Easy Synthesis and Different Conformational Behavior of Purine and Pyrimidine .beta.-D-glycero-Pent-2'-enopyranosyl Nucleosides

Synthesis and Pairing Properties of Oligonucleotides Containing 3-Hydroxy-4-hydroxymethyl-1-cyclohexanyl Nucleosides

“…For both series nucleosides with both a thymine base moiety and an adenine base moiety were analyzed, because we had previously observed that purine and pyrimidine bases had different effects on nucleoside conformation. [20,21] The lowest energy conformations of hT, hA, cT and cA with the base moieties situated both equatorially and axially were calculated together with the energy differences between each pair of conformers with a simple dielectric appropriate for water solvation (Table 5). The calculations showed that hA prefers an axial base moiety and that hT prefers an equatorial base moiety, but that the energy differences between the conformers are small (1.7 and 5.9 kJ mol À1 , respectively).…”

Trifluoromethylated Thiopyranoid Glycals: Synthesis and Ferrier (I) Type Reactions

“…As a rule, glycals bearing carboxylate as leaving group [ Figure 1, LG = RC(O)O] are not very reactive glycosylating agents and their reactions with nucleophiles require catalysts (Lewis or Brønsted acids, palladium complexes) [4] or drastic conditions. [30,31] The "simplest" Ferrier (I) reaction consists in the thermal rearrangement of acylated glycals to unsaturated glycosyl carboxylates, [32] whereby the incoming group and leaving one are the same (see Figure 1, Nu = LG). But, we have found that diacetate 7 does not rearrange upon heating in acetic acid.…”

Nucleic Acids with a Six‐Membered ‘Carbohydrate’ Mimic in the Backbone

“…30; 28 and 29). The a-and b-d-glycero-pent-2-enopyranosyl nucleosides were obtained by condensation of 3,4-bis-O-(4-nitrobenzoyl)-d-xylal with the trimethylsilyl derivative (or sodium salt) of the protected bases, followed by deprotection in basic circumstances [87]. Initial structural analysis by NMR shows that the purine bases are preferentially oriented pseudoaxially (b-nucleosides), and that pyrimidine b-nucleosides shows an equilibrium with preference for pseudoaxially oriented aglycons.…”

“…Initial structural analysis by NMR shows that the purine bases are preferentially oriented pseudoaxially (b-nucleosides), and that pyrimidine b-nucleosides shows an equilibrium with preference for pseudoaxially oriented aglycons. This was attributed to an interplay between anomeric effect, allylic effect, gauche-effect, and steric repulsion (which is higher for pyrimidine bases than for purine bases) [87] (Fig. 31).…”

“…In cyclohexane nucleosides, the anomeric effect does not play a role, but introduction of unsaturation induces similar flexibility in the system. Cyclohexenyl nucleosides, in addition to being somewhat flexible (and more flattened at one side of the ring), possess the properties of carbocyclic nucleosides, [87] which, due to the absence of an anomeric center, are stable against chemical and enzymatic degradation. The cyclohexenyl nucleoside 31 with an adenine base was synthesized first using an enantioselective approach starting from (R)-carvone [90] (Scheme 12).…”