RESUMEN
4,4-Dimethyloxazolones derived from N-protected aminoisobutyric acid (AIB) are particularly known as poor electrophiles due to the steric hindrance around the carbonyl and not employed as useful intermediates for amidation whereas numerous examples have been reported to support the utility of other oxazolones in amidation. AIB is an important and strategical synthon in medicinal chemistry but the peptide bond formation of the N-protected urethane derivatives of AIB is known to be often unproductive due to the rapid formation of the stable 4,4-dimethyloxazolone via an intramolecular cyclization. We discovered that the 4,4-dimethyloxazolone of an AIB urethane is in fact an excellent electrophile that enables efficient amidation even with weakly reactive nucleophiles. The 4,4-dimethyloxazolone can be stored in a pure form and used as a reagent offering an efficient and convenient synthetic tool for generating AIB-peptide analogs.
Asunto(s)
Amidas/química , Ácidos Aminoisobutíricos/síntesis química , Oxazolona/química , Ácidos Aminoisobutíricos/química , Estructura MolecularRESUMEN
Aminoisobutyric acid (AIB) is an important building block widely incorporated by medicinal chemists in molecular design. Owing to the steric challenge, elaborating AIB's carboxylic acid using conventional amidation protocols is often problematic. We discovered that an amidation protocol utilizing methyl Boc-aminoisobutyrate and magnesium amidates of various reactivities produces the corresponding amide derivatives in good to excellent yields.
Asunto(s)
Amidas/síntesis química , Ácidos Aminoisobutíricos/síntesis química , Química Farmacéutica/métodosRESUMEN
Penetration of the blood brain barrier (BBB) by appropriate fluorescent probes remains a challenge in optical imaging and diagnostics. We designed, synthesized and observed the in vivo BBB penetration of a LASER syn-bimane probe. Results demonstrate that the Aib transporter unit in our probe may lead a fluorescent bimanyl moiety across the BBB.
Asunto(s)
Ácidos Aminoisobutíricos/farmacocinética , Compuestos de Azabiciclo/farmacocinética , Barrera Hematoencefálica/metabolismo , Compuestos Bicíclicos Heterocíclicos con Puentes/farmacocinética , Colorantes Fluorescentes/farmacocinética , Ácidos Aminoisobutíricos/síntesis química , Animales , Compuestos de Azabiciclo/síntesis química , Compuestos Bicíclicos Heterocíclicos con Puentes/síntesis química , Colorantes Fluorescentes/síntesis química , Masculino , Ratones , Microscopía Fluorescente , Distribución TisularRESUMEN
The biological activity of antibiotic peptaibols has been linked to their ability to aggregate, but the structure-activity relationship for aggregation is not well understood. Herein, we report a systematic study of a class of synthetic helical oligomer (foldamer) composed of aminoisobutyric acid (Aib) residues, which mimic the folding behavior of peptaibols. NMR spectroscopic analysis was used to quantify the dimerization constants in solution, which showed hydrogen-bond donors at the N terminus promoted aggregation more effectively than similar modifications at the C terminus. Elongation of the peptide chain also favored aggregation. The geometry of aggregation in solution was investigated by means of titrations with [D6]DMSO and 2D NOE NMR spectroscopy, which allowed the NH protons most involved in intermolecular hydrogen bonds in solution to be identified. X-ray crystallography studies of two oligomers allowed a comparison of the inter- and intramolecular hydrogen-bonding interactions in the solid state and in solution and gave further insight into the geometry of foldamer-foldamer interactions. These solution-based and solid-state studies indicated that the preferred geometry for aggregation is through head-to-tail interactions between the N and C termini of adjacent Aib oligomers.
