This research was supported by the Korea Basic Science Institute (National Research Facilities and Equipment Center) grant funded by the Ministry of Education (2022R1A6C101A751). This work was also supported by the National Research Foundation of Korea (NRF) grants (2020R1A2C1007102 and 2021R1A5A6002803).

The details of all the synthesized products (1-5), including the structure, full NMR spectra, optical purity, and HRMS-MALDI data, are provided in Supplementary File 1.
1. Synthesis of 3-(aziridin-2-yl)acryl aldehyde (1a)
<ol>
	<li>Flame dry a 50 mL round-bottomed flask equipped with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add anhydrous toluene (19 mL) and (R)-1-((R)-1-phenylethyl)aziridine-2-carbaldehyde (1.00 g, 5.71 mmol) (see Table of Materials) to the flask. Then, stir the solution for 1 min.</li>
	<li>Add (triphenylphosphoranylidene)acetaldehyde (2.08 g, 6.85 mmol) (see Table of Materials) to the stirred solution.</li>
	<li>Heat the reaction mixture at 60 &#176;C for 18 h. Then, cool the reaction mixture to room temperature and remove volatile solvent from the reaction mixture under reduced pressure.</li>
	<li>Monitor the reaction progress by TLC using ethyl acetate:hexanes (1:6 v/v, Rf = 0.25) as an eluent.</li>
	<li>Purify the crude product by silica gel flash chromatography with ethyl acetate:hexanes (1:6 v/v) as the eluent to isolate pure product 1a (see Supplementary File 1) as a yellow liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements (see steps 8 and 9 for measurement methods).</li>
</ol>
2. Synthesis of contiguous bisaziridine (2a)
<ol>
	<li>Flame dry a 50 mL round-bottomed flask with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add anhydrous ethyl acetate (3 mL) and 1a (step 1.6, 201 mg, 1.0 mmol) to the flask, and then stir the solution for 1 min.</li>
	<li>Add catalyst (S)-2-(diphenyl((trimethylsilyl)oxy)methyl)pyrrolidine (BS, see Table of Materials) (0.02 mL, 7 mol%) to the mixture and stir at room temperature for 30 min.</li>
	<li>Add 316 mg, 1.10 mmol of tert-butyl tosyloxycarbamate (BocNHOTs, see Table of Materials) and 123 mg, 1.50 mmol of sodium acetate to the reaction mixture and stir for 24 h.</li>
	<li>Monitor the reaction progress by TLC using diethyl ether:hexanes (1:4 v/v, Rf = 0.27) as an eluent.</li>
	<li>Extract the reaction mixture with ethyl acetate (3 x 50 mL) in a separatory funnel.</li>
	<li>Dry the combined organic layer over anhydrous Na2SO4, filter, and concentrate in vacuo.</li>
	<li>Purify the resulting crude product by flash chromatography on silica gel with diethyl ether:hexanes (1:4 v/v) as eluent to isolate pure product 2a (see Supplementary File 1) as a yellow liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements (see steps 8 and 9).</li>
</ol>
3. Synthesis of compound 3
<ol>
	<li>Flame dry a 50 mL round-bottomed flask with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add anhydrous methanol (11 mL) and aldehyde 2a (step 2.8, 1.00 g, 3.16 mmol) [or 2b (1.17 g, 3.16 mmol, see Supplementary File 1)] to the flask, and then stir the solution for a minute.</li>
	<li>Add NaBH4 (95 mg, 2.53 mmol) to the stirred solution.</li>
	<li>Stir the reaction mixture at 0 &#176;C for 1 h.</li>
	<li>Monitor the reaction progress by TLC using ethyl acetate:hexanes (1:4 v/v, Rf = 0.27) as an eluent.</li>
	<li>After 1 h, quench the reaction mixture with distilled water and extract with ethyl acetate (3 x 50 mL) in a separatory funnel.</li>
	<li>Dry the combined organic layer over anhydrous Na2SO4, filter, and concentrate in vacuo.</li>
	<li>Purify the crude residue by silica gel flash chromatography with ethyl acetate:hexanes (1:4 v/v) as the eluent to isolate pure products 3a [or 3b] (see Supplementary File 1) as a yellow liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements (see steps 8 and 9).</li>
</ol>
4. Synthesis of compound 4
<ol>
	<li>Flame dry a 50 mL round-bottomed flask with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add anhydrous dichloromethane (11 mL) and alcohol 3a (step 3.8, 1.00 g, 3.14 mmol) [or 3b (1.17 g, 3.14 mmol)] to the flask, and then stir the solution for a minute.</li>
	<li>Add tert-butyldimethylsilyl chloride (TBSCl, 520 mg, 3.45 mmol) and imidazole (427 mg, 6.28 mmol) (see Table of Materials) to the stirred solution.</li>
	<li>Stir the reaction mixture at 0 &#176;C for 18 h.</li>
	<li>Monitor the reaction progress by TLC using ethyl acetate:hexanes (1:4 v/v, Rf = 0.26) as an eluent.</li>
	<li>After 18 h, quench the reaction mixture with deionized water and extract with methylene chloride (3 x 50 mL) in a separatory funnel.</li>
	<li>Dry the combined organic layer over the anhydrous sodium sulfate, filter, and then concentrate under reduced pressure.</li>
	<li>Purify the crude residue by silica gel flash chromatography with ethyl acetate:hexanes (1:4 v/v) as the eluent to isolate pure products 4a [or 4b] (see Supplementary File 1) as a yellow liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements.</li>
