Abstract
The unusual monosaccharaides such as Deoxy-hexose sugars, including
methyl-pentose and aldo-pentose are promising and important sugars in
life science, which have enormous chemotherapeutic and pharmaceutical
applications. However, little research on H-bond interactions in these
systems has been reported. The aldo-pentose has a proton instead of the
CH2OH group on C5; conversely, methyl-pentose has a CH3 group on C5. The
aim of the present study is to investigate the role and nature of
intramolecular H-bonds on acidity of CH3-pentose sugars (L-fucose and
L-rhamnose) and aldo-pentose sugars (D-xylose, L-lyxose, D-ribose and
L-arabinose) using B3LYP/6-311++G(d,p) level. The calculated acidity
values (∆Hacid) of these Dexoy-hexose were found to be from 343 to 369
kcal.mol-1, indicating they are stronger acid than ethanol and
2-propanol with the acidity values of 378.3 and 375.1 kcal.mol-1,
respectively. This is related to the stabilization of the conjugate
bases of these sugar through intramolecular H-bonds, which were analyzed
in this study using AIM and NBO methods.