Asunto(s)
Aminoácidos/química , Aminoácidos/síntesis química , Ácidos Aminoisobutíricos/química , Ácidos Aminoisobutíricos/síntesis química , Péptidos/química , Péptidos/síntesis química , Cristalografía por Rayos X , Dimerización , Enlace de Hidrógeno , Modelos Moleculares , Conformación Proteica , SolucionesRESUMEN
The effect of Schellman motifs on the adoption of stable 310 helical conformations in a series of aminoisobutyric (Aib) oligomers has been studied in the solid state and solution. The destabilising effect of the Schellman motif (a local inversion of helical screw-sense due to a C-terminal ester residue) was quantified in the solid state using X-ray crystallography through analysis of the torsion angles and their deviation from those observed in an ideal 310 helix. Investigation of the intramolecular hydrogen-bonding interactions in the solid state led to the identification of a fully extended C5 conformation in one oligomer, which is a novel folding motif for Aib oligomers. The effect of ester groups with differing steric demands on intermolecular hydrogen-bonding contacts in the solid state was also ascertained. In solution, the adoption of a 310 conformation in Aib oligomers appeared to be more finely tuned, depending on a number of factors, including chain length and the steric demands of the C-terminal destabilising Schellman motif.
Asunto(s)
Ácidos Aminoisobutíricos/química , Ésteres/química , Conformación Molecular , Ácidos Aminoisobutíricos/síntesis química , Cristalografía por Rayos X , Dimetilsulfóxido/química , Espectroscopía de Resonancia Magnética , Modelos Moleculares , Péptidos/química , Protones , SolucionesRESUMEN
Isotope-edited FT-IR spectroscopy is a combined synthetic and spectroscopic method used to characterize local (e.g., residue-level) vibrational environments of biomolecules. We have prepared the 3(10) helical peptide Z-Aib6-OtBu and seven (13)C-enriched analogues that vary only in the number and position(s) of (13)CâO isotopic enrichment. FT-IR spectra of these eight peptides solvated in the nonpolar aprotic solvent dichloromethane have been collected and compared to frequency, intensity, and normal mode results of DFT calculations. Single (13)C enrichment of amide functional groups tends to localize amide I vibrational eigenmodes, providing residue-specific information regarding the local environment (e.g., hydrogen bonding or solvent exposure) of the peptide bond. Double (13)C enrichment of Z-Aib6-OtBu allows for examination of interamide coupling between two labeled amide functional groups, providing experimental evidence of interamide coupling in the context of 3(10) helical structure. Although the calculated and observed interamide couplings of Z-Aib6-OtBu are a few cm(-1) and less, the eight peptides exhibit distinct infrared spectra, revealing details of interamide coupling and residue level vibrational environments.
Asunto(s)
Alanina/química , Ácidos Aminoisobutíricos/química , Péptidos/química , Teoría Cuántica , Ácidos Aminoisobutíricos/síntesis química , Isótopos de Carbono , Péptidos/síntesis química , Espectroscopía Infrarroja por Transformada de FourierRESUMEN
Reported is the synthesis of azo mutual prodrugs of the nonsteroidal anti-inflammatory agents (NSAIDs) 4-aminophenylacetic acid (4-APAA) or 5-aminosalicylic acid (5-ASA) with peptides, including an antibiotic peptide temporin analogue modified at the amino terminal by an α-aminoisobutyric acid (Aib) residue. These prodrugs are designed for colonic delivery of two agents to treat infection and inflammation by the bacterial pathogen Clostridium difficile .
Asunto(s)
Ácidos Aminoisobutíricos/síntesis química , Antibacterianos/síntesis química , Antiinflamatorios no Esteroideos/síntesis química , Compuestos Azo/síntesis química , Péptidos/química , Profármacos/síntesis química , Ácidos Aminoisobutíricos/química , Ácidos Aminoisobutíricos/farmacología , Antibacterianos/química , Antibacterianos/farmacología , Antiinflamatorios no Esteroideos/química , Antiinflamatorios no Esteroideos/farmacología , Compuestos Azo/química , Compuestos Azo/farmacología , Clostridioides difficile/efectos de los fármacos , Pruebas de Sensibilidad Microbiana , Estructura Molecular , Péptidos/farmacología , Profármacos/química , Profármacos/farmacologíaRESUMEN
We describe the synthesis of (11)C-labeled α-aminoisobutyric acid 2 from iodo[(11)C]methane and methyl N-(diphenylmethylen)-d,l-alaniate (5). The tetrabutylammonium fluoride (TBAF)-promoted α-[(11)C]methylation of sterically hindered analog 5 was a key step in our synthesis process. Total radiochemical conversion of 2 was high and a remote-controlled synthesis was carried out. A comparative tumor positron emission tomography (PET) imaging study using the same model mouse showed higher uptake of 2 than with (11)C-labeled methionine and [(18)F] fluorodeoxyglucose (FDG).
