Glycal Metallanitrenes for 2-Amino Sugar Synthesis: Amidoglycosylation of Gulal-, Allal-, Glucal-, and Galactal 3-Carbamates.
Glycal Metallanitrenes for 2-Amino Sugar Synthesis: Amidoglycosylation of Gulal-, Allal-, Glucal-, and Galactal 3-Carbamates.
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DOI：
10.1021/acs.joc.8b00893
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发表时间：
2018-08-03
期刊：
影响因子：
--
通讯作者：
Rojas CM
中科院分区：
文献类型：
--
作者：
Buttar S;Caine J;Goné E;Harris R;Gillman J;Atienza R;Gupta R;Sogi KM;Jain L;Abascal NC;Levine Y;Repka LM;Rojas CM
铑（II）催化的烯糖3 - 氨基甲酸酯的氧化环化反应，同时在异头位置原位引入醇亲核试剂，可用于合成一系列具有1,2 - 反 - 2,3 - 顺立体化学结构的2 - 氨基糖，这种结构模式存在于具有医学和生物学意义的化合物中，例如链丝菌素类抗生素和几丁质酶抑制剂阿洛氨菌素。对所有非对映异构的D - 烯糖3 - 氨基甲酸酯都进行了研究，结果表明，根据底物立体化学和保护基的不同，异头立体选择性存在显著差异。此外，一些底物在反应条件下容易形成C3 - 氧化的二氢吡喃酮副产物。阿洛糖和古洛糖的3 - 氨基甲酸酯表现出一致的高立体选择性和化学选择性，而对于葡糖烯糖底物，在4 - O和6 - O位置需要无环的、吸电子保护基。半乳糖烯糖3 - 氨基甲酸酯是最具挑战性的底物；带有吸电子的6 - O - Ts取代基和空间位阻较大的4 - O - TBS基团时，其酰胺基糖基化产物的形成最为有效。这些结果表明了一种反应机理，即构象和电子因素决定了中间体酰基氮宾在烯烃加成（导致酰胺基糖基化）和C3 - H插入（产生二氢吡喃酮副产物）之间的分配。在酰胺基糖基化途径中，当糖基氮丙啶中间体比氮丙啶开环的氧鎓离子供体更有利时，会产生高的异头选择性。
The rhodium(II)-catalyzed oxidative cyclization of glycal 3-carbamates with in situ incorporation of an alcohol nucleophile at the anomeric position provides access to a range of 2-amino sugars having 1,2-trans-2,3-cis stereochemistry, a structural motif present in compounds of medicinal and biological significance such as the streptothricin group of antibiotics and the Chitinase inhibitor allosamidin. All of the diastereomeric d-glycal 3-carbamates have been investigated, revealing significant differences in anomeric stereoselectivity depending on substrate stereochemistry and protecting groups. In addition, some substrates were prone to forming C3-oxidized dihydropyranone byproducts under the reaction conditions. Allal- and gulal 3-carbamates provided uniformly high stereo- and chemoselectivity, while for glucal substrates, acyclic, electron-withdrawing protecting groups at the 4O and 6O positions were required. Galactal 3-carbamates have been the most challenging substrates; formation of their amidoglycosylation products is most effective with an electron-withdrawing 6O-Ts substituent and a sterically demanding 4O-TBS group. These results suggest a mechanism whereby conformational and electronic factors determine the partitioning of an intermediate acyl nitrenoid between alkene addition, leading to amidoglycosylation, and C3—H insertion, providing the dihydropyranone byproduct. Along the amidoglycosylation pathway, high anomeric selectivity results when a glycosyl aziridine intermediate is favored over an aziridine-opened oxocarbenium donor.
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影响因子：
15
作者：
Choi GJ;Knowles RR
通讯作者：
Knowles RR
影响因子：
15
作者：
DENMARK, SE;DAPPEN, MS;JACOBS, RT
通讯作者：
JACOBS, RT
影响因子：
3.6
作者：
Bodner, R;Marcellino, BK;Rojas, CM
通讯作者：
Rojas, CM
DOI：
10.1039/p29740000728
发表时间：
1974-01-01
期刊：
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
影响因子：
--
作者：
CHALMERS, AA;HALL, RH
通讯作者：
HALL, RH
影响因子：
15
作者：
Dahl, RS;Finney, NS
通讯作者：
Finney, NS