Selective t-Butyl Ester Hydrolysis with FeCl3

Modification of peptide side chains, either to add a label to trace the peptide in subsequent applications or to modify the characteristics of the peptide, is one of the current challenges of peptide synthesis.

RS Giri, SR Manne, G Dolai, et al. recently published a report that they could use FeCl3 in DCM to cleave the t-butyl esters on the side chains of Asp and Glu residues while the peptide was still attached to Rink amide resin.  They subsequently modified these residues by forming a variety of esters, amides, and a thioester.  Alloc groups and allyl esters were stable to this treatment.

The scope of this method needs to be studied.  Presumably, t-Bu protected Ser and Thr side chains will be stable, but this should be verified.  The stabilities of Lys(Boc) and Arg(Pbf) also need to be determined.  Further, will FeCl3 cleave peptides from Wang resin?

This is not the first report of using Lewis acids to hydrolize t-butyl esters.  WD Lubell and co-workers have reported using ZnBr2 in DCM to hydrolize t-butyl esters.  They found N-Boc and N-trityl groups were also labile.  E Marcantoni, M Massaccesi and E Terrregiani selectively hydrolyzed t-butyl esters in the presence of N-Boc groups using NaI with CeCl3 in refluxing acetonitrile.

These reports are interesting for as yet, there are only limited choices for selective deprotection of Asp or Glu sidechains.  With further studies to determine the limitations of these Lewis acid promoted reactions, they could play an important role in peptide synthesis.

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Cyclization-Cleavage Synthesis of Peptide Thiolactams

B.H. Gless, et al have published an interesting solid phase synthesis of thiolactam peptides that utilizes a cyclization-cleavage strategy.  They synthesized the linear peptide on MeDbz linked resin, the resin that has been use to prepare peptide thioesters for use in native chemical ligation synthesis of large and complex peptides.  After synthesizing the linear peptide, they activated the MeDbz linker and deprotected the Cys residue to allow simultaneous cyclization and release of the peptide from the resin.  They used this strategy to prepare autoinducing peptide from the dog pathogen S. schlefeai and to prepare analogs for structure-activity studies.

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Avoiding antibiotic resistance with antimicrobial peptides

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Antimicrobial peptides with anticancer activity

The increasing occurrence of antibiotic resistance in disease-causing bacteria has spurred the search for new antimicrobial compounds, including peptides.  A large number of antibiotic peptides from natural sources have been reported and new ones are continually being discovered.  Some of these peptides also show selective activity against some lines of cancer cells.  Two novel phylloseptins isolated from the skin secretions of South American frogs recently were reported to have cytostatic effects on non-small cell lung cancer cells.  J. Liu, et al, in a paper published in Molecules, report that phylloseptin-PTa and phylloseptin-PHa exhibit cytostatic effects on the non-small cell cancer line, NCI-H157, with low cytotoxicity on human microvascular endothelial cells (J. Liu, et al., Molecules, 2017, 7(1): 7413).

BP100 is another recent example.  This peptide is membrane-active and has high antimicrobial activity.  B. Zhang, et al, in a paper recently submitted to the journal Amino Acids, report that aliphatic chain-conjugated peptides based on BP100 exhibited effective anti-tumor activity against multidrug resistant cells and had multidrug resistance-reversing effect.  In addition, conjugating the peptides with aliphatic acid improved their stability in plasma, making them potential drug leads for cancer treatment.

Evaluating other antimicrobial peptides for anti-cancer activity is likely to prove fruitful.  It is an intriguing possibility that new anticancer treatments may be developed from the search for new antimicrobial compounds.

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Substance P recovers beta -amyloid-induced cognitive deficits in rats

Systemic Administration of Substance P Recovers Beta Amyloid-Induced Cognitive Deficits in Rat: Involvement of Kv Potassium Channels

P Campolongo, P Ratano, MT Ciotti, F Florenzano, SL Nori, R Marolda, M Palmery, AM Rinaldi, C Zona, R Possenti, P Calissano, C Severini, PLos One, 2013, 8(11), e78036.

