Name: facile protocol for the synthesis of self-assembling polyamine-based peptide amphiphiles (ppas) and related biomaterials
Uploaded: 2018-06-25T14:00:00
Description: Watch this Scientific Journal Video about Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles PPAs and Related Biomaterials at JoVE.com

This project was funded by the University of Nebraska Medical Center (Start-up funds, MC-S); NIH-COBRE, 5P20GM103480 (T. Bronich) and the American Chemical Society, PRF# 57434-DNI7(MC-S).

1. General Protocol for Synthesis of PPAs
<ol>
	<li>Calculate the scale of synthesis (usually mmol). This scale is based on the mass of the target PPA amount. Keep in mind that the reaction efficiency of SPPS gradually decreases with an increase of amino acid sequence. Therefore, the exact reaction efficiency is difficult to calculate.</li>
	<li>Calculate the weight of the resin to be used according to the loading of the resin. The loading is found on the container or the analysis protocol of the resin and expressed in...

<ol>
	<li>Cui, H., Pashuck, E. T., Velichko, Y. S., Weigand, S. J., Cheetham, A. G., Newcomb, C. J., Stupp, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+and+x-ray-triggered+crystallization+at+long+range+in+self-assembling+filament+networks.">Spontaneous and x-ray-triggered crystallization at long range in self-assembling filament networks.</a> Science. 327, 555-559 (2010).</li><li>Pashuck, E. T., Cui, H., Stupp, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tuning+supramolecular+rigidity+of+peptide+fibers+through+molecular+structure.">Tuning supramolecular rigidity of peptide fibers through molecular structure.</a> Journal of the American Chemical Society. 132, 6041-6046 (2010).</li><li>Stupp, S. I., Zha, R. H., Palmer, L. C., Cui, H., Bitton, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembly+of+biomolecular+soft+matter.">Self-assembly of biomolecular soft matter.</a> Faraday Discussions. 166, 9-30 (2013).</li><li>Conda-Sheridan, M., Lee, S. S., Preslar, A. T., Stupp, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Esterase-activated+release+of+naproxen+from+supramolecular+nanofibres.">Esterase-activated release of naproxen from supramolecular nanofibres.</a> Chemical Communications. 50, 13757-13760 (2014).</li><li>Mata, A., Palmer, L., Tejeda-Montes, E., Stupp, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+of+biomolecules+for+nanoengineered+biomaterials+for+regenerative+medicine.">Design of biomolecules for nanoengineered biomaterials for regenerative medicine.</a> Nanotechnology in Regenerative Medicine. , 39-49 (2012).</li><li>Samad, M. B., Chhonker, Y. S., Contreras, J. I., McCarthy, A., McClanahan, M. M., Murry, D. J., Conda-Sheridan, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Developing+Polyamine-Based+Peptide+Amphiphiles+with+Tunable+Morphology+and+Physicochemical+Properties.">Developing Polyamine-Based Peptide Amphiphiles with Tunable Morphology and Physicochemical Properties.</a> Macromolecular bioscience. 17, (2017).</li><li>Nel, A. E., M&#228;dler, L., Velegol, D., Xia, T., Hoek, E. M., Somasundaran, P., Klaessig, F., Castranova, V., Thompson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+biophysicochemical+interactions+at+the+nano-bio+interface.">Understanding biophysicochemical interactions at the nano-bio interface.</a> Nature Materials. 8, 543 (2009).</li><li>Gujrati, M., Malamas, A., Shin, T., Jin, E., Sun, Y., Lu, Z. -. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multifunctional+cationic+lipid-based+nanoparticles+facilitate+endosomal+escape+and+reduction-triggered+cytosolic+siRNA+release.">Multifunctional cationic lipid-based nanoparticles facilitate endosomal escape and reduction-triggered cytosolic siRNA release.</a> Molecular Pharmaceutics. 11, 2734-2744 (2014).</li><li>Zhu, Y., Li, J., Kanvinde, S., Lin, Z., Hazeldine, S., Singh, R. K., Oupicky&#769;, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-immolative+polycations+as+gene+delivery+vectors+and+prodrugs+targeting+polyamine+metabolism+in+cancer.">Self-immolative polycations as gene delivery vectors and prodrugs targeting polyamine metabolism in cancer.</a> Molecular Pharmaceutics. 12, 332-341 (2014).</li><li>Planas-Portell, J., Gallart, M., Tiburcio, A. F., Altabella, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Copper-containing+amine+oxidases+contribute+to+terminal+polyamine+oxidation+in+peroxisomes+and+apoplast+of+Arabidopsis+thaliana.">Copper-containing amine oxidases contribute to terminal polyamine oxidation in peroxisomes and apoplast of Arabidopsis thaliana.</a> BMC Plant Biology. 13, 109 (2013).</li><li>Nash, I. A., Bycroft, B. W., Chan, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dde+-+A+selective+primary+amine+protecting+group:+A+facile+solid+phase+synthetic+approach+to+polyamine+conjugates.">Dde - A selective primary amine protecting group: A facile solid phase synthetic approach to polyamine conjugates.</a> Tetrahedron Letters. 37, 2625-2628 (1996).</li><li>Ralhan, K., KrishnaKumar, V. G., Gupta, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Piperazine+and+DBU:+a+safer+alternative+for+rapid+and+efficient+Fmoc+deprotection+in+solid+phase+peptide+synthesis.">Piperazine and DBU: a safer alternative for rapid and efficient Fmoc deprotection in solid phase peptide synthesis.</a> RSC Advances. 5, 104417-104425 (2015).</li><li>Casero, R. A., Marton, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+polyamine+metabolism+and+function+in+cancer+and+other+hyperproliferative+diseases.">Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases.</a> Nature Reviews Drug Discovery. 6, 373 (2007).</li><li>Wuts, P. G. M., Greene, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Protection for the Amino Group. In Greene's Protective Groups in Organic Synthesis. , 696-926 (2006).</li><li>Palasek, S. A., Cox, Z. J., Collins, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Limiting+racemization+and+aspartimide+formation+in+microwave-enhanced+Fmoc+solid+phase+peptide+synthesis.">Limiting racemization and aspartimide formation in microwave-enhanced Fmoc solid phase peptide synthesis.</a> Journal of Peptide Science. 13, 143-148 (2007).</li></ol>

