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Biomedical subjects

J Aubé

Publications and source records attributed to J Aubé.

At least 19 recordsLinked to original sources
PubMed2001

Effect of progressive benzyl substitution on the conformations of aminocaproic acid-cyclized dipeptides.

The constraint of dipeptides into a beta-turn conformation can be accomplished by linking the two ends of a standard dipeptide with a linker derived from aminocaproic acid (Aca). To elucidate the possibility of using substituted Aca linkers in peptidomimetic design, a series of five macrocycles composed of a monobenzylated Aca linker (containing the benzyl group on each of the five methylene groups of the parent linker) and Gly-Gly were synthesized. The requisite linkers were made by regiochemically controlled ring expansion techniques (for substitution on Aca positions C-3, C-4, or C-5), an Evans alkylation route (for C-2), or by chain extension of L-phenylalanal (for C-6). The solution-phase conformations of the macrocycles were examined by NMR and CD techniques; in addition, crystal structures of the C-4- and C-6-benzyl-substituted linkers were obtained. Four out of the five macrocycles were found to exist with the dipeptide portion taking up either a type II or II' beta-turn conformation, but the Gly-Gly unit in the compound derived from 4-benzyl-Aca did not correspond to one of the standard beta-turn types.

Aminocaproic Acid↗
PubMed2001

Intramolecular reactions of benzylic azides with ketones: competition between Schmidt and Mannich pathways.

The Lewis acid-promoted reactions of benzylic azides with ketones can proceed by two major pathways. The azido-Schmidt reaction involves simple addition of azide to the ketone followed by rearrangement and ring expansion. In addition, benzylic azides can undergo prior rearrangement to afford iminium ions that can subsequently participate in a Mannich reaction. A series of ketones containing an alpha CH2(CH2)nCH(N3)Ph substituent (n = 1-3) was prepared to investigate the dependence of products on ketone ring size and tether length. For all ketones examined, good yields of bicyclic lactams arising from intramolecular Schmidt reaction were obtained when a four-carbon linker was used (n = 1 in the above formulation), but Mannich products predominated for the longer tethers examined (n = 2, 3).

Azides↗
PubMed2001

A functional assay for quantitation of the apparent affinities of ligands of P-glycoprotein in Caco-2 cells.

PURPOSE: To develop a facile functional assay for quantitative determination of the apparent affinities of compounds that interact with the taxol binding site of P-glcoprotein (P-gp) in Caco-2 cell monolayers. METHODS: A transport inhibition approach was taken to determine the inhibitory effects of compounds on the active transport of [3H]-taxol, a known substrate of P-gp. The apparent affinities (K(I) values) of the compounds were quantitatively determined based on the inhibitory effects of the compounds on the active transport of [3H]-taxol. Intact Caco-2 cell monolayers were utilized for transport inhibition studies. Samples were analyzed by liquid scintillation counting. RESULTS: [3H]-Taxol (0.04 microM) showed polarized transport with the basolateral (BL) to apical (AP) flux rate being about 10-20 times faster than the flux rate in the AP-to-BL direction. This difference in [3H]-taxol flux could be totally abolished by inclusion of (+/-)-verapamil (0.2 mM), a known inhibitor of P-gp, in the incubation medium. However, inclusion of probenecid (1.0 mM), a known inhibitor for the multidrug resistance associated protein (MRP), did not significantly affect the transport of [3H]-taxol under the same conditions. These results suggest that P-gp, not MRP, was involved in taxol transport. Quinidine, daunorubicin, verapamil, taxol, doxorubicin, vinblastine, etoposide, and celiprolol were examined as inhibitors of the BL-to-AP transport of [3H]-taxol with resulting K(I) values of 1.5+/-0.8, 2.5+/-1.0, 3.0+/-0.3, 7.3+/-0.7, 8.5+/-2.8, 36.5+/-1.5, 276+/-69, and 313+/-112 microM, respectively. With the exception of that of quinidine, these K(I) values were comparable with literature values. CONCLUSIONS: This assay allows a facile quantitation of the apparent affinities of compounds to the taxol-binding site in P-gp, however, this assay does not permit the differentiation of substrates and inhibitors. The potential of drug-drug interactions involving the taxol binding site of P-gp can be conveniently estimated using the protocol described in this paper.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Transport characteristics of peptides and peptidomimetics: II. Hydroxyethylamine bioisostere-containing peptidomimetics as substrates for the oligopeptide transporter and P-glycoprotein in the intestinal mucosa.

Peptide bond bioisosteres, such as hydroxyethylamine (Hea), have frequently been used to stabilize metabolically labile peptide bonds in peptidomimetic drug design in an effort to increase the oral bioavailability of drug candidates. However, the impact of the peptide bond bioisosteres on the cell permeation characteristics of peptidomimetics is not well understood, particularly with respect to the effects on the substrate activity for proteins that can restrict (e.g. P-glycoprotein, P-gp) or facilitate (e.g. the oligopeptide transporter, OPT) intestinal mucosal permeation of peptidomimetics. In this study, terminally free and terminally modified (N-acetylated and C-amidated) peptidomimetics of H-Ala-Phe-OH and H-Ala-Phe-Ala-OH with the Ala-Phe peptide bonds replaced by Hea bioisosteres were synthesized. Transport characteristics of these peptidomimetics were investigated using Caco-2 cell monolayers as an in vitro model of the intestinal mucosa. The study showed that the Hea bioisostere stabilized the peptidomimetics to protease metabolism in Caco-2 cells. All terminally free peptidomimetics showed significant affinity and substrate activity for OPT. The affinity and substrate activity for OPT were stereoselective for peptidomimetics containing an S,S-configuration for the two adjacent chiral centers related to the Hea bioisostere. Three of the four terminally modified peptidomimetics showed significant substrate activity for P-gp and, interestingly, the substrate activity for P-gp was also stereoselective; however, it was in favor of an R,R-configuration for the two adjacent chiral centers related to the Hea bioisostere.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Transport characteristics of peptides and peptidomimetics: I. N-methylated peptides as substrates for the oligopeptide transporter and P-glycoprotein in the intestinal mucosa.

