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1.
Jinq-Chyi Lee 《Tetrahedron letters》2006,47(10):1621-1624
A high-yielding coupling of a new and stable type of glycosyl donors, namely 2-allyloxyphenyl glycoside, with a variety of alcohols via NIS/TfOH reagent combination as effective activators at room temperature is described here. 相似文献
2.
[formula: see text] TMS-OTf- or TBS-OTf-promoted glycosidation reactions of 2-deoxy-2-iodo-alpha-mannopyranosyl acetates 8-10 and the 2-deoxy-2-iodo-alpha-talopyranosyl acetate 11 provide the corresponding 2-deoxy-2-iodo-alpha-pyranosides, precursors to 2-deoxy-alpha-glycosides, as the only observed reaction products. 相似文献
3.
Fraser-Reid B Grimme S Piacenza M Mach M Schlueter U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(19):4687-4692
n-Pentenyl orthoesters (NPOEs) undergo routine acid catalyzed rearrangement into 2-O-acyl n-pentenyl glycosides (NPGs). The reactant and product can both function as glycosyl donors affording 1,2-trans linked glycosides predominantly. However, both donors differ in their rates of reactions, the yields they produce, and the nature of their byproducts, indicating that the NPOE/NPG pair may not be reacting through the same intermediates. We have therefore applied quantum chemical calculations using DFT methods and MP second order perturbation theory to learn more about orthoesters and their 2-O-acyl glycosidic counterparts. The calculations show that in the case of a manno NPG and NPOE pair, each donor goes initially to a different cationic intermediate. Thus, the former goes to a high-energy oxocarbenium ion before descending to a trioxolenium ion in which the charge is distributed over the pyrano ring oxygen, as well as the carbonyl and ether oxygen atoms of the putative C2 ester. On the other hand, ionization of the NPOE produces a dioxolenium ion lying slightly above the more stable trioxolenium counterpart. For the gluco pair, the NPG also goes to a very high-energy oxocarbenium ion, which also descends to a trioxolenium ion. However, unlike the manno analogue, the gluco NPOE does not give a dioxolenium ion; indeed, the dioxolenium is not energetically distinguishable from the trioxolenium counterpart. The theoretical observations have been tested experimentally. Thus, it was found that with manno derivatives, the orthoester is a more reactive donor than the corresponding NPG donor, whereas, for gluco derivatives, there is no advantage to using one over the other, unless one resorts to carefully selected promoters. 相似文献
4.
Bis(pyridinium) iodonium(I) tetrafluoroborate (IPy2BF4), a solid and stable reagent, can be used to transform n-pentenyl orthoesters (NPOEs) and n-pentenyl glycosides (NPGs) into glycosyl fluorides. The latter pair constitutes a new set of semiorthogonal glycosyl donors that can be used in glycosylation strategies, alone or in combination with NPOEs. 相似文献
5.
Kaname Sasaki 《Tetrahedron letters》2006,47(51):9039-9043
A novel class of ‘armed’ glycosyl donors containing a double bond at the C-2 position was designed by mimicking the mechanism of lysozyme-initiated hydrolysis. These donors were used to achieve chemoselective glycosidation of hex-2-enopyranosyl acetate and hexopyranosyl acetate, and synthesis of O-glycosidic linkages between highly deoxygenated sugars and tertiary alcohols. 相似文献
6.
Glycosyl donors protected with bulky silyl protective groups (tert-butyldimethylsilyl, TBS), on the 2-, 3-, and 4-OH groups were found to have superior reactivity compared with benzylated thioglucosides. The enhanced reactivity is explained by the stereoelectronic effects associated with the conformational change induced by the silylation. A TBS silylated thioglucoside donor has axial OR groups, whereas a benzylated thioglucoside has equatorial OR groups, leading to much more favorable charge-dipole interactions in the transition state. This concept could be used to create "super armed" glucosyl, mannosyl, rhamnosyl, and galactosyl donors, which could cross-couple with the armed acceptors, phenyl 2,3,4-tri-O-benzyl-beta-D-thioglucoside or phenyl 2,3,6-tri-O-benzyl-beta-D-thioglucoside, to give the corresponding armed disaccharides in good to excellent yields. 相似文献
7.
Haijing Liang Lixia Ma Changwei Li Qiang Peng Zhaoyan Wang Zhan-xin Zhang Lan Yu Huanxiang Liu Fengli An Weihua Xue 《Tetrahedron letters》2019,60(1):84-87
Glycosylation reactions are significant as they provide access to model compounds that are useful for elucidating biochemical pathways. Herein, we describe the development of glycosyl ortho-alkynylbenzoates as novel, bench-top stable, and readily available glycosyl donors. Glycosylation is promoted by inexpensive trimethylsilyl triflate (TMSOTf) in combination with N-iodosuccinimide (NIS) under mild reaction conditions; hence, the novel glycosyl donors are promising reagents for the synthesis of glycosides. 相似文献
8.
Glycosyl trifluoroacetimidates have been disclosed to be effective glycosyl donors for the synthesis of nucleosides; the present N-glycosylation protocol requires only a catalytic amount of TMSOTf as promoter and proceeds smoothly at room temperature. 相似文献
9.
