通过滑岩大学提供资助。我们要感谢T·博龙III（滑岩大学）和C·哈尼（宾夕法尼亚大学），他们的见解。

1.镍 - 席夫碱配合物的水解<ol><li>在室温下在250mL圆底烧瓶中，搅拌溶解1毫摩尔的Ni PBP-席夫碱配合物在40mL的N，N-二甲基甲酰胺（DMF）。 </li><li>添加60mL的0.2M的EDTA水溶液，pH为4.5。 </li><li>使用磁性搅拌棒，搅拌板，过夜搅拌该合并的溶液。作为席夫碱配合物被水解，颜色会从深红色转变为白色。 </li><li>通过不存在任何红色着色的指示反应完成后，转移反应至250mL分液漏斗中。 </li><li>加入50毫升二氯甲烷，帽分液漏斗，并混合。漏有机洗涤到废物烧杯中。重复此过程三次以去除PBP和任何残留的Ni-PBP-席夫碱配合物。收集在250mL圆底烧瓶中的剩余的水层。 </li></ol> 2.水解氨基酸的Fmoc保护<ol><li&gt;使用固体碳酸氢钠如上所述至pH 7步骤1.5调整分离水层。检查pH值周期性地用pH试纸。 </li><li>添加168毫克碳酸氢钠（2.00毫摩尔，2当量）到该溶液中，并使用磁力搅拌棒搅拌并搅拌板。 </li><li>在10mL小瓶最小量的二恶烷（大约4或5毫升）中溶解337毫克的Fmoc N-羟基酯（1.00毫摩尔，1当量）。转移该溶液到水溶液中并搅拌过夜。 </li><li>使反应搅拌过夜后，酸化，用1M盐酸将得到的溶液至pH为2。检查pH值周期性地用pH试纸。 </li><li>将反应转移到250mL分液漏斗，并添加50mL的乙酸乙酯中。帽分液漏斗中，充分混合，并收集在250mL锥形瓶中有机层。重复此过程，另外两次，结合的有机萃取物。干燥合并的有机萃取物用约3克镁sulfat的即</li><li>集中使用旋转蒸发器，得到粗的Fmoc保护的氨基酸将合并的有机萃取物。 </li></ol>