The protocols described here can be used to synthesize PPAs as wells as PAs and related peptide-based molecules (such as hybrid PA-peptoids). Although the synthesis of peptides using SPPS is a straightforward procedure, the synthesis of peptides containing biological homing molecules can be particularly challenging. Polyamines like spermine, spermidine, diethyelenetriamine, etc., can function as homing molecules for targeting cancer cells13. The PPAs can self-assemble into nanostructures ...

Self-assembling peptide amphiphiles (PAs) are a class of biomaterials typically comprised of the following segments: (a) hydrophilic head, (b) linker region, and (c) hydrophobic tail. Most PAs described in the literature possess a hydrophilic head comprised of charged or polar amino acid residues1,2,3,4. PAs have found a wide range of applications in biomedicine including drug delivery, disease diagnostics, regenerative medicine, etc.5. Based on their amino acid sequence, PAs can form a wide variety of nanostructures including spherical micelles, and nano-filaments. We have recently reported a class of hybrid polyamine-based peptide amphiphiles, termed PPAs6. The morphologies, self-assembling kinetics, and metabolic degradation, of these biomaterials, were found to be related to their solubilizing head group. Moreover, the PPA nanostructures did not show toxicity towards mammalian cells (MiaPaCa2 and HeLa cell lines) at the tested concentrations. PPA-based nanocarriers are attractive drug-delivery vehicles because: (1) polyamine uptake and metabolism has been shown to be increased in cancerous cells, (2) cationic nanostructures can achieve endosomal escape7,8, which leads to higher circulation and residence within a cell, and (3) they should have a distinct metabolic profile when compared with PA; for example, they will be more stable towards proteases found in the human body (although they maybe sensitive to other enzymes, such as amine oxidases)9,10. Also, PPAs have been found to have diverse morphologies, physicochemical properties, nanoparticle stiffness, and assembly kinetics depending on the length and charge of individual PPA molecule6. Herein, we describe a detailed protocol for the synthesis, identification, and purification of PPAs that can also be applied to the preparation of PAs or similar hybrid peptide molecules.
Because polyamines are not commonly commercially available in their protected forms, and because protecting the primary and secondary amines of polyamines is of utmost importance for conjugating them with amino acids and other molecules, we have outlined the synthetic steps to achieve their protection. The overall goal of this protocol is to provide a simple method for conjugating polyamines to amino acids. Polyamines lack a carboxylic group; thus, they cannot be coupled to Rink Amide or Wang resins. Instead, resins such as 2-chlorotrityl chloride are recommended for the synthetic protocol. The main challenge for PPA synthesis is the presence of primary and secondary amine functional groups. For our purposes, we protected all the secondary amines in the polyamine while keeping the primary amino group on the polyamine free to