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1.  The dependence of pyranose ring puckering on anomeric configuration: methyl idopyranosides 
The Journal of Physical Chemistry. B  2012;116(22):6380-6386.
In the aldohexopyranose idose, the unique presence of three axial ring hydroxyl groups causes considerable conformational flexibility, rendering it challenging to study experimentally and an excellent model for rationalising the relationship between puckering and anomeric configuration. Puckering in methyl α- and β-l-idopyranosides was predicted from kinetically rigorous 10 μs simulations using GLYCAM11 and three explicit water models (TIP3P, TIP4P and TIP4P-EW). In each case, computed pyranose ring three-bond (vicinal) 1H-1H spin-couplings (3JH,H) trended with NMR measurements. These values, calculated puckering exchange rates and free energies were independent of the water model. The α- and β-anomers were 1C4 chairs for 85% and >99% of their respective trajectories and underwent 1C4→4C1 exchange at rates of 20 μs-1 and 1 μs-1. Computed α-anomer 1C4↔4C1 puckering rates depended on the exocyclic C6 substituent, comparing hydroxymethyl with carboxyl from previous work. The slower kinetics and restricted pseudorotational profile of the β-anomer were caused by water occupying a cavity bounded by the anomeric 1-O-methyl and the C6 hydroxymethyl groups. This finding rationalises the different methyl α- and β-l-idopyranoside 3JH,H values. Identifying a relationship between idopyranose anomeric configuration, μs-puckering and water structure facilitates engineering of biologically and commercially important derivatives and underpins deciphering presently elusive structure-function relationships in the glycome.
doi:10.1021/jp303183y
PMCID: PMC3377936  PMID: 22577942
anomer; microsecond simulation; idopyranosides; pucker; water structure
2.  Co-crystals of 3-de­oxy-3-fluoro-α-d-glucopyran­ose and 3-de­oxy-3-fluoro-β-d-glucopyran­ose 
3-De­oxy-3-fluoro-d-glucopyran­ose crystallizes from acetone to give a unit cell containing two crystallographically independent mol­ecules. One of these mol­ecules (at site A) is structurally homogeneous and corresponds to 3-de­oxy-3-fluoro-β-d-glucopyran­ose, C6H11FO5, (I). The second mol­ecule (at site B) is structurally heterogeneous and corresponds to a mixture of (I) and 3-de­oxy-3-fluoro-α-d-glucopyran­ose, (II); treatment of the diffraction data using partial-occupancy oxygen at the anomeric center gave a high-quality packing model with an occupancy ratio of 0.84:0.16 for (II):(I) at site B. The mixture of α- and β-anomers at site B appears to be accommodated in the lattice because hydrogen-bonding partners are present to hydrogen bond to the anomeric OH group in either an axial or equatorial orientation. Cremer–Pople analysis of (I) and (II) shows the pyranosyl ring of (II) to be slightly more distorted than that of (I) [θ(I) = 3.85 (15)° and θ(II) = 6.35 (16)°], but the general direction of distortion is similar in both structures [ϕ(I) = 67 (2)° (B C1,C4) and ϕ(II) = 26.0 (15)° (C3 TB C1); B = boat conformation and TB = twist-boat conformation]. The exocyclic hy­droxy­methyl (–CH2OH) conformation is gg (gauche–gauche) (H5 anti to O6) in both (I) and (II). Structural comparisons of (I) and (II) to related unsubstituted, de­oxy and fluorine-substituted monosaccharides show that the gluco ring can assume a wide range of distorted chair structures in the crystalline state depending on ring substitution patterns.
doi:10.1107/S0108270110040096
PMCID: PMC3089378  PMID: 21051824
3.  4-De­oxy-4-fluoro-β-d-gluco­pyranose 
4-De­oxy-4-fluoro-β-d-glucopyran­ose, C6H11FO5, (I), crystallizes from water at room temperature in a slightly distorted 4 C 1 chair con­formation. The observed chair distortion differs from that observed in β-d-glucopyran­ose [Kouwijzer, van Eijck, Kooijman & Kroon (1995 ▶). Acta Cryst. B51, 209–220], (II), with the former skewed toward a B C3,O5 (boat) conformer and the latter toward an O5 TB C2 (twist–boat) conformer, based on Cremer–Pople analysis. The exocyclic hy­droxy­methyl group conformations in (I) and (II) are similar; in both cases, the O—C—C—O torsion angle is ∼−60° (gg con­former). Inter­molecular hydrogen bonding in the crystal structures of (I) and (II) is conserved in that identical patterns of donors and acceptors are observed for the exocyclic substituents and the ring O atom of each monosaccharide. Inspection of the crystal packing structures of (I) and (II) reveals an essentially identical packing configuration.
doi:10.1107/S0108270110034001
PMCID: PMC3089016  PMID: 20921614

Results 1-3 (3)