<ol><li>Wang, J., Shi, T., Deng, G., Jiang, H., Liu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Highly+Enantio-+and+Diastereoselective+Mannich+Reactions+of+Chiral+Ni%28II%29+Glycinates+with+amino+sulfones.+Efficient+asymmetric+synthesis+of+aromatic+%CE%B1%2C%CE%B2-diamino+acids%5BTitle%5D)+AND+%22J.+Org.+Chem%22%5BJournal%5D)">Highly Enantio- and Diastereoselective Mannich Reactions of Chiral Ni(II) Glycinates with amino sulfones. Efficient asymmetric synthesis of aromatic α,β-diamino acids.</a> J. Org. Chem. 73 (21), 8563-8570 (2011).</li>
<li>Wang, J., Lin, D., Zhou, S., Ding, X., Soloshonok, V. A., Liu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Asymmetric+synthesis+of+sterically+and+electronically+demanding+linear+%CF%89%2C-trifluoromethyl+containing+amino+acids+via+alkylation+of+chiral+equivalents+of+nucleophilic+glycine+and+alanine%5BTitle%5D)+AND+%22J.+Org.+Chem%22%5BJournal%5D)">Asymmetric synthesis of sterically and electronically demanding linear ω,-trifluoromethyl containing amino acids via alkylation of chiral equivalents of nucleophilic glycine and alanine.</a> J. Org. Chem. 76 (2), 684-687 (2011).</li>
<li>Wang, J., Zhou, S., Lin, D., Ding, X., Jiang, H., Liu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Highly+diastereo-+and+enantioselective+synthesis+of+syn-%CE%B2%2C-substituted+tryptophans+via+asymmetric+Michael+addition+of+a+chiral+equivalent+of+nucleophilic+glycine+and+sulfonylindoles%5BTitle%5D)+AND+%22Chem.+Commun%22%5BJournal%5D)">Highly diastereo- and enantioselective synthesis of syn-β,-substituted tryptophans via asymmetric Michael addition of a chiral equivalent of nucleophilic glycine and sulfonylindoles.</a> Chem. Commun. 47 (29), 8355-8357 (2011).</li>
<li>Belokon, Y. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Highly+efficient+catalytic+synthesis+of+%CE%B1%2C-amino+acids+under+phase-transfer+conditions+with+a+novel+catalyst%2Fsubstrate+pair%5BTitle%5D)+AND+%22Angew.+Chem.+Int.+Ed%22%5BJournal%5D)">Highly efficient catalytic synthesis of α,-amino acids under phase-transfer conditions with a novel catalyst/substrate pair.</a> Angew. Chem. Int. Ed. 40 (10), 1948-1951 (2001).</li>
<li>Zhou, S., Wang, J., Lin, D., Zhao, F., Liu, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Enantioselective+synthesis+of+2-substituted-tetrahydroisoquinolin-1-yl+glycine+derivatives+via+oxidative+cross-dehydrogenative+coupling+of+tertiary+amines+and+chiral+nickel%28II%29+glycinate%5BTitle%5D)+AND+%22J.+Org.+Chem%22%5BJournal%5D)">Enantioselective synthesis of 2-substituted-tetrahydroisoquinolin-1-yl glycine derivatives via oxidative cross-dehydrogenative coupling of tertiary amines and chiral nickel(II) glycinate.</a> J. Org. Chem. 78 (22), 11204-11212 (2013).</li>
<li>Belokon, Y. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Synthesis+of+%CE%B1%2C-amino+acids+via+asymmetric+phase+transfer-catalyzed+alkylation+of+achiral+nickel%28II%29+complexes+of+glycine-derived+Schiff+bases%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">Synthesis of α,-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases.</a> J. Am. Chem. Soc. 125 (42), 12860-12871 (2003).</li>
<li>Ueki, H., Ellis, T. K., Martin, C. H., Soloshonok, V. A. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/ejoc.200200688/abstract">Efficient large-scale synthesis of picolinic acid-derived nickel(II) complexes of glycine.</a> Eur. J. Org. Chem. 2003 (10), 1954-1957 (2003).</li>
<li>Dener, J. M., Fantauzzi, P. P., Kshirsagar, T. A., Kelly, D. E., Wolfe, A. B. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/op010204f">Large-scale syntheses of Fmoc-protected non-proteogenic amino acids: useful building blocks for combinatorial libraries.</a> Org. Process Res. Dev. 5 (4), 445-449 (2001).</li>
<li>Cruz, L. J., Beteta, N. G., Ewenson, A., Albericio, F. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/op049917z">&#34;One-pot&#34;, preparation of N-carbamate protected amino acids via the azide.</a> Org Process Res. Dev. 8 (6), 920-924 (2004).</li>
<li>Hart, J. R. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aHart%2C+JR+%22Ullmann%27s+Encyclopedia+of+Industrial+Chemistry%22">Ullmann's Encyclopedia of Industrial Chemistry</a>. , Wiley-VCH Verlag GmbH & Co. (2000).</li>
<li>Adamson, J. G., Blaskovich, M. A., Groenevelt, H., Lajoie, G. A. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/jo00010a050">Simple and convenient synthesis of tert-butyl ethers of Fmoc-serine, Fmoc-threonine, and Fmoc-tyrosine.</a> J. Org. Chem. 56 (10), 3447-3449 (1991).</li>
<li>Seyfried, M. S., Lauber, B. S., Luedtke, N. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Multiple-turnover+isotopic+labeling+of+Fmoc-+and+Boc-protected+amino+acids+with+oxygen+isotopes%5BTitle%5D)+AND+%22Org.+Lett%22%5BJournal%5D)">Multiple-turnover isotopic labeling of Fmoc- and Boc-protected amino acids with oxygen isotopes.</a> Org. Lett. 12 (1), 104-106 (2010).</li>
<li>Bonke, G., Vedel, L., Witt, M., Jaroszewski, J. W., Olsen, C. A., Franzyk, H. <a target="_blank" href="https://www.thieme-connect.de/DOI/DOI?10.1055/s-2008-1067171">Dimeric building blocks for solid-phase synthesis of α,-peptide-β,-peptoid chimeras.</a> Synthesis. 2008 (15), 2381-2390 (2008).</li>
</ol>