Reduced levels of Substance P (SP), an endogenous neuropeptide endowed with neuroprotective and anti-apoptotic properties, have been found in brain and spinal fluid of Alzheimer’s disease (AD) patients. Potassium (K+) channel dysfunction is implicated in AD development and the amyloid-β (Aβ)-induced up-regulation of voltage-gated potassium channel subunits could be considered a significant step in Aβ brain toxicity. The aim of this study was to evaluate whether SP could reduce, in vivo, Aβ-induced overexpression of Kv subunits. Rats were intracerebroventricularly infused with amyloid-β 25–35 (Aβ25–35, 20 µg) peptide. SP (50 µg/Kg, i.p.) was daily administered, for 7 days starting from the day of the surgery. Here we demonstrate that the Aβ infused rats showed impairment in cognitive performances in the Morris water maze task 4 weeks after Aβ25–35 infusion and that this impairing effect was prevented by SP administration.

Kv1.4, Kv2.1 and Kv4.2 subunit levels were quantified in hippocampus and in cerebral cortex by Western blot analysis and immunofluorescence. Interestingly, SP reduced Kv1.4 levels overexpressed by Aβ, both in hippocampus and cerebral cortex.

Our findings provide in vivo evidence for a neuroprotective activity of systemic administration of SP in a rat model of AD and suggest a possible mechanism underlying this effect.

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Adrenomedullin and Alzheimer’s Disease

Adrenomedullin Expression in Alzheimer’s Brain

AP Fernandez, JS Masa, MA Guedan, HS Futch, R Martínez-Murillo, Curr. Alzheimer Res., 201613, 428-38.

Adrenomedullin (AM) is a potent vasodilator peptide highly expressed throughout the brain and originally isolated from pheochromocytoma cells. In addition to its vasoactive properties, AM is considered a neuromodulator that possesses antiapoptotic and antioxidant properties that suggest that this peptide can protect the brain from damage. In a previous study, we found that AM exerts a neuroprotective action in the brain and that this effect may be mediated by regulation of nitric oxide synthases, matrix metalloproteases, and inflammatory mediators. AM upregulation contributes to neuroprotection, but understanding the precise roles played by AM and its receptor (RAMP2) in neurodegenerative diseases including Alzheimer´s disease (AD), awaits further research. In search of Alzheimer´s biomarkers, the expression levels of peptides with endothelial vasodilatory action, including AM, were found to be significantly altered in mild AD or during pre-dementia stage of mild cognitive impairment. These studies concluded that ratio of AM or its precursor fragment mid-regional proAM in blood hold promise as diagnostic marker for AD. We are now presenting a study regarding the hypothesis that the AMRAMP2 system might be implicated in the pathophysiology of AD.

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The effect of adrenomedullin and proadrenomedullin N- terminal 20 peptide on angiotensin II induced vascular smooth muscle cell proliferation

The effect of adrenomedullin and proadrenomedullin N- terminal 20 peptide on angiotensin II induced vascular smooth muscle cell proliferation

Thoracic aorta was obtained from Wistar rats and VSMCs were isolated from
aorta tissues and then cultured. In vitro cultured VSMCs were stimulated with Ang II (10‐8 mol/l) followed by various doses of PAMP or ADM (10‐9, 10‐8, or 10‐7 mol/l). Cell proliferation as assessed by 3H‐TdR incorporation. Protein kinase C (PKC) activity was measured by counting γ‐32P radioactivity with liquid scintillation. In a separate cohort, in vitro cultured rat aortic vessels were treated with different doses of Ang II or PAMP (10‐9, 10‐8, or 10‐7 mol/l). Cellular and secreted levels of PAMP, ADM and Ang II were measured using radioimmunoassay in the tissues and intubation mediums, respectively.

