Petrusová Mária, Vojtech Michal, Pribulová Bozena, Lattová Erika, Matulová Mária, Poláková Monika, BeMiller James N, Kren Vladimír, Petrus Ladislav
Institute of Chemistry, Slovak Academy of Sciences, SK-84538 Bratislava, Slovakia.
Carbohydr Res. 2006 Sep 4;341(12):2019-25. doi: 10.1016/j.carres.2006.04.050. Epub 2006 Jun 22.
Acid-catalysed methanolysis of 3,4,5,6-tetra-O-acetyl-1,2-dideoxy-l-arabino-hex-1-enitol proceeds via a cascade set of consecutive reactions resulting in its regiospecific conversion to a mixture of alpha- and beta-C-L-arabinofuranosylmethanal dimethyl acetals and a mixed internal methyl acetal. Structures of the final products of the overall process provide unique evidence that a kinetically controlled, five-membered-ring closure precedes a six-membered-ring closure in reversible systems capable of giving both five-membered and six-membered all-sp3-atom rings. Determination of the reaction intermediate enabled extension of the Nef reaction to C-glycosylnitromethanes. Protonated aci-nitro forms of C-glycosylnitromethanes that are resistant to the Nef reaction in aqueous acidic media undergo a modified Nef reaction in acidified methanol, and the corresponding C-glycosylmethanal dimethyl acetals with alpha-L-arabinopyranosyl, beta-D-glucopyranosyl, beta-D-galactopyranosyl, beta-D-mannopyranosyl and beta-L-rhamnopyranosyl configurations were obtained in moderate yields.
3,4,5,6-四-O-乙酰基-1,2-二脱氧-L-阿拉伯-己-1-烯醇的酸催化甲醇解通过一系列连续反应进行，其区域特异性转化为α-和β-C-L-阿拉伯呋喃糖基甲醛二甲基缩醛的混合物以及混合的内甲基缩醛。整个过程最终产物的结构提供了独特的证据，即在能够形成五元环和六元全sp3原子环的可逆体系中，动力学控制的五元环闭合先于六元环闭合。反应中间体的确定使得Nef反应能够扩展到C-糖基硝基甲烷。在水性酸性介质中对Nef反应具有抗性的C-糖基硝基甲烷的质子化酸硝基形式在酸化甲醇中发生改良的Nef反应，并以中等产率获得具有α-L-阿拉伯吡喃糖基、β-D-葡萄糖吡喃糖基、β-D-半乳糖吡喃糖基、β-D-甘露糖吡喃糖基和β-L-鼠李糖吡喃糖基构型的相应C-糖基甲醛二甲基缩醛。
