We have measured the 15N nuclear magnetic resonance frequencies in 15N-labeled molecules (NNO, NNO, NH3, N2, and HCN) in gas phase samples and also in CH3NO2 as neat liquid. By using the previously determined temperature dependence of samples of the these gases at various densities, we are able to reduce the measured frequencies to the zero-density limit at 300 K, and obtain shielding differences between rovibrationally averaged isolated molecules at this shielding measurements from molecular beam studies to provide an 15N absolute shielding scale based on 15NH3.

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Novel, highly fluorescent, monofunctional, water-soluble heptamethine cyanine dyes containing a robust C−C bond at the central position of the near-infrared fluorophore system were prepared by the Suzuki−Miyaura method. The reaction proceeded efficiently to replace the meso-chlorine atom with a carboxy-functionalized aryl moiety and afforded the desired compounds in high yields. This methodology is particularly attractive due to its versatility and the utilization of environmentally friendly water as solvent. The new compounds possess excellent spectral properties and readily label bioactive molecules on solid support. The results demonstrate the potential of using the new compounds as fluorescent antennae for molecular imaging, spectroscopy, microscopy, and chemical or biological molecular recognition studies.

The pyrimidine nucleoside beta-d-2'-deoxy-2'-fluoro-2'-C-methylcytidine (1) was designed as a hepatitis C virus RNA-dependent RNA polymerase (HCV RdRp) inhibitor. The title compound was obtained by a DAST fluorination of N(4)-benzoyl-1-(2-methyl-3,5-di-O-benzoyl-beta-d-arabinofuranosyl]cytosine to provide N(4)-benzoyl-1-[2-fluoro-2-methyl-3,5-di-O-benzoyl-beta-d-ribofuranosyl]cytosine. The protected 2'-C-methylcytidine was obtained as a byproduct from the DAST fluorination and allowed for the preparation of two biologically active compounds from a common precursor. Compound 1 and 2'-C-methylcytidine were assayed in a subgenomic HCV replicon assay system and found to be potent and selective inhibitors of HCV replication. Compound 1 shows increased inhibitory activity in the HCV replicon assay compared to 2'-C-methylcytidine and low cellular toxicity.

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