allow the coupling reaction. The reaction was done on a solid support following the principles of solid phase peptide synthesis (SPPS) to facilitate the work-up after each coupling and deprotection step. The following protocol is for both the manual and automated synthesis of PPAs (although the verification of some steps will be challenging in an automated system). The synthesis of these molecules can also be carried out on an automated synthesizer or with the aid of a microwave reactor (automated or semi-automated). The reaction scheme has been summarized in Figure 1.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57908/57908fig1.jpg" /> 
Figure 1: (A) A general reaction scheme for the synthesis of PPAs. (B) Representative polyamines that can be used to synthesized PPAs described here. <a href="/files/ftp_upload/57908/57908fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table>
	<tbody>
		<tr>
			<td>2-Chlorotrityl chloride resin&#160;</td>
			<td>AappTec</td>
			<td>RTZ001</td>
			<td></td>
		</tr>
		<tr>
			<td>SynthwareTM synthesis vessel&#160;</td>
			<td>Aldrich</td>
			<td>SYNP120050M</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Acros</td>
			<td>AC406920250</td>
			<td>Fisher Sci. Catalogue #</td>
		</tr>
		<tr>
			<td>Wrist Shaker</td>
			<td>Boekel Scientific</td>
			<td>401000-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Kaiser test kit</td>
			<td>Sigma-Aldrich</td>
			<td>60017</td>
			<td></td>
		</tr>
		<tr>
			<td>2-[(4,4-dimethyl-2,6-dioxocyclohex-1-ylidene)ethyl-amino]-ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>CDS004772</td>
			<td></td>
		</tr>
		<tr>
			<td>Anhydrous Methanol</td>
			<td>Acros</td>
			<td>AC610981000</td>
			<td>Fisher Sci. Catalogue #</td>
		</tr>
		<tr>
			<td>Chloranil test kit</td>
			<td>TCI</td>
			<td>TCC1771-KIT</td>
			<td>VWR Catalogue #</td>
		</tr>
		<tr>
			<td>Di-tert butyl di-carbonate&#160;</td>
			<td>Acros</td>
			<td>AC194670250</td>
			<td>Fisher Sci. Catalogue #</td>
		</tr>
		<tr>
			<td>Dimethylformamide</td>
			<td>Fisher Scientific</td>
			<td>BP1160-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrazine</td>
			<td>Acros</td>
			<td>AC296815000</td>
			<td>FIsher Sci. Catalogue #</td>
		</tr>
		<tr>
			<td>(2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate)</td>
			<td>p3biosystems</td>
			<td>31001</td>
			<td></td>
		</tr>
		<tr>
			<td>4-methyl piperidine&#160;</td>
			<td>Acros</td>
			<td>AC127515000</td>
			<td>FIsher Sci. Catalogue #</td>
		</tr>
		<tr>
			<td>Trifluoroacetic Acid</td>
			<td>AappTec</td>
			<td>CXZ035</td>
			<td></td>
		</tr>
		<tr>
			<td>Triisopropyl Silane</td>
			<td>Sigma-Aldrich</td>
			<td>233781</td>
			<td></td>
		</tr>
		<tr>
			<td>Ether</td>
			<td>Fisher Scientific</td>
			<td>E138-1</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-Cyano-4-hydroxycinnamic acid</td>
			<td>Sigma-Aldrich</td>
			<td>C8982</td>
			<td></td>
		</tr>
		<tr>
			<td>9-Aminoacridine</td>
			<td>Sigma-Aldrich</td>
			<td>92817</td>
			<td></td>
		</tr>
		<tr>
			<td>Fisherbrand&#160;Syringe Filters: PTFE Membrane</td>
			<td>Fisher Scientific</td>
			<td>09-730-21</td>
			<td></td>
		</tr>
	</tbody>
</table>

