一种中性条件下脱除THP保护基的简易方法

四氢吡喃醚(THP)是一种常用的保护基,在有机合成中被广泛地用于羟基的保护。它的脱除通常采用强酸(如三氟乙酸等)条件下进行。近来,曾报道了一些在弱酸性条件下脱除THP保护基的方法。我们利用Me_3SiCl/NaI在中性条件下有效地脱除了THP保护基,见式1。     

微波法合成S-苄基半胱氨酰甘氨酸乙酯

微波条件下,溴化氢醋酸对S-苄基-N-苄氧羰基半胱氨酰甘氨酸乙酯(1)进行脱保护反应,合成了S-苄基半胱氨酰甘氨酸乙酯(2).最佳反应条件为:1 2.9 mmol,n(1):n(HBr-AcOH)=1:6,微波功率200 W,于30 ℃辐射20 min,2的收率为87%.其结构经~1H NMR和IR表征.     

三甲硅基醚的断裂研究

Sommer等[1]首次应用（Me3SiO）2SO2向醇羟基引人三甲硅基（TMS）以保护羟基以来，已发展出很多方便有效的向醇羟基引人TMS保护基团的方法[2]．通常，立体阻碍越小的醇，其羟基越容易被硅基化，而且该TMS保护基团也就越容易在酸或碱性条件下被水解脱除[2]我们在天然产物PrehisPanolone的合成中[3]，羟基r-丁烯酸内酯2是一个关键的中间体．如何脱除前体三甲硅基醚的r-丁烯酸内酯1中的TMS保护基团是一个关键的问题．我们采用四了基氟化铵（TBAF）[4]（A）、酸性水解[5]（B）、碱性醇解[6]（C）和三氟化硼乙醚溶液（BF3-Et2O）[7]…     

N~6,N~6-二(叔丁氧羰基)-2',3'-O-异丙叉腺苷的合成

以腺苷(2)为原料,经丙酮叉保护2',3'-位羟基得2',3'-O-异丙叉腺苷(3);3经叔丁基二甲硅氯保护5'-羟基得5'-O-叔丁二甲基硅基-2',3'-O-异丙叉腺苷(4);4经二碳酸二叔丁酯保护氨基得到N~6,N~6-二(叔丁氧羰基)-2',3'-O-异丙叉基-5'-O-叔丁二甲基硅基腺苷(5);5用四丁基氟化铵脱去叔丁二甲基硅基合成了新化合物N`6,N~6-二(叔丁氧羰基)-2',3'-O-异丙叉腺苷,总收率54.3%,其结构经~1H NMR,~(13)C NMR,IR和HR-MS表征.     

氨基的脱保护——乙酰苯胺水解实验教学设计*

通过开放性设计实验完成氨基脱保护实验的教学。指导学生以回收的乙酰苯胺为原料,自主设计乙酰苯胺在酸、碱条件下水解正交实验方案并分组独立操作,制备并提纯苯胺,比较不同条件下的苯胺收率,筛选出乙酰苯胺最佳的水解条件。对所选实验班级近3年的实验结果进行统计和分析,并通过验证实验考察了结果的可重复性。     

1,3,4,6-四-O-乙酰基-β-D-氨基葡萄糖的合成

分别用对甲氧基苯甲醛和苯甲醛保护D-氨基葡萄糖的氨基，再将羟基用乙酰基保护，以氯化氢脱去氨基上的保护基团，最后脱去氯化氢得到1，3，4，6-四-0-乙酰基-β-D-氨基葡萄糖。两种方法的总产率分别为59％和61％。道关键中间体3b未见报，其结构经^1H NMR表征。     

酶催化脱保护方法及在生物有机化学中的应用

系统地介绍和评述了近年来氨基、羧基、巯基和羟基等到基团的酶催化脱保护方法的进展。由于酶催化脱保护方法具有反应条件温和(中性,水溶液)、选择性和专一性高、副反应少等到优点,故在多肽缀合物、糖等敏感多官能团化合物的研究中有很广阔的应用前景。     

