Name: microwave-assisted intramolecular dehydrogenative diels-alder reactions for the synthesis of functionalized naphthalenes/solvatochromic dyes
Uploaded: 2013-04-01T13:00:00
Description: Watch this Scientific Journal Video about Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes at JoVE.com

We thank the National Science Foundation (CHE0910597) and the National Institutes of Health (P50-GM067982) for supporting this work. We are grateful to professor Michael Trakselis (University of Pittsburgh) for helpful discussions regarding fluorescence measurements. We acknowledge Kristy Gogick and Robin Sloan (University of Pittsburgh) for their assistance in collecting fluorescence data.

1. Microwave-assisted Dehydrogenative DA Reaction
<ol>
	<li>Add the para-chloro-styrene derivative (0.045 g, 0.18 mmol) and 1,2-dichloroethane (3 ml) to a 2-5 ml microwave irradiation vial equipped with a stir bar to create a 0.060 M solution. This concentration is used because higher concentrations lead to the formation of undesired products.</li>
	<li>Cap the microwave irradiation vial and place it in the microwave synthesizer cavity.</li>
	<li>Irradiate the solution at 180 &deg;C for 200 min with stirring and with f...

<ol>
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Lett. 13 (19), 5390-5393 (2011).</li><li>Chackalamannil, 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=A+facile+Diels-Alder+route+to+dihydronaphthofuranones.">A facile Diels-Alder route to dihydronaphthofuranones.</a> Tetrahedron Lett. 41 (21), 4043-4047 (2000).</li><li>Ruijter, E., 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=Synthesis+of+Polycyclic+Alkaloid-Type+Compounds+by+an+N-Acyliminium+-Pictet-Spengler/Diels-Alder+Sequence.">Synthesis of Polycyclic Alkaloid-Type Compounds by an N-Acyliminium -Pictet-Spengler/Diels-Alder Sequence.</a> Synlett. 2010, 2485-2489 (2010).</li><li>Toyota, M., Terashima, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+synthesis+of+the+basic+carbon+framework+of+fredericamycin+A.+Promising+routes+for+the+spiro+chiral+center+construction+of+the+CD-ring+system.">A novel synthesis of the basic carbon framework of fredericamycin A. Promising routes for the spiro chiral center construction of the CD-ring system.</a> Tetrahedron Lett. 30 (7), 829-832 (1989).</li><li>de Koning, C. B., Rousseau, A. L., van Otterlo, W. A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modern+methods+for+the+synthesis+of+substituted+naphthalenes.">Modern methods for the synthesis of substituted naphthalenes.</a> Tetrahedron. 59 (1), 7-36 (2003).</li><li>Johnson, I., Spence, M. T. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Molecular Probes Handbook, A Guide to Fluorescent Probes and Labeling Technologies. , 1051 (2010).</li><li>Fern&#225;ndez-Su&#225;rez, M., Ting, A. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+probes+for+super-resolution+imaging+in+living+cells.">Fluorescent probes for super-resolution imaging in living cells.</a> Nat. Rev. Mol. Cell. Biol. 9 (12), 929-943 (2008).</li><li>Kappe, O. C., Dallinger, D., Murphree, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Practical Microwave Synthesis for Organic Chemists. , (2009).</li><li>Kocsis, L. S., Benedetti, E., Brummond, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Thermal+Dehydrogenative+Diels-Alder+Reaction+of+Styrenes+for+the+Concise+Synthesis+of+Functionalized+Naphthalenes.">A Thermal Dehydrogenative Diels-Alder Reaction of Styrenes for the Concise Synthesis of Functionalized Naphthalenes.</a> Org. Lett. 14 (17), 4430-4433 (2012).</li><li>Benedetti, E., Kocsis, L. S., Brummond, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+Photophysical+Properties+of+a+Series+of+Cyclopenta[b]naphthalene+Solvatochromic+Fluorophores.">Synthesis and Photophysical Properties of a Series of Cyclopenta[b]naphthalene Solvatochromic Fluorophores.</a> J. Am. Chem. Soc. 134 (30), 12418-12421 (2012).</li><li>OriginLab Corporation. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Origin 8 User Guide. , (2007).</li></ol>

Microwave-Assisted Dehydrogenative DA Reaction
The intramolecular dehydrogenative DA reaction of styrenyl precursors by microwave irradiation (MWI) produces diverse naphthalene structures in high yields of 71-100% and short reaction times, requiring as little as 30 min (Figure 1) 18. The most difficult aspect of performing the dehydrogenative DA reaction is solvent selection, which is often complicated because a variety of solvent characteristics need to be considere...

