Boc-protected Amino Acids Research Articles

Enantiopure β3-Trifluoromethyl-β3-homoalanine Derivatives: Coupling with Boc-Protected Amino Acids and Conformational Studies of Peptides in Solid State

AbstractThe use of enantiopure β3-trifluoromethyl-β3-alkyl β-amino acids for the design of peptides would contribute to drastically enhance peptide stability in vivo. Moreover, the steric hindrance generated by the substituents on the tetrasubstituted carbon adjacent to the nitrogen function coupled to the electron-withdrawing effect of the trifluoromethyl group is more likely to influence the 3D conformation of the peptide. Herein, we describe a short, scalable and robust method to synthesize N- and/or C-protected enantiopure (R)- and (S)-β3-trifluoromethyl-β3-methyl β-amino acid derivatives and liquid-phase coupling methods suitable for incorporation of Boc-protected amino acids into short α/β- and β-peptides. Conformational studies of some of these original peptides via X-ray diffraction analysis highlighted intraresidue C6 hydrogen bonds within trifluoromethylated amino acids.

Synthesis of aminoacylated ergosterols: A new lipid component of fungi

Aminoacylated ergosterol such as 1-ergosteryl aspartate (Erg-Asp) is a new lipid component recently discovered in fungi. In order to study physiological functions of this novel sterol derivative and to develop potential antifungal agents, we established the method to synthesize aminoacylated ergosterol derivatives. Herein, we report the synthesis of Erg-Asp as well as some other aminoacylated ergosterols (Erg-Gly, Erg-Ala, Erg-Leu, Erg-Ile, and Erg-Val) using Boc protected amino acids.

Molecular engineering of tyrosine and tyrosine derived peptides to produce organogel

This present work deals with the synthesis of a series of organogel derived from substituted tyrosine derivatives via applying the concept of molecular engineering. Phenylalanine and tyrosine are structurally very similar amino acids. But only phenylalanine forms gels in both water and organic solvents. That is why the challenge was taken to transform tyrosine into a gelator and the concept of molecular engineering was applied. It was observed that a single nitro group is sufficient enough to transform it into a gelator. Not only a Boc-protected amino acid but also dipeptide and tripeptide were also found to produce organogel. Theoretical studies were also performed to understand the interactions involved during the gelation process. The gels derived from 1, 2, and 4 were found to be responsive towards a strong base like hydroxide which also helped us to get information regarding the gel model.

S-Mg2(dobpdc): a metal-organic framework for determining chirality in amino acids.

Chirality is a key aspect of amino acids and is essential for life. Here, a chiral metal-organic framework, S-Mg2dobpdc, is used to determine the chirality of three BOC protected amino acids (alanine, valine and proline) by 13C solid-state NMR with chemical shift differences of up to 1.3 ppm observed between enantiomers. The chiral sensitivity persists upon in situ deprotection of the amino acids by thermolysis of the BOC group.

Promotion Mechanism of H2O for Stereoselectivity in Pd(II)-catalyzed C―H Arylation of Diarylphosphinamides with Arylboronic Acids

On the basis of a series of control experiments and nuclear magnetic resonance analyses, it is discovered that Boc-protected amino acid ligand coordinated to Pd center is partly replaced by N,N-dimethylformamide, and H2O can inhibit coordination of N,N-dimethylformamide to Pd center. The novel action mechanism perfectly explains H2O promotion for stereoselectivity in Pd(II)-catalyzed C―H arylation of diarylphosphinamides with arylboronic acids.

Diastereoselective Synthesis of (–)-Bestatin, Epibestatin, Phebestin and (3S,4R)-4-Amino-3-hydroxy-5-phenylpentanoic Acid from an Aldehyde Derived from d-Phenylalanine

A convenient and efficient method for the synthesis of (–)-bestatin, epibestatin, phebestin, and (3S,4R)-4-amino-3-hydroxy-5-phenylpentanoic acid is reported. The key step is a proline-catalyzed α-hydroxylation of an aldehyde derived from d-phenylalanine, which leads to incorporation of a hydroxyl group at the α-position of that aldehyde with good yield and very high diastereoselectivity. Bestatin and its dia­stereomer epibestatin are synthesized from the same starting material using the same sequence of reactions, except for proline as the catalyst. An O-MOM and Boc-protected amino acid, a common intermediate for bestatin, was coupled with a dipeptide, H-Val-Phe-OMe followed by global deprotection to yield phebestin. (3S,4R)-4-Amino-3-hydroxy-5-phenylpentanoic acid was also synthesized in eight steps from the same starting material. The reported synthetic route offers a general method for the synthesis of such types of compounds and their analogues by changing the proline catalyst and/or the starting material from d- to l-phenylalanine.

