Protected Amino Research Articles

Synthesis of N-peptide-6-amino-D-luciferin Conjugates.

A general strategy for the synthesis of N-peptide-6-amino-D-luciferin conjugates has been developed. The applicability of the strategy was demonstrated with the preparation of a known substrate, N-Z-Asp-Glu-Val-Asp-6-amino-D-luciferin (N-Z-DEVD-aLuc). N-Z-DEVD-aLuc was obtained via a hybrid liquid/solid phase synthesis method, in which the appropriately protected C-terminal amino acid was coupled to 6-amino-2-cyanobenzothiazole and the resulting conjugate was reacted with D-cysteine in order to get the protected amino acid-6-amino-D-luciferin conjugate, which was then attached to resin. The resulting loaded resin was used for the solid-phase synthesis of the desired N-peptide-6-amino-D-luciferin conjugate without difficulties, which was then attested with NMR spectroscopy and LC-MS, and successfully tested in a bioluminescent system.

Effect of different immobilization strategies on chiral recognition properties of Cinchona-based anion exchangers.

In the enantiomeric separation of highly polar compounds, a traditionally challenging task for high-performance liquid chromatography, ion-exchange chiral stationary phases have found the main field of application. In this contribution, we present a series of novel anion-exchange-type chiral stationary phases for enantiomer separation of protected amino phosphonates and N-protected amino acids. Two of the prepared selectors possessed a double and triple bond within a single molecule. Thus, they were immobilized onto silica support employing either a thiol-ene (radical) or an azide-yne (copper(I)-catalyzed) click reaction. We evaluated the selectivity and the effect of immobilization proceeding either by the double bond of the Cinchona alkaloid or a triple bond of the carbamoyl moiety on the chromatographic performance of the chiral stationary phases using analytes with protecting groups of different size, flexibility, and π-acidity. The previously observed preference toward protecting groups possessing π-acidic units, which is a typical feature of Cinchona-based chiral stationary phases, was preserved. In addition, increasing the bulkiness of the selectors' carbamoyl units leads to significantly reduced retention times, while very high selectivity toward the tested analytes is retained.

Synthesis and Properties of Alternating Polypeptoids and Polyampholytes as Protein-Resistant Polymers

Alternating polypeptoids are particularly appealing because alternating sequence may impart highly ordered structure and special functions, while their simple synthesis still remains a key challenge. We describe that natural amino acid monomers can be polymerized via Ugi reaction in a step-growth fashion as an AA' BB' system, which leads to alternating polypeptoids with molecular weight up to 15 kg/mol. These alternating polypeptoids are thermally responsive and exhibit cloud points ( Tcp) between 27 and 37 °C. Importantly, the marriage of high functionality of amino acids with Ugi reaction also enables the preparation of polypeptoids encoding both protected amino and carboxyl groups in the side chains with alternating arrangement. The cleavage of the protecting groups leads to alternating polyampholytes without any compositional drift. Such alternating polyampholytes not only exhibit high water solubility (>100 mg/mL) but also demonstrate the ability to resist aggregation with proteins. Moreover, the cell viability measurements reveal that these materials have minimal cytotoxicity to HeLa cells. Overall, this study offers us a simple way to prepare a variety of polypeptoids and polyampholytes as new protein-resistant materials for bioapplications.

Oxidative functionalization of aliphatic and aromatic amino acid derivatives with H2O2 catalyzed by a nonheme imine based iron complex.

The oxidation of a series of N-acetyl amino acid methyl esters with H2O2 catalyzed by a very simple iminopyridine iron(ii) complex 1 easily obtainable in situ by self-assembly of 2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 was investigated. Oxidation of protected aliphatic amino acids occurs at the α-C–H bond exclusively (N-AcAlaOMe) or in competition with the side-chain functionalization (N-AcValOMe and N-AcLeuOMe). N-AcProOMe is smoothly and cleanly oxidized with high regioselectivity affording exclusively C-5 oxidation products. Remarkably, complex 1 is also able to catalyze the oxidation of the aromatic N-AcPheOMe. A marked preference for the aromatic ring hydroxylation over Cα–H and benzylic C–H oxidation was observed, leading to the clean formation of tyrosine and its phenolic isomers.

