β-Selective Glucosylation in the Absence of Neighboring Group Participation: Influence of the 3,4-O-Bisacetal Protecting System

A 3,4-O-bisacetal 2,6-di-O-benzyl protected thioglucoside is converted to the corresponding glucosyl triflate with 1-benzenesulfinyl piperidine and trifluoromethanesulfonic anhydride. The moderate to excellent β-selectivity exhibited with this glucosyl triflate with a range of alcohols is generally higher than that observed with the more electronically disarmed corresponding 3,4-O-carbonate, for which a possible reason is advanced.     

Single-Atom Protecting Group for on-Surface Synthesis of Graphdiyne Nanowires

On-surface synthesis of semiconducting graphdiyne nanowires usually suffer severe side reactions owing to the high reactivity of the butadiynylene units at noble metal surfaces, limiting the production of isolated nanowires. In this work, we report the high-yield synthesis of branchless graphdiyne nanowires [-C≡C-Ph₂-C≡C-]_n via on-surface Ullmann coupling of 1,4-bis(4-bromophenyl)-1,3-butadiyne molecules with chemical vapor deposition method. Non-contact atomic force microscopy with single-bond resolution reveals that single gold adatoms act as effective protecting groups for butadiynylene units by forming Au-π ligand bonds, preventing unwanted branched coupling reactions and enabling the synthesis of ultralong isolated graphdiyne nanowires. This study will stimulate further investigation on the role of various surface adatoms in protecting on-surface reactions.     

Methyl esters: an alternative protecting group for the synthesis of O-glycosyl amino acid building blocks

The glycosyl amino acids α-GalNAc-Ser and α-GalNAc-Thr are fundamental building blocks for glycopeptide synthesis, Schmidt’s synthesis method often being chosen for this purpose. Methyl esters used as orthogonal carboxylic acid protecting group in this procedure were found to be an efficient and inexpensive alternative to other groups. The mild selective methyl ester deprotection by LiI improved the efficiency of the synthesis method.     

D-葡萄糖酸衍生物C5和C6羟基保护基迁移现象研究

2-O-甲基-3,4-O-丙酮叉基-D-葡萄糖酸甲酯(6)的C6羟基用乙酰基保护、C5仲羟基用TBS保护得到化合物8,碳酸钾脱除C6-O-乙酰基时,C5-O-TBS迁移到C6羟基得到了化合物9(74%收率),没有得到目标产物12;将化合物6的C6羟基用TBS保护、C5羟基乙酰基保护的化合物10,四丁基氟化铵脱除C6-O...     

一种新型磷酸基光控保护基的合成及其应用研究

以苯硫酚为起始原料,经脱水反应、碘代反应、Suzuki-Miyaura偶联反应和氧化反应制得4-酮基-3-苯基-4H-苯并噻喃-2-甲醛(4); 4经间氯过氧苯甲酸氧化后与对甲苯磺酰肼于室温反应制得2-甲苯磺酰腙-3-苯基-4H-磺酰基苯并噻喃(6); 6经Bamford-Stevens反应合成了一种新型磷酸基光控保护基--2-重氮基-3-苯基-4H-磺酰基苯并噻喃(7),其结构经¹H NMR, ¹³C NMR和HR-MS表征。将7应用于磷酸基团的保护和光控脱保护反应中。结果表明:保护反应可在温和条件下顺利进行。紫外光谱法和荧光光谱法对光控脱保护反应的监测结果表明:光控脱保护反应迅速(≤15 min),被保护化合物脱保护收率高(≥95％)。     

2‐[(Acetyloxy)methyl]‐4‐(acetylsulfanyl)‐2‐(ethoxycarbonyl)‐3‐oxobutyl Group: A Thermolabile Protecting Group for Phosphodiesters

The phosphodiester linkage of 3′‐O‐levulinoylthymidine 5′‐methylphosphate ( 5 ) has been protected with 2‐[(acetyloxy)methyl]‐4‐(acetylsulfanyl)‐2‐(ethoxycarbonyl)‐3‐oxobutyl group (to give 1 ) to study the potential of this group as an esterase‐ and thermolabile protecting group. The group turned out to be unexpectedly thermolabile, being removed as ethyl 3‐(acetyloxy)‐4‐(acetylsulfanyl)‐2‐methylidenebut‐3‐enoate ( 10 ) without accumulation of any intermediates. The half‐life of this reaction at pH 7.5 and 37° is 14 min. Hog liver esterase (HLE), in turn, removes the protecting group as ethyl 4‐(acetylsulfanyl)‐2‐methylidene‐3‐oxobutanoate ( 12 ). On using 2.6 units of HLE in 1 ml, the rate of the enzymatic deprotection was still only one third of that of the nonenzymatic reaction. The mechanisms of both reactions have been studied and discussed. The crucial step seems to be removal of the O‐bound Ac group, either by esterase or by migration to the neighboring 3‐oxo group (nonenzymatic removal). This triggers the removal by retro‐aldol condensation/elimination mechanism. No alkylation of glutathione (GSH) upon the deprotection of 1 could be detected.     