Small molecule design and synthesis is critical to the development of a range of scientific fields that includes pharmaceuticals, pesticides, organic dyes, and many more 1. The Diels-Alder (DA) and dehydro-Diels-Alder (DDA) reactions are especially powerful tools in the synthesis of small cyclic and aromatic compounds 2-4. Additionally, thermal dehydrogenative DA reactions of styrene dienes with alkyne dienophiles provide a potentially beneficial route to the synthesis of aromatic compounds by initially forming cycloadducts that can further aromatize under oxidative conditions 5. By employing a thermal intramolecular dehydrogenative DA reaction of styrene dienes with alkynes, the problems typically associated with utilizing styrene as a diene, such as undesired [2 + 2] cycloaddition 5,6 and polymerization reactions 7 and poor regioselectivity, are alleviated and naphthalene compounds can be generated.
The thermal intramolecular dehydrogenative DA reaction of styrenes with alkynes is not without considerable issues. First, most reactions suffer from low yields, long reaction times, and high reaction temperatures 8-11. Additionally, many reactions do not promote exclusive formation of the naphthalene product; both naphthalene and dihydronaphthalene are produced, often as inseparable mixtures by column chromatography 11,12. The tethers of the precursor styrene-ynes are also restricted to include heteroatoms and/or carbonyl moieties. Only one example is reported for an all carbon-containing tether, requiring conditions of 250 &deg;C neat for 48 hr in order to obtain naphthalene formation 10.
In addition to limited variety within the tethers of the starting materials, one of the most severe constraints of this methodology is the lack of functionality tolerated under the conventional thermal conditions. The alkyne terminus of the starting material is either unsubstituted or appended with a phenyl or trimethylsilyl (TMS) moiety 8-13. In one instance, an ester at the alkyne terminus is shown to undergo the dehydrogenative DA reaction, but this results in a mixture of naphthalene and dihydronaphthalene products 11. A later proposal suggests that a TMS group appended to the alkyne terminus is necessary to achieve exclusive naphthalene formation in high yields 10. The deficiency of diverse functionality reported for thermal dehydrogenative DA reactions severely limits the potential of this reaction toward the assembly of unique naphthalene structures.
The desire for variation in naphthalene structures stems from their function as small molecule building blocks in several scientific fields, especially organic fluorescent dyes 14,15. The excellent spatial resolution and response-times of small organic dyes for monitoring real-time events 16 has led to the development of hundreds of commercially available fluorescent compounds. Many of these dyes are naphthalenes with discrete photophysical and chemical properties 15. Choosing fluorescent dyes with specific properties to monitor individual functions is challenging, which leads to an increasing need for new classes of fluorophores with more diverse photophysical properties. To this end, a thermal intramolecular dehydrogenative DA reaction of styrenes with alkynes that allows for diversification of a unique naphthalene scaffold would be potentially beneficial with application to developing new naphthalene-containing fluorescent dyes.
As an alternative to conventional heating, microwave-assisted chemistry is advantageous because it offers more uniform heating of the chemical sample, which leads to higher chemical yields, faster reaction rates, milder reaction conditions, and often different selectivity of products 17. Employing microwave-assisted versus conventional heating conditions for the intramolecular dehydrogenative DA reaction of styrenes serves to eliminate many of the problems associated with this methodology by reducing reaction time from days to minutes, increasing previously poor yields, lowering reaction temperatures, and offering more selective formation of the desired naphthalene product. Microwave-assisted reaction conditions may also be more likely to facilitate incorporation of a greater variety of functionality into the naphthalene products that was previously unattainable. Only one prior example has been reported utilizing microwave-assisted conditions for the dehydrogenative DA reaction in which a 90% yield of both naphthalene and dihydronaphthalene was obtained in as little as 15 min at 170 &deg;C 12.
Herein is reported a microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives that leads to the exclusive formation of functionalized and diverse naphthalene products in as little as 30 min and in high to quantitative yields 18. The utility of this protocol is further demonstrated by the one-step conversion of a naphthalene product into a novel solvatochromic fluorescent dye with photophysical properties which rival that of the popular commercially available dye Prodan 19.

