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

Abstract

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 ³<I>J</I><SUB>HH</SUB>[Hz]) and the ratio of anomers. The conformation/configuration at anomeric position is <i>cis</i>: <i>trans</i> with <i>axial</i>:<i>axial</i> 3-α:3-β<i> </i>(³<I>J</I><SUB>H1H2</SUB> 3 or 4.5:0[Hz])<i> </i>or <i>equatorial</i>:<i>axial</i> 3-α:3-β (³<I>J</I><SUB>H1H2</SUB> 6 or 4.5:0[Hz]) as state based on dihedral angles θ<SUB>H1H2</SUB>[deg], recorded carbon chemical shift δ_Cn[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 θ<SUB>H3H4</SUB>^α <i>trans-ee</i>, or alternatively ³₂T conformation having the succession of sign (-, +, -) with θ<SUB>H3H4</SUB>^α <i>trans-aa</i>. An equilibrium between ₃E^α and ³₂T^α was confirmed by ³<I>J</I><SUB>H1H2</SUB> of 4.5[Hz], <i>i.e.</i> negative θ<SUB>H1H2</SUB>^α with ³₂T and <i>equatorial</i> OCH₃, or positive θ<SUB>H1H2</SUB>^α 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-<i>β</i>-D-ribofuranoside 2-β.