Borbás Anikó, Szabó Zoltán B, Szilágyi László, Bényei Attila, Lipták András
Research Group for Carbohydrates of the Hungarian Academy of Sciences, Debrecen, PO Box 55, H-4010, Hungary.
Carbohydr Res. 2002 Nov 19;337(21-23):1941-51. doi: 10.1016/s0008-6215(02)00180-5.
The cis axial/equatorial OH groups of methyl alpha-L- and ethyl 1-thio-alpha-L-rhamnopyranoside, 1,6-anhydro-beta-D-mannopyranose, and 1,6-anhydro-beta-D-galactopyranose were reacted with 2-naphthaldehyde dimethyl acetal to diastereomeric dioxolane-type 2,3-O-(2-naphthyl)methylene or 3,4-O-(2-naphthyl)methylene acetals. The glycosides yielded the exo- and endo-isomers in nearly 1:1 ratio, 1,6-anhydro-beta-D-mannopyranose gave predominantly the endo-, and 1,6-anhydro-beta-D-galactopyranose exclusively endo-isomer. The acetals and some of their fully protected derivatives bearing benzyl or tert-butyldimethylsilyl groups were hydrogenolised with AlH(3) (3LiAlH(4)-AlCl(3)) or with Me(3)N.BH(3)-AlCl(3) reagents. The endo-isomers were cleaved by both reagents to give axial NAP ethers, the exo-isomers of pyranosides furnished equatorial NAP ethers. However, the exo-isomers of pyranoses gave irregular axial ethers with a > 30-fold enhancement of the reaction rates with respect to the endo-isomer.
α-L-甲基吡喃鼠李糖苷、1-硫代-α-L-乙基吡喃鼠李糖苷、1,6-脱水-β-D-甘露吡喃糖和1,6-脱水-β-D-半乳糖吡喃糖的顺式轴向/赤道羟基与2-萘甲醛二甲基缩醛反应，生成非对映体二氧戊环型2,3-O-(2-萘基)亚甲基或3,4-O-(2-萘基)亚甲基缩醛。糖苷以近1:1的比例生成外型和内型异构体，1,6-脱水-β-D-甘露吡喃糖主要生成内型异构体，而1,6-脱水-β-D-半乳糖吡喃糖只生成内型异构体。带有苄基或叔丁基二甲基硅烷基的缩醛及其一些完全保护的衍生物用AlH(3)（3LiAlH(4)-AlCl(3)）或Me(3)N.BH(3)-AlCl(3)试剂进行氢化反应。两种试剂都能裂解内型异构体生成轴向萘基醚，吡喃糖苷的外型异构体生成赤道萘基醚。然而，吡喃糖的外型异构体生成不规则的轴向醚，其反应速率相对于内型异构体提高了30倍以上。
