Ribofuranose structures

Following a scheme similar to that described in Section 111,1, compounds having a complete D-ribofuranose structure and a ring-phosphorus atom were prepared.33,89... 

A solution of 5-0-(3-benzoylpropionyl)-3-deoxy-3-bromomethyl-l,2-di-O-acetyl-D-ribofuranose (2.35 g, 4.89 mmol) in triisopropyl phosphite (17 g, 81 mmol) was heated at 160 to 180°C with exclusion of moisture for 72 h. Volatile materials were removed under reduced pressure, and the residue was purified by chromatography on a silica gel column (48 x 2.7 cm) eluting with chloroform ethyl acetate (1 1). From the 150 to 500 ml eluent, there was isolated the pure 5-(3-benzoylpropionyl)-3-deoxy-3-diisopropoxyphosphinylmethyl-l,2-di-O-acetyl-D-ribofuranose (1.73 g, 68%) as an oil that exhibited IR and NMR spectra and analyses in accord with the proposed structure. 

The conformational properties of furanose rings have received considerable attention in recent years because of the impact these properties may have in mediating biological processes . Most notable in this respect are the p-D-ribofuranose 1 and 2-deoxy-p-D-erythro-pentose 2 (Scheme 1) components of ribo- (RNA) and deoxyribonucleic (DNA) acids. It is well known that the furanose ring adopts specific shapes depending on its local structural environment in a biopolymer. For example, in tRNA, the... 

Vitamin Bi2 is a D-ribofuranose derivative, and the structure of vitamin B12 5 -phosphate, a precursoi 11 of vitamin B12, has been determined. The a-D-glycosidic bond lies 16° (0.51 A) out of the plane of the 5,6-dimethylbenzimidazole ring, because of steric or nonbonded interactions. The D-ribofuranose moiety has that envelope conformation having C-2 exo (0.77 A exoplanar) C-3 and C-5 bear phosphate groups. 

Ribose Ribose is an aldopentose that is the structural sugar in RNA. Ribose cyclizes into a furanose (five-membered) ring system. The structures of D-ribose and (3-D-ribofuranose are given in Figure 12.66. 

No partly methylated ribose derivatives have been isolated from natural sources up to the present, for although such nucleic acids as yeast nucleic acid contain D-ribose phosphate residues, the methylation technique fails in structural studies in this group because of the hydrolytic action of alkaline reagents. Trimethyl-D-ribofuranose has, how-... 

Trimethyl-D-ribofuranose has been isolated by the hydrolysis of fully methylated adenosine46 and guanosine.47 The sugar has been synthesized by two routes. Firstly from 5-methyl-D-ribofuranose48 and secondly from methyl D-ribofuranosides50 (afi mixture), by methylation and hydrolysis. The proof of structure XLV follows from the fact... 

A 5-benzyl-D-ribose has been prepared by Kenner, Taylor and Todd,90 who etherified the methyl 2,3-isopropylidene-D-ribofuranoside (XXI) of Levene and Stiller91 with benzyl chloride to obtain methyl 2,3-iso-propylidene-5-benzyl-D-ribofuranoside (XXII), which was subsequently hydrolyzed to give amorphous 5-benzyl-D-ribose (XXIII). The structure of this ether was confirmed through acetylation to its triacetate (XXIV), hydrogenolysis to 1,2,3-triacetyl-D-ribofuranose (XXV) and further acetylation to the known, crystalline tetraacetyl-D-ribofuranose (XXVI). 

As confirmation of the structure of D-ribofuranose tetraacetate, may be mentioned its use in the synthesis of the naturally occurring D-ribo-furanoside xanthosine.100... 

Fig. 3-1. Structure of two nucleosides, 1, Uridine and 2, guanosine, which both contain /3-D-ribofuranose residue. The aglycon part is derived from a pyrimidine and purine base, respectively.

The crystal structures of the important ribofuranoses or 2-deoxy-ribofuranoses have not been determined, since these forms are in the minority with respect to the pyranoses in solution. There are numerous examples, however, in the crystal structures of the nucleosides and nucleotides. Those that contain the ribofuranose moieties quite commonly display vicinal 0(2 )H 0(3 ) or O(30H 0(2 ) intramolecular hydrogen bonding as the minor component of a three-center bond. This type of hydrogen bonding is described in Part IB, Chapter 9. 

One of the most fruitful developments in purine chemistry within the last two decades was the discovery that acyclic purine nucleoside derivatives are very potent inhibitors of the proliferation of certain viruses. " In acyclic purine nucleosides, the ribose moiety is replaced by an acyclic chain corresponding to the upper or lower part of the /I-D-ribofuranose ring. The most important acyclic purine nucleosides are shown by the structures of acyclovir (Zovirax, ACV, acyclo G, 1), DHPG (2), DHPA (3), and PMEA (4). 

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