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>

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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此过程的能力，允许其可以对某些pH敏感的侧链保护基团是必要的显著灵活性。 这种技术的一个潜在的限制是分离的氨基酸的Fmoc基保护的低反应浓度。作为促进èfficient水解需要几个当量的EDTA相对于底物，反应条件要求显著量EDTA水溶液（60毫升对于1毫摩尔规模的反应）。在试剂的相对低的（〜0.015 M）浓度在使用被Fmoc保护的结果这个体积的溶剂中。虽然使用这些条件中一个有希望的产率，尽管稀的反应条件为55％，得到产物证明的概念的反应，可能有必要利用具有相对nucleophilicty减少到甘氨酸从增加的空间体积导致氨基酸时，以增加该浓度。 总之，我们已经证明了EDTA的效用，以促进通常用于UAA的合成的Ni席夫碱配合物的水解。这些水解条件不需要强酸性条件典型这些水解，从而允许酸不稳定侧链保护基团的保持。今后的实验中应注重运用ŧ他的一般策略多种非天然氨基酸的衬底。为此工作正在进行中。

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="https://ecsource-jove-com.remotexs.ntu.edu.sg/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="https://ecsource-jove-com.remotexs.ntu.edu.sg/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水解，我们在室温下进行的Ni-PBP-Gly的溶液在DMF中增加EDTA的等同物在pH为4.5的水溶液，含水的EDTA二钠盐溶液的未经调整的pH值。水解反应的进程可通过溶液的观察颜色的被监测;未反应的镍PBP - 甘氨酸溶液中显示深红色而PBP分离从这个复杂的是白色的。我们通过监测溶液的颜色变化从红色到白色（ 表1）跟踪水解反应的进程。涉及少于八个当量反应显示从红色着色为白色的一些过渡，但反应在每种情况下不完全的。没有颜色变化的无EDTA的条件是显而易见的。 pH对水解的效果类似地进行评估。在Ni-PBP - 甘氨酸络合物，使用12个当量的EDTA的在室温下改变pH过夜水解条件的隶属表明复合物的成功的水解pH条件范围从4.5至7.5下进行。这表明EDTA水解的灵活性; pH值可以提高到占更多的酸敏感的侧链保护基团。 <table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody><tr><td>条件</td><tD&gt;当量（EDTA:镍PBP-GLY） </td><td> EDTA溶液pH </td><td>隔夜完成</td></tr><tr><td> 1 </td><td> 0 </td><td> 4.5 </td><td>没有</td></tr><tr><td> 2 </td><td> 2 </td><td> 4.5 </td><td>局部</td></tr><tr><td> 3 </td><td> 4 </td><td> 4.5 </td><td>局部</td></tr><tr><td> 4 </td><td> 6 </td><td> 4.5 </td><td>局部</td></tr><tr><td>五</td><td> 8 </td><td> 4.5 </td><td>充分</td></tr><tr><td> 6 </td><td> 10 </td><td> 4.5 </td><td>充分</td></tr><tr><td> 7 </td><td> 12 </td><td> 4.5 </td><td>充分</td></tr><tr><td> 8 </td><td> 12 </td><td> 5 </td><td>充分</td></tr><tr><td> 9 </td><td> 12 </td><td> 5.5 </td><td>充分</td></tr><tr><td> 10 </td><td> 12 </td><td> 6 </td><td>充分</td></tr><tr><td> 11 </td><td> 12 </td><td> 6.5 </td><td>充分</td></tr><tr><td> 12 </td><td> 12 </td><td> 7 </td><td>充分</td></tr><tr><td> 13 </td><td> 12 </td><td> 7.5 </td><td>充分</td></tr><tr><td> 14 </td><td> 12 </td><td> 8 </td><td>局部</td></tr></tbody></table> 表1:镍PBP-甘氨酸水解条件。 为了验证能使用的最有效的条件下，7，其水解完成，我们提取反应用二氯甲烷三次，合并并干燥有机层，并使用核磁共振波谱法（NMR）进行分析所得到的残余物。 NMR谱表明该样品中没有镍PBP - 甘氨酸的证据;在光谱中发现的唯一共振匹配PBP的文献报告，表明复合物的完全水解。 我们检查了我们的最佳水解条件下与氨基酸的可行性包含荷兰国际集团的范围内的侧链保护基团。的样品的Fmoc-L-谷氨酸5- 叔丁基酯（将Fmoc-GLU（ 吨丁基）-OH），将Fmoc- -O - 叔丁基-L-苏氨酸（将Fmoc-THR（ 吨丁基）-OH），FMOC - O - 叔丁基-L-酪氨酸（的Fmoc-Tyr（ 吨丁基）-OH），和N（在）-Boc- Nα-Fmoc-L-色氨酸（将Fmoc-色氨酸（BOC）-OH）溶解在DMF中，并在使用12个当量的EDTA在pH 4.5室温下进行水解。被允许搅拌过夜后，将溶液用二氯甲烷萃取，并通过NMR进行分析。代表性NMR被包括用于将Fmoc-GLU（TBU）-OH（ 图3）。在每种情况下，光谱的数据显示的侧链保护基团的完全保留。 11，12，13 <img alt="图3" src="/files/ftp_upload/55677/55677fig3.jpg" /> 图3:将Fmoc-单体轴承酸不稳定侧链屈从于水解条件后保护基团的代表性的NMR。 酸不稳定侧链保护基团被突出显示与蓝色框。对于该化合物的质子信号圆形积分值都包括在括号中。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55677/55677fig3large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> 水解和有机萃取后，将剩余的水层中含有游离氨基酸残余EDTA和Ni 2+离子一起。为了确保这些物质的存在不会与游离氨基酸的后续的Fmoc保护干扰，我们通过在含有EDTA和Ni 2+离子浓度与类似于水解条目7 W上的水性溶液中溶解甘氨酸执行测试反应È然后进行该溶液的标准水性的Fmoc保护。 8反应完成和工作后，我们确定，得到Fmoc-保护的甘氨酸的产率为25％的反应。这个百分比产率并不令人惊讶考虑反应的稀释浓度，并建议的Ni 2+离子和EDTA的存在不与一个标准的Fmoc保护干扰反应。 证据支持了我们的方法（水解，游离氨基酸的分离，和Fmoc保护）的每个单独的部件是可行的，我们进行了使用Ni-PBP - 甘氨酸证明的概念实验。我们评估的上述和使用标准方案8，得到在合理产率的Fmoc保护的氨基酸的Fmoc之后保护所描述的水解条件的可行性。到的镍PBP - 甘氨酸在40mL DMF中，在室温下的搅拌的溶液（404毫克，0.971毫摩尔，1个当量）erature在pH 4.5加入0.2M的EDTA溶液（65毫升，13毫摩尔，13当量）。将反应物搅拌过夜，然后用二氯甲烷洗涤4次。然后将水层用固体碳酸氢钠调节至pH 7。向溶解于二恶烷中的最小量添加水层碳酸氢钠（163毫克，1.93毫摩尔，2当量）和Fmoc-OSu的（327毫克，0.971毫摩尔，1个当量）。允许该反应，用乙酸乙酯搅拌过夜，然后用1M盐酸酸化，并萃取三次。将有机萃取物合并，用盐水洗涤六次，浓缩，用硫酸镁干燥，并在真空下干燥，得到未反应的Fmoc-OSu的和使Fmoc-Gly-OH（160毫克，0.540毫摩尔，产率54％）的混合物中。光谱数据进行匹配先前公布的光谱使Fmoc-Gly-OH。 9这最后的实验表明，它是可行的从镍PBP -甘氨酸络合物隔离自由甘氨酸和发扬，其将Fmoc-PROTected形式。