<table border="1">
	<tbody>
		<tr>
			<td>Reagent/Material</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>1,2-Dichloroethane, ACS reagent &ge;99.0%</td>
			<td>Sigma-Aldrich</td>
			<td>319929</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>SiliaPlate G TLC - glass-backed, 250 &mu;m</td>
			<td>Silicycle</td>
			<td>TLG-R10011B-323</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ethyl acetate, certified ACS &ge;99.5%</td>
			<td>Fisher Scientific</td>
			<td>E14520</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Hexanes, certified ACS &ge;98.5%</td>
			<td>Fisher Scientific</td>
			<td>H29220</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Silica gel, standard grade</td>
			<td>Sorbent Technologies</td>
			<td>30930M</td>
			<td>60 A, 40-63 &mu;M (230 x 400 mesh)</td>
		</tr>
		<tr>
			<td>RuPhos palladacycle</td>
			<td>Strem</td>
			<td>46-0266</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Nitrogen gas</td>
			<td>Matheson TRIGAS</td>
			<td>NI304</td>
			<td>Nitrogen 304cf, industrial</td>
		</tr>
		<tr>
			<td>Lithium bis(trimethylsilyl) amide solution</td>
			<td>Sigma-Aldrich</td>
			<td>225770</td>
			<td>1.0 M solution in THF</td>
		</tr>
		<tr>
			<td>Tetrahydrofuran anhydrous &ge;99.9%</td>
			<td>Sigma-Aldrich</td>
			<td>401757</td>
			<td>Inhibitor-free</td>
		</tr>
		<tr>
			<td>Dimethylamine solution</td>
			<td>Sigma-Aldrich</td>
			<td>391956</td>
			<td>2.0 M solution in THF</td>
		</tr>
		<tr>
			<td>Ammonium chloride</td>
			<td>Fisher Scientific</td>
			<td>A661-500</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Sodium sulfate, anhydrous (granular)</td>
			<td>Fisher Scientific</td>
			<td>S421-500</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Chromatography column</td>
			<td>Chemglass</td>
			<td>CG-1188-04</td>
			<td>&frac12; in ID x 18in E.L.</td>
		</tr>
		<tr>
			<td>Cyclohexane, &ge;99.0%</td>
			<td>Fisher Scientific</td>
			<td>C556-1</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Toluene anhydrous, 99.8%</td>
			<td>Sigma-Aldrich</td>
			<td>24451</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>1,4-Dioxane anhydrous, 99.8%</td>
			<td>Sigma-Aldrich</td>
			<td>296309</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Tetrahydrofuran anhydrous, &ge;99.9%</td>
			<td>Sigma-Aldrich</td>
			<td>186562</td>
			<td>250 ppm BHT as inhibitor</td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Sigma-Aldrich</td>
			<td>650463</td>
			<td>Chromasolv Plus</td>
		</tr>
		<tr>
			<td>Chloroform, &ge;99.8%</td>
			<td>Fisher Scientific</td>
			<td>C298-1</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Acetonitrile anhydrous, 99.8%</td>
			<td>Sigma-Aldrich</td>
			<td>271004</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide, &ge;99.9%</td>
			<td>Fisher Scientific</td>
			<td>D128</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Ethyl alcohol</td>
			<td>Pharmco-AAPER</td>
			<td>11ACS200</td>
			<td>Absolute</td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microwave Synthesizer</td>
			<td>Biotage</td>
			<td>Biotage Initiator Exp</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microwave Vial</td>
			<td>Biotage</td>
			<td>352016</td>
			<td>0.5 - 2 ml</td>
		</tr>
		<tr>
			<td>Microwave Vial</td>
			<td>Biotage</td>
			<td>351521</td>
			<td>2 - 5 ml</td>
		</tr>
		<tr>
			<td>Microwave Vial Cap</td>
			<td>Biotage</td>
			<td>352298</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microwave Synthesizer</td>
			<td>Anton Paar</td>
			<td>Monowave 300</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microwave Vial G4</td>
			<td>Anton Paar</td>
			<td>99135</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Microwave Vial Cap</td>
			<td>Anton Paar</td>
			<td>88882</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>NMR Spectrometer</td>
			<td>Bruker</td>
			<td>Avance</td>
			<td>300 or 400 MHz</td>
		</tr>
		<tr>
			<td>UV-Visible Spectrometer</td>
			<td>PerkinElmer</td>
			<td>Lamda 9</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Spectrophotometer cell</td>
			<td>Starna Cells</td>
			<td>29B-Q-10</td>
			<td>Spectrosil quartz, path length 10 mm, semi-micro, black wall</td>
		</tr>
		<tr>
			<td>Spectrofluorometer</td>
			<td>HORIBA Jobin Yvon</td>
			<td>FluoroMax-3 S4</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Fluorometer cell</td>
			<td>Starna Cells</td>
			<td>29F-Q-10</td>
			<td>Spectrosil quartz, path length 10 mm, semi-micro</td>
		</tr>
	</tbody>
</table>

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 irradiation (MWI) of styrenyl derivatives at 180 &deg;C results in complete cyclopenta[b]naphthalene formation in as little as 30 min and in high to quantitative yields (Figure 1) 18. No dihydronaphthalene byproduct is observed, and by 1H NMR spectroscopy the products appear pure without the need for additional purification after irradiation (Figure 2). Various changes to the naphthalene framework are well tolerated utilizing these the...