Synthesis of 3-Benzylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione

3-Benzylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione [cyclo(Pro-Phe)] was synthesized by cyclization of prolylphenylalanine and phenylalanylproline methyl esters which were prepared from the corresponding Boc-protected amino acids.

Amino acid conjugated antimicrobial drugs: Synthesis, lipophilicity- activity relationship, antibacterial and urease inhibition activity

Present work describes the in vitro antibacterial evaluation of some new amino acid conjugated antimicrobial drugs. Structural modification was attempted on the three existing antimicrobial pharmaceuticals namely trimethoprim, metronidazole, isoniazid. Twenty one compounds from seven series of conjugates of these drugs were synthesized by coupling with some selected Boc-protected amino acids. The effect of structural features and lipophilicity on the antibacterial activity was investigated. The synthesized compounds were evaluated against five standard American type culture collection (ATCC) i.e. Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi strains of bacteria. Our results identified a close relationship between the lipophilicity and the activity. Triazine skeleton proved beneficial for the increase in hydrophobicity and potency. Compounds with greater hydrophobicity have shown excellent activities against Gram-negative strains of bacteria than Gram-positive. 4-amino unsubstituted trimethoprim-triazine derivative 7b have shown superior activity with MIC = 3.4 μM (2 μg/mL) for S. aureus and 1.1 μM (0.66 μg/mL) for E. coli. The synthesized compounds were also evaluated for their urease inhibition study. Microbial urease from Bacillus pasteurii was chosen for this study. Triazine derivative 7a showed excellent inhibition with IC50 = 6.23 ± 0.09 μM. Docking studies on the crystal structure of B. pasteurii urease (PDB ID 4UBP) were carried out.

A new synthesis of 2-(aminoalkyl)-1,2,4-triazolo[1,5-a]pyrimidines

Nickel( ii ) acetylacetonate-promoted cycloaddition between Boc-protected amino acid hydrazides and benzoylcyanamide followed by deprotection gives 2-amino-5-aminoalkyl-1,2,4-triazoles, whose reaction with 1,3-dielectrophiles affords the title compounds.

Enantioselective recognition of sodium carboxylates by an 1,8-diaminoanthracene based ion pair receptor containing amino acid units

An anthracene based ion pair receptor containing two amino acid units supported by cation and anion binding domains has been synthesized and shown to exhibit enhanced anion binding affinities in the presence of sodium cations. The receptor’s ability to recognize enantiomers was studied using chiral carboxylates derived from 2-phenylbutyric acid, mandelic acid, and three Boc-protected amino acids. Sodium cation coordination does not influence chiral recognition but does affect the strength of anion binding. The greatest enhancement of anion binding in the presence of sodium cations was found for halides, and the highest enantiodiscrimination was found for Boc-N-tryptophan. Comparative anion and salt binding studies revealed that the simultaneous action of multiple binding domains in the structure of receptor 1 is responsible for its stronger salt association and better enantioselectivity than in the case of mono-supported receptor 2.

A new approach to the synthesis of 3-amino- and 3-benzoylamino-5-aminoalkyl-1,2,4-triazoles

Nickel(II) acetylacetonate for the first time was shown to efficiently catalyze the addition of Boc-protected amino acid hydrazides to the nitrile group of benzoylcyanamide with the formation of the corresponding 3-benzoylamino-substituted 1,2,4-triazoles with the Boc-aminoalkyl group at position 5. A further modification of the latter led, depending on the conditions, to mono- or dihydrochlorides of 1,2,4-triazole-derived amines.