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

Nanyang Technological University

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

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>

Protection and Deprotection of Alcohols and Phenols

醇类保护

This lesson delves into the concept of protection and deprotection of a functional group fundamental to synthetic organic chemistry. These phenomena are ...

醇类和酚类

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.

卤化物到羧酸:水解

Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction ...

Carboxylic Acid Derivatives

Protecting Groups for Aldehydes and Ketones: Introduction

Protecting groups are compounds that can bind to a specific functional group in the presence of other functional groups to protect them from undesired chemical reactions. These compounds can selectively bind to particular functional groups and advance chemoselective reactions in polyfunctional systems (Figure 1). After the functional group has served its purpose, it is removed by reacting it with specific compounds.
<img alt="Chemical structure of malonic acid, diagram showing bonding, central CH2 group, molecular geometry." src="/files/ftp_upload/12844/12844_PT_Figure_1.svg" style="text-align: center; height: 60px;" data-altupdatedat="1747908711000" data-alt="Chemical structure of malic acid, diagram, showing molecular arrangement, functional groups.">
The aldehydes and ketones can be selectively protected in the presence of other carbonyl groups such as esters or acids based upon their reactivity. This is important for the manipulation of one functional group over the other.
For instance, when carrying out a reduction reaction in the presence of an ester and a ketone, the ketone will always be preferentially reduced to alcohol. In order to achieve the selective reduction of an ester to an alcohol while keeping the ketone unaffected, the ketone group needs to be protected (Figure 2, first step). After the ketone is protected, the ester is reduced to an alcohol using LiAlH4 (Figure 2, second step). Finally, the ketone is regenerated by removing the protecting group (Figure 2, third step).
<img alt="Organic synthesis diagram, ketone protection with cyclic acetal and reduction with LiAlH4." src="/files/ftp_upload/12844/12844_PT_Figure_2.svg" style="text-align: center; height: 215px;" data-altupdatedat="1747908711000" data-alt="Chemical reaction diagram; acetal formation, protection, and reduction; TsOH, LiAlH4 used.">
Acetals and thioacetals are the most commonly used protecting groups for aldehydes and ketones and can be easily removed. In addition, they are resistant to chemical species such as nucleophiles, or reducing and oxidizing agents.

