Base- and Radical-Mediated Regio- and Stereoselective Additions of Thiols, Thio-Sugars, and Thiol-Containing Peptides to Trisubstituted Activated<i>exo</i>-Glycals
for the base-mediated coupling with aromatic and primary thiols, which included 6-thio-sugars, cysteinederivatives, and glutathione. The success of the radical-mediated method depended on the thiol partners as well as the nature of the sugar olefins. Neither of the conditions required the protection of the sugar or the cysteinederivatives.
Toward Bis<i>C</i>,<i>C</i>-Glycosyl Compounds and Anomeric γ-Glycoamino Acids through Michael Addition Reaction of Nitromethane on<i>Z</i>/<i>E</i>Push-Pull Sugar Olefins
of the nitro function of these bis C,C-glycosyl compounds led to a series of new γ-glycoamino acids, which are chiral building blocks that may be useful for the synthesis of glycopeptides oligomers or scaffolds for the construction of bioactive compounds. Under the same reaction conditions, pyranoglycosylidenes were more prone to migration of the double bond than to the expected 1,4 addition reaction
已经研究了硝基阴离子在推拉异头糖烯烃上的亲核加成,结果表明,当应用于呋喃糖基亚基时,该反应为获得异头 γ-硝基酯开辟了一条新的有效途径。1,4-加成反应主要发生在不太拥挤的面,即与4,5-异亚丙基保护基团相反的一侧。观察到 E 和 Z 异构体的反应性非常不同,并且该实验结果在量子力学计算的基础上得到了合理化。对这些双 C,C-糖基化合物的硝基功能的化学操作产生了一系列新的 γ-糖基氨基酸,它们是手性结构单元,可用于合成糖肽寡聚物或用于构建生物活性化合物的支架。在相同的反应条件下,
Cycloaddition reactions of activated exo-glycals and nitrones proceeded only under microwave activation, with excellent facial selectivities on furanoglycosylidenes and good stereocontrol on the nitrone producing only two diastereomeric spiroisoxazolidines. alpha/beta-Spiro sugar-isoxazolidines are obtained from pyrano exo-glycals. The cycloaddition reaction with nitrile oxide proceeds at room temperature and gives open-chain isoxazoles due to facile beta-elimination of the sugar ring oxygen on the intermediate isoxazoline ring system. All the heterocycles obtained this way can be regarded as nucleoside analogues. (C) 2005 Elsevier Ltd. All rights reserved.