facile protocol for the synthesis of self-assembling polyamine-based peptide amphiphiles (ppas) and related biomaterials

Polyamine-based Peptide Amphiphiles (PPAs) are a new class of self-assembling amphiphilic biomaterials-related to the peptide amphiphiles (PAs). Traditional PAs possess charged amino acids as solubilizing groups (lysine, arginine), which are directly connected to a lipid segment or can contain a linker region made of neutral amino acids. Tuning the peptide sequence of PAs can yield diverse morphologies. Similarly, PPAs possess a hydrophobic segment and neutral amino acids, but also contain polyamine molecules as water solubilizing (hydrophilic) groups. As is the case with PAs, PPAs can also self-assemble into diverse morphologies, including small rods, twisted nano-ribbons, and fused nano-sheets, when dissolved in water. However, the presence of both primary and secondary amines on a single polyamine molecule poses a significant challenge when synthesizing PPAs. In this paper, we show a simple protocol, based on literature precedents, to achieve a facile synthesis of PPAs using solid phase peptide synthesis (SPPS). This protocol can be extended to the synthesis of PAs and other similar systems. We also illustrate the steps that are needed for cleavage from the resin, identification, and purification.

After the synthesis and purification and before physicochemical or biological evaluation, it is recommended the masses of the PPAs are re-checked and the purity ascertained using analytical HPLC. For material characterization or biological evaluation, PPAs need to have a purity of &#62;95%. Figure 2 shows the HPLC trace (Top) and MALDI spectra (Bottom) confirming the presence of the product. HPLC analytical systems will integrate the area under the curve (AUC...

Watch this Scientific Journal Video about Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles PPAs and Related Biomaterials at JoVE.com

Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles PPAs and Related Biomaterials

The synthesis of polyamine-based peptide amphiphiles (PPAs) is a significant challenge due to the presence of multiple amine nitrogens, which requires judicious use of protecting groups to mask these reactive functionalities. In this paper, we describe a facile method for the preparation of these new class of self-assembling molecules.

Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles (PPAs) and Related Biomaterials

Polyamine-based Peptide Amphiphiles (PPAs) are a new class of self-assembling amphiphilic biomaterials-related to the peptide amphiphiles (PAs). ...

