Pseudorotation, furanose rings

Correlated variations of bond lengths in pseudorotating furanose rings have been estimated by a theoretical method, and the quantisation of hydrogen bond lengths in carbohydrate crystals has been investigated by use of a 1-dimensional anharmonic oscillator model. ... 

The furanose rings of the deoxyribose units of DNA are conformationally labile. All flexible forms of cyclopentane and related rings are of nearly constant strain and pseudorotations take place by a fast wave-like motion around the ring The flexibility of the furanose rings (M, Levitt, 1978) is presumably responsible for the partial unraveling of the DNA double helix in biological processes. 

Ab initio molecular orbital calculations (using the Gaussian 80 computer program) on the barrier to pseudorotation (for the furanose ring) of two model compounds, 2-deoxy-/ -D- /) cero-tetrofuranosylamine (781) and 2-deoxy-2-fluoro-)3-D-erythrofuranosylamine (782) were reported. Al-... 

The conformational dynamics of furanose rings may be described by the mechanisms of pseudorotation and inversion. The former mechanism describes a continuous pathway of interconversion between twenty idealized non-planar (envelope, twist) conformers (Figures 1 and 2) that does not involve the planar form (e.g., - E4 — ... 

Energy profiles in Figure 14 also reveal that planar furanose forms are often of lower energy than puckered conformers. For example, relative conformational energies determined for 7 with the 3-21G basis set indicate that the planar conformer is more stable than the Eq conformer in 8, the planar conformer is calculated to be more stable than. These observations suggest that the conformational dynamics of some furanose rings may not be completely described by pseudorotation in these cases,conformer interconversion may occur by both inversion and pseudorotational pathways, with the latter being the more preferred route. 

ROder O, LUdemann HD, von Goldammer E (1975) Determination of the activation energy for pseudorotation of the furanose ring in nucleosides by 13C nuclear-magnetic resonance relaxation. Eur J Biochem 53 517-524... 

A module for unsubstituted 2-deoxy-cryt/iro-jS-pentofuranose permits the calculation from the pseudorotation angle of all the /ch, 2./ci i, and 3/CH couplings around the furanose ring, except that, in some cases, the relative proportions of the two... 

Roder, 0., Ludemann, H. D., and Von Goldammer, E. (1975). Eur. J. Biochem. 53, 517. Determination of the Activation Energy for Pseudorotation of the Furanose Ring in Nucleosides by 13C Nuclear Magnetic Resonance Relaxation. 

The historic development of the understanding of carbohydrate stereochemistry has been briefly reviewed, and a lecture with four references on the energetics and geometry of furanoid tems has been published. Two complementary descriptions of the conformational behaviour of furanose rings have been presented (i) quantum-mechanical energy calculations and (ii) by a geometrical model of pseudorotation in five-membered rings. ... 

Furanose ring two preferred areas of pseudorotational space have been commonly observed those with 0 < P < 36 , where the Ci -endo is the main di lacement and 144 < P < 180 where C2 -endo is the main displacement. In 2 -deoxynucleosides, the C2 -endo conformation is much more likely to be observed than the C3 -endo conformation. The area around P 270 is much higher in energy than the others because in this conformation both bulky substituents, C5 and the base, are maximally axial and substituents on C2 and C3 are eclipsed. Transitions from the C2 -endo to the C3 -endo conformations are expected to happen over the P 90° conformation. 

Furanose flve-membered rings are never planar. They adopt a puckered form for which a family of pseudorotational conformers [541] are possible. The main conformations are the envelope and twist forms denoted by atom names, Le., C(2 ) and C(3 ), and descriptors endo and exo. They refer to the displacement of these atoms from the mean plane through the other atoms of the five-membered ring, with reference to the exocyclic C(4 )-C(5 ) bond (Fig. 17.4). 

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