</ol>
5. Selective ring-opening of non-activated aziridines: Synthesis of 5d
<ol>
	<li>Flame dry a 50 mL round-bottomed flask with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add 3b (step 4.2, 100 mg, 0.27 mmol) and acetic acid (0.12 mL, 2.14 mmol) to the flask, and then stir the mixture at room temperature for 5 h.</li>
	<li>Monitor the reaction progress by TLC using ethyl acetate:hexanes (2:3 v/v, Rf = 0.28) as an eluent.</li>
	<li>After 5 h, remove the acetic acid in vacuo.</li>
	<li>Purify the crude residue by silica gel flash chromatography with ethyl acetate:hexanes (2:3 v/v) as the eluent to isolate pure product 5d (see Supplementary File 1) as a yellow liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements.</li>
</ol>
6. Selective ring-opening of activated aziridines: Synthesis of 5f
<ol>
	<li>Flame dry a 50 mL round-bottomed flask with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add anhydrous methanol (8 mL) and 4b (step 4.8, 100 mg, 0.21 mmol) to the flask, and then stir the solution for 1 min.</li>
	<li>Add NaN3 (39 mg, 0.6 mmol) and NH4Cl (21 mg, 0.41 mmol) in H2O (1 mL) to the above solution.</li>
	<li>Stir the reaction mixture at 0 &#176;C for 4 h.</li>
	<li>Monitor the reaction progress by TLC using ethyl acetate:hexanes (1:4 v/v, Rf = 0.30) as an eluent.</li>
	<li>After 4 h, quench the reaction mixture with H2O and extract with ethyl acetate (3 x 50 mL) in a separatory funnel.</li>
	<li>Dry the combined organic layer over anhydrous Na2SO4, filter, and concentrate in vacuo.</li>
	<li>Purify the crude residue by silica gel flash chromatography with ethyl acetate:hexanes (1:4 v/v) as the eluent to isolate pure product 5f (see Supplementary File 1) as a yellow liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements.</li>
</ol>
7. Pd-catalyzed hydrogenation of contiguous aziridines: Synthesis of 5h
<ol>
	<li>Flame dry a 50 mL round-bottomed flask with a stirrer bar and a septum under vacuum conditions. Cool it to room temperature while filling it with argon gas.</li>
	<li>Add anhydrous methanol (5 mL), 2b (step 3.2, 100 mg, 0.27 mmol), Boc2O (70 mg, 0.32 mmol), and 20% Pd(OH)2/C (37 mg) to the flask.</li>
	<li>Stir the mixture under H2 atmosphere (balloon, 1 atm) at room temperature for 12 h.</li>
	<li>Monitor the reaction progress by TLC using ethyl acetate:hexanes (2:3 v/v, Rf = 0.29) as an eluent.</li>
	<li>Filter the reaction mixture through a commercially available celite pad (see Table of Materials) and wash with methanol.</li>
	<li>Evaporate in vacuo the filtrate and purify the residue by silica gel flash chromatography with ethyl acetate:hexanes (2:3 v/v) as the eluent to isolate pure product 5h (see Supplementary File 1) as a colorless liquid.</li>
	<li>Confirm the product by NMR and polarimeter measurements.</li>
</ol>
8. Polarimeter analysis
<ol>
	<li>Prepare an appropriate amount of the sample (~100 mg) to be measured.</li>
	<li>Dissolve the prepared sample in CHCl3 (c 0.05-1.00).</li>
	<li>Transfer the sample solution into the sample chamber, ensuring that there are no air bubbles 
	[&#248; = 1.8 mm, l&#160;= 10-1 m].</li>
	<li>Load the sample chamber into the polarimeter instrument (see Table of Materials) and check the orientation of the chamber.</li>
	<li>Set 0 as click zero clear in the &#39;control&#39; section.</li>
	<li>Measure the specific rotation of CHCl3 for the blank. 
	NOTE: Light source: Na; &#955; = 589 nm; D.I.T: 5 s; cycle times: 5; cycle interval: 5 s; temperature: 20 &#176;C.</li>
	<li>Measure the specific rotation of the sample solution at a constant temperature. 
	NOTE: Light source: Na; &#955; = 589 nm; D.I.T: 5 s; cycle times: 5; cycle interval: 5 s; temperature: 20 &#176;C.</li>
	<li>Measure the specific rotation of the sample solution three times in the same way to obtain the average value.</li>
	<li>Calculate the specific rotation using the following equation27: 
	<img alt="Equation 1" src="/files/ftp_upload/64019/64019eq01.jpg" style="margin: auto;" /> 
	&#945; = observed rotation (degrees), c = concentration (g/mL),&#160;l = path length (10-1 m).</li>
</ol>
9. 1H and 13C NMR analysis
<ol>
	<li>Prepare approximately 0.6-1.0 mL of the NMR solvent (CDCl3).</li>
	<li>Dissolve ~50 mg of sample in the solvent at a concentration of 0.02 M for 1H NMR and 0.05 M for 13C NMR measurements.</li>
	<li>Transfer the sample solution into an NMR tube using a Pasteur pipette.</li>
	<li>Load the tube into the NMR instrument (see Table of Materials). 
	NOTE: NMR measurements were performed using 400 MHz or 500 MHz spectrometers. Spin number: 16 (1H NMR), 256 or 512 (13C NMR); measurement time: 10 min (1H NMR), 20 or 30 min (13C NMR)].</li>
	<li>Record the NMR spectra and analyze the data. 
	NOTE: Reference the chemical shift of spectrum to CDCl3 signal [&#948; (1H NMR spectrum) = 7.26 ppm; &#948; (13C NMR spectrum) = 77.0 ppm)].</li>
</ol>