Asunto(s)
Ácidos Aminoisobutíricos/química , Neoplasias/diagnóstico por imagen , Radiofármacos/química , Ácidos Aminoisobutíricos/síntesis química , Animales , Radioisótopos de Carbono/química , Modelos Animales de Enfermedad , Ratones , Tomografía de Emisión de Positrones , Radiofármacos/síntesis químicaRESUMEN
The non-natural amino acids (R)- and (S)-2-amino-3-fluoro-2-methylpropanoic acid 5 and (R)- and (S)-3-fluoro-2-methyl-2-N-(methylamino)propanoic acid 8 were synthesized in shorter reaction sequences than in the original report starting from enantiomerically pure (S)- and (R)-alpha-methyl-serine, respectively. The reaction sequence provided the cyclic sulfamidate precursors for radiosynthesis of (R)- and (S)-[(18)F]5 and (R)- and (S)-[(18)F]8 in fewer steps than in the original report. (R)- and (S)-[(18)F]5 and(R)- and (S)-[(18)F]8 were synthesized by no-carrier-added nucleophilic [(18)F]fluorination in 52-66% decay-corrected yields with radiochemical purity over 99%. The cell assays showed that all four compounds were substrates for amino acid transport and enter 9L rat gliosarcoma cells in vitro at least in part by system A amino acid transport. The biodistribution studies demonstrated that in vivo tumor to normal brain ratios for all compounds were high with ratios of 20:1 to115:1 in rats with intracranial 9L tumors. The (R)-enantiomers of [(18)F]5 and [(18)F]8 demonstrated higher tumor uptake in vivo compared to the (S)-enantiomers.
Asunto(s)
Ácidos Aminoisobutíricos , Neoplasias Encefálicas/diagnóstico , Tomografía de Emisión de Positrones/métodos , Aminoácidos/farmacocinética , Ácidos Aminoisobutíricos/síntesis química , Ácidos Aminoisobutíricos/farmacocinética , Animales , Transporte Biológico , Línea Celular Tumoral , Marcaje Isotópico/métodos , Radiofármacos/síntesis química , Radiofármacos/farmacocinética , Ratas , Distribución TisularRESUMEN
L-Leu hexapeptide containing alpha-aminoisobutyric acid (Aib) forms a right-handed (P) 3(10)-helix, whereas that containing cyclic alpha,alpha-disubstituted amino acid Ac(5)c(dOM) assumes a right-handed (P) alpha-helix in the solid state.
Asunto(s)
Péptidos/química , Ácidos Aminoisobutíricos/síntesis química , Dicroismo Circular , Cristalografía por Rayos X , Conformación Proteica , Estructura Secundaria de Proteína , Espectrofotometría Infrarroja , Espectroscopía Infrarroja por Transformada de FourierRESUMEN
With biologically important "peptide bundling" as the motif, new chromophoric cyclic host 1 was designed, which consists of two zinc porphyrin units that are connected by dynamic peptide helices of nonameric aminoisobutyric acid (Aib) units. Upon inclusion of pyridine-anchored helical peptides between the zinc porphyrin units, 1 displayed an intense exciton-coupled circular dichroism (CD) band at 410-450 nm, whose sign reflected the helical sense of the guest peptides. Studies with conformationally defined dehydrophenylalanine-containing analogues indicated that the dynamic helical chains in the host are stereochemically harmonized with right- or left-handed helices of the guest peptides in a confined nano space, leading to either clockwise- or anticlockwise-twisted geometry (chiroptical output) of the connecting zinc porphyrin chromophores.