Amino Aldehydes Revisited

The enzymatic oxidation of amino alcohols was studied to address the long‐standing problem of product stability. Amino aldehydes, highly sought and unstable compounds, can be generated under mild conditions if they are immediately protected. Utilizing a range of alcohol dehydrogenases (ADHs) and semicarbazide as a scavenger, the enantioselective synthesis of protected amino aldehydes is possible. Glycerol dehydrogenase from Gluconobacter oxydans (GoGDH) displayed excellent enantioselectivity but limited substrate scope, whereas horse liver ADH catalyzed a broad range of conversions with low enantioselectivities.

17O MAS NMR Correlation Spectroscopy at High Magnetic Fields.

The structure of two protected amino acids, FMOC-l-leucine and FMOC-l-valine, and a dipeptide, N-acetyl-l-valyl-l-leucine (N-Ac-VL), were studied via one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy. Utilizing 17O magic-angle spinning (MAS) NMR at multiple magnetic fields (17.6-35.2 T/750-1500 MHz for 1H) the 17O quadrupolar and chemical shift parameters were determined for the two oxygen sites of each FMOC-protected amino acids and the three distinct oxygen environments of the dipeptide. The one- and two-dimensional, 17O, 15N-17O, 13C-17O, and 1H-17O double-resonance correlation experiments performed on the uniformly 13C,15N and 70% 17O-labeled dipeptide prove the attainability of 17O as a probe for structure studies of biological systems. 15N-17O and 13C-17O distances were measured via one-dimensional REAPDOR and ZF-TEDOR experimental buildup curves and determined to be within 15% of previously reported distances, thus demonstrating the use of 17O NMR to quantitate interatomic distances in a fully labeled dipeptide. Through-space hydrogen bonding of N-Ac-VL was investigated by a two-dimensional 1H-detected 17O R3-R-INEPT experiment, furthering the importance of 17O for studies of structure in biomolecular solids.

Facile Organocatalyzed Synthesis of Poly(ε-lysine) under Mild Conditions

Functional poly(amino acid)s such as poly(e-lysine) have many potential high-value applications. However, the effective chemosynthetic strategy for these materials remains a big challenge in polymer chemistry; the key issue is how to design and protect amino groups for the effective ring-opening polymerization (ROP). Our lab succeeded in chemosynthesis of poly(e-lysine) via delicate design of a 2,5-dimethylpyrrole protecting group and metal-catalyzed ROP processes, but harsh reaction conditions (e.g., ca. 260 °C) were required. Herein, we developed a superbase t-BuP4-catalyzed ROP of e-lactam derivatives, affording high molecular weight poly(e-lysine) bearing pendant protected amino groups with high monomer conversion (up to 95%). The organocatalytic polymerization could proceed at low reaction temperature (e.g., 60 °C) compatible with readily removable protecting groups, providing a sustainable and new methodology toward facile preparation of poly(e-lysine).

Scaling the Amphiphilic Character and Antimicrobial Activity of Gramicidin S by Dihydroxylation or Ketal Formation.

The acid lability of aliphatic ketals, which often serve as protection groups for 1,2-diols, is influenced by their local structural environment. The acetonide of the protected amino acid cis-dihydroxyproline (Dyp) is a typical protecting group cleavable by traces of TFA. The tricyclic acetonide of the dipeptide d-Hot═Tap is resistant to TFA and thus can serve as a bioorthogonal modification of bioactive peptides. With the aim of improving antimicrobial activity and hemolytic properties, we use these reactivity differences to scale the membrane affinity of the decapeptide Gramicidin S cyclo(d-Phe-Pro-Val-Orn-Leu-)2 (GS). The cis-dihydroxylated amino acids are used to increase the polarity of GS or obversely decrease the polarity by stereoselective ketal formation with an aliphatic ketone. While Dyp (GS mimetic 15) has only minimal influence on the biological properties of GS, d-Hot═Tap at the position of d-Phe1-Pro2 eradicates the biological activity (GS mimetic 16). The acid-stable ketals 17-19 are bioorthogonal modifications which reconstitute the biological activity of GS. We describe an improved synthesis of orthogonally protected Fmoc-Dyp-acetonide (9) and of several Fmoc-d-Hot═Tap-ketals for solid-phase peptide synthesis.

