Studies on cytochrome c. VI. Synthesis of the protected pentadecapeptide (sequence 64-81) of Baker's yeast iso-1-cytochrome c

The syntheses are reported of two N-benzloxycarbonylpeptide tert-butoxycarbonylhydrazides corresponding to the amino acid sequences 67–74 and 75–81 of the baker's yeast iso-1-cytochrome c and their subsequent assembly to the N-benzyloxycarbonylpentadecapeptide tert-butoxycarbonylhydrazide corresponding to the sequence 67–81 of the protein.     

Studies on cytochrome c. VII. Synthesis of the protected undecapeptide (sequence 82-92) of Baker's yeast iso-1-cytochrome c

The synthesis is described of the N-benzyloxycarbonylundecapeptide tert-butoxycarbonylhydrazide corresponding to the sequence 82–92 of baker's yeast iso-I-cytochrome c.     

Studies on cytochrome c. Part IV. Synthesis of the protected dodecapeptide (sequence 45–56) of Baker's yeast iso-1-cytochrome c

The synthesis is described for the N-benzyloxycarbonyldodecapeptide tert-butoxycarbonylhydrazide corresponding to the sequence 45–56 of baker's yeast iso-1-cytochrome c by fragment condensation using the Rudinger modified azide procedure for the assembly of the small subunits.     

Studies on cytochrome c. Part II. Synthesis of the protected heptapeptide (sequence 17–23) of Baker's yeast iso-1-cytochrome c

Synthesis is described for the N-o-nitrophenylsulfenylheptapeptide tert-butoxycarbonylhydrazide corresponding to positions 17–23 of the amino acid sequence of baker's yeast iso-1-cytochrome c. Moreover a new method of selective removal of the S-acetamidomethyl group for analytical and preparative purpose is reported.     

Studies on cytochrome c. Part I. Synthesis of the protected hexadecapeptide (sequence 1–16) of Baker's Yeast iso-1-cytochrome c

The general strategy for the synthesis by conventional procedure of N- and C-terminal fragments and of the entire sequence of baker's yeast iso-1-cytochrome c is discussed. The synthesis of the N-benzyloxycarbonylhexadecapeptide tert-butoxycarbonylhydrazide corresponding to the sequence 1–16 of the apoprotein is described in detail.     

Interaction of tert -butyl Hydroperoxide with Hypochlorous Acid. A Spin Trapping and Chemiluminescence Study

The formation of radical species during the reaction of tert-butyl hydroperoxide and hypochlorous acid has been investigated by spin trapping and chemiluminescence. A superposition of two signals appeared incubating tert-butyl hydroperoxide with hypochlorous acid in the presence of the spin trap &#102 -(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). The first signal (a_N = 1.537mT, a^&#103_H = 0.148mT) was an oxidation product of POBN caused by the action of hypochlorous acid. The second spin adduct (a_N = 1.484mT, a^&#103_H = 0.233mT) was derived from a radical species that was formed in the result of reaction of tert-butyl hydroperoxide with hypochlorous acid. Similarly, a superposition of two signals was also obtained using the spin trap N-tert-butyl- &#102 -phenylnitrone (PBN). tert-Butyl hydroperoxide was also treated with Fe²⁺ or Ce⁴⁺ in the presence of POBN. Using Fe²⁺ a spin adduct with a _N= 1.633mT and a^&#103_H = 0.276mT was observed. The major spin adduct formed with Ce⁴⁺ was characterised by α_N = 1.480mT and a^&#103_H = 0.233mT. The reaction of tert-butyl hydroperoxide with hypochlorous acid was accompanied by a light emission, that time profile and intensity were identical to those emission using Ce⁴⁺. The addition of Fe²⁺ to tert-butyl hydroperoxide yielded a much smaller chemiluminescence. Thus, tert-butyl hydroperoxide yielded in its reaction with hypochlorous acid or Ce⁴⁺ the same spin adduct and the same luminescence profile. Because Ce⁴⁺ is known to oxidise organic hydroperoxides to peroxyl radical species, it can be concluded that a similar reaction takes place in the case of hypochlorous acid.     

Preparative separation of amino acid enantiomers as N-TFA,O-isopropyl derivatives by continuous countercurrent gas-liquid chromatography

Preparative separation of derivatives of amino acid enantiomers was carried out by a countercurrent gas–liquid chromatography (CCGLC) with chiral liquid phases, N-stearoyl-L -valine tert-butylamide and/or N-stearoyl-L -leucine tert-butylamide. In order to make effective use of these phases and also to lower the viscosity, Apiezon C was added as diluent. Through a repeated operation of a temperature gradient, purities more than 99% of leucine and α-amino butyric acid derivatives were proved to be obtained. © 1993 Wiley-Liss, Inc.     