Asunto(s)
Ácidos Aminoisobutíricos/química , Materiales Biomiméticos/química , Metaloporfirinas/química , Oligopéptidos/química , Ácidos Aminoisobutíricos/síntesis química , Materiales Biomiméticos/síntesis química , Dicroismo Circular , Metaloporfirinas/síntesis química , Modelos Moleculares , Oligopéptidos/síntesis química , Estructura Secundaria de Proteína , Estereoisomerismo , Relación Estructura-ActividadRESUMEN
The 18-membered Aib-containing cyclohexapeptides, cyclo(-Gly-Aib-Aib-Gly-Aib-Phe-) (22), cyclo(-Gly-Aib-Phe(2Me)-Gly-Aib-Aib-) (24a), cyclo(-Gly-Phe(2Me)-Aib-Gly-Aib-Aib-) (24b), and cyclo(-Gly-Phe(2Me)-Aib-Gly-Aib-Phe-) (25), have efficiently been synthesized by solution-phase techniques. The linear precursors 1a-1d were prepared by combining the 'azirine/oxazolone method' for incorporation of alpha,alpha-disubstituted alpha-amino acids (Aib, Phe(2Me)) into the peptide chains by classical peptide coupling methods for segment condensations. Deprotection of the amino and carboxy termini of 1a-1d, followed by cyclization with DEPC as the coupling reagent, gave the above-mentioned cyclic hexapeptides 22, 24a, 24b, and 25 in good yields (26-57%). The solid-state conformations of the linear hexapeptides 1d, 16 and 27, and of the cyclohexapeptides 22 and 25 have been established by X-ray crystallography.
Asunto(s)
Ácidos Aminoisobutíricos/síntesis química , Oligopéptidos/síntesis química , Estructura Molecular , Soluciones/síntesis químicaRESUMEN
Novel radiopharmaceuticals, including amino acids, that target neoplasms through their altered metabolic states have shown promising results in preclinical and clinical studies. Two fluorinated analogues of alpha-aminoisobutyric acid, 2-amino-3-fluoro-2-methylpropanoic acid (FAMP) and 3-fluoro-2-methyl-2-(methylamino)propanoic acid (N-MeFAMP), have been radiolabeled with fluorine-18, characterized in amino acid uptake assays, and evaluated in vivo in normal rats and a rodent tumor model. The key steps in the syntheses of both radiotracers involved the preparation of cyclic sulfamidate precursors. Radiosyntheses of both [18F]FAMP and [18F]N-MeFAMP via no-carrier-added nucleophilic substitution provided high yields (>78% decay-corrected) in high radiochemical purity (>99%). Amino acid transport assays using 9L gliosarcoma cells demonstrated that both compounds are substrates for the A type amino acid transport system, with [18F]N-MeFAMP showing higher specificity than [18F]FAMP for A type transport. Tissue distribution studies in normal Fischer rats and Fischer rats implanted intracranially with 9L gliosarcoma tumor cells were also performed. At 60 min postinjection, the tumor vs normal brain ratio of radioactivity was 36:1 in animals receiving [18F]FAMP and 104:1 in animals receiving [18F]N-MeFAMP. On the basis of these studies, both [18F]FAMP and [18F]N-MeFAMP are promising imaging agents for the detection of intracranial neoplasms via positron emission tomography.
Asunto(s)
Aminoácidos/síntesis química , Ácidos Aminoisobutíricos/síntesis química , Propionatos/síntesis química , Radiofármacos/síntesis química , Sistema de Transporte de Aminoácidos A/antagonistas & inhibidores , Sistema de Transporte de Aminoácidos A/metabolismo , Aminoácidos/química , Aminoácidos/farmacocinética , Ácidos Aminoisobutíricos/química , Ácidos Aminoisobutíricos/farmacocinética , Animales , Encéfalo/metabolismo , Neoplasias Encefálicas/metabolismo , Radioisótopos de Flúor , Gliosarcoma/metabolismo , Marcaje Isotópico , Ligandos , Masculino , Trasplante de Neoplasias , Propionatos/química , Propionatos/farmacocinética , Radiofármacos/química , Radiofármacos/farmacocinética , Ratas , Ratas Endogámicas F344 , Relación Estructura-Actividad , Distribución Tisular , Tomografía Computarizada de Emisión , Células Tumorales CultivadasRESUMEN
The preparation, characterization, and molecular and crystal structures of succinimido 2-(tosylamino)isobutyrate, C(15)H(18)N(2)O(6)S, are described. The succinimido ring is nearly orthogonal to the ester group.