一种利用酰胺基转移反应脱除酰基保护基的实用方法（英文）

酰胺化合物中的酰基脱除是有机合成化学的重要研究方向之一.但是,由于酰胺键较为惰性,在温和条件下脱除酰基保护基的报道较少.为了解决上述问题,发展了一种使用氨水脱除酰基保护基的新方法.该方法不但条件温和,而且可以放大规模反应(10 mmol).一系列药物分子或者药物分子衍生物,例如吲哚美辛、N-乙酰基褪黑素及N-乙酰基卡布洛芬中的酰基都可以采用此方法高产率脱除.该方法具有较好的官能团容忍性、操作简便、条件温和、产率高以及所用的试剂廉价易得等优势.因此,该方法有望成为N-酰基脱保护的实用方法之一.     

烯啶虫胺在超高交联吸附树脂上的吸附性能研究

研究了烯啶虫胺在NDA-150和NDA-1800超高交联吸附树脂上的静态吸附行为。静态吸附等温线表明:两种树脂对烯啶虫胺的吸附均为放热过程,吸附量随着温度的升高而降低,适当降低温度有利于吸附。吸附等温线符合Freundlich方程,为多分子层吸附。吸附速率随着温度的升高而增大,且表观活化能小于20KJ.mol-1,说明吸附较容易进行。NDA-150树脂对烯啶虫胺吸附及脱附性能较好,动态吸附量为351.1 mg.g-1。在323 K温度条件下,用95%乙醇作脱附剂,体积10BV(床体积)时,脱附率为96.43%。     

GaCl_3催化胺与碳二亚胺的加成反应合成胍的研究

以路易斯酸Ga Cl3为催化剂,在无水、无氧、氮气保护无溶剂条件下催化胺与碳二亚胺合成胍的反应,得到一系列胍产物,研究了催化剂用量,反应温度和反应时间对催化反应的影响,研究发现Ga Cl3具有良好的催化活性,以5mol%催化剂用量,无溶剂条件下一级芳香胺与碳二亚胺反应在一小时内得到高于90%产率的胍产物,二级胺也能得到较好产率。     

Selective deprotection of trityl group on carbohydrate by microflow reaction inhibiting migration of acetyl group

The trityl group is an important and useful protecting group for primary hydroxy groups on carbohydrates. However, during deprotection, neighboring acetyl groups can easily migrate to the deprotected hydroxy groups. Hence, deprotection of trityl groups was optimized using a microreactor with regard to flow rate, reagent concentration, reaction time, and substrate concentration. The optimized microflow reaction conditions inhibited migration and could be applied to large-scale reactions and other substrates.     

Catalyst-free alcoholysis of phosphane-boranes: a smooth, cheap, and efficient deprotection procedure

Catalyst-free alcoholytic deprotection of borane-protected phosphorus compounds offers a smooth, efficient, and clean alternative to existing deprotection methods. In this paper we report our results on the general applicability of deprotecting phosphane- and phosphite-borane adducts by means of simple alcoholysis without the use of molecular sieves as a catalyst. Phosphane-boranes bearing at least one aromatic substituent are readily deprotected in high yields. Borane complexes of trialkylphosphanes or phosphites, however, cannot be deprotected in this way. The main merit of our method is its simplicity: apart from evaporation of the solvent, no further work-up or purification is needed.     

Solution-phase synthesis of a hindered N-methylated tetrapeptide using Bts-protected amino acid chlorides: efficient coupling and methylation steps allow purification by extraction

N-Benzothiazole-2-sulfonyl (Bts)-protected amino acid chlorides were used to prepare the hindered cyclosporin 8-11 tetrapeptide subunit 1. The synthesis was performed via 3a and the deprotected amines 5a, 13, and 19, including three repeated cycles involving N-methylation using iodomethane/potassium carbonate, deprotection of the Bts group, and N-acylation with a N-Bts-amino acid chloride such as 9b or 9c. Among three Bts cleavage methods compared (H3PO2/THF; NaBH4/EtOH; PhSH/K2CO3), the third gave somewhat higher overall yields. N-Acylation of 5a with the Bts-protected N-methylamino acid chloride 10b followed by deprotection was also highly efficient and could be used as an alternative route to 11. Each of the deprotected amines was isolated without chromatography using simple extraction methods to remove neutral byproducts. The tetrapeptide 1 was obtained in analytically pure form as the monohydrate.     