This method can answer key questions on how to decorate peptide amphiphiles to polyamines and on the use of octagonal protecting groups The main advantage of this technique is that you can generate hybrid peptide amphiphiles with unprotected chemical building blocks containing multiple reactive sides. Demonstrating the procedure will be Mehdi, Nathalia and Krishnaiah, laboratory students from the Conda Sheridan Laboratory. First, carefully weigh out 2-Chlorotrityl chloride resin place the resin in a fritted, medium porocity, synthesis vessel with 50 milliliter capacity.Next, affix the synethesis vessel to a variable speed mechanical shaker and turn the vessel to a 45 degree angle to maximize agitation. Then add 15 milliliters of DCM to the resin. After allowing the resin beads to swell for 15 minutes, add eight equivalents of the desired polyamine to the resin, and allow it to react for five hours.After five hours, perform a kaiser test to confirm a successful reaction of the polyamine to the resin. Following this, protect the primary amine group by adding four equivalents of DDE in anhydrous methanol and shaking the reaction mixture overnight. On the following day, perform a kaiser test to confirm successful protection by the absence of blue color from the resin bead.Then, drain the DCM and wash the resin twice with a two to one mixture of DCM and DMF. Now, add 20 equivalents of Boc Anhydride in DCM to the resin and allow the reaction to proceed for three hours. After performing a chloranil test to confirm protection of the secondary amine, drain the solvent mixture and wash the resin twice with a two to one mixture of DCM and DMF.Following this, add 10 milliliters of a 2%solution of hydrazine in DMF to the resin. After shaking for one hour, perform a kaiser test to confirm successful deprotection of the primary amine. Next, mix four equivalents of the Fmoc protected amino acid, 3.95 equivalents of HBTU, and 15 equivalents of DIPEA.Add a one to one mixture of DCM and DMF and sonicate the cocktail until complete dissolution. Make sure the amino acid, coupling agent, and DIPEA are truly mixed and activated before adding the mixture to the resin. After waiting three to five minutes to ensure carboxylic acid activation, add the reaction mixture to the vessel containing the resin and allow the reaction to proceed for two to four hours at ambient temperature.Perform a kaiser or chloranil test at every step to confirm successful coupling. After performing a kaiser test to confirm successful coupling, deprotect the Fmoc group from the amino acid by adding 10 milliliters of a 20%solution of 4-Methylpyridine in DMF. Once the reaction is finished, perform a kaiser test to confirm successful deprotection of the amino acid.Then, wash the resin twice with 10 milliliters of DMF each wash lasting for 5 minutes, and finally with 10 milliliters of DCM for 10 minutes. After coupling all the required amino acids, conjugate the hydrophobic tail to the last amino acid by adding 10 equivalents of the desired carboxylic acid functionality to 9.5 equivalents of HBTU, and 12 equivalents of DIPEA. Sonicate the cocktail until complete dissolution, then add the cocktail to the vessel.Carry out the reaction for at least five hours, although it is advisable to carry it out overnight for the highest yield. Wash the resin with eight milliliters of DMF for two minutes, and twice with eight milliliters of DCM for five minutes. Before each addition, drain the solvent from the vessel.Once the last wash is performed, dry the resin under vacuum for 15 minutes. To prepare 15 milliliters of cleavage cocktail, add 14 milliliters of TFA to 0.5 milliliters of water, and 0.5 milliliters of Triisopropylsilane. Add this cleavage cocktail to the resin, and shake for two to four hours at room temperature.After the cleavage reaction is complete, collect the solution in a 50 milliliter round bottom flask. Then, concentrate the TFA in vacuo to one to two milliliters using a rotary evaporator at reduced pressure, while heating the mixture at 40 degrees Celsius After evaporation, add the obtained TFA solution, dropwise, to a round bottom flask containing 15 milliliters of anhydrous cold ether to precipitate the PPA. Next, add 5 milliliters anhydrous cold ether to the original flask containing the concentrated TFA solution.Sonicate to recover additional solids. Then, combine with the ether solution from the previous step. Cover the flask and place it inside the refrigerator overnight to maximize precipitation.On the following day, collect the precipitated material by vacuum filtration using a fine or medium pour size center disk filter funnel. Finally, wash the precipitate twice with five to ten milliliters of cold ether to remove any residual organics. The HPLC trace and MALDI Spectrum confirm the presence of the PPA product which should have a purity of greater than 95%for material characterization or biological evaluation.A single sharp peak is observed in the UV based HPLC trace and the MALDI Spectrum corresponds to that of the calculated molecular weight of the PPA within plus or minus one dalton. The self assembly of the PPAs can be visualized and analyzed by transmission electron microscopy, atomic force microscopy, small angle X-Ray scattering, scanning electron microscopy, and dynamic light scattering. Successful self assembly will result in well defined nanostructures, in both transmission electron microscopy and atomic force microscopy.Once mastered, this protocol can be done in three days if performed properly. While attempting this procedure, remember to purify the products and assess their purity before any subsequent studies. Following this procedure, other molecules, such as peptide amphiphiles, peptides, and peptide-polyamine hybrids can be prepared.After its development, this technique helps research in the field of self assembly peptide amphiphiles to explore the influence of polyamine nano structures in areas such as drug delivery, imaging, or catalysis After watching this video, you should have a good understanding of how to carry the synthesis of polyamine-based peptide amphiphiles and related peptide amphiphiles. Trifluoroacetic acid and 4-Methylpyridine can be hazardous, and precautions such as wearing gloves, lab coats and working in the fume hood should be taken while performing this procedure.