An N-protection free ligation of the peptide thioester and the peptide with an N-alkoxy- or N-aryloxyamino group at its N-terminus

Peptides with an N-alkoxy or N-aryloxy amino acid at their N-terminus were synthesized and successfully ligated with a peptide thioester by silver ion activation under a slightly acidic condition without requiring protection of the side chain amino groups. The N-methoxy group was easily cleaved by the SmI2 reduction in CH3OH aq. to obtain the desired peptide with a native peptide bond. This method was successfully applied to the synthesis of the human atrial natriuretic peptide showing the efficiency of the novel ligation.

Synthesis of Nα-protected formamides from amino acids using MgO nano catalyst: Study of molecular docking and antibacterial activity

Green synthesis of nano MgO particles and their application for the formylation of isocyanates of N-Fmoc/Cbz/Boc protected amino acids were reported. Nano magnesium oxide catalysed reaction of isocyanate with 96% formic acid has been established to obtain formamides. For this, the carboxyl group of protected amino acids were activated via mixed anhydride method and treated with NaN3. The formed azides were converted into its isocyanates through Curtius rearrangement and treated with HCOOH and catalytic amount of nano MgO. The advantages of this method were remarkably simple and economically low cost nano metal oxide under milder reaction conditions. Most importantly, MgO can be easily separated and other basic impurities were removed through a simple work-up. This protocol showed high efficiency in catalysing this transformation in a greener fashion. The molecular docking study of the synthesized compounds was performed against the macromolecules sortase-A and glucosamine 6-phosphate synthase to understand the binding interactions. The results of in vitro antibacterial activities of the synthesized compounds were supported by docking analysis.

Facile Synthesis of Novel Amino Acids Derivatives as Potential Antibacterial Agents using Sustainable Materials

Following the principles of green chemistry, cardanol derivatives have been used as renewable, low‐cost, and available natural starting materials to construct a variety of protected and unprotected amino acids derivatives. The reaction of cardanol derivatives with different phthaloylamino acids including glycine, alanine, phenylalanine, and valine in the presence N,N'‐dicyclohexylcarbodiimide (DCC) as coupling reagent afforded high yields of the target compounds. Deprotection of phthaloylamino acids derivatives was achieved by heating with hydrazine hydrate. The chemical structures of all products were confirmed by spectral data (IR, MS, 1H NMR, 13C NMR) and elemental analyses. Antibacterial evaluation of the synthesized products was performed, which exhibited potent to weak activity in comparison with a standard drug.

Novel Synthesis of N-Glycosyl Amino Acids Using T3P®: Propylphosphonic Acid Cyclic Anhydride as Coupling Reagent

In this paper is presented a novel and simple synthetic pathway for obtaining new protected and unprotected N-glucosyl amino acids from 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl amine and Fmoc-l-amino acids. Three methodologies were evaluated, using the coupling reagents: N,N,N′,N′-Tetramethyl-O-(benzotriazol-1-yl)uronium tetrafluoroborate, diisopropylcarbodiimide and propylphosphonic acid cyclic anhydride. The obtained products using propylphosphonic acid cyclic anhydride showed less undesired species, easy purification and higher yields than the other two methodologies. Deprotection strategies widely used in solid phase peptide synthesis were applied to develop the synthetic pathway reported and achieve the final products. The protected and unprotected N-glucosyl amino acids were purified using solid phase extraction chromatography and characterized by high performance liquid Chromatography and nuclear magnetic resonance spectroscopy. Different amino acids (Fmoc-l-Asp(OtBu)OH, Fmoc-l-Phe(OH) and Fmoc-l-Lys(Boc)-OH) have been employed to demonstrate the simple and reproducible coupling methodology using propylphosphonic acid cyclic anhydride. The results showed that new protected and unprotected N-glucosyl amino acids can be obtained with high purity and the methodology could be used with any Fmoc-amino acid. The methodology developed could be considered as a synthetic tool for obtaining building blocks for glycopeptide synthesis and potential drugs candidates based on glycoconjugates.