作者什么都没有透露。

上述方案是在其通过两个关键步骤，以便于从温和的pH条件和此分离的氨基酸的后续的Fmoc保护下的Ni席夫碱配合物的氨基酸主链的隔离能力是有用的。第一步包括搅拌含有EDTA以促进从复合物中的氨基酸的释放的DMF /水的溶液。残余络合物或有机副产物可以容易地与萃取除去。本协议的第二步骤包括在第一步骤中通过萃取水层中的发现在分离后的氨基酸的Fmoc基保护。我们已经证明修改的pH范围4.5-7.5?...

非天然氨基酸（UAA的）轴承侧链从那些在自然界中发现的20个天然存在的氨基酸的变化已经在广泛的应用范围中找到效用。这些UAA的合成，但是，可以根据侧链的结构和氨基酸主链的立体化学是困难的。在镍席夫碱络合物的情况下甘氨酸克·邦德活化已被用来生产多种氨基酸衍生物，包括α，β二氨基酸1和UAA的轴承氟化2或杂环侧链。 3 另外的非天然侧链后，官能UAA的典型地由在盐酸4通过回流席夫碱配合物中取出，使用离子交换色谱法，随后分离。虽然通常是有效，该协议生成美浓酸，可能是不适合用于固相肽合成（SPPS）的使用。 SPPS的性质要求酸不稳定侧链保护基团的存在和的典型镍席夫碱分解条件强酸性性质防止UAA的隔离用这些保护基团完整。据我们所知，只有一个选择分解方法已经报道了:使用乙二胺四乙酸（EDTA）和肼的在升高的温度下，5个条件本身可能不适合于某些侧链保护基团，例如邻苯二甲酰亚胺。 <img alt="图1" src="/files/ftp_upload/55677/55677fig1.jpg" /> 图1:选自Ni 2+，PBP，和甘氨酸（GLY）的Ni-PBP -甘氨酸的合成。 <a href="http://ecsource.jove.com/files/ftp_upload/55677/55677fig1large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> </一&gt; 在本文中，我们报道了镍席夫碱配合物的水解的方法，镍- PBP -甘氨酸（ 图1）。这种复杂的，选自Ni 2+，甘氨酸，和吡啶-2-羧酸（2-苯甲酰基苯基） -酰胺（PBP），6得出的已被证明是用于多种UAA的合成有用的平台，并容易访问使用两步合成路线。这种复杂的7种合成是文献先例的高收率。 6我们的研究结果如下所述证明利用EDTA中在温和的酸性至适合于与UAA的轴承酸不稳定侧链保护基团的使用中性pH条件的水解条件的适用性。水解之后，所得的水溶液可被分离，并立即进行标准Fmoc保护的条件，得到Fmoc-保护的氨基酸（ 图2）。 图2:水解和氨基酸选自Ni-PBP -甘氨酸隔离的的Fmoc保护。反应条件:一。 EDTA（12当量），pH值4.5; II。乙酸乙酯洗涤并调整至pH 7; III。将Fmoc-OSu的（1当量）， 碳酸氢钠 （2当量）。 <a href="http://ecsource.jove.com/files/ftp_upload/55677/55677fig2large.jpg" target="_blank">请点击此处查看该图的放大版本。</a>