The authors have nothing to disclose.

The formation of an inseparable mixture of diastereomers has occasionally been observed during the course of organocatalytic aziridination of chiral 3-[1-(1-phenylethyl)aziridin-2-yl)]acrylaldehyde, when N-Boc-O-tosyl or N-Ts-O-tosyl hydroxylamine was used as the nitrogen source. Further, the yield of contiguous bisaziridine product decreased when the amount of diaryl silyl ether prolinol as catalyst was increased from 7 mol% to 20 mol%47,<sup class="...

Rational design of small organic molecules with diverse reactive sites that precisely control product selectivity is a key goal in modern organic synthesis and green chemistry1,2,3,4,5,6,7,8. To achieve this goal, we were interested in the modular synthesis of aziridines. Aziridines are of interest to most organic chemists, owing to their structurally important framework9 with an electronically diverse set of N-substituents that can lead to regioselective ring-opening reactions with multiple nucleophiles10,11,12,13,14,15,16,17,18,19, and varied pharmacological activities such as antitumor, antimicrobial, and antibacterial properties. Despite the advances in aziridine chemistry, non-activated aziridine and activated aziridine have independent syntheses and ring-opening reactions in the literature20.
Therefore, we aimed to synthesize contiguous bisaziridines comprising both the non-activated and activated aziridines. These contiguous bisaziridines can be used to systematically rationalize a chemoselective ring-opening pattern based on the following electronic properties of the two different aziridines and their reactivity to nucleophiles20,21,22,23,24: a) activated aziridines, in which the electron-withdrawing substituents conjugatively stabilize the negative charge on the nitrogen, readily react with multiple nucleophiles to allow ring-opened products; b) non-activated aziridines, in which the nitrogen is bound to the electron-donating substituents, are considerably inert toward nucleophiles; hence, a pre-activation step with a suitable activator (mainly Br&#248;nsted or Lewis acids) is required to afford the ring-opened products in high yields20,21,25,26.
The present study describes the rational design of contiguous bisaziridines as chiral building blocks via transition-metal-free organocatalysis and the synthesis of diverse nitrogen-rich molecules utilizing predictive modeling tools for ring-opening reactions of bisaziridines. This study aims to stimulate the advancement of practical methods for the construction of nitrogen-enriched bioactive compounds and natural products and the polymerization of aziridines.