The new esters derivatives of betulin and betulinic acid in epidermoid squamous carcinoma treatment – In vitro studies

BackgroundBetulinic acid and betulin are triterpenes with documented cytotoxic properties toward various cell lines. Unfortunately both betulinic acid and its metabolic precursor, betulin, are very poorly soluble in aqueous buffers, thus their bioavailability and bio-distribution are insufficient in terms of medical applications. ObjectiveTo investigate the specific anticancer role of the newly synthesized betulin derivatives in human epidermoid carcinoma cells. MethodsIn the present study we synthesized five amino acid esters of betulin. For the synthesis we selected alanine (Boc-l-Ala-OH, negative control) and four basic amino acids – natural lysine (Boc-l-Lys(Boc)-OH) and three its unnatural derivatives (Boc-l-Dap(Boc)-OH, Boc-l-Dab(Boc)-OH, and Boc-l-Orn(Boc)-OH). Boc-protected amino acids were most convenient for the synthesis. All new esters have one (betulin-l-Ala-NH2) or two free amino groups which significantly increase their solubility in water and facilitate their transport through the cell membrane. It is worth noting that the biological activity of new esters of betulin is positive correlated with the length of the side chain of l-amino acid. The highest biological activity displayed compound containing lysine side chain (Lys, –CH2–CH2–CH2–CH2–NH2). Considering the biological activity, other derivatives can be set in the following series: Orn (–CH2–CH2–CH2–NH2)>Dab (–CH2–CH2–NH2)>Dap (–CH2–NH2)>Ala (CH3)>betulin. New betulin esters were tested in normal human keratinocytes (HaCaT) and human epidermoid carcinoma cells (A431). To assess cytotoxicity, MTT test was performed after 24, 48 and 72h of incubation with the test compounds at a concentration range of 0.75–100μM. In case of apoptotic activity, a TUNEL method and comet assay were performed. Additionally expression of caspase-3 and PARP1 was evaluated immunocytochemically. ResultsThe highest cytotoxicity in cells induced skin cancer new compounds, particularly compound containing a lysine side chain (IC50=7μM) and ornithine (IC50=10μM). The highest number of apoptotic cells was observed in case incubation with compound containing Orn, Dab and Dap side chain. ConclusionsThe new betulin ester derivatives display enhanced antitumor activity compared to their non-modified precursors. It is worth emphasizing their specific toxicity against epidermoid carcinoma cells.

Water compatible photoarylation of amino acids and peptides.

A novel photoarylation of amino acids and peptides is described, which tolerates the presence of water. Irradiation of Boc-protected amino acids in the presence of N-protected 2-azidobenzimidazoles leads to selective arylation of carboxy termini or side chains. The new reaction also works for peptides. Irradiation of the nonapeptide H-SPSYVYHQF-OH also resulted in selective arylation of the tyrosine side chains, as indicated by ESI-MS/MS fragmentation. Chemo- and regioselectivity could add the title reaction to the repertoire of photoaffinity labeling methods.

Rapid Determination of Enantiomeric Excess of Tert-Butoxycarbonyl (BOC-Protected) Amino Acids Based on Infrared Spectra Technique with Optimal Wavelet Packet Transform Decomposition Frequency Band

A method was employed to determine enantiomeric excess (ee) value of chiral tert-butoxycarbonyl (Boc-protected) amino acids in a rapid way by using an infrared spectroscopy technique combined with wavelet packet transform (WPT) and least squares support vector machines (LS-SVM). Infrared spectral data were decomposed by using WPT algorithm. Simulated annealing (SA) algorithm was then used to search the optimal decomposed frequency band that had the greatest contribution to the quantitative analysis of ee values. As a result, the band (7, 34) with 34 variables and the band (5, 1) with 116 variables were determined as the optimal ones for the determination of Boc-protected proline and alanine, respectively. The selected variables in the optimal band were used as the inputs of LS-SVM models. The spectral variables selected by the WPT-SA method had lower predicting errors than full range spectra and the spectral variables selected by some traditional variable selection methods. Reasonable good results with root mean-square error of prediction (RMSEP) of 7.51 and 3.80 were obtained for the determination of ee values of two Boc-protected amino acids, showing that it is possible to rapidly determine ee values of amino acids by using IR spectroscopy rapidly.

Efficient α-Mannosylation of Phenols: The Role of Carbamates as Scavengers for Activated Glycosyl Donors

The boron trifluoride activation of trichloroacetimidate donors was found to be an efficient method for the α-mannosylation of tyrosine-containing acceptors. Most notably, these conditions are compatible with the commonly used carbamate protecting groups, whereas trichloroacetimidate activation with trimethylsilyl triflate or the use of glycosyl sulfoxides led to diminished yields in the presence of carbamates. In these cases, the competing reaction of the activated donors with the carbamate group was identified as a problematic side reaction. Taking advantage of this reactivity, various glycosyl carbamates were generated for the first time under non-acidic glycosylation conditions by reaction of different Boc-protected amino acids and dipeptides with glycosyl sulfoxides under triflic anhydride activation.