<table><tbody><tr><td>Ni-PBP-Gly</td><td></td><td></td><td>Synthesized from published protocol</td></tr><tr><td>DMF</td><td>Fisher</td><td>D119-4</td><td></td></tr><tr><td>EDTA</td><td>Fisher</td><td>S311-100</td><td></td></tr><tr><td>Dichloromethane</td><td>Acros</td><td>AC610050040</td><td></td></tr><tr><td>Sodium Bicarbonate</td><td>Fisher</td><td>S233-500</td><td></td></tr><tr><td>Fmoc-OSu</td><td>Chem-Impex</td><td>&quot;00147&quot;</td><td></td></tr><tr><td>Dioxane</td><td>Fisher</td><td>D111-500</td><td></td></tr><tr><td>Hydrochloric Acid</td><td>Fisher</td><td>A144-500</td><td></td></tr><tr><td>Ethyl Acetate</td><td>Acros</td><td>AC610060040</td><td></td></tr><tr><td>Magnesium Sulfate</td><td>Fisher</td><td>M65-500</td><td></td></tr><tr><td>ZEOPrep 60ECO Silica Gel</td><td>ZEOChem</td><td></td><td></td></tr><tr><td>Hexanes</td><td>Fisher</td><td>3200250.650.443</td><td></td></tr><tr><td>Chromatography Column</td><td></td><td></td><td></td></tr><tr><td>pH Test Strips</td><td></td><td></td><td></td></tr><tr><td>Rotary Evaporator</td><td></td><td></td><td></td></tr><tr><td>250 mL Separatory Funnel</td><td></td><td></td><td></td></tr><tr><td>250 mL Round Bottom Flask</td><td></td><td></td><td></td></tr><tr><td>Stir Bar</td><td></td><td></td><td></td></tr><tr><td>Stir Plate</td><td></td><td></td><td></td></tr></tbody></table>

hydrolysis of a ni-schiff-base complex using conditions suitable for retention of acid-labile protecting groups

非天然氨基酸，含有侧链官能自然界中不常见的氨基酸，正越来越多地在合成的肽序列中发现。某些非天然氨基酸的合成通常包括使用由通过镍阳离子稳定化的席夫碱的前体。非天然侧链可以安装在在该席夫碱配合物中发现的氨基酸主链。将所得的非天然氨基酸可随后从所述席夫碱的这种复杂的使用水解分离，典型地通过采用回流在强酸性溶液中。这些高酸性条件可除去对酸不稳定的侧链保护基团所需的用于向微波辅助固相肽合成中使用的非天然氨基酸。在这项工作中，我们提出了一种有效的水解和从镍席夫碱配合物中分离的氨基酸的后续的Fmoc保护。在这项工作中提出水解条件适合于酸不稳定S的保持IDE-侧链保护基，并且可以是适于多种非天然氨基酸的衬底。

我们假设，除去从镍PBP -甘氨酸络合物在Ni 2+的可允许的席夫碱的有效水溶液水解，而不需要苛刻的pH条件。如EDTA是一种廉价的和充分研究的螯合剂，10我们推测，加入EDTA至镍PBP-Gly的溶液将促进的Ni 2+离子的螯合，从而促进复合物的水解。 为了测试我们的理论，即单独EDTA能有效促进复合物的?...

Watch this Scientific Journal Video about Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups at JoVE.com

Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups

这里，我们提出一种有效的水解和从镍席夫碱配合物中分离的氨基酸的后续的Fmoc保护。是必需的酸不稳定侧链保护基团的保留时这里介绍的水解条件是适合使用的。这种技术可以适用于各种非天然氨基酸的衬底。

镍 - 席夫碱的水解复杂环境条件适宜酸不稳定保护基团的保留

Unnatural amino acids, amino acids containing side-chain functionalities not commonly seen in nature, are increasingly found in synthetic peptide ...

hydrolysis-ni-schiff-base-complex-using-conditions-suitable-for

Research

JoVE Journal

Biochemistry

9.6K 次观看.  Slippery Rock University. 这里，我们提出一种有效的水解和从镍席夫碱配合物中分离的氨基酸的后续的Fmoc保护。是必需的酸不稳定侧链保护基团的保留时这里介绍的水解条件是适合使用的。这种技术可以适用于各种非天然氨基酸的衬底。 

视频: Hydrolysis of a Ni-Schiff-Base Complex Using Conditions Suitable for Retention of Acid-labile Protecting Groups

Separation of Aldehydes and Reactive Ketones from Mixtures Using a Bisulfite Extraction Protocol

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer by generating a charged structure provides an opportunity to use extraction as a simple purification technique. By combining the use of a miscible organic solvent with saturated sodium bisulfite, aldehydes and reactive ketones can be successfully transformed into charged bisulfite adducts that can then be separated from other organic components of a mixture by the introduction of an immiscible organic layer. Here, we describe a simple protocol for the removal of aldehydes, including sterically-hindered neopentyl aldehydes and some ketones, from chemical mixtures. Ketones can be separated if they are sterically unhindered cyclic or methyl ketones. For aliphatic aldehydes and ketones, dimethylformamide is used as the miscible solvent to improve removal rates. The bisulfite addition reaction can be reversed by basification of the aqueous layer, allowing for the re-isolation of the reactive carbonyl component of a mixture.

