Structures of furanosides: geometrical analysis of low-temperature X-ray and neutron crystal structures of five crystalline methyl pentofuranosides

Abstract

Crystal structures of all ®ve crystalline methyl d-pentofuranosides, methyl -d-arabinofuranoside (1), methyl -d-arabinofuranoside (2), methyl -d-lyxofuranoside (3), methyl -dribofuranoside (4) and methyl -d-xylofuranoside (5) have been determined by means of cryogenic X-ray and neutron crystallography. The neutron diffraction experiments provide accurate, unbiased H-atom positions which are especially important because of the critical role of hydrogen bonding in these systems. This paper summarizes the geometrical and conformational parameters of the structures of all ®ve crystalline methyl pentofuranosides, several of them reported here for the ®rst time. The methyl pentofuranoside structures are compared with the structures of the ®ve crystalline methyl hexopyranosides for which accurate X-ray and neutron structures have been determined. Unlike the methyl hexopyranosides, which crystallize exclusively in the C 1 chair conformation, the ®ve crystalline methyl pentofuranosides represent a very wide range of ring conformations.

The Structure of N‐(1‐Deoxy‐β‐D‐fructopyranos‐1‐yl)‐L‐proline Monohydrate (“D‐Fructose‐L‐proline”) and N‐(1,6‐Dideoxy‐α‐L‐fructofuranos‐1‐yl)‐L‐proline (“L‐Rhamnulose‐L‐proline”)

“…The 1,6-dideoxy-a-L-fructofuranose in 2 also has no significant deviations in the mean bond distances (1.523 Å and 1.421 Å correspondingly) from those determined for the b-fructopyranose in 1, the b-fructofuranose in L-rhamnulose-dibenzylamine, [35] and the averaged values for furanose structures. [40,47] In the proline part of both 1 and 2, the N1-C7 bond (Table 3) is about 0.04 Å longer than respective bonds in a number of known proline structures, [41,43,45,48] while the rest of the bond lengths compare well. Differences were observed with respect to the carboxyl-oxygen bond lengths for 1 and 2.…”

“…However, the angle values for 2 compare well, with the exception of the C2-C3-O3 angle, within 38, with respective values in L-rhamnulose-dibenzylamine [35] and the averaged values for furanosides. [40,47] There is also a great deal of similarity in the valence angles for reported proline structures and the amino acid portion of the Amadori compounds 1 and 2 ( Table 3). The carboxyl group in 1 shows a small dissymmetry due to unequal participation of the oxygens in hydrogen bonding (see below).…”

“…[28] In a crystal of 1-cyclohexylamino-1,6-dideoxy-a-D-tagatofuranose-6-C-sulfonic acid, [39] the sugar ring of this Amadori compound assumes a conformation intermediate between E 5 and 4 T 5 ; it is also in the same energy minimum as the conformation of 2. In crystalline methyl a-D-arabinofuranoside, [40] which is a configurational equivalent to the carbohydrate ring in 2, the ring conformation is E 4 and thus is a mirror image of the ring form 5 E in 2.…”

Structural Insights into Antibody Recognition of Mycobacterial Polysaccharides

“…Additional rounds of refinement and model building were performed using stereochemical restraints for the carbohydrate derived from previous crystallographic studies. 49,50 Only bond-length and bond-angle parameters, as well as the chirality of carbon atoms, were included as conformational restraints during refinement. Torsion angles and ring puckering parameters were not explicitly restrained at any point of the refinement.…”

Conformational Analysis of Furanoside-Containing Mono- and Oligosaccharides

“…Monomeric furanosyl units occurring in rhamnogalacturonan II oligosaccharides, apiose(27) and aceric acid(28).…”