Synthesis and Properties of a Novel Pyridineoxazoline Containing Optically Active Helical Polymer as a Catalyst Ligand for Asymmetric Diels–Alder Reaction

A novel pyridineoxazoline (PyOx) containing helical polymer, poly{(–)‐(S)‐4‐tert‐butyl‐2‐[5‐(4‐tert‐butylphenyl)‐3‐vinylpyridin‐2‐yl]‐oxazoline} ( PA ), was designed and synthesized to approach the effect of chain conformation on the catalytic property. Its complex with Cu(OTf)₂, i.e., Cu(II)-PA , was employed to catalyze the homogeneous Diels–Alder (D–A) reaction of alkenoyl pyridine N‐oxides with cyclopentadiene in tetrahydrofuran. Compared with the previously reported copper complex, Cu(II)-P1 (RSC Advances, 2015, 5 , 2882), which was derived from a nonhelical poly[(–)‐(S)‐4‐tert‐butyl‐2‐(3‐vinylpyridin‐2‐yl)‐oxazoline], Cu(II)-PA exhibited a remarkably enhanced enantioselectivity and reaction rate. However, its enantioselectivity was lower than the Cu(II) complex of (–)‐(S)‐4‐tert‐butyl‐2‐[5‐(4‐tert‐butylphenyl)‐3‐vinylpyridin‐2‐yl]‐oxazoline ( Cu(II)-A ), a low molar mass model compound. Chirality 27:523–531, 2015. © 2015 Wiley Periodicals, Inc.     

Investigating the free radical trapping ability of NXY-059, S-PBN and PBN

The spin trapping ability of the nitrones 2,4-disulphophenyl-N-tert-butyl nitrone (NXY-059), 2-sulphophenyl-N-tert-butyl nitrone (S-PBN) and α-phenyl-N-tert-butyl nitrone (PBN) for both hydroxyl and methanol radicals was investigated using electron paramagnetic resonance (EPR) spectroscopy. The radicals of interest were generated in situ in the spectrometer under constant flow conditions in the presence of each nitrone. The spin adducts formed were detected by EPR spectroscopy. This approach allowed for quantitative comparison of the EPR spectra of the spin adducts of each nitrone. The results obtained showed that NXY-059 trapped a greater number of hydroxyl and methanol radicals than the other two nitrones, under the conditions studied.     

Identification of a radical formed in the reaction mixture of rat brain homogenate with a ferrous ion/ascorbic acid system using HPLC–EPR and HPLC–EPR–MS

Identification of a free radical is performed for the reaction mixture of rat brain homogenate with a ferrous ion/ascorbic acid system using EPR, high performance liquid chromatography–electron paramagnetic resonance spectrometry (HPLC–EPR) and high performance liquid chromatography–electron paramagnetic resonance–mass spectrometry (HPLC–EPR–MS). EPR measurements of the reaction mixtures showed prominent signals with hyperfine coupling constants (α^N = 1.58 mT and α^Hβ = 0.26 mT). No EPR spectrum was detectable without rat brain homogenate, suggesting that the radical is derived from rat brain homogenate. An HPLC–EPR analysis of the reaction mixture showed a peak with retention time of 33.7 min. An HPLC–EPR–MS analysis of the peak gave two ions at m/z 224 and 137, suggesting that α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN)/ethyl radical adduct forms in the reaction mixture.     

Studies on cyclic peptides. II. Synthesis of cyclic peptides containing sarcosine.

Cyclic peptides containing sarcosine, cyclo-(Pro-Sar-Gly)₂, cyclo-(Sar-Sar-Gly)₂, cyclo-(Sar₄), and cyclo-(Sar₆) have been synthesized by the cyclization of the p-nitrophenyl ester of linear peptides. The tert-butoxycarbonyl group was used as the N^α-protecting group, which was removed by acid. Benzyl ester was used to protect the C-terminal. tert-butoxycarbonylpeptide was obtained by the stepwise elongation of the peptide bond by the carbodiimide method. Deblocking and cyclization of the linear peptides gave the cyclic peptides.     

G-Octamer Formation from N9-Modified Guanine Derivatives

The properties of the self-assembly of two lipophilic guanine derivatives, 2′,3′,5′-O-tris(tert-butyldimethylsilyl)-guanosine and N⁹-(3,5-bis(tert-butyldimethylsilyloxy)-benzyl)-guanine, are described. In the presence of K⁺, both guanine derivatives self-associate into D ₄-symmetric octamers consisting of two G-quartets stacked around a central ion.     

