Octa- O-propanoyl-β-maltose: crystal structure, acyl stacking, related structures, and conformational analysis

• Published in: Carbohydrate research 2007-07, Vol.342 (9), p.1210-1222
• Main Authors: Johnson, Glenn P., Stevens, Edwin D., French, Alfred D.
• Format: Article
• Language: English
• Subjects: Carbohydrate; Carbohydrate Conformation; Conformation; Crystallization; Crystallography, X-Ray - methods; Hybrid; Hydrogen Bonding; Maltose - analogs & derivatives; Maltose - chemistry; Models, Molecular; Molecular; Molecular Structure; Propionate; Quantum mechanics; Starch
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/j.carres.2007.02.029

The crystal structure of β-maltose octapropanoate ( 1) was solved to improve understanding of di-, oligo-, and polysaccharide conformations. The O6 and O6′ atoms are in gg and gt orientations, respectively. Extrapolation of the coordinates of the non-reducing residue and observed linkage bond and torsion angles of 1 ( τ C1 ′ – O4 – C4 = 116.0 ° , ϕ O5 ′ – C1 ′ – O4 – C4 = 77.1 ° , ψ C5 – C4 – O4 – C1 ′ = - 157.5 ° ) yields a left-handed helix similar to amylose triacetate I. The ϕ and ψ values of 1 are also similar to those of other crystalline, acylated maltose compounds as well as some hydroxyl-bearing molecules. Acylated maltose moieties are often stabilized by stacking of the carbonyl groups and α-carbons on O3 and O2′ as well as by the exo-anomeric effect. The conformation of 1 is within the 1-kcal/mol contour on a hybrid energy map built with a dielectric constant of 7.5, but corresponds to higher energies on maps made with lower dielectric constants. In one region of ϕ, ψ space, both hydroxyl-bearing and derivatized maltose moieties are found but no inter-residue, intramolecular hydrogen-bonding occurs. In another region, only hydroxyl-bearing molecules crystallize and O2′⋯O3 hydrogen bonds are always found. In agreement with the energy surfaces, amylose helices extrapolated from available linkage geometries were almost all left-handed.