Structures of Side Products from Helferich Reaction Synthesis of 3α,12β,25-Trihydroxy-20S,24R-Epoxydammarane Glucosides
作者:L. N. Atopkina、V. A. Denisenko
DOI:10.1007/s10600-014-0824-0
日期:2014.1
Glycosylation of 3α-acetoxy-12β,25-dihydroxy-20S,24R-epoxydammarane (2) by 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosylbromide (5) in the presence of Hg(CN)2 in nitromethane at 22°C produced the acetylated 12,25-di-O-β-D-glucopyranoside of 3α,12β,25-trihydroxy-20S,24R-epoxydammarane (6) and also formed the side product 3α-acetoxy-12β-(2′,3′,4′,6′-tetra-O-acetyl-β-D-glucopyranosyloxy)-24-cyano-20S,24S-epoxydammarane (8). Condensation of 3α,12β-diacetoxy-25-hydroxy-20S,24R-epoxydammarane (3) with glycosyl donor (5) under the same conditions gave the hexaacetate of the 25-O-β-D-glucopyranoside of 3α,12β,25-trihydroxy-20S,24R-epoxydammarane and also formed a mixture of C-24-epimers (1:1) of 3α,12β-diacetoxy-24-cyano-20S,24ξ-epoxydammarane (10a,b).
2,3,4,6-etra-O-acetyl-α-D-glucopyranosylbromide (5) 在 Hg(CN)2 的存在下,于 22°C 在硝基甲烷中对 3α-乙酰氧基-12β,25-二羟基-20S,24R-环氧达玛烷 (2) 进行糖基化,生成乙酰化的 12、25-二-O-β-D-吡喃葡萄糖苷的 3α,12β,25-三羟基-20S,24R-环氧达玛烷 (6),并生成副产物 3α-乙酰氧基-12β-(2′,3′,4′,6′-四-O-乙酰基-β-D-吡喃葡萄糖氧基)-24-氰基-20S,24S-环氧达玛烷 (8)。在相同条件下,3α,12β-二乙酰氧基-25-羟基-20S,24R-环氧达玛烷(3)与糖基供体(5)缩合,得到了 3α,12β,25-三羟基-20S,24R-环氧达玛烷的 25-O-β-D-吡喃葡萄糖苷的六乙酸酯,还形成了 C-24 表聚物的混合物(1:1)的 3α,12β-二乙酰氧基-24-氰基-20S,24ξ-环氧达玛烷(10a,b)的混合物。