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      Elizabeth Denton


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      How long should I let my cleavage reaction stir at room temperature?

      Sep 27, 2019 3:30:52 PM / by Elizabeth Denton posted in Mass Detection, optimization, Peptides, peptide, solid phase peptide synthesis, method development

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      As the rules for cell permeability continue to be elucidated, peptides are increasingly being used to deliver either themselves or cargo to the cell’s interior.  One thing is clear, increasing the overall cationic charge of the peptide enhances it’s delivery to not only the cytoplasm, but also the nucleus or other subcellular compartments.  To achieve the positive charge, large numbers of arginine residues are most often incorporated into the peptide sequence.

      This begs the question though, should I change my cleavage protocol?  In today’s post, I’ll evaluate several lengths of time used to cleave and fully deprotect an Arg-rich peptide sequence.

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      Five Tips and Tricks for Success in Solid Phase Peptide Synthesis

      Sep 27, 2019 3:26:17 PM / by Elizabeth Denton posted in peptide, peptide synthesis, method development

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      In my role as a peptide application scientist, I have had the pleasure of working with many groups that are venturing into the world of peptides for the first time.  Although it seems rather  straightforward to experienced synthetic chemists, producing acceptable yield and purity certainly comes with unique challenges in solid phase peptide synthesis .

      In this post I would like to present some of the tips and tricks that I have picked up along the way.

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      How does media pore size impact peptide resolution?

      Sep 27, 2019 3:19:01 PM / by Elizabeth Denton posted in Developments, Peptides, reversed-phase, flash purification, solid phase peptide synthesis, peptide purification, peptides and flash chromatography, stationary phase, particle pore size

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      Purification by reversed-phase chromatography relies primarily on a hydrophobic interaction of the molecule with the alkyl chains bonded to the stationary phase for column retention and elution through a partitioning mechanism.  While this is certainly true for purification of peptides, surface area accessibility and media particle size also play critical roles in the resolving power of a particular stationary phase.  The particle size influences the loading capacity, however pore size greatly influences molecular accessibility and therefore resolving power.

      In today’s post, I will demonstrate how pore size can impact your peptide purification using flash column chromatography.

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      How to use a scouting column for your peptide purification

      Sep 27, 2019 3:13:39 PM / by Elizabeth Denton posted in reversed-phase, flash purification, peptide, solid phase peptide synthesis, peptide purification, peptides and flash chromatography, stationary phase, particle pore size, method development

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      In the past, when I have synthesized a new peptide, I always ran a “scout run” – a small scale injection, usually with an analytical HPLC column – to both get an idea of the crude purity and also to identify a shorter, more optimal gradient for the actual purification.  This strategy is still recommended when you want to use reversed phase flash chromatography for your purification strategy, but is there a better way?

      In today’s post, I’ll discuss using a scouting column to screen gradient conditions prior to peptide purification with reversed phase flash chromatography.

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      What is solid phase peptide synthesis?

      Sep 25, 2019 9:47:21 PM / by Elizabeth Denton posted in Biotage, Developments, synthesis, peptide, peptide synthesis, solid phase peptide synthesis, cleavage, synthesis tips, orthogonal protecting groups, synthesis optimization, method development, FMOC, BOC

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      More and more groups are exploring the utility of peptides with an ever widening variety of applications. And although peptides are getting cheaper to purchase outright, many groups are continuing to bring peptide synthesis in house. As more groups join the peptide community, I frequently encounter questions about the basics of peptide synthesis.

      In today's post, I'd like to cover a little history of solid phase synthesis as well as highlight some differences between the chemistries.

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      Peptides containing cysteine: the role of scavengers in cleavage cocktail

      Sep 11, 2019 10:48:03 PM / by Elizabeth Denton posted in peptide synthesis, cleavage

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      Since the development of Fmoc-based solid phase peptide synthesis, a wide variety of cleavage cocktails have emerged.  Each cleavage cocktail contains a unique combination of scavengers designed to prevent either side reactions mediated by the released protecting groups or the side chains themselves, or both during the peptide cleavage reaction.  As the number of scientists performing peptide synthesis grows, the question “which cleavage cocktail should I use?” comes up more often than not.

