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Crystal and molecular structures of substituted α-d-glucopyranosides

✍ Scribed by Živa Ružić-Toroš; Biserka Kojić-Prodić; Ljubo Golič; Srðanka Tomić

Publisher
Elsevier Science
Year
1987
Tongue
English
Weight
486 KB
Volume
162
Category
Article
ISSN
0008-6215

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✦ Synopsis

The crystal and molecular structures of methyl 2,4,6-tri-O-pivaloyl-o-Dglucopyranoside (l), methyl 4,6-0-(R)-benzylidene-2-O-pivaloyl-a-D-glucopyranoside (2), and methyl 4,6-O-(R)-benzylidene-2,3-di-O-pivaloyl-a-D-glucopyranoside (3) were determined by X-ray analysis. Crystals of 1 are orthorhombic, space group P2,2,2r with the unit cell a = 13.026(2), b = 16.832, c = 11.929(2) A, 2 = 4. Crystals of 2 are monoclinic, space group P2,. The unit-cell parameters are a = 6.519(l), b = 14.664(4), c = 10.635(4) A, p = 93.18(l)", Z = 2. Crystals of 3 are orthorhombic, space group P2,2r2, with a = 10.006(3), b = 13.874(3), c = l&527(5) A, Z = 4. The structures were solved by MULTAN and refined by a full-matrix procedure to final values of R = 0.084 (l), 0.048 (2), and 0.069 (3). The pyranose ring in each compound adopts the 4C, conformation. The 1,fdioxane rings in 2 and 3 show a chair conformation. The molecular packing in 1 is through the hydrogen bonds involving HO-3 and the 6-0-pivaloyl carbonyl group [HO-3 . --O-9, 2.855(8) A], which connect the molecules into a chain along b. The endocyclic oxygen atom is involved in an intermolecular hydrogen-bond with HO-3 [2.848( 4) A], joining molecules of 2 into the chains along 2. There are no free hydroxyl groups in 3 and molecular packing reflects van der Waals interactions only. lNTRODUCTION Protection of carbohydrates has been often achieved by esterification; the pivaloyl group is an excellent ester protecting group, and pivaloylation may be used for the partial or total protection of sugar@. The high selectivity of the esterification process, ease in identification of products, and the stability of the derivatives in solution make pivaloyl the group of choice in solving various problems in preparative carbohydrate chemistry.

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