Watch this Scientific Journal Video about Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes at JoVE.com

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

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 ...

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Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

The Preparation and Properties of Thermo-reversibly Cross-linked Rubber Via Diels-Alder Chemistry

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ethylene-propylene rubber, grafted with maleic anhydride, is thermo-reversibly cross-linked in two steps. The pending anhydride moieties are first modified with furfurylamine to graft furan groups to the rubber backbone. These pendant furan groups are then cross-linked with a bis-maleimide via a Diels-Alder coupling reaction. Both reactions can be performed under a broad range of experimental conditions and can easily be applied on a large scale. The material properties of the resulting Diels-Alder cross-linked rubbers are similar to a peroxide-cured ethylene/propylene/diene rubber (EPDM) reference. The cross-links break at elevated temperatures (&#62; 150 &#176;C) via the retro-Diels-Alder reaction and can be reformed by thermal annealing at lower temperatures (50-70 &#176;C). Reversibility of the system was proven with infrared spectroscopy, solubility tests and mechanical properties. Recyclability of the material was also shown in a practical way, i.e., by cutting a cross-linked sample into small parts and compression molding them into new samples displaying comparable mechanical properties, which is not possible for conventionally cross-linked rubbers.

A simple two-step approach involving rubber modification and cross-linking yields fully reworkable, elastic rubber products.

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ...

Synthesis of Plant Phenol-derived Polymeric Dyes for Direct or Mordant-based Hair Dyeing

Effective hair dyeing through in situ incubation of keratin hair with the products of fungal laccase-catalyzed polymerization of plant phenols has been previously demonstrated. However, the dyeing process takes a long time to complete compared to commercial hair-dyeing products. To overcome this bottleneck, pre-synthesized polymeric products of the oxidative reaction of Trametes versicolor laccase on catechin and catechol, either with or without mordant agents (e.g., FeSO4), were here employed to achieve permanent keratin hair dyeing in various colors and shades. The laccase action in acidic sodium acetate buffer led to a deep black coloration after coupling reactions between the plant phenols. The colored dye products were then desalted and concentrated with ultrafiltration. The dyes, with or without mordant agents, caused a significant increase in &#916;E values (i.e., color difference value) in gray human hair within 2.5 hours. In addition, different keratin colors and shades were induced depending upon the mordanting and pH changes. The dyed hair also exhibited a strong resistance to detergent treatments, indicating that our methods can give rise to permanent hair dyeing.&#160;Overall, our work has provided novel insight into developing eco-friendly hair-dyeing methods as alternatives to commercial toxic diamine-based dyes.

Here, we present a protocol to use pre-synthesized polymeric products derived from fungal laccase-catalyzed polymerization of plant phenols, either with or without mordant agents (e.g., FeSO4), to induce detergent-resistant keratin hair dyeing within 2.5 hours.

Effective hair dyeing through in situ incubation of keratin hair with the products of fungal laccase-catalyzed polymerization of plant phenols has been ...

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate glycosyl donor. Following azido-nitration of a glycal, the product 2-azido-1-nitrate ester can be hydrolyzed under microwave-assisted irradiation. This transformation is usually achieved using strongly nucleophilic reagents and extended reaction times. Microwave irradiation induces hydrolysis, in the absence of reagents, with short reaction times. Following denitration, the intermediate anomeric alcohol is converted, in the same pot, to the corresponding 2-azido-1-trichloroacetimidate.

A 2-azido-1-nitrate-ester can be converted to the corresponding 2-azido-1-trichloroacetimidate in a one-pot procedure. The goal of the manuscript is to demonstrate utility of the microwave reactor in carbohydrate synthesis.

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Enzymatic Cascade Reactions for the Synthesis of Chiral Amino Alcohols from L-lysine