Protecting Group Strategies in Organic Synthesis

The choice of protecting groups is one of the decisive factors in the successful realization of a complex, demanding synthetic project. The protecting groups used influence the length and efficiency of the synthesis and are often responsible for its success or failure. A wide range of blocking groups are currently available for the different functional groups; however, an overall strategy combining these different masking techniques in an advantageous and reliable manner has never been proposed or at best only for individual cases. This review attempts to make a contribution to filling this gap. First a very short overview of the most commonly used protecting groups will be given, in which they are classified according to their lability and not according to the functional group they protect. This classification clarifies coherent concepts for the development of blocking strategies. On the basis of this brief summary reliable strategies will then be illustrated and developed with selected examples from the recent literature by which protecting groups may be combined successfully and advantageously in synthetic projects of differing degrees of complexity and difficulty.     

Allyl Protecting Group Mediated Intramolecular Aglycon Delivery (IAD) of Glycosyl Fluorides

Summary.  Stereospecific 1,2-cis-glycosylation of 2-O-allyl protected glucosyl and mannosyl fluorides can be achieved via a sequence of allyl isomerization, N-iodosuccinimide mediated tethering, and intramolecular aglycon delivery (IAD). Fluoride is advantageous as an anomeric leaving group since extended reaction times can be employed to tether hindered aglycon alcohols without competitive anomeric activation. Tin(II) chloride mediated intramolecular glycosylation furnishes the desired α-glucosides and β-mannosides in an entirely stereoselective manner. Received August 24, 2001. Accepted November 6, 2001     

An Economic and Practical Synthesis of the 2-Tetrahydrofuranyl Ether Protective Group

Primary, secondary, and tertiary alcohols as well as phenols and carbohydrates are efficiently transformed into the corresponding 2-tetrahydrofuranyl ethers by a combination of Mn(0) powder and CCl₄ in tetrahydrofuran.     

New Protecting Group Strategies for the Solid-Phase Synthesis and Modification of Peptides,Oligonucleotides, and Oligosaccharides

Blocking and activation can be achieved with protecting groups such as the ortho-nitrobenzenesulfonyl group (see picture). In solid-phase peptide synthesis, this group can be used for temporary protection (path A) as well as the activation and selective N-alkylation (path B) of an amino group.     

3,3-Dimethoxypropylsulfonyl Group: A new versatile protecting and activating group for amine synthesis

3,3-Dimethoxypropylsulfonyl (Dimps) chloride was prepared and used as a new versatile sulfonating agent for ammonia, primary and secondary amines to afford corresponding Dimps-amides in excellent yields. The resulting N-nonsubstituted and N-monosubstituted Dimps-amides, activated amines, were alkylated satisfactorily under new Mitsunobu conditions. The Dimps group was removed by treatment in aqueous solution under acidic followed by basic conditions. Furthermore, epilachnene, the defensive droplets from the Mexican bean beetle, Epilachna varivestis, was synthesized utilizing this Dimps methodology in short steps.     

Selective Michael Reaction Controlled by Supersilyl Protecting Group

Selective Michael reaction of organolithium reagents to supersilyl methacrylate is reported. The method was able to control a single and double Michael addition. The successful termination of the process using the supersilyl protecting group allows for the controlled, chemoselective, and diastereoselective Michael reaction.     

Acridin-9-ylmethoxycarbonyl （Amoc）： A New Photochemically Removable Protecting Group for Alcohols

Synthesis and photochemistry of acridin-9-ylmethoxycarbonyl(Amoc)as a new photochemically removableprotecting group for alcohols were described.Three carbonates of alcohols 1—3 were synthesized throughcondensation of 9-hydroxymethylacridine and chloroformates of alcohols,including benzyl alcohol,phenethylalcohol and one galactose derivative.The photolysis of protected alcohols can efficiently release the correspondingalcohol in the efficiencies(Q_(u1)ε)of 100—200(quantum yield Q_(u1)=0.011—0.023,and molar absorptivity ε=9.1×10~3—9.8×10~3 mol~(-1)·L·cm~(-1))under 360 nm light.     