<table><tbody><tr><td>(R)-(+)-&amp;alpha;,&amp;alpha;-Diphenyl-2-pyrrolidinemethanol trimethylsilyl ether</td><td>Sigma-Aldrich</td><td>677191</td><td>reagent</td></tr><tr><td>(R)-1-((R)-1-phenylethyl)aziridine-2-carbaldehyde</td><td>Imagene Co.,Ltd.</td><td></td><td>reagent</td></tr><tr><td>(S)-(&amp;ndash;)-&amp;alpha;,&amp;alpha;-Diphenyl-2-pyrrolidinemethanol trimethylsilyl ether</td><td>Sigma-Aldrich</td><td>677183</td><td>reagent</td></tr><tr><td>(S)-2-(diphenyl((trim ethylsilyl)oxy)methyl)pyrrolidine</td><td>Sigma-Aldrich</td><td>677183</td><td>reagent</td></tr><tr><td>(Triphenylphosphoranylidene) acetaldehyde</td><td>Sigma-Aldrich</td><td>280933</td><td>reagent</td></tr><tr><td>1,2-Dichloroethane</td><td>Sigma-Aldrich</td><td>284505</td><td>solvent</td></tr><tr><td>AB Sciex 4800 Plus MALDI TOFTM (2,5-dihydroxybenzoic acid (DHB) matrix</td><td>Sciex</td><td></td><td>High resolution mass spectra</td></tr><tr><td>Acetic acid</td><td>Sigma-Aldrich</td><td>A6283</td><td>reagent</td></tr><tr><td>Ammonium chloride</td><td>Sigma-Aldrich</td><td>254134</td><td>reagent</td></tr><tr><td>aniline</td><td>Sigma-Aldrich</td><td>132934</td><td>reagent</td></tr><tr><td>Autopol III digital polarimeter</td><td>Rudolph Research Analytical</td><td></td><td>polarimeter</td></tr><tr><td>AVANCE III HD (400 MHz) spectrometer</td><td>Bruker</td><td></td><td>NMR spectrometer</td></tr><tr><td>Bruker Ascend 500 (500 MHz)</td><td>Bruker</td><td></td><td>NMR spectrometer</td></tr><tr><td>Celite 535</td><td>Sigma-Aldrich</td><td>22138</td><td>For Celite pad</td></tr><tr><td>Dichloromethane</td><td>Sigma-Aldrich</td><td>270997</td><td>solvent</td></tr><tr><td>Di-tert-butyl dicarbonate</td><td>Sigma-Aldrich</td><td>361941</td><td>reagent</td></tr><tr><td>Ethyl Acetate</td><td>Sigma-Aldrich</td><td>270989</td><td>solvent</td></tr><tr><td>Ethyl nitroacetate</td><td>Sigma-Aldrich</td><td>192333</td><td>reagent</td></tr><tr><td>Imidazole</td><td>Sigma-Aldrich</td><td>I2399</td><td>reagent</td></tr><tr><td>INOVA 400WB (400 MHz)</td><td>Varian</td><td></td><td>NMR spectrometer</td></tr><tr><td>JMS-700</td><td>JEOL</td><td></td><td>High resolution mass spectra</td></tr><tr><td>Methanol</td><td>Sigma-Aldrich</td><td>322415</td><td>solvent</td></tr><tr><td>N-Boc-O-tosylhydroxylamine</td><td>Sigma-Aldrich</td><td>775037</td><td>reagent</td></tr><tr><td>P-2000</td><td>JASCO</td><td></td><td>polarimeter</td></tr><tr><td>Palladium hydroxide on carbon</td><td>Sigma-Aldrich</td><td>212911</td><td>reagent</td></tr><tr><td>Phenyl-1H-tetrazole-5-thiol</td><td>TCI</td><td>P0640</td><td>reagent</td></tr><tr><td>Silica gel</td><td>Sigma-Aldrich</td><td>227196</td><td>For flash clromatography</td></tr><tr><td>Silica gel on TLC plates</td><td>Merck</td><td>60768</td><td>TLC plate</td></tr><tr><td>Sodium acetate</td><td>Sigma-Aldrich</td><td>S8750</td><td>reagent</td></tr><tr><td>Sodium azide</td><td>Sigma-Aldrich</td><td>S2002</td><td>reagent</td></tr><tr><td>Sodium borohydride</td><td>Sigma-Aldrich</td><td>452882</td><td>reagent</td></tr><tr><td>Sodium carbonate</td><td>Sigma-Aldrich</td><td>S2127</td><td>reagent</td></tr><tr><td>tert-Butyldimethylsilyl chloride</td><td>Sigma-Aldrich</td><td>190500</td><td>reagent</td></tr><tr><td>Tetrahydrofuran</td><td>Sigma-Aldrich</td><td>401757</td><td>solvent</td></tr><tr><td>Toluene</td><td>Sigma-Aldrich</td><td>244511</td><td>solvent</td></tr><tr><td>Zinc bromide</td><td>Sigma-Aldrich</td><td>230022</td><td>reagent</td></tr><tr><td>Zinc chloride</td><td>Sigma-Aldrich</td><td>429430</td><td>reagent</td></tr></tbody></table>

preparation of contiguous bisaziridines for regioselective ring-opening reactions