facile-protocol-for-synthesis-self-assembling-polyamine-based-peptide

Research

JoVE Journal

Chemistry

Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

Physical interactions among the lipid-embedded alpha-helical domains of membrane proteins play a crucial role in folding and assembly of membrane protein complexes and in dynamic processes such as transmembrane (TM) signaling and regulation of cell-surface protein levels. Understanding the structural features driving the association of particular sequences requires sophisticated biophysical and biochemical analyses of TM peptide complexes. However, the extreme hydrophobicity of TM domains makes them very difficult to manipulate using standard peptide chemistry techniques, and production of suitable study material often proves prohibitively challenging. Identifying conditions under which peptides can adopt stable helical conformations and form complexes spontaneously adds a further level of difficulty. Here we present a procedure for the production of homo- or hetero-dimeric TM peptide complexes from materials that are expressed in E. coli, thus allowing incorporation of stable isotope labels for nuclear magnetic resonance (NMR) or non-natural amino acids for other applications relatively inexpensively. The key innovation in this method is that TM complexes are produced and purified as covalently associated (disulfide-crosslinked) assemblies that can form stable, stoichiometric and homogeneous structures when reconstituted into detergent, lipid or other membrane-mimetic materials. We also present carefully optimized procedures for expression and purification that are equally applicable whether producing single TM domains or crosslinked complexes and provide advice for adapting these methods to new TM sequences.

Biophysical and biochemical studies of interactions among membrane-embedded protein domains face many technical challenges, the first of which is obtaining appropriate study material. This article describes a protocol for producing and purifying disulfide-stabilized transmembrane peptide complexes that are suitable for structural analysis by solution nuclear magnetic resonance (NMR) and other analytical applications.

Physical  interactions among the lipid-embedded alpha-helical domains of membrane  proteins play a crucial role in folding and assembly of membrane ...

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox reactions. The Cu (I) complex of the peptide model of a Cu (I) binding metallochaperone protein, which includes the sequence MTCSGCSRPG (underlined is conserved), was determined in solution under inert conditions by NMR spectroscopy.
NMR is a widely accepted technique for the determination of solution structures of proteins and peptides. Due to difficulty in crystallization to provide single crystals suitable for X-ray crystallography, the NMR technique is extremely valuable, especially as it provides information on the solution state rather than the solid state. Herein we describe all steps that are required for full three-dimensional structure determinations by NMR. The protocol includes sample preparation in an NMR tube, 1D and 2D data collection and processing, peak assignment and integration, molecular mechanics calculations, and structure analysis. Importantly, the analysis was first conducted without any preset metal-ligand bonds, to assure a reliable structure determination in an unbiased manner.

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

The NMR-solution structure of a metallochaperone model peptide with Cu (I) was determined, and a detailed protocol from sample preparation and 1D and 2D data collection to a three-dimensional structure is described.

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox ...

Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid phase by using combinatorial chemistry. One of the most well studied classes of peptidomimetics is peptoids. Peptoids are easy to synthesize and have been shown to be proteolysis-resistant and cell-permeable. Over the past decade, many useful protein ligands have been identified through screening of peptoid libraries. However, most of the ligands identified from peptoid libraries do not display high affinity, with rare exceptions. This may be due, in part, to the lack of chiral centers and conformational constraints in peptoid molecules. Recently, we described a new synthetic route to access peptide tertiary amides (PTAs). PTAs are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. With side chains on both &#945;-carbon and main chain nitrogen atoms, the conformation of these molecules are greatly constrained by sterical hindrance and allylic 1,3 strain. (Figure 1) Our study suggests that these PTA molecules are highly structured in solution and can be used to identify protein ligands. We believe that these molecules can be a future source of high-affinity protein ligands. Here we describe the synthetic method combining the power of both split-and-pool and sub-monomer strategies to synthesize a sample one-bead one-compound (OBOC) library of PTAs.

