The influence of the purine 2-amino group on DNA conformation and stability-II: Synthesis and physical characterization of d[CGT(2-NH2)ACG], d[CGU(2-NH2)ACG], and d[CGT(2-NH2)AT(2-NH2)ACG]

Synthesis of an N-protected derivative of 2-amino-2'-deoxyadenosine (dA') from 2'-deoxyguanosine is reported. The syntheses of several oligodeoxynucleotides containing this modified nucleoside are described, together with physical characterization via melting studies and CD conformational analysis. As expected, the 2-amino group is seen to add to the duplex stability. Although the sequence d(TA')₃ was found to undergo a salt-induced conformational transition, mixed sequences such as d(CGTA'CG) did not display this behavior. All guanine residues present in these sequences were O⁶ protected, either with the cyanoethyl group or the 4-nitrophenylethyl group, to eliminate guanine degradation during phosphorylation and condensation reactions. Procedures for the introduction and removal of these O⁶ protecting groups are described.     

Differential binding of Mg2+, Zn2+, and Cd2+ at two sites in a hammerhead ribozyme motif, determined by 15N NMR

A decamer duplex model of Domain II of the hammerhead ribozyme was synthesized with [8-13C-1,7,NH2-15N3]-guanosine at the known metal binding site, G10.1 and, for comparison, [2-13C-1,7,NH2-15N3]-guanosine at G16.2. The 15N NMR chemical shifts of the labeled N7s monitored during addition of Mg2+, Cd2+, and Zn2+ showed the same preference for binding at G10.1 over G16.2 for each metal. These results demonstrate that 15N labeling can be used to evaluate the binding of different metals, including Mg2+, to a given nitrogen, as well as to compare the binding potential of different sites.     

Synthesis of O-6-alkylated deoxyguanosine nucleosides

A general route for synthesis of 6-$\text{O}$-alkyl-2∝deoxyguanosine nucleosides is described. The key step is conversion of the 6-$\text{O}$-TPS derivative $\text{2}$ to the 6-trimethylamino compound $\text{3}$. The trimethylamino group is readily displaced by alcohols in the presence of DBU. Using this route the 6-$\text{O}$-methyl, ethyl and n-butyl 2∝-deoxyguanosine derivatives $\text{5a-c}$ have been prepared in excellent overall yields.     

The effect of alcoholic mobile phase modifiers on retention and stereoselectivity on a commercially available cellulose-based HPLC chiral stationary phase: An unexpected reversal in enantiometric elution order

Summary High pressure liquid chromatographic methods for the determination of diphenylmethane-4,4-diisocyanate (MDI) and toluene diisocyanate (TDI) in chemical products are described. The MDI- and TDI monomers were determined as their urea derivative formed by the reaction with 9-(methyl aminomethyl)-anthracene. Using these methods MDI- and TDI monomer concentrations have been determined in 55 chemical products: sealing waxes, insulating- and adhesive foam, hardener, primer, adhesives and surface coatings. The recovery of both MDI and TDI monomers from various types of chemical product was found to be 92–97%, and the relative standard deviations of the methods was <5% for all types of products.     

Topography of Nucleic Acid Helices in Solutions

A number of reporter molecules of the structure R-(CH₂)_n-N⁺(CH₃)₂(CH₂)_mN⁺(CH₃)₃·2Br^?, where R is a chromophore absorbing in the 300–500 mp region, have been synthesized. The effect of DNA and RNA on the absorption, induced circular dichroism, and proton magnetic resonance spectra is reported. A red shift and a hypochromic effect on the absorption spectra of the bound chromophore is observed. In all cases where R is an “unsymmetrical” 4-nitroaniline chromophore, it is found that DNA and RNA induce an opposite CD in the absorption band of the bound reporter molecules. These results together with PMR studies are interpreted in terms of the structure of the nucleic acid systems in solutions.