Name: preparation of enantiopure non-activated aziridines and synthesis of biemamide b, d, and epiallo-isomuscarine
Uploaded: 2022-06-13T15:00:00
Description: Watch this Scientific Journal Video about Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine at JoVE.com

This research was supported by the National Research Foundation of Korea (NRF-2020R1A2C1007102 and 2021R1A5A6002803) with the Center for New Directions in Organic Synthesis and an HUFS Grant 2022.

1. Synthesis of the diastereomeric mixture of chiral aziridine (-)-mentholyl ester derivative (1)
<ol>
	<li>Add 2,3-dibromopropane (-)-menthol ester 1a (5.0 g, 13.58 mM, 1.0 equiv) and a magnetic stirring bar into an oven-dried 250 mL two-neck round-bottom flask under nitrogen (N2) atmosphere.</li>
	<li>Add anhydrous acetonitrile (60 mL) to the reaction flask using an airtight syringe.</li>
	<li>Then cool the reaction mixture at 0 &#176;C using an ice bath and stir the reaction mixture for 5...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthetic+applications+of+aziridinium+ions.">Synthetic applications of aziridinium ions.</a> Molecules. 26 (6), 1744 (2021).</li><li>Sweeney, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aziridines:+epoxides'+ugly+cousins.">Aziridines: epoxides' ugly cousins.</a> Chemical Society Reviews. 31 (5), 247-258 (2002).</li><li>Stankovic, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regioselectivity+in+the+ring+opening+of+non-activated+aziridines.">Regioselectivity in the ring opening of non-activated aziridines.</a> Chemical Society Reviews. 41 (2), 643-665 (2012).</li><li>Lee, W. K., Ha, H. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highlights+of+the+chemistry+of+enantiomerically+pure+aziridine-2-carboxylates.">Highlights of the chemistry of enantiomerically pure aziridine-2-carboxylates.</a> Aldrichimica Acta. 36 (2), 57-63 (2003).</li><li>Tranchant, M. J., Dalla, V., Jabin, I., Decroix, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reaction+of+vinyl+triflates+of+&#945;-keto+esters+with+primary+amines:+efficient+synthesis+of+aziridine+carboxylates.">Reaction of vinyl triflates of &#945;-keto esters with primary amines: efficient synthesis of aziridine carboxylates.</a> Tetrahedron. 58 (42), 8425-8432 (2002).</li><li>Ha, H. -. J., Jung, J. -. H., Lee, W. 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Aziridines as nitrogen-containing three-membered heterocycles have enormous potential for synthetic starting martials or intermediates to prepare nitrogen-rich organic molecules. Based on the group bearing at the ring nitrogen, they are classified as "activated" and "non-activated" aziridines whose chemical reactivity and selectivity are different. However, very limited methods are available to prepare this valuable aziridine in an optically active form. 
The protocol in this paper describes a...

