Configurational and Conformational Analysis of 5-deoxy-5-iodo-α,β-D-ribose with 3-Sphere Approach

Configurational and conformational analysis with 3-Sphere approach on selective iodination of α, β-methyl D-ribofuranose (2-α:2-β) with iodotriphenilphosphonium iodide complex [Ph₃P⁺I]I⁻ generated in situ, under RT, reflux, microwave and sonochemistry. Introduction of the unit and hypersphere trigonometric equations, under Hopf fibration and Lie algebra theories, on Lambert-Wu methods enable calculation of the dihedral angles from NMR data (¹³C chemical shift, vicinal coupling constant ³JHH[Hz]) and the ratio of anomers. The conformation/configuration at anomeric position is cis: trans with axial:axial 3-α:3-β (³JH1H2 3 or 4.5:0[Hz]) or equatorial:axial 3-α:3-β (³JH1H2 6 or 4.5:0[Hz]) as state based on dihedral angles θH1H2[deg], recorded carbon chemical shift δCn[deg] and VISION molecular models. The conformation of 3-β anomer is ³E, and in case of 3-α anomer ₃E on Altona’s map, the last having the succession of sign (+, -, -) with θH3H4α trans-ee, or alternatively ³₂T conformation having the succession of sign (-, +, -) with θH3H4α trans-aa. An equilibrium between ₃Eα and ³₂Tα was confirmed by ³JH1H2 of 4.5[Hz], i.e. negative θH1H2α with ³₂T and equatorial OCH₃, or positive θH1H2α with ₃E and axial OCH₃. The APT experiment (attached proton test) demonstrated the formation of tetrahydro 2H-pyran-2-ol as side product after selective iodination of methyl 5-deoxy-β-D-ribofuranoside 2-β.