A comprehensive conformational space analysis of N-formyl-l-tryptophanamide system by using a genetic algorithm for multi-modal search

The conformational space of protected amino acid HCO-Tryptophane-NH2 was explored by using a new optimization procedure, in order to localize the stable minima on its potential energy surface (PES). The genetic algorithm based on the Multi-Niche Crowding (MNC) technique was used initially to generate a set of optimized structures for title compound. Resulting structures from the genetic algorithm technique will be used hereafter as input conformers at a hierarchy of increasingly more accurate electronic structure calculations (RHF/6-31G+(d) and DFT/B3LYP/6-31G+(d) geometry optimizations). The lowest energy conformer γL(g+g+) presents a folded Backbone that is stabilized by strong hydrogen bond noted C7. This links the carbonyl oxygen of the formyl group and the hydrogen of the amine group. There are further interactions from one hand between the carbonyl oxygen of the formyl group and the neighboring CH group on the pyrrole ring and from other hand between the N-terminus hydrogen and the indole ring in accordance with the experimental results. This work includes also a comparison between the theoretical calculations and the experimental results of X-ray crystallography extracted from protein data bank (PDB).

A convenient synthesis of novel amino acid derivatives with potential antibacterial activity using sustainable materials

Following the principles of green chemistry, cardanol derivatives have been used as renewable, low-cost and easily available natural starting materials to construct a variety of protected and unprotected amino acid derivatives. The reaction of cardanol derivatives with different phthalylamino acids including glycine, alanine, phenylalanine and valine in the presence of N,N′-dicyclohexylcarbodiimide (DCC) as coupling reagent yielded the target compounds in high yields. Deprotection of phthalylamino acid derivatives was achieved by heating with hydrazine hydrate. The chemical structures of all products were confirmed by spectral (FTIR, MS, 1H NMR, 13C NMR) and elemental analyses. The synthesised products were evaluated for their antibacterial activity, and the compounds exhibited potent to weak activity in comparison with a standard drug.

Digestión de materia seca, proteína cruda y aminoácidos de la dieta de vacas lecheras

The aim of this study was to determine the digestion of dry matter (MS), crude protein (PC) and amino acids (AA) in dairy cows. Two cannulated cows were used for the determination of passage rate (Kp), in situ ruminal degradability (DR) and intestinal digestibility (DI) by abomasal catheter. The data to calculate Kp was analyzed with NLIN procedure by SAS, and descriptive statistics for DR and DI of MS, PC and AA from Kikuyu grass (Pennisetum clandestinum), a commercial supplement and two sources of rumen-protected AA. The study showed a Kp and a ruminal retention time of 0.036 h-1 and 27.4 h. The highest values from DR of MS and CP were from Kikuyu grass (69.0 and 61.8%) and concentrate (84.7 and 77.2%), followed by MetP (60.2 and 66.7%) and LysP (6.72 and 11.4%). The highest percentages of rumen indegradable amino acids (AADR) were from Kikuyu and concentrate, varying between 58.7 and 68% in forage, and 76.1 and 82.9% in the concentrate. The DR was 11.5 and 65.8% in LysP and MetP, respectively. The DI of AA (%AADR) varied between 42.3 and 77.4% for Kikuyu and 42.2 and 59.3% for concentrate. The values for the protected amino acids were 42.1 for LysP and 58.6 for MetP.

Fmoc-OPhth, the reagent of Fmoc protection

Fmoc-OSu has been widely used for Fmoc protection of amino groups, especially amino acids, in solid phase peptide synthesis. However, it has been recognized that Fmoc-βAla-OH is formed as a by-product via the Lossen rearrangement during the reaction. Since we reconfirmed the formation of Fmoc-βAla-OH during the preparation of Fmoc-AA-OH by Fmoc-OSu, Fmoc-OPhth was designed and synthesized as a new Fmoc reagent to avoid the formation of Fmoc-βAla-OH. Furthermore, Fmoc protection by Fmoc-OPhth and Fmoc-SPPS were evaluated. The various Fmoc-amino acids prepared by Fmoc-OPhth were carried out in good yields and these are applicable in Fmoc-SPPS.