      In today’s post, I’ll highlight the role of of scavengers for peptides containing cysteine residues.

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      How to purify your peptide using mass directed flash chromatography

      Jul 31, 2019 4:02:19 PM / by Elizabeth Denton posted in Developments, Mass Detection, solid phase peptide synthesis, purify, loading capacity, peptide purification, peptides and flash chromatography, mass-directed purification

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      We've all used mass spectrometry to characterize our synthetic peptides.  It's often used to confirm that the peptide was in fact synthesized, then again as part of the purification process to make sure that we're collecting the correct peak.  But how many of you had the opportunity to use in-line mass spectrometry as an integral component during the purification itself?

      In today's post, I'll highlight some of the advantages to using in-line mass mass spectrometry for purification of peptides using reversed phase flash chromatography.

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      How much peptide is recovered from a reversed-phase C18 cartridge during flash purification?

      Jul 25, 2019 2:13:43 PM / by Elizabeth Denton posted in Developments, reversed-phase, flash chromatography, peptide, solid phase peptide synthesis, peptide purification, peptides and flash chromatography

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      Whether it’s the bonded stationary phase, particle size, or even particle pore size, scientists today are offered a plethora of choices when it comes to reversed phase HPLC columns.  An often acknowledged concern in the peptide community though is peptide recovery from reversed phase purification efforts, particularly for precious peptide mixtures.  But how is peptide recovery impacted when you use reversed phase flash chromatography for purification?

      In today’s post, I’ll compare recovery levels for two peptides that differ in length as well as crude purity using reversed phase flash chromatography.  In addition to comparing two peptides, I’ll also evaluate how recovery is impacted by altering the mobile phase pH.

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      How to choose an ion pairing agent to improve your peptide purification

      Jul 22, 2019 4:28:04 PM / by Elizabeth Denton posted in Developments, reversed-phase, flash chromatography, peptide, solid phase peptide synthesis, peptide purification, peptides and flash chromatography, ion pairing agents

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      Ion pairing agents are used in a variety of strategies to improve overall purification efficiency. In a previous post, I utilized ion pairing agents to increase the peptide’s hydrophobicity, improving retention by the stationary phase and enabling purification.  But what other strategies can be improved by using ion pairing agents?

      In this post, I’ll utilize ion pairing agents to enable rapid peptide purification by flash chromatography.  The use of ion pairing agents can in fact alter the peptide’s apparent hydrophobicity sufficiently that the desired peptide and it’s closely eluting impurities can be resolved.  The question is, which one to choose?

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      Peptide purification with flash column chromatography - a beginner's experience

      Jul 18, 2019 8:59:34 PM / by Elizabeth Denton posted in Developments, Peptides, reversed-phase, flash chromatography, solid phase peptide synthesis, peptide purification

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      As a peptide chemist, I was trained to purify my peptides with reversed-phase HPLC, just as many a peptide chemist before me. Despite the hundreds of hours I’ve logged in front of an HPLC, injecting samples and collecting peak fractions, I can’t imagine using any other method to purify my freshly synthesized and cleaved peptides.  In fact, you’d be hard pressed to convince me to try something else.  But here I am, trying something new.  Wish me luck!

      In this post, I’ll describe my experiences using flash chromatography to purify a new peptide sample.

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      How does methanol as a mobile phase solvent impact peptide purification by reversed-phase flash chromatography?

      Jul 18, 2019 2:10:15 PM / by Elizabeth Denton posted in Peptides, reversed-phase, selectivity, solvent strength, solid phase peptide synthesis, peptide purification

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      Recently there has been substantial motivation to consider and evaluate alternative, more environmentally friendly solvents.  Some countries have even gone so far as to ban some of the more toxic, yet commonly used solvents.  In addition to general toxicity, additional consideration in the green chemistry movement is the volume of solvent used in any particular application.  In this regard, purification solvent selection is closely monitored as they are often used in large quantities.

      One alternative that is growing in popularity is the use of methanol in place of acetonitrile for reversed phase purification of small molecules.  Methanol is certainly less expensive, but is also a more environmentally-friendly solvent for use in purification applications.  But it’s use for peptide purification has not been widely adopted to date.  In today’s post, I’ll compare the purification efficiency of methanol when compared to acetonitrile for peptide purification by reversed phase flash chromatography.