Small rings consisting of cyclopropanes, oxiranes, and aziridines are found in various compounds such as natural products and drugs1,2.&#160;They are primarily used as starting materials exploiting their ring strain. Among the three-ring compounds, aziridine has been studied less extensively due to its instability and uncontrollable reactivity3. As shown in the electrostatic potential maps (Figure 1), a group attached to the aziridine ring-nitrogen, whether electron-donating or electron-attracting, makes the basicity of nitrogen different. This difference provides a striking contrast to the reactivity and selectivity of the corresponding aziridines.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63705/63705fig01.jpg" /> 
Figure 1: Chemical structures of &#34;activated&#34; and &#34;non-activated&#34; aziridines and electrostatic potential maps of their representative examples N-methylaziridine, and N-acetylaziridine4. This figure has been modified with permission from Ranjith et al.4. <a href="https://www.jove.com/files/ftp_upload/63705/63705fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
When the ring nitrogen has an electron-withdrawing group, such as sulfonate, phosphonate, and carbamate, we call it &#34;activated&#34; aziridine. This is readily reactive with nucleophiles to compensate for its instability with a limited scope of regiochemistry. These activated aziridines are prepared through various catalytic methods and used as a starting material. Much of recent aziridine chemistry has dealt with these activated aziridines. However, activated aziridines suffer certain restrictions resulting from their instability and limited reaction scope of the ring opening. On the other hand, aziridines bearing electron-donating substituents, like alkyl or substituted alkyl groups, at the ring nitrogen called &#34;non-activated&#34;4, are relatively stable under most circumstances and can be left on the bench for a long time without significant decomposition. The nucleophilic ring-opening reactions of non-activated aziridine occur via the formation of aziridinium ions. Most reactions of aziridine ring-opening and ring transformations proceed in a highly regiochemical manner. However, very few literature reports discuss the preparation of optically pure non-activated aziridines with substituents at the C2 or C3 positions5,6.
This paper shows the successful preparation of &#945;-methylbenzyl group-containing chiral aziridine-2-carboxylate derivatives, specifically (-)-mentholyl (1R)-phenylethylaziridine-2-carboxylates as its diastereomeric mixture, from the reaction of 2,3-dibromopropionate and (1R)-phenylethylamine. From this diastereomeric mixture, enantiopure (1R)-phenylethyl-(2R)- and (2S)-aziridine-2-carboxylates as their (-)-mentholyl esters were obtained in optically pure forms by selective recrystallization from MeOH and n-pentane on multi-hundred-kilo scales (Figure 1)7. These (-)-mentholyl esters can be easily converted into their ethyl or methyl esters by transesterification in the presence of magnesium or potassium carbonate7. These compounds can also be prepared easily on a laboratory scale from the reactions of alkyl 2,3-dibromopropionates or the vinyl triflate of &#945;-ketoester with chiral 2-phenylethylamine followed by separation of the diastereomeric mixture using simple flash column chromatography8.
Once we have enantiopure chiral aziridine-2-carboxylate, we can synthesize various cyclic and acyclic nitrogen-containing biologically important target molecules based on functional group transformations of carboxylate and highly regio- and stereoselective aziridine-ring opening reactions6,9,10. The first expedient asymmetric synthesis was applied for both enantiomers of 5, 6-dihydrouracil-type marine natural products biemamide B and D as potential TGF-&#946; inhibitors11,12. Secondly, the diastereoselective synthesis of &#946;-(aziridin-2-yl)-&#946;-hydroxy ketones was achieved by Mukaiyama aldol reaction of optically pure 1-(1-phenylethyl)-aziridine-2-carboxaldehyde and various enol silanes in the presence of ZnCl2, in high yield (&#62;82%) with almost perfect stereoselectivity (98:2 dr) via a chelation-controlled transition state. These were used for the asymmetric synthesis of epiallo-isomuscarine alkaloids13,14,15.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>(2R)-1-[(1R)-1-Phenylethyl]-2-aziridinecarboxylic acid (-)-menthol ester, 98%</td>
			<td>Sigma-Aldrich</td>
			<td>57054-0</td>
			<td></td>
		</tr>
		<tr>
			<td>(2S)-1-[(1R)-1-Phenylethyl]-2-aziridinecarboxylic acid (-)-menthol ester</td>
			<td>Sigma-Aldrich</td>
			<td>57051-6</td>
			<td></td>
		</tr>
		<tr>
			<td>1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride</td>
			<td>TCI</td>
			<td>424331-25 g</td>
			<td>CAS No: 25952-53-8</td>
		</tr>
		<tr>
			<td>1,4-Dioxane</td>
			<td>SAMCHUN</td>