Nano structures through self-assembly of protected hydrophobic amino acids: encapsulation of rhodamine B dye by proline-based nanovesicles

The development of novel molecules for the creation of nanometer structures with specific properties has been the current interest of this research. We have developed a set of molecules from hydrophobic ω- and α-amino acids by protecting the –NH2 with Boc (t-butyloxycarbonyl) group and –CO2H with para-nitroanilide such as BocHN–Xx–CONH–(p–NO2)·C6H4, where Xx is γ-aminobutyric acid (γ-Abu), (l)-isoleucine, α-aminoisobutyric acid, proline, etc. These molecules generate various nanometer structures, such as nanofibrils, nanotubes and nanovesicles, in methanol/water through the self-assembly of bilayers in which the nitro benzene moieties are stacked in the middle and the Boc-protected amino acids parts are packed in the outer surface. The bilayers can be further stacked one over the other through hydrophobic interactions to form multilayer structure, which helps to generate different kinds of nanoscopic structures. The formation of the nanostructures has been facilitated through the participation of various noncovalent interactions, such as hydrophobic interactions, hydrogen bonding and aromatic π-stacking interactions. Fluorescence microscopy and UV studies reveal that the nanovesicles generated from pro-based molecule can encapsulate dye molecules which can be released by addition of acid (at pH 2). These single amino acid based molecules are both easy to synthesize and cost-effective and therefore offer novel scaffolds for the future design of nanoscale structures.

N , N ′-Dialkylaminoalkylcarbonyl (DAAC) prodrugs and aminoalkylcarbonyl (AAC) prodrugs of 4-hydroxyacetanilide and naltrexone with improved skin permeation properties

N,N'-Dialkylaminoalkylcarbonyl (DAAC) and aminoalkylcarbonyl (AAC) prodrugs of phenolic drugs acetaminophen (APAP) and naltrexone (NTX) are reported. The effects of incorporation of a basic amine group into the promoiety of an acyl prodrug of a phenolic drug on its skin permeation properties are also presented. DAAC-APAP prodrugs were synthesized via a three-step procedure starting with haloalkylcarbonyl esters which were reacted with five different amines: dimethylamine, diethylamine, dipropylamine, morpholine, and piperidine. The spacing between the amino group and the carbonyl group of the acyl group was 1-3 CH(2). After the hydrolysis of the ester, the carboxylic acid product was subsequently coupled with the parent drug via a dicyclohexyl carbodiimide (DCC) mediated coupling to yield the DAAC-APAP-HCl prodrugs in excellent yields. The AAC prodrugs were synthesized using commercially available Boc-protected amino acids using DCC or EDCI as coupling agents. The yields of the prodrugs synthesized using these two different methods have been compared. Half-lives (t(1/2)) of a few members of the DAAC and AAC series were measured in buffer (pH 6.0, 20mM). The members evaluated in hydrolysis experiments exhibit a t(1/2) range of 15-113min. Among AAC-APAP prodrugs, the isopropyl group in valinate-APAP-HCl exerted a steric effect that increased the t(1/2) value for this prodrug compared to alaninate-APAP-HCl or prolinate-APAP-HCl. The 2-morpholinylacetate-APAP prodrug was able to achieve twice the flux of APAP in in vitro diffusion cell experiments through hairless mouse skin.

Oligonuclear Ferrocene Amides: Mixed‐Valent Peptides and Potential Redox‐Switchable Foldamers

Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic ¹H NMR and Mössbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin-Day class II mixed-valent systems. Mössbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form).

One-pot microwave-assisted synthesis and antimalarial activity of ferrocenyl benzodiazepines

An efficient synthesis of 1,4-benzodiazepin-2-ones is described by condensation between 2-aminobenzophenone and Boc-protected amino acids via microwave-assisted irradiation. This produces higher yields in shorter reaction times than with traditional methods. The antiplasmodial activity of the corresponding ferrocenyl benzodiazepines was evaluated in vitro against Plasmodium falciparum F32 (chloroquine-sensitive) and FCB1 and K1 (chloroquine-resistant) strains and gabonese clinical isolates.

ChemInform Abstract: An Efficient Method for the Reduction of N-Protected Amino Acids and Peptides to the Corresponding Alcohols.

Reduction of pentachlorophenyl esters of Boc protected amino acids and peptides to the corresponding alcohols is described.