Aziridines, a class of reactive organic molecules containing a three-membered ring, are important synthons for the synthesis of a large variety of functionalized nitrogen-containing target compounds through the regiocontrolled ring-opening of C-substituted aziridines. Despite the tremendous progress in aziridine synthesis over the past decade, accessing contiguous bisaziridines efficiently remains difficult. Therefore, we were interested in synthesizing contiguous bisaziridines bearing an electronically diverse set of N-substituents beyond the single aziridine backbone for regioselective ring-opening reactions with diverse nucleophiles. In this study, chiral contiguous bisaziridines were prepared by organocatalytic asymmetric aziridination of chiral (E)-3-((S)-1-((R)-1-phenylethyl)aziridin-2-yl)acrylaldehyde with N-Ts-O-tosyl or N-Boc-O-tosyl hydroxylamine as the nitrogen source in the presence of (2S)-[diphenyl(trimethylsilyloxy)methyl]pyrrolidine as a chiral organocatalyst. Also demonstrated here are representative examples of regioselective ring-opening reactions of contiguous bisaziridines with a variety of nucleophiles such as sulfur, nitrogen, carbon, and oxygen, and the application of contiguous bisaziridines to the synthesis of multi-substituted chiral pyrrolidines by Pd-catalyzed hydrogenation.

To investigate the achievability of preparing a contiguous bisaziridine, (E)-3-((S)-1-((R)-1-phenylethyl)aziridin-2-yl)acrylaldehyde (1a) was first synthesized as a model substrate according to the procedure mentioned in step 1 (Figure 1)28.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/64019/64019fig01.jpg" /> 
Figu...

Watch this Scientific Journal Video about Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions at JoVE.com

Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions

Contiguous bisaziridines containing non-activated and activated aziridines were synthesized by asymmetric organocatalytic aziridinations and then subjected to chemoselective ring-opening reactions under acidic or basic conditions. The non-activated aziridine ring opens with less reactive nucleophiles under acidic conditions, whereas the activated aziridine ring opens with more reactive nucleophiles under basic conditions.

Aziridines, a class of reactive organic molecules containing a three-membered ring, are important synthons for the synthesis of a large variety of ...

preparation-contiguous-bisaziridines-for-regioselective-ring-opening

Research

JoVE Journal

Chemistry

2.9K Views.  Sungkyunkwan University. Contiguous bisaziridines containing non-activated and activated aziridines were synthesized by asymmetric organocatalytic aziridinations and then subjected to chemoselective ring-opening reactions under acidic or basic conditions. The non-activated aziridine ring opens with less reactive nucleophiles under acidic conditions, whereas the activated aziridine ring opens with more reactive nucleophiles under basic conditions.

Video: Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable.
The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts.
The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

Microwave-assisted intramolecular dehydrogenative Diels-Alder (DA) reactions provide concise access to functionalized cyclopenta[b]naphthalene building blocks. The utility of this methodology is demonstrated by one-step conversion of the dehydrogenative DA cycloadducts into novel solvatochromic fluorescent dyes via Buchwald-Hartwig palladium-catalyzed cross-coupling reactions.

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to ...

Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor diffusion. Oxygen- and moisture-sensitive compounds are prepared and isolated under an inert atmosphere (N2) using either a vacuum gas manifold or a glove box. As an example of azaborine synthesis, we demonstrate the synthesis and purification of the volatile N-H-B-ethyl-1,2-azaborine by a five-step sequence involving distillation and column chromatography for the isolation of products. T4 lysozyme mutants L99A and L99A/M102Q are expressed with Escherichia coli RR1 strain. Standard protocols for chemical cell lysis followed by purification using carboxymethyl ion exchange column affords protein of sufficiently high purity for crystallization. Protein crystallization is performed in various concentrations of precipitant at different pH ranges using the hanging drop vapor diffusion method. Complex preparation with the small molecules is carried out by vapor diffusion method under an inert atmosphere. X-ray diffraction analysis of the crystal complex provides unambiguous structural evidence of binding interactions between the protein binding site and 1,2-azaborines.

A protocol for the synthesis of 1,2-azaborines and the preparation of their protein complexes with T4 lysozyme mutants is presented.

