- Chiral Hydroxymethyl Groups: 1H NMR Assignments of the Prochiral C-5'Protons of 2'-Deoxyribonucleosides
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2'-Deoxyadenosine, 2'-deoxycytidine, 2'-deoxyguanosine and 2'-deoxyuridine were prepared with stereoselective deuteration at C-5' and used to assign the prochiral C-5' protons in 300 MHz 1H NMR spectra obtained in 2H2O.In all cases, the more shielded C-5'proton was found to be the pro-R proton.From these assignments, C-4'-C-5' rotamer populations were determined using three previously published methods based on the spin couplings, 3J(H-4',H-5'R) and 3J(H-4',H-5'S), and the errors associated with these methods were assessed.The effects of base structure, furanose and N-glycoside bond conformation on the relative populations of hydroxymethyl rotamers in nucleosides are discussed.
- Kline, Paul C.,Serianni, Anthony S.
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- Tandem intramolecular silylformylation and silicon-assisted cross-coupling reactions. Synthesis of geometrically defined α,β-unsaturated aldehydes
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The palladium- and copper-catalyzed cross-coupling reactions of cyclic silyl ethers with aryl iodides are reported. Silyl ethers 3 were readily prepared by intramolecular silylformylation of homopropargyl silyl ethers 2 under a carbon monoxide atmosphere. The reaction of cyclic silyl ethers 3 with various aryl iodides 7 in the presence of [(allyl)PdCl]2, CuI, a hydrosilane, and KF·2H2O in DMF at room temperature provided the α,β-unsaturated aldehyde coupling products 8 in high yields. The need for copper in this process suggested that transmetalation from silicon to copper is an important step in the mechanism. Although siloxane 3 and the product 8 are not stable under basic conditions, KF·2H2O provided the appropriate balance of reactivity toward silicon and reduced basicity. The addition of a hydrosilane to [(allyl)PdCl]2 was needed to reduce the palladium(II) to the active palladium(0) form.
- Denmark, Scott E.,Kobayashi, Tetsuya
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p. 5153 - 5159
(2007/10/03)
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- Process for the preparation of 1,3-dihalo-1,1,3,3-tetra(organyl) disiloxanes
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1,3-dihalo-1,1,3,3-tetra(organyl)disiloxanes of the general formula XR2Si—O—SiR2X??(1) are prepared by reacting hydrogen halide with the corresponding 1,3-dihydro-1,1,3,3-tetra(organyl)disiloxanes of the general formula HR2Si—O—SiR2H??(2), in which R is an alkyl or halogen substituted alkyl group and X is halogen, in the presence of a catalyst selected from transition metals of the 8th subgroup of the periodic table of the elements, or compounds or complexes of these transition metals.
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- (3-ethoxypropionate) esters of cyclaradine
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Antiviral (3-ethoxypropionate) esters of (+)-cyclaradine having the formula: STR1 In the monoester Ry and Rz are hydrogen. In the diester Ry is the 3-ethoxypropionyl group and Rz is hydrogen. In the triester, Ry and Rz are each 3-ethoxypropionyl groups.
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- NUCLEIC ACID RELATED COMPOUNDS. 42. A GENERAL PROCEDURE FOR THE EFFICIENT DEOXYGENATION OF SECONDARY ALCOHOLS. REGIOSPECIFIC AND STEREOSELECTIVE CONVERSION OF RIBONUCLEOSIDES TO 2 prime -DEOXYNUCLEOSIDES.
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Treatment of unhindered secondary alcohols with phenoxythiocarbonyl chloride (phenyl chlorothionocarbonate) in pyridine/dichloromethane, or in acetonitrile with 4-dimethylaminopyridine catalysis for hindered alcohols, gave clean conversion to their O-phenoxythiocarbonyl derivatives. Reductive deoxygenation of these phenyl thionocarbonate esters proceeded smoothly, using tri-n-butyltin hydride and a free radical initiator in warm toluene. Overall conversion yields ranged from 57 to 78% for the naturally occurring nucleosides, nucleoside antibiotics, and methyl beta -D-ribofuranoside.
- Robins,Wilson,Hansske
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p. 4059 - 4065
(2007/10/02)
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