Formation of radicals during heating lysine and glucose in solution with an intermediate water activity

Abstract

Heating glucose with lysine under alkaline conditions (pH 7.0–10.0) was found to take place with consumption of oxygen together with formation of brown-colored compounds. Highly reactive intermediary radicals were detected when lysine and glucose were heated at intermediate water activity at pH 7.0 and 8.0. The detection was based on initial trapping of highly reactive radicals by ethanol followed by spin trapping of 1-hydroxyethylradicals with α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) and Electron Spin Resonance (ESR) spectroscopy. The generation of reactive intermediary radicals from the Maillard reactions was favored by enhancing alkaline conditions (pH 8.0) and stimulated by presence of the transition metal ion Fe²⁺. The stability of the nitrone spin traps, N-tert-butyl-α-phenylnitrone and POBN was examined in buffered aqueous solutions within the pH range 1–12, and found to be less temperature dependent at acidic pH compared to alkaline conditions. A low rate (k_obs) of hydrolysis of POBN was found at the used experimental conditions of 70°C and pH 7.0 and 8.0, which made this spin trap method suitable for the detection of radicals in the Maillard reaction system.     

Protective role of ortho-substituted Mn(III) N-alkylpyridylporphyrins against the oxidative injury induced by tert-butylhydroperoxide

Abstract

The present work addresses the role of two ortho-substituted Mn(III) N-alkylpyridylporphyrins, alkyl being ethyl in MnTE-2-PyP⁵⁺ and n-hexyl in MnTnHex-2-PyP⁵⁺, on the protection against the oxidant tert-butylhydroperoxide (TBHP). Their protective role was studied in V79 cells using endpoints of cell viability (MTT and crystal violet assays), intracellular O₂?– generation (dihydroethidium assay) and glutathione status (DTNB and monochlorobimane assays). MnPs per se did not show cytotoxicity (up to 25 μM, 24 h). The exposure to TBHP resulted in a significant decrease in cell viability and in an increase in the intracellular O₂^?– levels. Also, TBHP depleted total and reduced glutathione and increased GSSG. The two MnPs counteracted remarkably the effects of TBHP. Even at low concentrations, both MnPs were protective in terms of cell viability and abrogated the intracellular O₂^?– increase in a significant way. Also, they augmented markedly the total and reduced glutathione contents in TBHP-treated cells, highlighting the multiple mechanisms of protection of these SOD mimics, which at least in part may be ascribed to their electron-donating ability.     

Synthesis of peptide nucleic acid oligomers carrying 5-methylcytosine derivatives by postsynthetic substitution

The preparation of the thymine peptide nucleicacid (PNA) monomer carrying a 2-nitrophenyl group in position4 is described. This monomer is incorporated into PNAoligomers and reacted with amines to yield PNA oligomerscarrying 5-methylcytosine derivatives. During thedeprotection-modification step two side reactions weredetected: degradation of PNA oligomer from the N-terminal residue and modification of N ⁴-tert-butylbenzoyl cytosine residue. Protection of the N-terminal position and the use of N ⁴-acetyl group for the protection of cytosine eliminate these side reactions.     

Solution‐phase submonomer diversification of aza‐dipeptide building blocks and their application in aza‐peptide and aza‐DKP synthesis

Aza‐peptides have been used as tools for studying SARs in programs aimed at drug discovery and chemical biology. Protected aza‐dipeptides were synthesized by a solution‐phase submonomer approach featuring alkylation of N‐terminal benzophenone semicarbazone aza‐Gly‐Xaa dipeptides using different alkyl halides in the presence of potassium tert‐butoxide as base. Benzophenone protected aza‐dipeptide tert‐butyl ester 31c was selectively deprotected at the C‐terminal ester or N‐terminal hydrazone to afford, respectively, aza‐dipeptide acid and amine building blocks 36c and 40c, which were introduced into longer aza‐peptides. Alternatively, removal of the benzophenone semicarbazone protection from aza‐dipeptide methyl esters 29a–c led to intramolecular cyclization to produce aza‐DKPs 39a–c. In light of the importance of aza‐peptides and DKPs as therapeutic agents and probes of biological processes, this diversity‐oriented solution‐phase approach may provide useful tools for studying peptide science. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Steric structure of L-proline oligopeptides. I. Infrared absorption spectra of the oligopeptides and poly-L-proline

Poly-L -prolines I and II were differentiated by the characteristic bands in the far infrared region. Form I showed two broad bands at about 280 and 160 cm^?1 and form II two bands at, 400 and 670 cm.^?1. Furthermore, three broad bands at about 250, 200, and 100 cm.^?1 were observed in the spectrum for form II. Infrared absorption bands of the pentamer, hexamer, and octamer of tert-amyloxycarbonyl-L -proline were almost similar to those of poly-L -proline II in the 1800–75 cm.^?1 region. In the far-infrared region, especially, the absorption bands of these three oligopeptides were in good agreement with that of poly–L –proline II. Accordingly we concluded that the molecules of pentamer, hexamer, and octamer had a helical structure of a left-handed threefold screw axis. The tetrapeptide of tert-amyloxycarbonyl-L -proline might also have a left-handed helix, probably one turn, since the tetramer clearly showed an absorption band at about 400 cm.^?-1 characteristic of poly–L –proline II.     

