Proton and fluorine nuclear magnetic resonance spectroscopy was used to investigate the favoured forms of several furanosyl fluorides. The low energy barrier to pseudo-rotation in these systems precludes the assignment of only one favoured conformation for each molecule. A systematic study of five membered ring sugar conformations was undertaken by examining three types of systems, varying from a relatively rigid molecule involving three fused rings, to more flexible molecules involving a "free" furanosyl fluoride ring. The spectral assignment was greatly facilitated by heteronuclear fluorine decoupling and computer analysis.
5-fluoro-3,6-anhydro-α-L-idofuranose was synthesized
in good yield from several precursors and the molecule's
furanose ring conformation of ₂T³was assigned on the
basis of vicinal ¹H-¹H coupling constants. Using the values
for vicinal ¹H- ¹⁹F couplings obtained from this molecule,
together with data from other workers, a partial Karplus
type curve was constructed relating vicinal ¹H- ¹⁹F couplings to dihedral angles. This curve - which was found to be more asymmetric than the Karplus relationship for vicinal ¹H-¹H couplings - was then used, together with the known
Karplus curve for vicinal ¹H-¹H couplings, to determine the
conformations of the triester furanosyl fluorides of ribose,
arabinose and xylose. Assuming pure sp³ hybridization and
maximum ring puckering, the conformations for most of the
sugars studied were found to involve the displacement of
C₂ and/or C₃ positions out of the plane of the ring formed
by the other atoms. The conformation for α-fluoro-ribo-furanosyl triester ( ₃T⁴ ) was found to be different than that
of the β-fluoro-ribofuranosyl triester (₃T⁴). A significant
and apparently stereospecific long-range ⁴J[subscript H].₄,F coupling
through oxygen of ca. 6.5 Hz, is observed when H₄ and F are
in a trans arrangement, while a much smaller coupling for
⁴J[subscript H].₄,F of ca. 1.0 Hz. is observed when these two nuclei are
in a cis or approximately "planar M" arrangement. On the
other hand, ⁴J[subscript H].₃,F couplings were found to have a value of
ca. 2.2 Hz. in the cis or "planar M" geometry, while in the
trans geometry, ⁴J[subscript H].₄,F is ca. 0.5 Hz. / Science, Faculty of / Chemistry, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/35233 |
| Date | January 1969 |
| Creators | Steiner, Paul Robert |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
Page generated in 0.0061 seconds