Ruth R. Inners

A multinuclear double-tuned probe for applications with solids or liquids utilizing lumped tuning elements

Abstract A high-efficiency multinuclear double-tuned probe using lumped-element construction is compared and contrasted with a transmission line probe. A rationale for improved efficiency at the high frequency and a commensurate improvement in the signal-to-noise ratio is developed. Powder spectra obtained at 44.4 MHz with the lumped-element probe are shown and pertinent construction details are given.

Synthesis of C-arabinofuranosyl compounds. Phosphonate and carboxylate isosteres of d-arabinose 1,5-bisphosphate☆

Abstract Electrophile-mediated cyclization of 3,4,6-tri- O -benzyl-1,2-dideoxy- d - arabino -hex-1-enitol with N -bromosuccinimide yielded primarily 2,5-anhydro-3,4,6-tri- O -benzyl-1-bromo-1-deoxy- d -glucitol ( 10 ). This apparently kinetically controlled reaction was of key importance in the successful synthesis of a phosphonate analog of β- d -arabinose 1,5-bisphosphate ( 1 ), namely, 2,5-anhydro-1-deoxy-1-phosphono- d -glucitol 6-phosphate ( 4 ), whith high stereoselectivity. By contrast, condensation of the sodium salt of tetraethyl methylenediphosphonate and 2,3,5-tri- O -benzyl- d -arabinose ( 7 ) gave a phosphonate compound slightly enriched in the 2,5-anhydro- d -mannitol (α) isomer. In the Wittig—Michael reaction of stabilized phosphoranes with 7 , the α isomer preponderated. Since equilibration of methyl 3,6-anhydro-4,5,7-tri- O -benzyl-2-deoxy- d - glycero - d - galacto - ( 33 ) and - d - gulo -heptonate ( 34 ) (5:1) resulted in a 1:1 α:β ratio, the preference for the 2,5-anhydro- d -mannitol (α) isomer probably reflects a kinetic bias. The carbomethoxy anomers were converted independently into the α and β carboxylate isosteres ( 5 and 6 , respectively) of d -arabinose 1,5-diphosphate. Empirical force field calculations (MMP2) and n.m.r. experiments were conducted on the pairs of diastereomers 9 and 10 , and 33 and 34 . The calculations predict that the α and β anomers of each pair have similar energies, differing by only 2.1 kJ/mol. Compounds 4, 5 , and 6 were evaluated for biological activity.