Stereodirecting Effect of Esters at the 4-Position of Galacto- and Glucopyranosyl Donors: Effect of 4-C-Methylation on Side-Chain Conformation and Donor Reactivity, and Influence of Concentration and Stoichiometry on Distal Group Participation.
Stereodirecting Effect of Esters at the 4-Position of Galacto- and Glucopyranosyl Donors: Effect of 4-C-Methylation on Side-Chain Conformation and Donor Reactivity, and Influence of Concentration and Stoichiometry on Distal Group Participation.
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DOI：
10.1021/acs.joc.3c01496
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发表时间：
2023-10-06
期刊：
影响因子：
--
通讯作者：
Crich D
中科院分区：
文献类型：
--
作者：
Ande C;Crich D
当在质谱仪中产生来自4-O-酰基吡喃半乳糖基的桥连双环1，3-二氧杂环戊烯离子时，可以在低温下通过红外光谱法观察到供体，但与相邻基团参与的稠合双环1，3-二氧杂环戊烯离子相比，在溶液相中看不到它们。将4-C-甲基纳入4-O-苯甲酰基吡喃半乳糖基供体使得能够核磁共振观察由远端酯参与产生的双环离子，甲基的影响归因于酯基态构象不稳定。我们发现，一个4-C-甲基基团也影响侧链构象，执行一个gauche，反式构象的葡萄糖和半乳糖苷。竞争实验表明，4-C-甲基对4-O-苯甲酰基或4-O-苯甲基-半乳糖和吡喃葡萄糖供体的反应速率只有很小的影响，因此，远端酯的参与不会导致动力学加速（邻位协助）。我们证明，4-O-苯甲酰基-4-C-甲基半乳糖基供体的立体选择性取决于反应浓度和添加剂（二苯基亚砜）的化学计量，因此，远端酯的参与是一个边界现象，在与标准的糖基化机制的竞争。最近的一篇论文肯定了远程特戊酸酯的参与分析与所观察到的现象的替代解释。
When generated in a mass spectrometer bridged bicyclic 1,3-dioxenium ions derived from 4-O-acylgalactopyranosyl, donors can be observed by infrared spectroscopy at cryogenic temperatures, but they are not seen in the solution phase in contrast to the fused bicyclic 1,3-dioxalenium ions of neighboring group participation. The inclusion of a 4-C-methyl group into a 4-O-benzoyl galactopyranosyl donor enables nuclear magnetic resonance observation of the bicyclic ion arising from participation by the distal ester, with the methyl group influence attributed to ester ground state conformation destabilization. We show that a 4-C-methyl group also influences the side-chain conformation, enforcing a gauche,trans conformation in gluco and galactopyranosides. Competition experiments reveal that the 4-C-methyl group has only a minor influence on the rate of reaction of 4-O-benzoyl or 4-O-benzyl-galacto and glucopyranosyl donors and, consequently, that participation by the distal ester does not result in kinetic acceleration (anchimeric assistance). We demonstrate that the stereoselectivity of the 4-O-benzoyl-4-C-methyl galactopyranosyl donor depends on reaction concentration and additive (diphenyl sulfoxide) stoichiometry and hence that participation by the distal ester is a borderline phenomenon in competition with standard glycosylation mechanisms. An analysis of a recent paper affirming participation by a remote pivalate ester is presented with alternative explanations for the observed phenomena.
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构象锁定的顺式和反式 - 脱叶[4.4.0]单，二 - 二烷糖的修饰；实验限制（3）J（H，H）耦合常数，用于估计碳水化合物侧链种群及其他。
DOI：
10.1021/acs.joc.7b02891
发表时间：
2018-01-19
期刊：
The Journal of organic chemistry
影响因子：
--
作者：
Amarasekara H;Dharuman S;Kato T;Crich D
通讯作者：
Crich D
影响因子：
15
作者：
Greis, Kim;Leichnitz, Sabrina;Kirschbaum, Carla;Chang, Chun-Wei;Lin, Mei-Huei;Meijer, Gerard;von Helden, Gert;Seeberger, Peter H.;Pagel, Kevin
通讯作者：
Pagel, Kevin
影响因子：
16.6
作者：
Elferink, Hidde;Mensink, Rens A.;Boltje, Thomas J.
通讯作者：
Boltje, Thomas J.
影响因子：
15
作者：
Garcia, BA;Gin, DY
通讯作者：
Gin, DY
影响因子：
1
作者：
Gerbst, AG;Ustuzhanina, NE;Nifantiev, NE
通讯作者：
Nifantiev, NE