Furanoid systems

Non-selective proton spin-lattice relaxation times for several furanoid systems have been measured. Since epimers give significantly different values the method is of value for structural analysis. Methyl tetrofuranosides have been studied 

Yoshimoto, Y. Itatani, and Y. Tsuda, Chem. Pharm. Bull., 1980, 28, 2065. 

Replacement of the ring oxygen in naturally occurring, as well as synthetic, nucleosides for therapeutic reasons has been a major task of carbohydrate chemistry. Starting in the early 1960s, all diastereomeric 4-thio analogs of natural pentofuranoses, as well as some of their enantiomers, were prepared and, based on these approaches, a wide range of synthetic 4 -thionucleosides has been made available. 

Various protected bicyclic 2,5-anhydro derivatives of 5-thio-D-mannitol were obtained from methyl 2,3,4-tri-(9-acetyl-6-(9-mesyl-5-thio-a-D-glucopyranoside by transannular participation of the ring sulfur atom and ring opening of the thiiranium ion [35]. Similar reactions were earlier observed with, for example, a 4-(9-methanesulfony 1-5-thio-D-xylopyranose [36]. 

Hudson s Rules of isorotation have been applied to furanosides and a correlation with known conformations of methyl aldofuranosides made. The molecular rotations and differences in molecular rotation were tabulated for all aldo-pentoses, aldohexoses, and hexuloses as their methyl furanosides, and hence their conformations were deduced. The jS-D-pentofuranosides were mainly in the T2 form with the 0-methyl group quasi-axial and the side-chain quasi-equatorial, whereas the a-D-pentofuranosides were either in the E form or a mixture of T forms. The optical rotations for all a-D-furanosides are negative, but for 3-d-furanosides they are all positive.  

The crystal structure of d-deoxy-ct-L-sorbofuranose has been determined the furanoid ring had a C-i -exo-CA -endoCTf) conformation. The paper contains a discussion of the conformations adopted by ketofuranosides. Some Vh-2,h-5 couplings of 0.8-0.95 Hz have been observed in 3,6-anhydro-D-idofuranose 

Application of long-range selective proton decoupling using low-power irradiation has enabled the assignment of indirect coupling in the 

The D-ribofuranosyl ring in the glycosylamine (448) [previously thought to have the structure (449)] adopts the unusual conformation in the solid state.  

Semi-empirical potential-energy calculations have been carried out on purine and pyrimidine ribonucleoside 2, 3 -cyclic phosphates and the 5 -phosphates.  

Kitano, Y. Mizuno, M. Ueyama, K. Tori, M. Kamisaku, and K. Ajisaka, Biochem. Biophys. Res. Comm., 1975, 64, 996. 

Guschlbauer, Tran Dinh Son, M. Blandin, and J. C. Catlin, Nucleic Acids Res., 1974, 1, 855. 

7(9s Darzynkiewicz, M. Remin, A. Dworak, and D. Shugar, Cancer Biochem. Biophys., 1975, 1, 85 Chem. Abs., 1975, 83, 114 801f). 

High-resolution H n.m.r. spectroscopy has been used to probe the conformations of a number of o-ribofuranosylamine derivatives and such rigid molecules as 2,2 -cyclonucleosides and nucleoside 3, 5 -phosphates in aqueous solution. H N.m.r. spectroscopy has also been used to study details of the intramolecular association and conformations of a- and j8-linked pyridine ribo-nucleosides and their 5 -phosphates. The results were analysed in terms of base-D-ribose, o-ribose-side-chain, and base-side-chain interactions and the conformational restraints imposed by the cis HO-2-HO-3 interaction in jS-nucleo-tides and the additional cis HO-2 -base interaction in a-nucleotides. H N.m.r. measurements - including measurements of nuclear Overhauser effects and paramagnetic relaxations effected by Mn + cations - have been used to investigate the preferred conformation about the jV-glycosidic bond of 8-amino-, 8-methyl-amino-, and 8-dimethylamino-adenylic acid, all of which competitively inhibit the coenzyme NADH in the reaction with chicken-muscle lactate dehydrogenase. The primary and secondary amines were shown to prefer anti conformations, whereas the tertiary amine prefers a syn conformation. 

de Bruyn, D. Danneels, M. Anteunis, and E. Saman, J. Carbohydrates, Nucleosides, 

Studies of mono- and di-nucleotides using n.m.r. spectroscopy have reported chemical shifts and coupling constants. Both and n.m.r. spectroscopy were used to examine the stereoisomeric spirophosphoranes obtained by the joint action of tris(dimethyIamino)phosphine and carbon tetrachloride on 3-0-benzyl-l, 2-O-isopropylidene-ot-D-gluco- and -allo-furanose (see Vol. 9, p. 47), and, in conjunction with n.m.r. spectroscopy, the stereochemistries of 1,2-substituted 6-deoxy-6-halogeno-D-glucofuranose 3,5-phosphates.  

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The stability of the unsaturated furanuronate 159 at room temperature is limited spontaneous polymerization occurs within several days, resulting in a white solid that is insoluble in most organic solvents. The instability may be attributable to its acrylic ester structure, involved in the furanoid system. Nevertheless, other 3,4-unsaturated 3-deoxyfuranu-ronate conjugates obtained from divers mononucleotides did not prove to be unstable. 

Similar endocyclic, enolacetal-forming j8-elimination on a furanoid system (176) having nitrile or carbonamide activating groups has been reported to afford 177. For tiiese elimination experiments, 1,5-diazabi-cyclo [5.4.0] undec-5-ene (DBU) was used it is soluble in such aprotic solvents as ether and chloroform. 

In contrast to the stability of furanoid systems having an exocyclic, enolacetal double bond are the less stable (more reactive) furanoid compounds possessing an endocyclic enolacetal linkage. Todd and co-workers and Vizsolyi and Tener reported the instability of the 3,4-unsaturated 3-deoxypentofuranoid conjugates obtained by alkaline j3-elimination of phosphate from terminally oxidized, nucleotide model compounds such as 240. The unstable, endocyclic enolacetal conjugates (241) were transformed by a second elimination reaction into the more-stable furan derivatives (242). The extent to which the stability of the... 

J. Cleophax, S. D. Gero, and J. Hildesheim, Displacements on furanoid systems. Stepwise introductions of azide functions into methyl pentofuranosides, Chem. Commun. (1968) 94-95. 

The occurrence of highly functionalized furanoid systems either as a key entity or key substructure of more complex molecules in various biologically active natural products, such as the entire class of polyether antibiotics, prostaglandins, prostacyclins, and marine Laurencia metabolites, initiated new developments in their syntheses. 

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