Here, we present a protocol to remove aldehydes and reactive ketones from mixtures by a liquid-liquid extraction protocol directly with saturated sodium bisulfite in a miscible solvent. This combined protocol is rapid and facile to perform. The aldehyde or ketone can be re-isolated by the basification of the aqueous layer.

用亚硫酸氢萃取协议分离混合物中的醛和反应性酮

The purification of organic compounds is an essential component of routine synthetic operations. The ability to remove contaminants into an aqueous layer ...

科研

化学

Preparation of SNS Cobalt(II) Pincer Model Complexes of Liver Alcohol Dehydrogenase

Chemical model complexes are prepared to represent the active site of an enzyme. In this protocol, a family of tridentate pincer ligand precursors (each possessing two sulfur and one nitrogen donor atom functionalities (SNS) and based on bis-imidazole or bis-triazole compounds) are metallated with CoCl2&#183;6H2O to afford tridentate SNS pincer cobalt(II) complexes. Preparation of the cobalt(II) model complexes for liver alcohol dehydrogenase is facile. Based on a quick color change upon adding the CoCl2&#183;6H2O to acetonitrile solution that contains the ligand precursor, the complex forms rapidly. Formation of the metal complex is complete after allowing the solution to reflux overnight. These cobalt(II) complexes serve as models for the zinc active site in liver alcohol dehydrogenase (LADH). The complexes are characterized using single crystal X-ray diffraction, electrospray mass spectrometry, ultra-violet visible spectroscopy, and elemental analysis. To accurately determine the structure of the complex, its single crystal structure must be determined. Single crystals of the complexes that are suitable for X-ray diffraction are then grown via slow vapor diffusion of diethyl ether into an acetonitrile solution that contains the cobalt(II) complex. For high quality crystals, recrystallization typically takes place over a 1 week period, or longer. The method can be applied to the preparation of other model coordination complexes and can be used in undergraduate teaching laboratories. Finally, it is believed that others may find this recrystallization method to obtain single crystals beneficial to their research.

Preparation of SNS CobaltII Pincer Model Complexes of Liver Alcohol Dehydrogenase

The preparation of SNS pincer cobalt(II) model complexes of liver alcohol dehydrogenase is presented here. The complexes can be prepared by reacting the ligand precursor with CoCl2&#183;6H2O and can then be recrystallized by allowing diethyl ether to slowly diffuse into an acetonitrile solution that contains the cobalt complex.

制备SNS钴（II）针质模型复合物肝酒精脱氢酶

Chemical model complexes are prepared to represent the active site of an enzyme. In this protocol, a family of tridentate pincer ligand precursors (each ...

Targeted Antibody Blocking by a Dual-Functional Conjugate of Antigenic Peptide and Fc-III Mimetics (DCAF)

Elimination of harmful antibodies from organisms is a valuable approach for the intervention of antibody-associated diseases, such as Dengue hemorrhagic fever and autoimmune diseases. Since thousands of antibodies with different epitopes are circulating in blood, no universal method, except for the dual-functional conjugate of antigenic peptide and Fc-III mimetics (DCAF), was reported to target specific harmful antibodies. The development of DCAF molecules makes significant contribution to the progress of targeted therapy, which were demonstrated to eliminate the antibody dependent enhancement (ADE) effect in a Dengue virus (DENV) infection model and to boost the acetylcholine receptor activity in a myasthenia gravis model. Here, we describe a protocol for the synthesis of a DCAF molecule (DCAF1), which can selectively block 4G2 antibody to attenuate ADE effect during Dengue virus infection, and illustrate the binding of DCAF1 to 4G2 antibody by an ELISA assay. In our method, DCAF1 is synthesized by the conjugation of a hydrazine derivative of a Fc-III peptide and a recombinant expressed long &#945;-helix with antigenic sequence through native chemical ligation (NCL). This protocol has been successfully applied to DCAF1 as well as other DCAF molecules for targeting their cognate antibodies.