Asunto(s)
Ácidos Aminoisobutíricos/síntesis química , Péptidos/síntesis química , Succinimidas/química , Sulfonamidas/síntesis química , Ácidos Aminoisobutíricos/química , Cristalografía por Rayos X , Conformación Molecular , Sulfonamidas/químicaRESUMEN
The preparation, characterization, and molecular and crystal structures of the title compound [IUPAC name: 2-nitrophenyl 2-methyl-2-(para-toluenesulfonylamino)propanoate], C(17)H(18)N(2)O(6)S, are reported. The phenyl group is almost perpendicular to the plane of the adjacent ester moiety. One O atom of the nitro group is wedged between the two ester O atoms. The implications of this peculiar conformation for the chemistry of ortho-nitrophenyl esters in peptide synthesis are discussed.
Asunto(s)
Ácidos Aminoisobutíricos/síntesis química , Péptidos/síntesis química , Ácidos Aminoisobutíricos/química , Cristalografía por Rayos X , Indicadores y Reactivos , Modelos Moleculares , Conformación MolecularRESUMEN
An eight-membered cyclic beta-amino acid, 8-aminocyclooct-4-enecarboxylic acid, was designed as a conformationally restricted non-proteinogenic amino acid. A hybrid tripeptide containing this eight-membered cyclic beta-amino acid and 2-aminoisobutyric acids was synthesized by conventional solution methods. The conformation of the tripeptide was studied using X-ray analysis and was shown to form an eleven-membered hydrogen-bonded turn (3(11)-helical structure) in the solid state.
Asunto(s)
Aminoácidos Cíclicos/síntesis química , Aminoácidos/química , Ácidos Aminoisobutíricos/síntesis química , Oligopéptidos/química , Cristalografía por Rayos X , Enlace de Hidrógeno , Indicadores y Reactivos , Modelos Moleculares , Conformación ProteicaRESUMEN
It has been proposed that 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase catalyzes the oxidation of ACC to ethylene via N-hydroxyl-ACC as an intermediate. However, due to its chemical instability the putative intermediate has never been isolated. Here, we have shown that a purified recombinant ACC oxidase can utilize alpha-aminoisobutyric acid (AIB), an analog of ACC, as an alternative substrate, converting AIB into CO2, acetone, and ammonia. We chemically synthesized the putative intermediate compound, N-hydroxyl-AIB (HAIB), and tested whether it serves as an intermediate in the oxidation of AIB. When [1-(14)C]AIB was incubated with ACC oxidase in the presence of excess unlabeled HAIB as a trap, no labeled HAIB was detected. By comparing the acetone production rates employing HAIB and AIB as substrates, the conversion of HAIB to acetone was found to be much slower than that of using AIB as substrate. Based on these observations, we conclude that ACC oxidase does not catalyze via the N-hydroxylation of its amino acid substrate. ACC oxidase also catalyzes the oxidation of other amino acids, with preference for the D-enantiomers, indicating a stereoselectivity of the enzyme.