Amino alcohols are versatile compounds with a wide range of applications. For instance, they have been used as chiral scaffolds in organic synthesis. Their synthesis by conventional organic chemistry often requires tedious multi-step synthesis processes, with difficult control of the stereochemical outcome. We present a protocol to enzymatically synthetize amino alcohols starting from the readily available L-lysine in 48 h. This protocol combines two chemical reactions that are very difficult to conduct by conventional organic synthesis. In the first step, the regio- and diastereoselective oxidation of an unactivated C-H bond of the lysine side-chain is catalyzed by a dioxygenase; a second regio- and diastereoselective oxidation catalyzed by a regiodivergent dioxygenase can lead to the formation of the 1,2-diols. In the last step, the carboxylic group of the alpha amino acid is cleaved by a pyridoxal-phosphate (PLP) decarboxylase (DC). This decarboxylative step only affects the alpha carbon of the amino acid, retaining the hydroxy-substituted stereogenic center in a beta/gamma position. The resulting amino alcohols are therefore optically enriched. The protocol was successfully applied to the semipreparative-scale synthesis of four amino alcohols. Monitoring of the reactions was conducted by high performance liquid chromatography (HPLC) after derivatization by 1-fluoro-2,4-dinitrobenzene. Straightforward purification by solid-phase extraction (SPE) afforded the amino alcohols with excellent yields (93% to &#62;95%).

Chiral amino alcohols are versatile molecules for use as scaffolds in organic synthesis. Starting from L-lysine, we synthesize amino alcohols by an enzymatic cascade reaction combining diastereoselective C-H oxidation catalyzed by dioxygenase followed by cleavage of the carboxylic acid moiety of the corresponding hydroxyl amino acid by a decarboxylase.

Amino alcohols are versatile compounds with a wide range of applications. For instance, they have been used as chiral scaffolds in organic synthesis. ...

Pretargeted Radioimmunotherapy Based on the Inverse Electron Demand Diels-Alder Reaction

While radioimmunotherapy (RIT) is a promising approach for the treatment of cancer, the long pharmacokinetic half-life of radiolabeled antibodies can result in high radiation doses to healthy tissues. Perhaps not surprisingly, several different strategies have been developed to circumvent this troubling limitation. One of the most promising of these approaches is pretargeted radioimmunotherapy (PRIT). PRIT is predicated on decoupling the radionuclide from the immunoglobulin, injecting them separately, and then allowing them to combine in vivo at the target tissue. This approach harnesses the exceptional tumor-targeting properties of antibodies while skirting their pharmacokinetic drawbacks, thereby lowering radiation doses to non-target tissues and facilitating the use of radionuclides with half-lives that are considered too short for use in traditional radioimmunoconjugates. Over the last five years, our laboratory and others have developed an approach to in vivo pretargeting based on the inverse electron-demand Diels-Alder (IEDDA) reaction between trans-cyclooctene (TCO) and tetrazine (Tz). This strategy has been successfully applied to pretargeted positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging with a variety of antibody-antigen systems. In a pair of recent publications, we have demonstrated the efficacy of IEDDA-based PRIT in murine models of pancreatic ductal adenocarcinoma and colorectal carcinoma. In this protocol, we describe protocols for PRIT using a 177Lu-DOTA-labeled tetrazine radioligand ([177Lu]Lu-DOTA-PEG7-Tz) and a TCO-modified variant of the colorectal cancer targeting huA33 antibody (huA33-TCO). More specifically, we will describe the construction of huA33-TCO, the synthesis and radiolabeling of [177Lu]Lu-DOTA-PEG7-Tz, and the performance of in vivo biodistribution and longitudinal therapy studies in murine models of colorectal carcinoma.

This protocol describes the synthesis and characterization of a trans-cyclooctene (TCO)-modified antibody and a 177Lu-labeled tetrazine (Tz) radioligand for pretargeted radioimmunotherapy (PRIT). In addition, it details the use of these two constructs for in vivo biodistribution and longitudinal therapy studies in a murine model of colorectal cancer.

While radioimmunotherapy (RIT) is a promising approach for the treatment of cancer, the long pharmacokinetic half-life of radiolabeled antibodies can ...

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 ...

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it efficient in both time and resources and utilizes water as the solvent. 3-Aminocrotononitrile or an appropriate &#945;-cyanoketone is combined with an aryl hydrazine and dissolved in 1 M HCl. The mixture is then heated in a microwave reactor at 150 &#176;C, typically for 10-15 min. The product can be readily obtained by basifying the solution with 10% NaOH and isolating the desired compound with a simple vacuum filtration. The use of water as a solvent in this reaction lends to its ease and utility in production, and this method is easily reproducible with a variety of functional groups. Typical isolated yields range from 70-90%, and reactions can be performed on the milligram to gram scale with little to no change in observed yields. Some of the applications of these molecules and their derivatives include pesticides, anti-malarials, and chemotherapeutics, among many others.

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

1-Aryl-1H-pyrazole-5-amines are prepared from aryl hydrazines combined with either 3-aminocrotononitrile or an &#945;-cyanoketone in a 1 M HCl solution using a microwave reactor. Most reactions are done in 10-15 minutes and pure product can be obtained via vacuum filtration with typical isolated yields of 70-90%.

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...