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor ...

Biochemistry

Synthesis and Purification of Iodoaziridines Involving Quantitative Selection of the Optimal Stationary Phase for Chromatography

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. Diiodomethyllithium is prepared by the deprotonation of diiodomethane with LiHMDS, in a THF/diethyl ether mixture, at -78 &#176;C in the dark. These conditions are essential for the stability of the LiCHI2 reagent generated. The subsequent dropwise addition of N-Ts aldimines to the preformed diiodomethyllithium solution affords an amino-diiodide intermediate, which is not isolated. Rapid warming of the reaction mixture to 0 &#176;C promotes cyclization to afford iodoaziridines with exclusive cis-diastereoselectivity. The addition and cyclization stages of the reaction are mediated in one reaction flask by careful temperature control.
Due to the sensitivity of the iodoaziridines to purification, assessment of suitable methods of purification is required. A protocol to assess the stability of sensitive compounds to stationary phases for column chromatography is described. This method is suitable to apply to new iodoaziridines, or other potentially sensitive novel compounds. Consequently this method may find application in range of synthetic projects. The procedure involves firstly the assessment of the reaction yield, prior to purification, by 1H NMR spectroscopy with comparison to an internal standard. Portions of impure product mixture are then exposed to slurries of various stationary phases appropriate for chromatography, in a solvent system suitable as the eluent in flash chromatography. After stirring for 30 min to mimic chromatography, followed by filtering, the samples are analyzed by 1H NMR spectroscopy. Calculated yields for each stationary phase are then compared to that initially obtained from the crude reaction mixture. The results obtained provide a quantitative assessment of the stability of the compound to the different stationary phases; hence the optimal can be selected. The choice of basic alumina, modified to activity IV, as a suitable stationary phase has allowed isolation of certain iodoaziridines in excellent yield and purity.

A protocol for the diastereoselective one-pot preparation of cis-N-Ts-iodoaziridines is described. The generation of diiodomethyllithium, addition to N-Ts aldimines and cyclization of the amino gem-diiodide intermediate to iodoaziridines is demonstrated. Also included is a protocol to rapidly and quantitatively assess the most appropriate stationary phase for purification by chromatography.

The highly diastereoselective preparation of cis-N-Ts-iodoaziridines through reaction of diiodomethyllithium with N-Ts aldimines is described. ...

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Bicyclic aziridinium ions were generated by the removal of an appropriate leaving group through internal nucleophilic attack by nitrogen atom in the aziridine ring. The utility of bicyclic aziridinium ions, specifically 1-azoniabicyclo[3.1.0]hexane and 1-azoniabicyclo[4.1.0]heptane tosylate highlighted in the aziridine ring openings by the nucleophile with the release of the ring strain to yield the corresponding ring-expanded azaheterocycles such as pyrrolidine, piperidine and azepane with diverse substituents on the ring in regio- and stereospecific manner. Herein, we report a simple and convenient method for the preparation of the stable 1-azabicyclo[4.1.0]heptane tosylate followed by selective ring opening via a nucleophilic attack either at the bridge or at the bridgehead carbon to yield piperidine and azepane rings, respectively. This synthetic strategy allowed us to prepare biologically active natural products containing piperidine and azepane motif including sedamine, allosedamine, fagomine and balanol in highly efficient manner.

Bicyclic aziridinium ions such as 1-azoniabicyclo[4.1.0]heptane tosylate were generated from 2-[4-tolenesulfonyloxybutyl]aziridine, which was utilized for the preparation of substituted piperidines and azepanes via regio- and stereospecific ring-expansion with various nucleophiles. This highly efficient protocol allowed us to prepare diverse azaheterocycles including natural products such as fagomine, febrifugine analogue and balanol.

Bicyclic aziridinium ions were generated by the removal of an appropriate leaving group through internal nucleophilic attack by nitrogen atom in the ...

