Studies of specifically fluorinated carbohydrates. Part VI. Some pentofuranosyl fluorides

Abstract

Detailed analyses of the 'H and 19F nuclear magnetic resonance spectra of seven pentofuranosyl fluoride derivatives are reported. With the help of 'H-{lgF) heteronuclear decoupling experiments, some unexpectedly large 4J co~~plings have been detected between F and H-4; when these substiti~ents are tmns the coupling is 5.5-7.9 Hz while the cis relationship gives couplings of 1.0-1.8 Hz. The 4J couplings between F and H-3 are sn~aller when these groups are tr.arzs (i 0.7 Hz) than when they are cis oriented (1.7-2.4 Hz). These, and the other coupling constants are discussed in terms of the favored conformations of these derivatives. The ring conformations of the anomeric tri-0-benzoyl-D-ribofuranosyl fluorides differ from each other.

Fluorinated carbohydrates. Part VI. Studies of derivatives of 3-deoxy-3-fluoro-D-galactose

“…The present discussion reinforces a previous suggestion (17,18) that even approximate conformational evaluations of furanose systems can yield chemically significant conclusions. In the present situation, it could well be that the derivative has both the 'V and the V2 conformers significantly populated, and that the observed coupling constants represent a timeaverage of the couplings of these two forms.…”

“…As has been discussed in detail elsewhere (17,18) it is questionable whether it is realistic to couch any conformational discussion of a furanose system in terms of a single, exclusively populated conformation. The present discussion reinforces a previous suggestion (17,18) that even approximate conformational evaluations of furanose systems can yield chemically significant conclusions.…”

A Comparative Proton Magnetic Resonance Study of the Molecular Conformation of Uracil and 6-Aza Uracil Nucleosides and Nucleotides

“…We also realize that use of p.m.r. data to confirm the presence of one particular mode is futile and consider the approach outlined recently (27) which discusses segments of the pseudorotational cycle thought to be significantly populated. By C-2' endo we mean simply that conformation in which HI., HZ, assume a quasi axial :axial (a :a) relationship and H3,, H4.…”

The Crystal and Molecular Structure of 3-Chloro-3-deoxy-1,2;5,6-di-O-isopropylidene-β-D-idose

“…At this point down-weighting of the weak reflections was indicated by an analysis of oA2 as a function of sin 011, IFol, and h, k, and I. The final weighting scheme was such that OF= 1.14 for Fo 2 12 An electron density difference map computed after the refinement was complete showed large peaks and troughs of f0.22 (near C(6)) and -0.24 e k 3 (near C(7)) respectively, the standard error in the electron density is 0.12 eA-3.…”