The inframolecular protonation process of myo-inositol 1,4,5-tris(phosphate) (1, Ins(1,4,5)P3) and
the closely related analogues myo-inositol 1,4,6-tris(phosphate) (2, Ins(1,4,6)P3), and 3-deoxy-myo-inositol
1,4,5-tris(phosphate) (3) and the latter's epimer, 3-deoxy-muco-inositol 1,4,5-tris(phosphate) (4), were explored
by performing 31P and 1H NMR titration experiments. The microprotonation scheme for compounds 1, 2, and
4 were quantitatively derived. The influence of the configuration of the functional groups and of the presence
of the hydroxyls on the 31P and 1H chemical shifts and phosphate basicity was discussed. Thus, the basicity
increase of the phosphates and the shielding of the related phosphorus nuclei observed upon deletion of a
vicinal hydroxyl is mainly attributed to solvation changes around the phosphate groups. A concerted wrongway
shift of some protons and phosphorus nuclei provides information on the conformational dynamics of the
phosphates upon protonation. These wrongway shifts may be the result of electrostatic interactions between a
ring proton and a doubly negatively charged phosphate group in a trans diequatorial configuration. According
to G. R. Desiraju, such an interaction may be considered as a C−H···O hydrogen bond. The necessary condition
to observe this bond is a constraint of the phosphate group such that it closely approaches the ring proton.
This may occur as shown by molecular modeling studies when two phosphates strongly repel each other
either directly or via the relaying effect of an intervening equatorial hydroxyl.
published as an Advance Article on the web 13th November 2001 b-(3,4-Dimethoxyphenyl)serine methyl ester was obtained in high diastereomeric and enantiomeric excesses under transfer hydrogenation using chiral Ru(h 6 -arene)-N-perfluorosulfonyl-1,2-diamine catalysts.
1H NMR hydroxy proton titration experiments for myo-inositol 2-phosphate and myo-inositol 1,2,6-tris(phosphates) in aqueous solution are presented to demonstrate that by following OH signals versus pH, evidence can be brought for HB interaction between the hydroxyl and phosphate groups. The chemical shifts of the OH protons vicinal to phosphate groups appear deshielded by ca. 2.5 ppm with regard to those two centers removed from the phosphates. Remarkably, the deshielded protons are only present when their neighboring phosphate groups are fully deprotonated but persist until high pHs. From these results, C-OH...2-O3P-O type I, C-HO...-HO3P-O type II and C-OH...-HO3P-O type III hydrogen bonds are evidenced and discussed.
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