Crystal and molecular structure of .beta.-maltose octaacetate. A model in retrospect for amylose triacetate?

Intramolecular 1,8-Hydrogen Abstraction Between Glucopyranose Units in a Disaccharide Model Promoted by Alkoxy Radicals

“…Two other conditions should be fulfilled: a low-energy transition state and a distance of around 3 ä between the O radical and the hydrogen atom to be abstracted. [8] It soon became evident that the Glc-a1 34-Glc unit in compound 1 (see Scheme 1) [9,10] has a preferred syn conformation of the glycosidic bond (F À 34.28, Y À 28.38) and a C 6 O ¥¥¥ HC 5' distance of 2.5 ä in accord with previously reported X-ray crystallographic [11] and molecular mechanics [12] analyses of b-d-maltose octaacetate and methyl b-d-maltoside, respectively. A study of the transition state of the C 6 -O ¥¥¥ H-C 5' IHA reaction gave a similar situation for the glycosidic torsion angles (F À 32.78, Y À 37.38) and a distance of 3.14 ä between the O radical and H-C 5' .…”

Intramolecular 1,8-Hydrogen Abstraction Between Glucopyranose Units in a Disaccharide Model Promoted by Alkoxy Radicals

“…[6] IHA reactions through eight-or higher membered transition states are practically unknown; entropic effects are probably responsible for the failure of these processes. [8] It soon became evident that the Glc-a1 34-Glc unit in compound 1 (see Scheme 1) [9,10] has a preferred syn conformation of the glycosidic bond (F À 34.28, Y À 28.38) and a C 6 O ¥¥¥ HC 5' distance of 2.5 ä in accord with previously reported X-ray crystallographic [11] and molecular mechanics [12] analyses of b-d-maltose octaacetate and methyl b-d-maltoside, respectively. Two other conditions should be fulfilled: a low-energy transition state and a distance of around 3 ä between the O radical and the hydrogen atom to be abstracted.…”

“…Two other conditions should be fulfilled: a low-energy transition state and a distance of around 3 ä between the O radical and the hydrogen atom to be abstracted. [8] It soon became evident that the Glc-a1 34-Glc unit in compound 1 (see Scheme 1) [9,10] has a preferred syn conformation of the glycosidic bond (F À 34.28, Y À 28.38) and a C 6 O ¥¥¥ HC 5' distance of 2.5 ä in accord with previously reported X-ray crystallographic [11] and molecular mechanics [12] analyses of b-d-maltose octaacetate and methyl b-d-maltoside, respectively. A study of the transition state of the C 6 -O ¥¥¥ H-C 5' IHA reaction gave a similar situation for the glycosidic torsion angles (F À 32.78, Y À 37.38) and a distance of 3.14 ä between the O radical and H-C 5' .…”

Peracetylated α-D-glucopyranosyl fluoride and peracetylated α-maltosyl fluoride

“…It is interesting to observe in (II) the orientation of the contiguous pyranose rings, which is described by the torsion angles around the glycosidic bonds, C4-O4 and O4-C41, denoted as conformational angles É and È [in (II), É = H4-C4-O4-C41 = À29 and È = C4-O4-C41-H41 = À32 ], and by the valence angle = C4-O4-C41, which is 116.66 (14) in (II). All these values are in good agreement with those in -maltoseoctaacetate (Brisse et al, 1982) and -octapropanoate (Johnson et al, 2007) and conform closely with those in other maltose derivatives discussed by Johnson et al (2007) in respect of having short chains containing an -(1!4) intersugar glycosidic linkage, and are therefore useful as models to study starch structure. The twist of the nonreducing sugar ring is defined by the virtual torsion angle O44-C44Á Á ÁC41-O4; this has a value of À4.8 (3) in compound (II), which, if inserted in an amylose chain of starch (see, for example, Takahashi & Nishikawa, 2003), would add to the bias of successive residues, forming a left-handed helix (French & Johnson, 2007).…”