A Synthetic Strategy for Conjugation of Paromomycin to Cell-Penetrating Tat(48-60) for Delivery and Visualization into Leishmania Parasites.

A successful approach to deliver paromomycin, a poorly absorbed aminoglycoside antibiotic, to parasite cells is reported, based on selective protection of amino and hydroxyl groups followed by conjugation to a fluorolabeled, PEG-functionalized cell-penetrating Tat(48-60) peptide. The resulting construct is efficiently internalized into Leishmania cells, evidencing the fitness of cell-penetrating peptides as vectors for efficiently transporting low-bioavailability drugs into cells.

A Synthetic MUC1 Glycopeptide Bearing βGalNAc-Thr as a Tn Antigen Isomer Induces the Production of Antibodies against Tumor Cells.

This study presents the synthesis of the novel protected O-glycosylated amino acid derivatives 1 and 2, containing βGalNAc-SerOBn and βGalNAc-ThrOBn units, respectively, as mimetics of the natural Tn antigen (αGalNAc-Ser/Thr), along with the solid-phase assembly of the glycopeptides NHAcSer-Ala-Pro-Asp-Thr[αGalNAc]-Arg-Pro-Ala-Pro-Gly-BSA (3-BSA) and NHAcSer-Ala-Pro-Asp-Thr[βGalNAc]-Arg-Pro-Ala-Pro-Gly-BSA (4-BSA), bearing αGalNAc-Thr or βGalNAc-Thr units, respectively, as mimetics of MUC1 tumor mucin glycoproteins. According to ELISA tests, immunizations of mice with βGalNAc-glycopeptide 4-BSA induced higher sera titers (1:320 000) than immunizations with αGalNAc-glycopeptide 3-BSA (1:40 000). Likewise, flow cytometry assays showed higher capacity of the obtained anti-glycopeptide 4-BSA antibodies to recognize MCF-7 tumor cells. Cross-recognition between immunopurified anti-βGalNAc antibodies and αGalNAc-glycopeptide and vice versa was also verified. Lastly, molecular dynamics simulations and surface plasmon resonance (SPR) showed that βGalNAc-glycopeptide 4 can interact with a model antitumor monoclonal antibody (SM3). Taken together, these data highlight the improved immunogenicity of the unnatural glycopeptide 4-BSA, bearing βGalNAc-Thr as Tn antigen isomer.

Individual (f,tA)‐ and (f,tC)‐Fullerene‐Based Nickel(II) Glycinates: Protected Chiral Amino Acids Directly Linked to a Chiral π‐Electron System

AbstractStereoselective electrosynthesis of the first individual (f,tA)‐ and (f,tC)‐1,4‐fullerene derivatives with a non‐inherently chiral functionalization pattern is described, as well as the first example of an optically pure protected primary amino acid directly linked to the fullerene through only the chiral α‐amino‐acid carbon atom. An application of an auxiliary chiral nickel‐Schiff base moiety as derivatizing agent allowed separation of (f,tA)‐ and (f,tC)‐1,4‐fullerene derivatives using an achiral stationary phase, a separation which has never been done before.

Individual (f,t A)- and (f,t C)-Fullerene-Based Nickel(II) Glycinates: Protected Chiral Amino Acids Directly Linked to a Chiral π-Electron System.

Stereoselective electrosynthesis of the first individual (f,t A)- and (f,t C)-1,4-fullerene derivatives with a non-inherently chiral functionalization pattern is described, as well as the first example of an optically pure protected primary amino acid directly linked to the fullerene through only the chiral α-amino-acid carbon atom. An application of an auxiliary chiral nickel-Schiff base moiety as derivatizing agent allowed separation of (f,t A)- and (f,t C)-1,4-fullerene derivatives using an achiral stationary phase, a separation which has never been done before.