiviral activity. Excision of the key elements hypothesized to be responsible for antiviral activity based on SAR observations reduced 48 to a simplified, symmetrical, pharmacophore realized most effectively with the stilbene 55, a compound that demonstrated potent inhibition of HCV in a genotype 1b replicon with an EC 50 = 86 pM.

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