Konformacje pierścienia monosacharydowego

Conformational studies of the pyranose and furanose rings are important and have been carried out for years. Knowledge of the conformation of monosaccharide is essential for understanding its physical, chemical and biological properties. Additionally, conformation of the sugar ring plays a crucial role in the stereochemistry of the reaction in which it participates. This paper provides a basic knowledge concerning the conformational preferences of a monosaccharide ring. The pyranose ring conformations are defined with reference to a cyclohexane ring [1–3]. Factors influencing stability of the pyranose chair conformation are discussed: the 1,3-diaxial interactions [4–6] and anomeric effect [7–10]. It is shown how to estimate the relative stabilities of the two chair conformations on the basis of the Angyal destabilizing factors [11, 12]. It is also demonstrated how to use the NMR spectroscopy for conformational analysis [13–23]. Conformations of the unsaturated pyranose rings are defined and studied mainly on the glycals [24–29], the monosaccharides with a double bond between the C1 and C2 carbon atoms. Factors influencing stability of the unsaturated pyranose ring are disscused: the allylic effect [30] also named the vinylogous anomeric effect [31–34], and quasi 1,3-diaxial interactions [35, 36]. Finally, the furanose ring conformations and pseudorotational itinerary for a d-aldofuranose ring are presented [37]. Two parameters defining the furanose ring conformation are introduced: the amplitude of pseudorotation [38, 39], named also the maximum torsion angle [4] and pseudorotational phase angle [4]. The possible ways to study the conformation of the furanose ring are disscused [40–44].