Asunto(s)
Aminoácido Oxidorreductasas/metabolismo , Acetona/metabolismo , Aminoácido Oxidorreductasas/química , Ácidos Aminoisobutíricos/síntesis química , Ácidos Aminoisobutíricos/metabolismo , Amoníaco/metabolismo , Catálisis , Relación Dosis-Respuesta a Droga , Escherichia coli/metabolismo , Etilenos/metabolismo , Radicales Libres , Frutas/enzimología , Hidroxilación , Cinética , Modelos Químicos , Proteínas Recombinantes/metabolismo , Estereoisomerismo , Especificidad por SustratoRESUMEN
An approach to the determination of the orientation of the carbonyl chemical shift (CS) tensor in a 13C-15N-1H dipolar coupled spin network is proposed. The method involves the measurement of the Euler angles of the 13C'-15N and 15N-1H dipolar vectors in the 13C' CS tensor principal axes system, respectively, via a 13C-15N REDOR experiment and by a 2D relayed anisotropy correlation of the 13C' CSA (omega2) and 15N-1H dipolar interaction (omega1). Via numerical simulations the sensitivity of the omega1 cross sections of the 2D spectrum to the Euler angles of the 15N-1H bond vector in the 13C' CSA frame is shown. Employing the procedure outlined in this work, we have determined the orientation of the 13C' CS tensor in the peptide plane of the dipeptide AibAib-NH2 (Aib = alpha-aminoisobutyric acid). The Euler angles are found to be (chiCN, psiCN) = (34 degrees +/- 2 degrees, 88 degrees +/- 2 degrees) and (chiNH, psiNH) = (90 degrees +/- 10 degrees, 80 degrees +/- 10 degrees). From the measured Euler angles it is seen that the sigma33 and sigma22 components of the 13C' CS tensor approximately lie in the peptide plane.
Asunto(s)
Ácidos Aminoisobutíricos/química , Dipéptidos/química , Ácidos Aminoisobutíricos/síntesis química , Anisotropía , Isótopos de Carbono , Dipéptidos/síntesis química , Hidrógeno/química , Enlace de Hidrógeno , Espectroscopía de Resonancia Magnética , Isótopos de Nitrógeno/químicaRESUMEN
The introduction into peptide chains of alpha-aminoisobutyric acid (Aib) has proven to stabilize the helical structure in short peptides by restricting the available range of polypeptide backbone conformations. In order to evaluate the potential stabilizing effect of Aib at the protein level, we have studied the conformational and stability properties of Aib-containing analogs of the carboxy-terminal subdomain 255-316 of thermolysin. Previous NMR studies have shown that this disulfide-free 62-residue fragment forms a dimer in solution and that the global 3D structure of each monomer (3 alpha-helices encompassing residues 260-274, 281-295, and 301-311) is largely coincident with that of the corresponding region in the X-ray structure of intact thermolysin. The Aib analogs of fragment 255-316 were prepared by a semisynthetic approach in which the natural fragment 255-316 was coupled to synthetic analogs of peptide 303-316 using V8-protease in 50% (v/v) aqueous glycerol [De Filippis, V., and Fontana, A. (1990) Int. J. Pept. Protein Res. 35, 219-227]. The Ala residue in position 304, 309, or 312 of fragment 255-316 was replaced by Aib, leading to the singly substituted fragments Ala304Aib, Ala309Aib, and Ala312Aib. Moreover, fragment Ala304Aib/Ala309Aib with a double Ala-->Aib exchange in positions 304 and 309 was produced. Far- and near-UV circular dichroism measurements demonstrated that both secondary and tertiary structures of the natural fragment 255-316 are fully retained upon Ala-->Aib substitution(s). Thermal unfolding measurements, carried out by recording the ellipticity at 222 nm upon heating, showed that the melting temperatures (Tm) of analogs Ala304Aib and Ala309Aib were 2.2 and 5.4 degrees C higher than that of the Ala-containing natural species (Tm = 63.5 degrees C), respectively, whereas the Tm of the Ala312Aib analog was lowered by -0.6 degree C. The enhanced stability of the Ala304Aib analog can be quantitatively explained on the basis of a reduced backbone entropy of unfolding due to the restriction of the conformational space allowed to Aib in respect to Ala, while the larger stabilization observed for the Ala309Aib analog can be accounted for by both entropic and hydrophobic effects. In fact, whereas Ala304 is a surface residue, Ala309 is shielded from the solvent, and thus the enhanced stability of fragment Ala309Aib is also due to the burial of an additional -CH3 group with respect to the natural fragment. The slightly destabilizing effect of the Ala-->Aib exchange in position 312 appears to derive from unfavorable strain energy effects, since phi and psi values for Ala312 are out of the allowed angles for Aib. Of interest, the simultaneous incorporation of Aib at positions 304 and 309 leads to a significant and additive increase of +8 degrees C in Tm. The results of this study indicate that the rational incorporation of Aib into a polypeptide chain can be a general procedure to significantly stabilize proteins.