N-Boc ethyl oxamate: a new nitrogen nucleophile for use in Mitsunobu reactions

N-Boc ethyl oxamate can be directly coupled with primary and secondary alcohols under Mitsunobu conditions to afford various N-Boc amines after mild deprotection.     

Chloral Hydrate as a Water Carrier for the Efficient Deprotection of Acetals,Dithioacetals, and Tetrahydropyranyl Ethers in Organic Solvents

The efficient deprotection of several acetals, dithioacetals, and tetrahydropyranyl (THP) ethers under ambient conditions, using chloral hydrate in hexane, is described. Excellent yields were realized for a wide range of both aliphatic and aromatic substrates. The method is characterized by mild conditions (room temperatures or below), simple workup, and the ready availability of chloral hydrate. High chemoselectivity was also observed in the deprotection, acetonides, esters, and amides being unaffected under the reaction conditions. Products were generally purified chromatographically and identified spectrally. These results constitute a novel addition to current methodology involving a widely employed deprotection tactic in organic synthesis. It seems likely that the mechanism of the reaction involves adsorption of the substrate on the surface of the sparingly soluble chloral hydrate.     

Boron trichloride as an efficient and selective agent for deprotection of tert-butyl aryl sulfonamides

A fast, mild and selective method for deprotection of tert-butyl aryl sulfonamides utilizing BCl₃ as deprotection reagent has been developed. A variety of tert-butyl aryl sulfonamides used under these conditions gave the corresponding primary sulfonamides in high yields. The method does not cleave methoxy groups and prevents incorporation of tert-butyl groups onto electron-rich aromatic rings.     

Na_3PO_4·12H_2O选择性催化脱去芳香性叔丁基二甲基硅醚

报道了以磷酸盐为催化剂选择性脱去芳香性叔丁基二甲基硅醚的方法.以DMF为溶剂,室温下在0.5质量分数的Na3PO4.12H2O催化下,能顺利地脱去芳香性叔丁基二甲基硅醚得到相应的酚类化合物,而不影响其他的保护基和官能团.     

Simple and Highly Efficient Method for the Deprotection of Allyl Ethers Using Dimethylsulfoxide–Sodium Iodide

A simple and highly efficient method for deprotection of allyl ethers has been developed using dimethylsulfoxide–sodium iodide (catalytic amount). This method is inexpensive, has simple reaction conditions, has an easy workup procedure, proceduces excellent yields (60–99%), and is effective for several structurally varied allyl ethers.     

Acid-Facilitated Debenzylation of N-Boc, N-Benzyl Double Protected 2-Aminopyridinomethylpyrrolidine Derivatives

2-Aminopyridinomethyl pyrrolidines represent a class of highly potent and selective neuronal nitric oxide synthase inhibitors. Conditions for a Mitsunobu reaction of a naphthol and a hindered secondary alcohol were optimized to give good to excellent yields. A key step in the synthesis of these inhibitors is the deprotection of the benzyl group from the N-Boc and N-Bn double protected 2-aminopyridine ring at a late stage of the synthesis, which has been proven difficult in our previous syntheses. Acetic acid was found to facilitate the N-Bn deprotection.     

Selective tert-butyl ester deprotection in the presence of acid labile protecting groups with use of ZnBr2

Chemoselective hydrolysis of tert-butyl esters in the presence of other acid-labile groups has been explored by employing alpha-amino esters and ZnBr(2) in DCM. Although N-Boc and N-trityl groups were found to be labile, PhF protected amines were compatible with these Lewis acid deprotection conditions such that a variety of N-(PhF)amino acids were prepared in good yields from their corresponding tert-butyl esters.