			<td>D0654-1 kg</td>
			<td>CAS No: 123-91-1</td>
		</tr>
		<tr>
			<td>1-Hydroxybenzotriazole hydrate</td>
			<td>Aldrich</td>
			<td>219-989-7-50 g</td>
			<td>CAS No: 123333-53-9</td>
		</tr>
		<tr>
			<td>2,6-Lutidine</td>
			<td>Alfa Aesar</td>
			<td>A10478-AP, 500 mL</td>
			<td>CAS No: 108-48-5</td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>SAMCHUN</td>
			<td>A0127-18&#160; L</td>
			<td>CAS No: 75-05-8</td>
		</tr>
		<tr>
			<td>Acetonitrile-d3</td>
			<td>Cambridge Isotope Laboratories,</td>
			<td>15G-744-25 g</td>
			<td>CAS No: 2206-26-0</td>
		</tr>
		<tr>
			<td>Aluminum chloride hexahydrate</td>
			<td>Aldrich</td>
			<td>231-208-1, 500 g</td>
			<td>CAS No : 7784-13-6</td>
		</tr>
		<tr>
			<td>Bruker AVANCE III HD (400 MHz) spectrometer</td>
			<td>Bruker</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform-d</td>
			<td>Cambridge Isotope Laboratories,</td>
			<td>&#160;100 g</td>
			<td>CAS No: 865-49-6</td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>SAMCHUN</td>
			<td>M0822-18 L</td>
			<td>CAS No: 75-09-2</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide-d6</td>
			<td>Cambridge Isotope Laboratories,</td>
			<td>25 g</td>
			<td>CAS No: 2206-27-1</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>EMSURE</td>
			<td>&#160;1009831000,1L</td>
			<td>CAS No: 64-17-5</td>
		</tr>
		<tr>
			<td>Ethyl acetate</td>
			<td>SAMCHUN</td>
			<td>E0191-18 L</td>
			<td>CAS No: 141-78-6</td>
		</tr>
		<tr>
			<td>High resolution mass spectra/MALDI-TOF/TOF Mass Spectrometry</td>
			<td>AB SCIEX</td>
			<td>4800 Plus</td>
			<td>High resolution mass spectra</td>
		</tr>
		<tr>
			<td>JASCO P-2000</td>
			<td>JASCO</td>
			<td>P-2000</td>
			<td>For optical rotation</td>
		</tr>
		<tr>
			<td>Lithium aluminum hydride</td>
			<td>TCI</td>
			<td>L0203-100 g</td>
			<td>CAS No: 16853-85-3</td>
		</tr>
		<tr>
			<td>L-Selectride, 1 M solution in THF</td>
			<td>Acros</td>
			<td>176451000, 100 mL</td>
			<td>CAS No: 38721-52-7</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>SAMCHUN</td>
			<td>M0585-18 L</td>
			<td>CAS No: 67-56-1</td>
		</tr>
		<tr>
			<td>N-[(9H-Fluoren-9-ylmethoxy)carbonyl]-&#946;-alanine</td>
			<td>TCI</td>
			<td>F08825G-5 g</td>
			<td>CAS No: 35737-10-1</td>
		</tr>
		<tr>
			<td>N-Ethyldiisopropylamine</td>
			<td>Aldrich</td>
			<td>230-392-0, 100 mL</td>
			<td>CAS No: 7087-68-5</td>
		</tr>
		<tr>
			<td>n-Hexane</td>
			<td>SAMCHUN</td>
			<td>H0114-18 L</td>
			<td>CAS No: 110-54-3</td>
		</tr>
		<tr>
			<td>Ninhydrin</td>
			<td>Alfa Aesar</td>
			<td>A10409-250 g</td>
			<td>CAS No: 485-47-2</td>
		</tr>
		<tr>
			<td>p-Anisaldehyde</td>
			<td>aldrich</td>
			<td>A88107-5 g</td>
			<td>CAS No: 123-11-5</td>
		</tr>
		<tr>
			<td>Phosphomolybdic acid hydrate</td>
			<td>TCI</td>
			<td>P1910-100 g</td>
			<td>CAS No: 51429-74-4</td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>D.S.P</td>
			<td>703301-500 g</td>
			<td>CAS No: 26628-22-8</td>
		</tr>
		<tr>
			<td>Sodium Hydride 60% dispersion in mineral oil</td>
			<td>Sigma-Aldrich</td>
			<td>452912-100 G</td>
			<td>CAS No: 7646-69-7</td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>DUKSAN</td>
			<td>A31226-1 kg</td>
			<td>CAS No: 1310-73-2</td>
		</tr>
		<tr>
			<td>Sodium sulfate</td>
			<td>SAMCHUN</td>
			<td>S1011-1 kg</td>
			<td>CAS No: 7757-82-6</td>
		</tr>
		<tr>
			<td>Thin Layer Chromatography (TLC)</td>
			<td>Merck</td>
			<td>100390</td>
			<td></td>
		</tr>
		<tr>
			<td>Tert-Butyldimethylsilyl trifluoromethanesulfonate, 98%</td>
			<td>Aldrich</td>
			<td>274-102-0, 25 g</td>
			<td>CAS NO: 69739-34-0</td>
		</tr>
		<tr>
			<td>Tetrahydrofuran</td>
			<td>SAMCHUN</td>
			<td>T0148-18 L</td>
			<td>CAS No: 109-99-9</td>
		</tr>
		<tr>
			<td>Triethylethylamine</td>
			<td>DAEJUNG</td>
			<td>8556-4400-1 L</td>
			<td>CAS No: 121-44-8</td>
		</tr>
		<tr>
			<td>UV light</td>
			<td>Korea Ace Sci</td>
			<td>TN-4C</td>
			<td>254 nm</td>
		</tr>
		<tr>
			<td>Zinc chloride, anhydrous, 98+%</td>
			<td>Alfa Aesar</td>
			<td>A16281-22100 g</td>
			<td>CAS No : 7646-85-7</td>
		</tr>
	</tbody>
</table>

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.

Here, we report the synthesis of enantiopure aziridine-2-carboxylates. The diastereomeric mixture of (R)-(1R,2S,5R)-2-isopropyl-5-methylcyclohexyl1-((R)-1-phenylethyl)aziridine-2-carboxylate (2) and (S)-(1R,2S,5R)-2-isopropyl-5-methylcyclohexyl1-((R)-1-phenylethyl)aziridine-2-carboxylate (3) (4.1 g, 90%) were prepared in quantitative yield from 2,3 -dibromopropane (-)-mentholyl ester and (1R</em...

Watch this Scientific Journal Video about Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine at JoVE.com

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.

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 ...

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