Furanose Systems

The orientation of C1-0-H of 2,3s5 6-di-0-isopro ylidene-o(-D-manno-furanose has been determined by measurement of C- H coupling constants, n.O.e., spin-lattice relaxation rates for the relevant 

NMR spectroscopic experiments on L-ascorbic acid and on metal complexes of D-glucuronic and D-galacturonic acid in the furanose form are covered in Section 8 below and a conformational analysis of AZT is referred to in Section 1 above. 

Quantum mechanical studies on 2a -deoxycytosin and its 2, 2 -difluoro analogue (gemcitabine), and on cyclic 3, 5 -AMP have been reported. In an extensive new investigation, the pseudorotational equilibria of P-D-ribo- and 2-deoxy-p-D-ribo-furanosyl nucleosides have been correlated with the anomeric effects and pKa values of the nucleoside bases.  

D-(7/ cero-D-/Jo-2-octulose, the major sugar found in the resurrection plant Craterostigma plantagineum, has been identified by an NMR analysis of its 1,3 4,6 7,8-tri-0-isopropylidene-a-furanose derivative.  

I he mode of interaction of copper(II and manganese(ll) with D-ribose and U-arabinose has been studied by G-n.m.r. spectroscopy. Specific line-broadening effects were used to determine the principal sites of chelation, which were found to be the cis-diol at C-1 and 

C-2 is always downfleld relative to the C-3 signal. Conformational assignments of 4-0-ethyl-2 -deoxythymidine from H-n.m.r. 

The conformations, determined by H n.m.r. spectra, of t-L-arabino-furanosyl pyridinium salt (4.) and its tri-O-benzoyl derivative are 

D-gluco- and /S-L-ido-furanurono-6,3-lactones have been unambiguously 

3-di-O-acetyl-o -D-riburonofuranoside methyl ester has shown that it 

---

It must be stressed that any discussion of furanose systems in terms of a single, exclusively populated conformation may be unrealistic. However, even approximate conformational evaluations of these systems can yield chemically significant conclusions.102,105... 

A variety of NMR spectroscopic methods have been applied to structural and conformational analyses of the following furanose systems sugar em-dimethyl substituted alkenyl ethers, e.g. a-D-xylofuranose derivatives 13 (see Chapter 5 for synthesis), " the diastereomeric 6-chloro-6-deoxy-l,2-0-isopropylidene-a-D-gulofuranose cyclic 3,5-piperididomonophosphates 14, several 4 -thionucleo-sides, 6-formyl- and 6-(hydroxymethyl)-uridine 5 -carboxaldehydes 15 and 16, respectively, and their 2, 3 -0-isopropylidene derivatives, two double-... 

N.M.R. Spectroscopy and Conformational Features Theoretical and General Considerations Acyclic Systems Furanose Systems Pyranose Systems Oligosaccharides Nucleosides Other Molecules... 

---