Conformational Studies on the 1,2;5,6-Di-O-isopropylidene-D-hexoses

Abstract

Nuclear magnetic resonance studies on the 1,2;5,6-di-0-isopropylidene-D-hexofuranose sugars have provided information on the conformational preferences of the five-membered rings in these molecules. They appear to have strong conformational preferences rather than existing as freely pseudorotating systems. The furanose rings of the 3-deoxy-ribo and lyxo derivatives are found to preferentially exist in an envelope conformation in which C 4 is displaced from the plane of the ring. The arabino and xylo derivatives are found to be much less distorted, with preferred conformations approaching twist forms involving displacements of C-1 and -2. Substitution of various endo and exo groups at C-3 appears to have only minor influence on the parent furanose conformation.Les etudes r.m.n. sur les sucres de la serie des di-0-isopropylidine-1 ,2;5,6-D-hexofuranoses ont fourni des renseignements sur les conformations privilegites des cycles a cinq dans ces mol6cules. PlutBt que d'etre en pseudo-rotation libre, ces systemes apparaissent sous des conformations nettement prkfkrentielles. Les cycles furanoses des derives dtoxy-3 rib0 et Iyxo existent preferentiellement dans la conformation enveloppe dans laquelle le C 4 est au dehors du plan du cycle. Les derives arabino et xylo sont nettement moins tordus et adoptent la conformation privilkgik proche des formes "twist" impliquant les dkplacements des C-1 et -2. La substitution des divers groupes endo et exo sur le C-3 semble n'avoir qu'une influence mineure sur la conformation du furanose parent.

Sugar-Installed Polymer Micelles: Synthesis and Micellization of Poly(ethylene glycol)−Poly(d,l-lactide) Block Copolymers Having Sugar Groups at the PEG Chain End

“…All the peaks in the 1 H NMR spectra were assignable to protons in the assumed structure of the block copolymers. The assignment was performed by reference to the previous papers. − M n of the PLA segment was then calculated using the peak intensity ratio of methylene protons of PEG and the methine proton of PLA in the 1 H NMR spectra based on the M n of PEG determined by GPC.

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“…The assignment was performed by reference to the previous papers. [54][55][56][57][58] M n of the PLA segment was then calculated using the peak intensity ratio of methylene protons of PEG and the methine proton of PLA in the 1 H NMR spectra based on the M n of PEG determined by GPC.…”

Synthesis of Glucose Based Water Soluble Molecular Tweezers as Molecular Recognition Scaffolds

“…The NMR signal assignments were based on previous studies by Hall et al 31 (for 1 H NMR) and Vyas et al 32 (for 13 The spectra for 2a and 2b are different for the aromatic region. In the former the signal corresponding to these protons were assigned at δ 6.53-6.58 and 6.89-6.96 as double doublets, whereas the later gave the same signals at δ 6.57 and 6.94 as AB quartet.…”

Etude RMN 13C d'un Dérivé Uniformément Enrichi en 13C. Signe des Valeurs des Constantes de Couplage Observées

“…6 qui postulent l'existence de rotamixes dans lesquels l'oxygkne du cycle et l'oxygkne port6 par le C-5 sont gauches l'un par rapport B l'autre dans des dkrivks de la mCme skrie, il semble qu'une valeur de l'ordre de + 60" pour l'angle di&dre C-3-C-"-5-C-6 corresponde certainement B une conformation privilkgike mais non exclusive.…”