The relative reactivity of conformationally armed thioglycosides is quantified. 相似文献
10.
11.
细菌内毒素(LPS)是革兰氏阳性阴性菌细胞外膜层的主要成分,由其引起的革兰氏阴性杆菌脓度症和休克是导致战创伤病人死亡的主要原因之一。而从类脂A(LipidA)的结构出发,以非肽类物质拮抗内毒素受体CD-14为治疗手段的研究在国外刚刚起步。2-乙酰氨基-3,4,6-三乙酰葡萄糖是合成LipidA结构类似物的重要中间体[1,2]。它的合成一般是通过氨基葡萄糖五乙酸酯的选择性水解[3-6]脱去一个乙酰基得到。氨基葡萄糖五乙酸酯是通过氨基葡萄糖的乙酰化反应得到的,由于氨基葡萄糖不稳定,一般是用氨基葡萄糖的盐酸盐作为起始原料。由于… 相似文献
12.
2-Deoxy-2-iodo-beta-glucopyranosyl fluoride 14 is a highly stereoselective glucopyranosyl donor that may be activated under mild conditions. Application of this new glycosyl donor to the glycosidation reactions of a variety of acceptors including beta-hydroxy ketones affords beta-glycosides with high efficiency and stereoselectivity. [reaction--see text] 相似文献
13.
Facile synthesis of saponins containing 2,3-branched oligosaccharides by using partially protected glycosyl donors 总被引:6,自引:0,他引:6
Two natural saponins 1 and 2, isolated from Solanum indicum L., and containing 2,3-branched sugar moieties, have been efficiently synthesized. Partially protected monosaccharide and disaccharide donors were used to facilitate target synthesis. Stereo factors were critical in incorporating 2,3-branched sugars on steroid aglycones. Saponin 1 was synthesized in five steps and 30% overall yield, while saponin 2 was obtained using six straightforward sequential reactions in 31% overall yield. Saponin 2 shows promising cytotoxic activity toward human hepatocellular carcinoma BEL-7402 with an IC50 of <6 microg/mL. 相似文献
14.
15.
Shaikh AY Sureshkumar G Pati D Sen Gupta S Hotha S 《Organic & biomolecular chemistry》2011,9(17):5951-5959
Propargyl 1,2-O-orthoesters are exploited for the synthesis of 1,2-trans O-glycosides of protected amino acids. N-Fmoc- and N-Cbz protected serine/threonine - benzyl/methyl esters reacted well with glucosyl-, galactosyl-, mannosyl- and lactosyl- derived propargyl 1,2-orthoesters affording respective 1,2-trans glycosides in good yields under AuBr(3)/4 ? MS Powder/CH(2)Cl(2)/rt. t-Boc serine derivative gave serine 1,2-orthoester and glycosyl carbamate. Optimized conditions enabled preparation of new glycosyl carbamates from N-Boc protected amines in a single step using gold catalysts and propargyl 1,2-orthoesters in excellent yields. 相似文献
16.
Fraser-Reid B Lopez JC Radhakrishnan KV Mach M Schlueter U Gomez AM Uriel C 《Journal of the American Chemical Society》2002,124(13):3198-3199
Glycosidation of several vicinal diols reveals that exquisite regioselectivity can be achieved by using 2-O-benzoyl n-pentenyl glycoside donors and/or their cyclic 1,2-ortho ester counterparts. The regioselective preferences for both are the same, although ratios and yields may differ. In stark contrast, glycosidation of the diols with the corresponding 2-O-benzylated donors gives poor, if any, regioselectivity. 相似文献
17.
[reaction: see text] The new class of glycosyl donors with a methyl 3,5-dinitrosalicylate (DISAL) anomeric leaving group has proved efficient for glycosylation under strictly neutral, mildly basic, or mildly acidic conditions. Here, we report the synthesis of novel DISAL disaccharide glycosyl donors prepared by easy nucleophilic aromatic substitution. These DISAL donors proved efficient in the synthesis of a starch-related hexasaccharide under very mild conditions. Glycosylations proceeded with alpha-selectivity and were compatible with Trt protecting groups. 相似文献
18.
19.
Silica-supported perchloric acid (HClO4-SiO2) has been used as an efficient promoter, as a replacement of TMSOTf, in various glycosylation reactions using sugar trichloroacetimidates as glycosyl donors. Operational simplicity, economic considerations, high yield, short reaction time and low toxicity were the key features associated with this protocol. 相似文献
20.
《Tetrahedron: Asymmetry》2001,12(12):1727-1735
α- and β-Glycosyl cyanides, per-O-acetyl-1,2-O-1-cyanoethylidenes and C-allyl glycopyranosides were efficiently prepared by treatment of 2,3,4-tri-O-acetyl-α,β-l-rhamno-, l-fuco- and 2,3,4,6-tetra-O-acetyl-α,β-d-galactopyranosyl propane-1,3-diyl phosphates with trimethylsilyl cyanide (TMSCN) and allyltrimethylsilane in the presence of trimethylsilyl triflate (TMSOTf). Similarly 2,3,4,6-tetra-O-benzyl-α,β-d-manno- and d-glucopyranosyl propane-1,3-diyl phosphates were employed in the synthesis of C-glycosides. 相似文献