Peptide tertiary amides (PTAs) are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. Here we describe a synthetic method which combines&#160;both split-and-pool and sub-monomer strategies to synthesize a one-bead one-compound library of PTAs.

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid ...

Facile Preparation of Internally Self-assembled Lipid Particles Stabilized by Carbon Nanotubes

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled (functionalized) CNTs are used as stabilizers to produce Pickering type oil-in-water (O/W) emulsions. Lipids namely, Dimodan U and Phytantriol are used as emulsifiers, which in excess water self-assemble into the bicontinuous cubic Pn3m phase. This highly viscous phase is fragmented into smaller particles using a probe ultrasonicator in presence of conventional surfactant stabilizers or CNTs as done here. Initially, the CNTs (powder form) are dispersed in water followed by further ultrasonication with the molten lipid to form the final emulsion. During this process the CNTs get coated with lipid molecules, which in turn are presumed to surround the lipid droplets to form a particulate emulsion that is stable for months. The average size of CNT-stabilized nanostructured lipid particles is in the submicron range, which compares well with the particles stabilized using conventional surfactants. Small angle X-ray scattering data confirms the retention of the original Pn3m cubic phase in the CNT-stabilized lipid dispersions as compared to the pure lipid phase (bulk state). Blue shift and lowering of the intensities in characteristic G and G&#39; bands of CNTs observed in Raman spectroscopy characterize the interaction between CNT surface and lipid molecules. These results suggest that the interactions between the CNTs and lipids are responsible for their mutual stabilization in aqueous solutions. As the concentrations of CNTs employed for stabilization are very low and lipid molecules are able to functionalize the CNTs, the toxicity of CNTs is expected to be insignificant while their biocompatibility is greatly enhanced. Hence the present approach finds a great potential in various biomedical applications, for instance, for developing hybrid nanocarrier systems for the delivery of multiple functional molecules as in combination therapy or polytherapy.

We report on a smart application of carbon nanotubes for kinetic stabilization of lipid particles that contain self-assembled nanostructures in their cores. The preparation of lipid particles requires rather low concentrations of carbon nanotubes permitting their use in biomedical applications such as drug delivery.

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled ...

A Direct, Early Stage Guanidinylation Protocol for the Synthesis of Complex Aminoguanidine-containing Natural Products

The guanidine functional group, displayed most prominently in the amino acid arginine, one of the fundamental building blocks of life, is an important structural element found in many complex natural products and pharmaceuticals. Owing to the continual discovery of new guanidine-containing natural products and designed small molecules, rapid and efficient guanidinylation methods are of keen interest to synthetic and medicinal organic chemists. Because the nucleophilicity and basicity of guanidines can affect subsequent chemical transformations, traditional, indirect guanidinylation is typically pursued. Indirect methods commonly employ multiple protection steps involving a latent amine precursor, such as an azide, phthalimide, or carbamate. By circumventing these circuitous methods and employing a direct guanidinylation reaction early in the synthetic sequence, it was possible to forge the linear terminal guanidine containing backbone of clavatadine A to realize a short and streamlined synthesis of this potent factor XIa inhibitor. In practice, guanidine hydrochloride is elaborated with a carefully constructed protecting array that is optimized to survive the synthetic steps to come. In the preparation of clavatadine A, direct guanidinylation of a commercially available diamine eliminated two unnecessary steps from its synthesis. Coupled with the wide variety of known guanidine protecting groups, direct guanidinylation evinces a succinct and efficient practicality inherent to methods that find a home in a synthetic chemist&#39;s toolbox.

Here, we present a protocol for direct, early stage guanidinylation that enables rapid total synthesis of aminoguanidine-containing small organic molecules. An advanced synthetic intermediate used in the synthesis of a blood coagulation factor XIa inhibitor was prepared using this protocol.

The guanidine functional group, displayed most prominently in the amino acid arginine, one of the fundamental building blocks of life, is an important ...