Glycosyl esters of amino acids. V. Synthesis and properties of 1-O-acylaminoacyl-alpha- and -beta-D-glucopyranoses and 1-O-(1-beta-aspartyl)-beta-D-glucopyranose

Catalytic hydrogenation of the tetrabenzyl ethers of 1-O-acetamidoacyl- and 1-O-tert-butyloxycarbonylaminoacyl-α- and -β-D-glucopyranoses (1–6) afforded the corresponding 1-O-acylaminoacyl-D-glucopyranoses 8–13 which were fully characterised by physical methods and by conversion into the peracetylated derivatives 14–19. The α anomers of 1-O-tert-butyloxycarbonylaminoacyl-D-glucopyranoses underwent 1→2 acyl migration, and, in order to characterize the rearrangement product of 1-O-(tert-butyloxycarbonyl-L-alanyl)-α-D-glucopyranose (12α), 1,3,4,6-tetra-O-acetyl-2-O-(tert-butyloxycarbonyl-L-alanyl)-α- and -β-D-glucopyranoses (22 and 23) were synthesized by definitive methods. Initial studies of the simultaneous deprotection of the amino and hydroxyl functions were performed with D-glucose-amino acid 6-esters; catalytic hydrogenation of methyl 2,3,4-tri-O-benzyl-6-O-(N-benzyloxycarbonylglycyl)-β-D-glucopyranose (24) gave methyl 6-O-glycyl-β-D-glucopyranose (25) as the stable hydrochloride. Hydrogenolysis of the β anomer of 2,3,4,6-tetra-O-benzyl-1-O-[1-benzyl N-(benzyloxycarbonyl)-L-aspart-4-oyl]-D-glucopyranose (7) afforded 1-O-(L-β-aspartyl)-β-D-glucopyranose (27). The rates of hydrolysis of the unprotected D-glucose-amino acid 1-ester 27 in water and in 0.1M hydrochloric acid were compared with those of the D-glucose-amino acid 6-ester 25.     

Synthesis and use of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-di-Boc-glutamate γ-semialdehydes and related aldehydes

Summary.  This review article focuses on the synthesis and reactions of N,N-di-Boc glutamate and aspartate semialdehydes as well as related aldehydes. These building blocks are prepared according to various strategies from glutamic and aspartic acids and find interesting synthetic applications. In the first part, the methods for the synthesis of N,N-di-Boc-amino aldehydes are summarized. The applications of these chiral synthons for the synthesis of unnatural amino acids and other bioactive compounds are discussed in the second section. Received April 24, 2002 Accepted August 13, 2002 Published online January 30, 2003 Authors' address: Prof. Violetta Constantinou-Kokotou, Chemical Laboratories, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece, E-mail: vikon@aua.gr Abbreviations: AcNH-TEMPO, 4-acetamido-2,2,6,6-tetramethyl-1-piperidinyloxy free radical; AIBN, 2,2′-azobis(2-methylpropionitrile); Aliquat, methyltrioctylammonium chloride; Bn, benzyl; Boc, tert-butoxycarbonyl; Bu^t, tert-butyl; m-CPBA, 3-chloroperoxybenzoic acid; DAST, diethylaminosulfur trifluoride; DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene; (R,R)-(+)-DET, (R,R)-(+)-diethyltartrate; DIBALH, diisobutyl aluminium hydride; DMAP, 4-dimethylaminopyridine; DMF, dimethylformamide; Et₃N, triethylamine; KHMDS, potassium bis(trimethylsilyl)amide; (S)-LLB, lanthanium-lithium-bis-metallic binaphthol catalyst; MsCl, methanesulfonyl chloride; NEM, N-ethylmorpholine; NMO, 4-methylmorpholine N-oxide; PPA, propylphosphonic acid anhydride; TBHP, tert-butyl hydroperoxide; TFA, trifluoroacetic acid; THF, tetrahydrofuran; TMSI, 1-(trimethylsilyl)imidazole; Trt, trityl.     

Synthesis of peptide nucleic acid oligomers carrying 5-methylcytosine derivatives by postsynthetic substitution

Summary The preparation of the thymine peptide nucleic acid (PNA) monomer carrying a 2-nitrophenyl group in position 4 is described. This monomer is incorporated into PNA oligomers and reacted with amines to yield PNA oligomers carrying 5-methylcytosine derivatives. During the deprotection-modification step two side reactions were detected: degradation of PNA oligomer from theN-terminal residue and modification ofN ⁴-tert-butylbenzoyl cytosine residue. Protection of theN-terminal position and the use ofN ⁴-acetyl group for the protection of cytosine eliminate these side reactions.