Targeted Antibody Blocking by a Dual-Functional Conjugate of Antigenic Peptide and Fc-III Mimetics DCAF

Development of a dual-functional conjugate of antigenic peptide and Fc-III mimetics (DCAF) is novel for the elimination of harmful antibodies. Here, we describe a detailed protocol for the synthesis of DCAF1 molecule, which can selectively block 4G2 antibody to eliminate antibody dependent enhancement effect during Dengue virus infection.

通过抗原肽和Fc-III三氧化二甲物的双功能结合阻断靶向抗体

Elimination of harmful antibodies from organisms is a valuable approach for the intervention of antibody-associated diseases, such as Dengue hemorrhagic ...

免疫与感染

Molecular Orbital (MO) Theory

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes featuring the ligand 1,1&#39;-bis(diphenylphosphino)ferrocene (dppf): M(dppf)Cl2, where M = Ni or Pd. While both of these transition metal complexes are 4-coordinate, they exhibit different geometries at the metal center. Using molecular orbital (MO) theory in conjunction with 1H NMR and Evans method, we will determine the geometry of these two compounds.

Molecular Orbital MO Theory: Predicting Geometry of Transition Metal Complexes

分子轨道 (MO) 理论

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes ...

教育

JoVE Science Education

无机化学

Preparation of Carboxylic Acids: Hydrolysis of Nitriles

Nitriles (R–CN) can be converted into carboxylic acids (R–COOH) upon treatment with aqueous acids, i.e., upon hydrolysis of nitriles. Under base-catalyzed conditions, carboxylate anions (R–COO−) are formed.
<img alt="Hydrolysis reaction mechanism diagram, showing conversion of nitrile to carboxylic acid with arrows." src="/files/ftp_upload/13085/13085_PT_Figure_1.svg" style="text-align: center; height: 56px;" data-altupdatedat="1747908711000" data-alt="Figure1">
The reaction facilitates a two-step conversion of haloalkanes to carboxylic acids. Here, haloalkanes are first converted to nitriles using sodium cyanide via an SN2 reaction. The resultant nitrile is then hydrolyzed to yield carboxylic acids bearing one more carbon than the haloalkane used. The reaction uses dimethyl sulfoxide, alcohols, or water as solvents. As the process involves the SN2 mechanism, tertiary alkyl halides are seldom used.
<img alt="Organic synthesis reaction sequence; diagram illustrating nucleophilic substitution to carboxylic acid." src="/files/ftp_upload/13085/13085_PT_Figure_2.svg" style="text-align: center; height: 46px;" data-altupdatedat="1747908711000" data-alt="Figure2">

羧酸的制备:腈的水解

Nitriles (R&#8211;CN) can be converted into carboxylic acids (R&#8211;COOH) upon treatment with aqueous acids, i.e., upon hydrolysis of nitriles. Under ...