Facile Preparation of 4-Substituted Quinazoline Derivatives

Reported in this paper is a very simple method for direct preparation of 4-substituted quinazoline derivatives from a reaction between substituted 2-aminobenzophenones and thiourea in the presence of dimethyl sulfoxide (DMSO). This is a unique complementary reaction system in which thiourea undergoes thermal decomposition to form carbodiimide and hydrogen sulfide, where the former reacts with 2-aminobenzophenone to form 4-phenylquinazolin-2(1H)-imine intermediate, whilst hydrogen sulfide reacts with DMSO to give methanethiol or other sulfur-containing molecule which then functions as a complementary reducing agent to reduce 4-phenylquinazolin-2(1H)-imine intermediate into 4-phenyl-1,2-dihydroquinazolin-2-amine. Subsequently, the elimination of ammonia from 4-phenyl-1,2-dihydroquinazolin-2-amine affords substituted quinazoline derivative. This reaction usually gives quinazoline derivative as a single product arising from 2-aminobenzophenone as monitored by GC/MS analysis, along with small amount of sulfur-containing molecules such as dimethyl disulfide, dimethyl trisulfide, etc. The reaction usually completes in 4-6 hr at 160 &#186;C in small scale but may last over 24 hr when carried out in large scale. The reaction product can be easily purified by means of washing off DMSO with water followed by column chromatography or thin layer chromatography.

A protocol for facile preparation of 4-substituted quinazoline derivatives from 2-aminobenzophenones, thiourea and dimethyl sulfoxide is presented.

Reported in this paper is a very simple method for direct preparation of 4-substituted quinazoline derivatives from a reaction between substituted ...

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of trifluoromethoxylated aromatic compounds remains a formidable challenge in organic synthesis. Conventional approaches often suffer from poor substrate scope, or require use of highly toxic, difficult-to-handle, and/or thermally labile reagents. Herein, we report a user-friendly protocol for the synthesis of methyl 4-acetamido-3-(trifluoromethoxy)benzoate using 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one (Togni reagent II). Treating methyl 4-(N-hydroxyacetamido)benzoate (1a) with Togni reagent II in the presence of a catalytic amount of cesium carbonate (Cs2CO3) in chloroform at RT afforded methyl 4-(N-(trifluoromethoxy)acetamido)benzoate (2a). This intermediate was then converted to the final product methyl 4-acetamido-3-(trifluoromethoxy)benzoate (3a) in nitromethane at 120 &#176;C. This procedure is general and can be applied to the synthesis of a broad spectrum of ortho-trifluoromethoxylated aniline derivatives, which could serve as useful synthetic building blocks for the discovery and development of new pharmaceuticals, agrochemicals, and functional materials.

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

An operationally simple procedure for the synthesis of ortho-trifluoromethoxylated aniline derivatives via a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxyacetamide followed by thermally induced intramolecular OCF3-migration is reported.

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous networks, ribbons, worm-like aggregates, toroidal structures, and spherical particles) is described. These aggregates are morphologically influenced by extensive hydrophobic side chain-side chain interactions of the singular polycarbodiimide strands, as inferred by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques. Polycarbodiimide-g-polystyrene copolymers (PS-PCDs) were prepared by a combination of synthetic methods, including coordination-insertion polymerization, copper(I)-catalyzed azide alkyne cycloaddition (CuAAC) &#34;click&#34; chemistry, and atom transfer radical polymerization (ATRP). PS-PCDs were found to form specific toroidal architectures at low concentrations in CHCl3. To determine the influence of a more polar solvent medium (i.e., THF and THF/EtOH) on polymer aggregation behavior, a number of representative PS-PCD composites have been tested to show discrete concentration-dependent spherical particles. These fundamental studies are of practical interest to the development of experimental procedures for desirable architectures by directed self-assembly in thin film. These architectures may be exploited as drug carriers, whereas other morphological findings represent certain interest in the area of novel functional materials.

Here, we present a protocol to prepare and visualize secondary structures (e.g., fibers, toroidal architectures, and nano-spheres) derived from helical polycarbodiimides. The morphology characterized by both atomic force microscopy (AFM) and scanning electron microscopy (SEM) was shown to depend on molecular structure, concentration, and the solvent of choice.

A facile method for the preparation of polycarbodiimide-based secondary structures (e.g., nano-rings, &#34;craters,&#34; fibers, looped fibers, fibrous ...