Structural determination of the isomeric L-arabinosylureas (1a, 2a, and 3a) and their facile isomerization into the thermodynamically stable isomer (3a) by acid are described. The reaction of L-arabinose with 3-methoxy-n-propylamine followed by treatment with 2-chloroethyl isocyanate gave a mixture of the ureas (1a, 2a, and 3a) in a ratio of 3 : 2 : 1. They were determined to be the β anomer (1a) and the α anomer (3a) of 3-(L-arabinopyranosyl)-1-(2-chloroethyl)-3-(3-methoxy-n-propyl) urea and the β anomer (2a) of the corresponding L-arabinofuranosyl derivative, respectively. Isomerization of these ureas was examined in formic acid solution by monitoring their thin layer chromatography. Complete isomerization of both 1a and 2a into 3a was observed, while 1a isomerized into 3a via 2a. Consequently, the selective isomerization of a mixture of these ureas into 3a could readily be effected by formic acid treatment. The nitrosation of these ureas by the use of dinitrogen tetroxide gave the corresponding nitrosoureas (4a, 5a, and 6a), and their structures are discussed.
                                    本文介绍了 L-阿拉伯
呋喃糖异构体(1a、2a 和 3a)的结构测定,以及它们在酸的作用下容易异构成热力学稳定的异构体(3a)。L-arabinose 与 3-甲氧基-
正丙胺反应,然后用 2-
氯乙基异氰酸酯处理,可得到比例为 3 : 2 : 1 的
脲类化合物混合物(1a、2a 和 3a)。经测定,它们分别是 3-(L-阿拉伯
吡喃糖基)-1-(2-
氯乙基)-3-(3-甲氧基-正丙基)
脲的β异构体(1a)和α异构体(3a),以及相应的 L-阿拉伯
呋喃糖基衍
生物的β异构体(2a)。在
甲酸溶液中,通过薄层色谱监测这些
脲的异构化情况。观察到 1a 和 2a 完全异构化为 3a,而 1a 则通过 2a 异构化为 3a。因此,通
过甲酸处理,可以很容易地将这些
脲的混合物选择性异构化成 3a。使用
四氧化二氮对这些
脲进行亚硝基化反应,得到了相应的亚硝基
脲(4a、5a 和 6a),并讨论了它们的结构。