对羟基苯甲醛磷酸酯席夫碱衍生物的合成及其抗抑郁活性

以对羟基苯甲醛为起始原料,经醚化和酯化反应制得中间体4-（2-羟乙氧基）苯甲醛磷酸二甲酯（2）; 2分别与伯胺经缩合反应合成了4个对羟基苯甲醛磷酸酯席夫碱衍生物（4a~4d）,其结构经¹H NMR, ¹³C NMR, IR和ESI-MS确证。采用应急模型对4a~4d进行抗抑郁活性研究。初步结果表明： 2和4-（2-羟乙氧基）苯甲醛磷酸二甲酯甲氧基胺席夫碱（4d）表现出较好的抗抑郁活性,2的活性优于丙咪嗪,4d的活性与丙咪嗪接近。     

Concise Synthesis of [1,1′‐Biisoquinoline]‐4,4′‐diol via a Protecting Group Strategy and Its Application for Potential Liquid‐Crystalline Compounds

The [1,1′‐biisoquinoline]‐4,4′‐diol ( 4a ), which was obtained as hydrochloride 4a ?2 HCl in two steps starting from the methoxymethyl (MOM)‐protected 1‐chloroisoquinoline 8 (Scheme 3), opens access to further O‐functionalized biisoquinoline derivatives. Compound 4a ?2 HCl was esterified with 4‐(hexadecyloxy)benzoyl chloride ( 5b ) to give the corresponding diester 3b (Scheme 4), which could not be obtained by Ni‐mediated homocoupling of 6b (Scheme 2). The ether derivative 2b was accessible in good yield by reaction of 4a ?2 HCl with the respective alkyl bromide 9 under the conditions of Williamson etherification (Scheme 4). Slightly modified conditions were applied to the esterification of 4a ?2 HCl with galloyl chlorides 10a – h as well as etherification of 4a ?2 HCl with 6‐bromohexyl tris(alkyloxy)benzoates 11b , d – h and [(6‐bromohexyl)oxy]‐substituted pentakis(alkyloxy)triphenylenes 14a – c (Scheme 5). Despite the bulky substituents, the respective target 1,1′‐biisoquinolines 12, 13 , and 15 were isolated in 14–86% yield (Table).     

Application of the PMC Protecting Group in the Efficient Synthesis of 4,4‐Disubstituted Piperidines

Abstract

An efficient synthesis of the 4,4‐disubstituted piperidine scaffold 1 was accomplished by treating the PMC N‐protected α,β‐unsaturated ethyl cyanoacetate 9 with various Grignard reagents (R₁MgX). Subsequent heating at 190°C in a strong base provided carboxylic acids 12–20b in good yield. The PMC group was easily removed at room temperature with 33% HBr in acetic acid.     

二-(氨基葡萄糖)磷酸酯的合成研究

用2-乙酰胺-3,4,6-三-O-乙酰-2-脱氧-a-D-葡萄吡喃糖-1-磷酸吡啶盐(3)和2-乙酰胺-1,3,4-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖(4)进行缩合,没有得到6-O-(2-乙酰胺-3,4,6-三-O-乙酰-2-脱氧-D-葡萄吡哺糖-1-磷酰)-2-乙酰胺-1,3,4-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖(7),而分离到了6-O-(2-乙酰胺-3,4,6-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖基)-2-乙酰胺-1,3,4-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖(9)和二-(2-乙酰胺-1,3,4-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖-6)-磷酸酯(10)。它们是由7的二个分解产物再次与4反应生成的。用1-溴-2-N-DNP-3,4,6-三-O-乙酰-1,2-二-脱氧-α-D-葡萄吡喃糖(13)和2-乙酰胺-1,3,4-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖-6-磷酸三乙胺盐(8)反应,得到了6-O-(2-N-DNP-3,4,6-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖-1-磷酰)-2-乙酰胺-1,3,4-三-O-乙酰-2-脱氧-β-D-葡萄吡喃糖(16)。16性质稳定,说明氨基葡萄糖的2-位乙酰基的存在使其1-位磷酸基团较易离去,而2-位 DNP 基则没有这种影响。     

制备二苄基磷酸酯的工艺改进

以苯甲醇和三氯化磷为原料,通过三步反应合成了二苄基磷酸酯,总收率67.4%,其结构经IR表征。以三乙胺为缚酸剂,四氯化碳为前两步反应共同的溶剂,省略了第一步反应结束后的溶剂分离操作。     

层状磷酸锆的合成与性质研究

用回流、水热晶化和HF沉淀三种方法制备了α－Zr(HPO₄)₂·H₂O(α－ZrP)晶体.HF沉淀法制备的α－ZrP晶体尺寸最大,层板有序度最高,水热法次之,回流法最差.水热法合成的α－ZrP尾板本身的结晶度最高.随α－ZrP晶粒增大,层板有序度和层间水的脱除温度均提高,并且需要嵌入更多的烷基胺和醇胺才能导致层板胶体化.HF沉淀法和回流法制备的α－ZrP层板较易水解,水热法制备的样品水解率较低,但三种样品在有机胺浓度为等当点时水解率均不超过20％.