摘要:
The reaction of 2,2'- (10), 3,2'- (11), and 3,3'-di-O-benzyl-4,6:4',6'-di-O-benzylidene-alpha,alpha-trehalose (12) with tetraethylene glycol ditosylate gave the corresponding chiral crowns mono-trehalo-3,3'- (1), bis-trehalo-3,3'- (3), mono-trehalo-2,3'- (5) and mono-trehalo-2,2'-tetraethylene glycol (7). The crystal structure of 1 was determined by X-ray analysis and the solution conformation of 1, 3, 5, and 7 by NMR spectroscopy and, in the case of 1, 3, and 7, molecular mechanics calculations. The geometry of the disaccharide moiety of 1,3, and 5 was as expected according to the exo anomeric effect. However, an unexpected conformation around the glycosidic linkage was found for the 18-crown-6 mono-trehalo-2,2'-tetraethylene glycol (7). This conformation can be accounted for by semiempirical calculations of possible intermediate dianionic structures.