醛类和酮类的保护基团:简介

Protecting groups are compounds that can bind to a specific functional group in the presence of other functional groups to protect them from undesired ...

Aldehydes and Ketones

Acetals and Thioacetals as Protecting Groups for Aldehydes and Ketones

Acetals are formed by reacting two equivalents of alcohol with carbonyl compounds like aldehydes or ketones. Acetals are unaffected by bases, nucleophiles, oxidizing agents, and reducing agents. They serve as protecting groups for aldehydes and ketones. Acetals can be easily formed and also easily removed via mild acid hydrolysis.
In the presence of multiple functional groups, when selective reduction of one group over the other is desired, groups like aldehydes and ketones that form acetals readily can be protected from undergoing undesirable reactions. For instance, if a compound contains a ketone and an ester group, the ketone can be protected by converting it into acetal. On the other hand, the ester does not form acetal; hence it can be subjected to the desired reaction, and in the end, the ketone can be deprotected.
<img alt="Chemical reaction process, acetal formation and reduction, organic chemistry mechanism diagram." src="/files/ftp_upload/12333/12333_Figure_1.svg" style="opacity: 0.9; text-align: center; height: 200px;" data-altupdatedat="1747908711000" data-alt="Figure1">
The sulfur-containing analogs of acetals are called thioacetals that can act as an efficient protecting group for aldehydes and ketones. The thioacetals are stable in acidic conditions. Due to this, they cannot be deprotected by acid hydrolysis. Instead, mercuric chloride in aqueous acetonitrile is used for its deprotection.
<img alt="Chemical reaction: Dithiolane to Acetone transformation; HgCl₂ catalyst; reaction mechanism diagram." src="/files/ftp_upload/12333/12333_Figure_2.svg" style="text-align: center; height: 55px;" data-altupdatedat="1747908711000" data-alt="Figure2">
Apart from acting as protecting groups, thioacetals also play a major role in organic synthesis, especially in reduction reactions. Thioacetals can undergo desulfurization in the presence of Raney nickel and hydrogen to form hydrocarbons.
<img alt="Organic reaction diagram, hydrogenation using H2, Raney Ni; forming hydrocarbons, thiols." src="/files/ftp_upload/12333/12333_Figure_3.svg" style="text-align: center; height: 55px;" data-altupdatedat="1747908711000" data-alt="Figure3">

缩醛和硫代缩醛作为醛和酮的保护基团

Acetals are formed by reacting two equivalents of alcohol with carbonyl compounds like aldehydes or ketones. Acetals are unaffected by bases, ...

Amides to Carboxylic Acids: Hydrolysis

Amides can undergo either acid-catalyzed hydrolysis or base-promoted hydrolysis through a typical nucleophilic acyl substitution. Each hydrolysis requires severe conditions.
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more electrophilic. Next, water acts as a nucleophile and attacks the carbonyl carbon to form a tetrahedral intermediate. Further, deprotonation of the tetrahedral intermediate gives a neutral tetrahedral addition intermediate. Subsequent protonation of the amino nitrogen converts the amino group into a better leaving group. In the next step, the carbonyl group is re-formed with the departure of ammonia as a leaving group. A final deprotonation step yields a carboxylic acid.
<img alt="Figure1" src="/files/ftp_upload/12372/12372_PT_Figure_1_.svg" style="text-align: center; height: 225px;" />
The formation of ammonium ion drives the equilibrium favoring the product formation.
Base-promoted hydrolysis: 
Base-promoted hydrolysis is another nucleophilic acyl substitution reaction, where hydroxide acts as a nucleophile. Amides undergo hydrolysis when heated under basic aqueous solutions to produce carboxylic acid.
The base-promoted mechanism involves a nucleophilic attack by the hydroxide ion at the amide carbonyl carbon to form a tetrahedral intermediate. In the second step, the carbonyl group is reconstructed with the departure of an amide ion as a leaving group. Next, deprotonation yields a carboxylate ion and ammonia. This step drives the reaction to completion, which pushes the equilibrium towards the product. A final step involves acidification of the carboxylate ion to give free acid.
<img alt="Figure2" src="/files/ftp_upload/12372/12372_PT_Figure_2.svg" style="text-align: center; height: 200px;" />

酰胺制羧酸:水解

Amides can undergo either acid-catalyzed hydrolysis or base-promoted hydrolysis through a typical nucleophilic acyl substitution. Each hydrolysis requires ...