Tatsuta K, Fujimoto K, Kinoshita M
Carbohydr Res. 1977 Mar;54(1):85-104. doi: 10.1016/s0008-6215(00)80558-3.
The key step of the synthesis involves the reaction of glycals [3,4,6-tri-O-acetyl-D-glucal (1), the new glycal derivative 4-O-acetyl-1,5-anhydro-2,6-dideoxy-3-C-methyl-3-O-methyl-L-ribo-hex-1-enitol (2), and 3-acetamido-4,6-di-O-acetyl-1,5-anhydro-2,3-dideoxy-D-arabino-hex-1-enitol (3)] with 1.5 molar equivalents of several alcohols in the presence of N-bromosuccinimide in acetonitrile to give mainly the corresponding 2-bromo-2-deoxy-alpha-glycopyranosides (4--21). The glycopyranosides (4-8 and 16-21) from 1 and 3 have the alpha-D-manno configuration and those (10--15) from 2 have the alpha-L-altro configuration. The yields are high from 1, virtually quantitative from 2, and moderate from 3. Debromination of the 2-bromo-2-deoxy compounds with tributylstannane and a radical initiator gives the corresponding 2-deoxy-alpha-glycopyranosides (22-38) in quantitative yields. In particular, the branched-chain glycal 2 reacts with alcohols to give exclusively the corresponding alpha-glycopyranosides (27--32) of cladinose in strikingly high overall yields. The stereoselectivity and regiospecificity of the bromination reaction are described. 1,3-Dibromo-5,5-dimethylhydantoin and N-bromoacetamide are also found to be useful for the reaction.
合成的关键步骤包括在乙腈中，在N-溴代琥珀酰亚胺存在下，使糖烯[3,4,6-三-O-乙酰基-D-葡萄糖烯（1）、新的糖烯衍生物4-O-乙酰基-1,5-脱水-2,6-二脱氧-3-C-甲基-3-O-甲基-L-核糖己-1-烯醇（2）和3-乙酰氨基-4,6-二-O-乙酰基-1,5-脱水-2,3-二脱氧-D-阿拉伯己-1-烯醇（3）]与1.5摩尔当量的几种醇反应，主要生成相应的2-溴-2-脱氧-α-吡喃糖苷（4 - 21）。来自1和3的吡喃糖苷（4 - 8和16 - 21）具有α-D-甘露糖构型，来自2的那些（10 - 15）具有α-L-阿卓构型。1的产率很高，2的产率几乎是定量的，3的产率适中。用三丁基锡烷和自由基引发剂对2-溴-2-脱氧化合物进行脱溴反应，以定量产率得到相应的2-脱氧-α-吡喃糖苷（22 - 38）。特别地，支链糖烯2与醇反应，以极高的总产率仅生成相应的克拉定糖α-吡喃糖苷（27 - 32）。描述了溴化反应的立体选择性和区域特异性。还发现1,3-二溴-5,5-二甲基乙内酰脲和N-溴代乙酰胺对该反应有用。