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      Does loading method influence my peptide recovery after purification?

      Jul 17, 2019 6:25:29 PM / by Elizabeth Denton posted in Peptides, reversed-phase, solid phase peptide synthesis, peptide purification, peptides and flash chromatography, loading method

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      In peptide purification, sample loading onto the column is rarely considered.  Most, if not all, HPLC instruments come equipped with a sample injection loop which demands a liquid injection of the sample for purification.  If you decide to use flash chromatography to purify your peptides though, liquid injection is no longer the exclusive method for sample introduction to the column.  Alternatively, dry loading crude material is a strategy often used in small molecule purification, particularly when sample solubility concerns arise.

      The first question I asked myself when considering a new sample loading strategy is whether or not the purification efficiency will be maintained.  A close second though is whether or not the loading method will cause significant differences in peptide recovery.

      In today's post, I'll compare recovery efficiencies for peptides purified using reversed phase flash chromatography but loaded onto the cartridge using either direct liquid injection or dry loaded onto reversed phase material.

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      Post synthesis workup: What steps are necessary and what aren't?

      Jun 19, 2019 5:35:32 PM / by Elizabeth Denton posted in Developments, Peptides, workflow, peptide workflow, solid phase peptide synthesis, cleavage

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      You’ve just finished a peptide synthesis and now it’s time to cleave the peptide from the resin. You’ve selected a specific cleavage cocktail, performed the reaction and now what? The vast majority of peptide chemists will precipitate their peptide using an ether solution, lyophilize, and move on to purification. But is that the only option?

      In today’s post I’ll highlight an alternative strategy that saves both processing time, potentially dangerous reagents, all without compromising the integrity of the recently synthesized peptide.

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      Room temperature allyl ester and alloc deprotections - what is the lifetime of palladium?

      Jun 11, 2019 8:30:33 PM / by Elizabeth Denton posted in solid phase peptide synthesis, orthogonal protecting groups, selecting deprotection, synthesis optimization

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      In a previous post, I did some work evaluating the efficiency of alloc removal with tetrakis palladium using microwave assistance and atmospheric conditions, which worked beautifully.  Given the known sensitivity of palladium catalysts (see Derek Lowe's post for a humorous dialogue), I sought to further explore the sensitivity of palladium towards the alloc removal in the context of a peptide.

      In this post, I'll explore a variety of atmospheric, room temperature alloc deprotection conditions aimed at evaluating the catalytic lifetime of palladium tetrakis for effective alloc removal. 

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      How to choose the right resin functionality for solid phase peptide synthesis

      Jun 11, 2019 8:30:01 PM / by Elizabeth Denton posted in Peptides, solid phase peptide synthesis, synthesis tips, synthesis optimization

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      As a chemist new to the peptide community, there are many choices that have to be made.  Which coupling reagents to use? Heat or no heat to promote chemistry? And most importantly, which resin?  I have talked previously about resin choices, from loading levels to swelling capacity and how they affect the synthesis outcome.  But I haven't addressed yet a fundamental feature of commercially available resins, and that's the functional handle to which the peptide chain is conjugated.

      In today's post, I'll describe some, and I mean only some, of the most commonly used chemical functionalities for Fmoc-based solid phase peptide synthesis and some scenarios in which you would choose one resin type over another.

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      Can you use normal phase chromatography to purify protected peptides?

      Jun 11, 2019 8:29:38 PM / by Elizabeth Denton posted in normal phase, reversed-phase, flash purification, peptide synthesis, solid phase peptide synthesis, peptides and flash chromatography

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      Chemical synthesis of peptides, and even proteins, offers the possibility to expand the functionality and stability imbued by nature.  However, chemical synthesis of very long peptides and small proteins remains today an exceedingly difficult task.  Several ligation strategies have been developed that help to alleviate this challenge.  These strategies though, require a purified, yet fully protected peptide fragment.

      Purification of a fully protected peptide species can be challenging by standard reversed-phase techniques, primarily due to the limited solubility of protected peptides in aqueous solutions.  In today’s post, I will discuss using normal-phase chromatography for purification of protected peptides.

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