Solid-phase Synthesis of [4.4] Spirocyclic Oximes

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of solid-phase synthesis, regenerating Michael (REM) linker strategies, and 1,3-dipolar cycloaddition, a library of structurally similar heterocycles, both with and without a spirocyclic center, can be constructed. The main advantages of the solid-support synthesis are as follows: first, each reaction step can be driven to completion using a large excess of reagents resulting in high yields; next, the use of commercially available starting materials and reagents keep the costs low; finally, the reaction steps are easy to purify via simple filtration. The REM linker strategy is attractive because of its recyclability and traceless nature. Once a reaction scheme is completed, the linker can be reused multiple times. In a typical solid-phase synthesis, the product contains either a part of or the whole linker, which can prove undesirable. The REM linker is &#34;traceless&#34; and the point of attachment between the product and the polymer is indistinguishable. The high diastereoselectivity of the intramolecular 1,3-dipolar cycloaddition is well documented. Limited by the insolubility of the solid support, the reaction progression can only be monitored by a change in the functional groups (if any) via infrared (IR) spectroscopy. Thus, the structural identification of intermediates cannot be characterized by conventional nuclear magnetic resonance (NMR) spectroscopy. Other limitations to this method stem from the compatibilities of the polymer/linker to the desired chemical reaction scheme. Herein we report a protocol that allows for the convenient production of spirocyclic heterocycles that, with simple modifications, can be automated with high-throughput techniques.

Here we present a protocol to demonstrate an efficient method for the synthesis of spirocyclic heterocycles. The five-step process utilizes solid-phase synthesis and regenerating Michael linker strategies. Generally difficult to synthesize, we present a customizable method for the synthesis of spirocyclic molecules otherwise inaccessible to other modern approaches.

A convenient synthetic route for spirocyclic heterocycles is well sought after due to the molecule&#39;s potential use in biological systems. By means of ...

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of &#945;-Imino &#947;-Lactones and Alkylidene Pyrazolones

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. Recently, we have developed an efficient organocatalytic strategy, which provides facile access to a variety of enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons. In this paper, we demonstrate a detailed protocol for the asymmetric synthesis of drug-like bispirocyclic compounds with two spirocyclic carbon centers via an organocatyltic 1,3-dipolar cycloaddition reaction. Spirocyclization synthons &#945;-imino &#947;-lactones and alkylidene pyrazolones are prepared first, which are then subjected to a cycloaddition reaction in the presence of a bifunctional squaramide organocatalyst to afford the desired bispirocycles in high yields and excellent stereoselectivities. Chiral high-performance liquid chromatography (HPLC) is carried out to determine the enantiomeric purity of the products, and the d.r. value is examined by proton nuclear magnetic resonance (1H NMR). The absolute configuration of the product is assigned according to an X-ray crystallographic analysis. This synthetic strategy allows scientists to prepare a diversity of bispirocyclic scaffolds in high yields and excellent diastereo- and enantioselectivities.

Enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons are asymmetrically synthesized through a simple organocatalytic 1,3-dipolar cycloaddition reaction.

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. ...

Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides

The conjugate addition of organometallic reagents to &#945;,&#946;-unsaturated carbonyls represents an important method to generate C&#8211;C bonds in the preparation of all-carbon quaternary centers. Though conjugate additions of organometallic reagents are typically performed utilizing highly reactive organolithium or Grignard reagents, organozinc reagents have garnered attention for their enhanced chemoselectivity and mild reactivity. Despite numerous recent advances with more reactive diorganozinc and mixed diorganozinc reagents, the generation of all-carbon quaternary centers via the conjugate addition of functionalized monoorganozinc reagents remains a challenge. This protocol details a convenient and mild &#8220;one-pot&#8221; preparation and copper mediated conjugate addition of functionalized monoorganozinc bromides to cyclic &#945;,&#946;-unsaturated carbonyls to afford a broad scope of all-carbon quaternary centers in generally excellent yield and diastereoselectivity. Key to the development of this technology is the utilization of DMA as a reaction solvent with TMSCl as a Lewis acid. Notable advantages to this methodology include the operational simplicity of the organozinc reagent preparation afforded by the utilization of DMA as a solvent, as well as an efficient conjugate addition mediated by various Cu(I) and Cu(II) salts. Moreover, an intermediate silyl enol ether can be isolated utilizing a modified workup procedure. The substrate scope is limited to cyclic unsaturated ketones, and the conjugate addition is impeded by stabilized (e.g., allyl, enolate, homoenolate) and sterically encumbered (e.g., neopentyl, o-aryl) monoorganozinc reagents. Conjugate additions to five- and seven-membered rings were effective, albeit in lower yields compared with six-membered ring substrates.

A simple and practical protocol for the efficient conjugate addition of functionalized monoorganozinc bromides to cyclic &#945;,&#946;-unsaturated carbonyls to furnish all-carbon quaternary centers was developed.

The conjugate addition of organometallic reagents to &#945;,&#946;-unsaturated carbonyls represents an important method to generate C&#8211;C bonds in the ...

