Synthesis of 2,3:4,6-di-O-isopropylidene derivatives of alkyl α- and β-d-galactopyranosides, and elucidation of structure by n.m.r. and x-ray analysis

✍ Scribed by Pier Luigi Barili; Giorgio Catelani; Fabrizia Colonna; Alberto Marra; Silvio Cerrini; Doriano Lamba

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 821 KB
• Volume: 177
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(88)85039-0

✦ Synopsis

Kinetically controlled reaction of 4.5 equiv. of 2-methoxypropene with some alkyl (Y-and /3-o-galactopyranosides gave the 2,3:4,6-di-O-isopropylidene derivatives in high yields @O--85%). With 2 equiv. of 2-methoxypropene, benzyl P-Dgalactopyranoside gave the 4,6-and the 3,4-monoacetals in the ratio 30: 1 together with -20% of the 2,3:4,6-diacetal. The structures of methyl 2,3:4,6-di-O-isopropylidene-cu-and -/?-D-galactopyranosides were determined by X-ray analysis. The former crystallised in the orthorhombic system, p2,2,2,, with a = 5.503, b = 16.105, c = 16.822 A, and 2 = 4, the latter in the monoclinic system, P2,, with a = 10.400, b = 13.344, c = 11.647 A, /3 = 111.50, and 2 = 4. The (Y anomer and the two molecules of the /3 anomer had the D-galactopyranoside and the 1,3dioxane rings in twist-chair conformations and the dioxolane ring in a half-chair conformation. N.m.r. spectroscopy suggested the occurrence of similar conformations in solution.