Ang II (10‐8 mol/l) treatment significantly increased both 3H‐TdR incorporation and PKC activity in VSMCs (by 2.68 and 1.02‐fold, respectively; both P<0.01 vs. the control). However, Ang II‐ induced elevation of 3H‐TdR incorporation, and PKC activity was significantly inhibited by various doses of ADM and PAMP (all P<0.01 vs. the Ang II group). In rat aortic vascular tissues or intubation media, Ang II treatments stimulated the expression and secretion of PAMP and ADM in a dose‐ dependent manner, while PAMP treatments had no significant effects on Ang II levels. Conclusion: ADM and PAMP inhibit Ang II‐induced VSMCs proliferation. The interaction of Ang II, ADM and PAMP may regulate VSMCs and cardiovascular function.

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Design and Synthesis of Aphicidal Peptides

Eco-friendly Insecticide Discovery via Peptidomimetics: Design, Synthesis and Aphicidal Activity of Novel Insect Kinin Analogs

Chuan-liang Zhang, Yanyan Qv, Xiaoqing Wu, Dunlun Song, Yun Ling, and Xinling Yang, J. Agric. Food Chem., Just Accepted Manuscript  Publication Date (Web): April 26, 2015  Copyright © 2015 American Chemical Society

The insect kinin neuropeptides are pleiotropic peptides that are involved in the regulation of hindgut contraction, diuresis and digestive enzyme release. They share a common C-terminal pentapeptide sequence Phe1-Xaa2-Yaa3-Trp4-Gly5-NH2 (where Xaa2 = His, Asn, Phe, Ser or Tyr; Yaa3 = Pro, Ser or Ala). Recently, the aphicidal activity of insect kinin analogs attracted the attention of researchers. Our previous work demonstrated that the sequence-simplified insect kinin pentapeptide analogue Phe-Phe-[Aib]-Trp-Gly-NH2 could retain good aphicidal activity and be the lead compound for the further discovery of eco-friendly insecticides which encompassed a broad array of biochemicals derived from micro-organisms and other natural sources. Using the peptidomimetics strategy, we chose Phe-Phe-[Aib]-Trp-Gly-NH2 as the lead compound, designed and synthesized three series, including 31 novel insect kinin analogues. The aphicidal activity of the new analogs against soybean aphid was determined. The results showed that all the analogs exhibited aphicidal activity. Of particular interest was the analogue II-1 which exhibited improved aphicidal activity with an LC50 of 0.019mmol/L compared with the lead compound (LC50=0.045mmol/L) or the commercial insecticide pymetrozine (LC50=0.034mmol/L). This suggests that the analogue II-1 could be used as a new lead for the discovery of potential eco-friendly insecticides.

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Stereocontrolled Construction of (E)-2-Amino-2-butenamide

Solid-Phase Total Synthesis of Bogorol A: Stereocontrolled Construction of Thermodynamically Unfavored (E)-2-Amino-2-butenamide

Tomoya Yamashita, Takefumi Kuranaga, and Masayuki Inoue, Org. Lett., Article ASAP Publication Date (Web): April 13, 2015 Copyright © 2015 American Chemical Society

Bogorol A [(E)-1], a potent antibiotic against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus spp., possesses a thermodynamically unfavored (E)-2-amino-2-butenamide within its linear dodecapeptide sequence. The highly efficient totalsynthesis of natural (E)-isomer (E)-1 and its artificial (Z)-isomer (Z)-1 by employing a full solid-phase strategy is reported. The (E)- and (Z)-2-amino-2-butenamide moieties were stereoselectively constructed by applying traceless Staudinger ligation on the resin. Interestingly, (E)- and (Z)-1 showed comparable antimicrobial activity (MIC = 4 μg/mL).

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Expanded Application of Native Chemical Ligation Using beta-Thio Phenylalanine and Desulfurization

Synthesis of β-Thiol Phenylalanine for Applications in One-Pot Ligation–Desulfurization Chemistry

Lara R. Malins, Andrew M. Giltrap, Luke J. Dowman, and Richard J. Payne, Org. Lett., Article ASAP   Publication Date (Web): April 10, 2015   Copyright © 2015 American Chemical Society

The efficient synthesis of a β-thiol phenylalanine derivative is described starting from Garner’s aldehyde. The utility of this amino acid in peptide ligation–desulfurization chemistry is described, including the trifluoroethanethiol (TFET)-promoted one-pot assembly of the 62 residue peptide hormone augurin.

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