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

Nitrogen-containing heterocycle aziridines are synthetically very valuable for the preparation of azacyclic and acyclic molecules. However, it is very difficult and laborious to make aziridines in optically pure forms on a large scale to apply asymmetric synthesis of aza compounds. Fortunately, we successfully achieved both enantiomers (2R)- and (2S)-aziridine-2-carboxylates with the electron-donating &#945;-methylbenzyl group at the ring nitrogen as non-activated aziridines. These starting aziridines have two distinct functional groups-highly reactive three-membered ring and versatile carboxylate. They are applicable in ring-opening or ring-transformation with aziridine and in functional group transformation to others from carboxylate. Both of these enantiomers were utilized in the preparation of biologically important amino acyclic and/or aza-heterocyclic compounds in an asymmetric manner. Specifically, this report describes the first expedient asymmetric synthesis of both enantiomers of 5, 6-dihydrouracil-type marine natural products biemamide B and D as potential TGF-&#946; inhibitors. This synthesis consisted of regio- and the stereoselective ring-opening reaction of aziridine-2-carboxylate and subsequent formation of 4-aminoteterahydropyrimidine-2,4-dione. One more example in this protocol dealt a highly stereoselective Mukaiyama reaction of aziridine-2-carboxylate and silyl enol ether, following intramolecular aziridine ring-opening to provide easy and facile access to (-)-epiallo-isomuscarine.

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

In this study, we prepare both enantiomers of aziridine-2-carboxylate, which are used in the asymmetric synthesis of alkaloids, including biemamide B and D, and (-)-epiallo-isomuscarine.

Nitrogen-containing heterocycle aziridines are synthetically very valuable for the preparation of azacyclic and acyclic molecules. However, it is very ...

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most common drugs used to manage and treat pain and inflammation. In 2016, a new class of boron functionalized NSAIDs (bora-NSAIDs) was synthesized under mild conditions via the copper-catalyzed regioselective boracarboxylation of vinyl arenes using carbon dioxide (CO2 balloon) and a diboron reductant at room temperature. This original method was performed primarily in a glovebox or with a vacuum gas manifold (Schlenk line) under rigorous air-free and moisture-free conditions, which often led to irreproducible reaction outcomes due to trace impurities. The present protocol describes a simpler and more convenient benchtop method for synthesizing a representative bora-NSAID, bora-ibuprofen. A Suzuki-Miyaura cross-coupling reaction between 1-bromo-4-isobutylbenzene and vinylboronic acid pinacol ester produces 4-isobutylstyrene. The styrene is subsequently boracarboxylated regioselectively to provide bora-ibuprofen, an &#945;-aryl-&#946;-boryl-propionic acid, with good yield on a multi-gram scale. This procedure allows for the broader utilization of copper-catalyzed boracarboxylation in synthetic laboratories, enabling further research on bora-NSAIDs and other unique boron-functionalized drug-like molecules.

The present protocol describes a detailed benchtop catalytic method that yields a unique borylated derivative of ibuprofen.&#160;

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most common drugs used to manage and treat pain and inflammation. In 2016, a new class of ...

Functionalized Spirocyclic Heterocycle Synthesis and Cytotoxicity Assay

Spirocyclic heterocycles have recently been reported in literature to be potential drugs for cancer therapy. The synthesis of these novel orthogonal ring systems is challenging. An efficient methodology to synthesize these compounds was recently published that described the solid phase synthesis in four steps rather than the previously reported five steps. The advantage of this shorter synthesis is the elimination of the use of toxic reagents. Low-loading Regenerating Michael (REM) linker-based resin was found to be crucial in the synthesis as high-loading versions prevented the addition of reagents containing bulky phenyl and aromatic side chains. The colorimetric 3-(4&#8242;,5&#8242;-dimethylthiazol-2&#8242;-yl)-2,5- diphenyltetrazolium bromide (MTT) assay was used to examine the cytotoxicity of micromolar concentrations of these novel spirocyclic molecules in vitro. MTT is readily available commercially and produces relatively fast, reliable results, making this assay ideal for these spirocyclic heterocycles. Orthogonal ring structures as well as furfurylamine (a precursor in the synthesis method containing a similar 5-member ring motif) were tested.

Here, we describe a bioassay using 3-(4&#8242;,5&#8242;-dimethylthiazol-2&#8242;-yl)-2,5- diphenyltetrazolium bromide (MTT) to test previously synthesized spirocyclic oximes.

Spirocyclic heterocycles have recently been reported in literature to be potential drugs for cancer therapy. The synthesis of these novel orthogonal ring ...

Preparation of Contiguous Bisaziridines for Regioselective Ring-Opening Reactions

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Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

Synthesis of a Borylated Ibuprofen Derivative Through Suzuki Cross-Coupling and Alkene Boracarboxylation Reactions

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