JoVE Core

有机化学

Unit 1

Carboxylic Acids

关键术语与概念

羧酸的制备：腈的水解

Protection of Alcohols

This lesson delves into the concept of protection and deprotection of a functional group fundamental to synthetic organic chemistry. These phenomena are explained in the context of aliphatic and aromatic alcohols.
<h4>Protection</h4>
It defines a protecting group as the masking agent to make the more reactive species inert to a given set of conditions. This concept is depicted via the illustration of liquid flow through different outlets in an assembly of pipes. The analogy helps to understand the role of a protecting group in reaction selectivity, as in the case of the organolithium alkylation of a halide in the presence of a competing acidic alcohol group. The example shows how protection of the alcohol group helps to achieve the alkylation of the halide. Popular protecting groups for alcohols include the trialkylsilyl family for nucleophiles or carbon and nitrogen bases and the tetrahydropyranyl (THP) group for strong bases. In the former example, the halide of the trialkylsilyl derivative reacts with the alcohol in the presence of a nucleophilic catalyst to generate a trialkylsilyl ether.
<h4>Deprotection</h4>
Every protection is followed by deprotection after the intended reaction. The deprotection restores the system to its native state. In protection with trialkylsilyl groups, deprotection is achieved using fluoride salts like tetra-n-butylammonium fluoride (TBAF) that are soluble in organic solvents. Here, the re-protonation of the oxygen regenerates the native alcohol. In the case of protection with THP, deprotection is achieved using acid hydrolysis.
<h4>Principle of design</h4>
The lesson also elucidates the principles behind the design of a protecting group using an illustration of a house under varying external weather conditions. It demonstrates the selectivity offered by a protecting group in a specific environment. For instance, THP protects alcohol from strong bases. The acetal formed in this case is stable towards bases but susceptible to acid hydrolysis.
Apart from the reaction conditions, the reactivity of the molecule to be protected also plays a key role in designing a suitable protecting group. For example, methyl ethers&#8217; ability to protect phenols is found inappropriate for aliphatic alcohols. Here, the stability of the corresponding leaving groups during deprotection plays a key role. For example, the alkoxides, unlike phenoxides, are poor leaving groups for deprotection with hydrogen bromide.
The following table summarizes the various protection/deprotection groups for different types of alcohols and related conditions:
<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Protecting group</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Structure</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Protects</td>
			<td style="color: black; border: 1px solid black; text-align: center;">From</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Protection</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Deprotection</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Trialkylsilyl (R3Si&#8211;), 
			e.g., TBDMS</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Me3Si&#8211;OR 
			(Me3C)Me2Si&#8211;OR</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Alcohols 
			(OH in general)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Nucleophiles, 
			C or N bases</td>
			<td style="color: black; border: 1px solid black; text-align: center;">R3SiCl, 
			base</td>
			<td style="color: black; border: 1px solid black; text-align: center;">H+, H2O, 
			or F&#8722;</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Tetrahydropyranyl 
			(THP)</td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Figure1" src="/files/ftp_upload/11927/Figure_1-11927.svg" style="text-align: center; height: 50px;" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Alcohols 
			(OH in general)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Strong bases</td>
			<td style="color: black; border: 1px solid black; text-align: center;">3,4-Dihydropyran, 
			H+</td>
			<td style="color: black; border: 1px solid black; text-align: center;">H+, H2O</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Benzyl ether 
			(OBn)</td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Figure2" src="/files/ftp_upload/11927/Figure_2-11927.svg" style="text-align: center; height: 50px;" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Alcohols 
			(OH in general)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Almost everything</td>
			<td style="color: black; border: 1px solid black; text-align: center;">NaH, BnBr</td>
			<td style="color: black; border: 1px solid black; text-align: center;">H2, Pd/C, 
			or HBr</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">Methyl ether 
			(ArOMe)</td>
			<td style="color: black; border: 1px solid black; text-align: center;"><img alt="Figure3" src="/files/ftp_upload/11927/Figure_3-11927.svg" style="text-align: center; height: 50px;" /></td>
			<td style="color: black; border: 1px solid black; text-align: center;">Phenols 
			(ArOH)</td>
			<td style="color: black; border: 1px solid black; text-align: center;">Bases</td>
			<td style="color: black; border: 1px solid black; text-align: center;">NaH, MeI, or 
			(MeO)2SO2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">BBr3, HBr, HI, 
			Me3SiI</td>
		</tr>
	</tbody>
</table>

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Acid Halides to Carboxylic Acids: Hydrolysis

Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid as the substitution product. 
<img alt="Organic reaction mechanism, diagram, showing nucleophilic substitution and product formation steps." src="/files/ftp_upload/12361/12361_PT_Figure_1_.svg" style="text-align: center; height: 200px;" data-altupdatedat="1747908711000" data-alt="Figure1">
The reaction produces a very strong acid, HCl, as a by-product. Therefore, a base such as pyridine is used in the reaction, which reacts with HCl to form pyridinium chloride. This process neutralizes the acid and prevents undesired side reactions.

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