Peptides and peptidomimetics often exhibit poor oral bioavailability due to their metabolic instability and low permeation across the intestinal mucosa. N-Methylation has been used successfully in peptide-based drug design in an attempt to improve the metabolic stability of a peptide-based lead compound. However, the effect of N-methylation on the absorption of peptides through the intestinal mucosa is not well understood, particularly when transporters, i.e. the oligopeptide transporter (OPT) and P-glycoprotein (P-gp), modulate the passive diffusion of these types of molecules. To examine this, terminally free and terminally modified (N-acetylated and C-amidated) analogs of H-Ala-Phe-Ala-OH with N-methyl groups on either the Ala-Phe or Phe-Ala peptide bond were synthesized. Transport studies using Caco-2 cell monolayers, an in vitro model of the intestinal mucosa, showed that N-methylation of the Ala-Phe peptide bond of H-Ala-Phe-Ala-OH stabilized the molecule to protease degradation, and the resulting analog exhibited significant substrate activity for OPT. However, N-methylation of the Phe-Ala peptide bond of H-Ala-Phe-Ala-OH did not stabilize the molecule to protease degradation, and the substrate activity of the resulting molecule for OPT could not be determined. Interestingly, N-methylation of the Phe-Ala peptide bond of the terminally modified tripeptide Ac-Ala-Phe-Ala-NH2 decreased the substrate activity of the molecule for the efflux transporter P-gp. In contrast, N-methylation of the Ala-Phe peptide bond of the terminally modified tripeptide Ac-Ala-Phe-Ala-NH2 increased the substrate activity of the molecule for P-gp.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Stereochemistry of the oxidation of imines derived from substituted cyclohexanones: axial vs equatorial attack and evidence for delivery by an adjacent hydroxyl group.

A set of conformationally biased imines derived from substituted cyclohexanones and benzylamine or diphenylmethylamine, respectively, were oxidized to the corresponding oxaziridines. The structures of the oxaziridines were determined via NMR comparison of two series of differently N-substituted oxaziridines. Thus, those compounds having an axially disposed nitrogen substituent displayed an upfield-shifted axial proton in a 1,3-relationship to the oxaziridine nitrogen in the N-diphenylmethyl series relative to the N-benzyl compounds. Analysis of the products obtained from these reactions suggests that (1) adjacent hydroxyl groups favor syn oxidant addition and (2) imines containing adjacent methoxy groups preferentially undergo attack anti to the resident alkoxy substituent.

Cyclohexanones↗
PubMed2000

Regiochemical studies of the ring expansion reactions of hydroxy azides with cyclic ketones.

The regiochemistry of ring expansions of 2-substituted cyclic ketones using 1,2-azidoethanol and 1,3-azidopropanol was examined. It was determined that the reactions of ketones with an adjacent methyl or ethyl group are generally unselective, but that bulkier substituents lead to preferential migration of the more highly substituted carbon. In addition, it was found that ketones bearing inductively electron-withdrawing substituents (OMe, Ph, Br) undergo selective migration of the less highly substituted carbon. For some substrates, alternative reaction pathways were also identified.

Azides↗
PubMed2000

Synthesis and conformation of Gly-Gly dipeptides constrained with phenylalanine-like aminocaproic acid linkers.

[structure: see text] The constraint of dipeptides with linkers derived from 6-aminocaproic acid (Aca) is a useful means of constructing a beta-turn peptidomimetic. The extension of this concept to the mimicry of a tripeptide entails the incorporation of a side chain moiety on either end of the Aca chain. The synthesis and conformational analysis of two exemplary compounds is discussed.

Aminocaproic Acid↗
PubMed2000

Synthesis of alpha-amino-alpha'-diazomethyl ketones via ring opening of substituted cyclopropanones with alkyl azides. A facile route to N-substituted 3-azetidinones.

[reaction: see text] The reaction of alkyl azides with triethyl(1-methoxy-2, 2-dimethyl-cyclopropoxy)silane affords a series of alpha-amino-alpha'-diazomethyl ketones in moderate yields (38-54%). The mechanism of this novel process is discussed. The diazomethyl ketones could also be cyclized to the corresponding N-substituted 3-azetidinones in good yield upon treatment with Rh(2)(OAc)(4).

Amines↗
PubMed2000

Cyclizations of substituted benzylidene-3-alkenylamines: synthesis of the tricyclic core of the martinellines.

The martinellines (1 and 2) are natural products that possess both interesting biological activity and chemical structure. During the investigation of a hetero Diels-Alder route to these molecules, alternate Lewis acid-dependent cyclizations of (2'-amino-N'-tert-butoxycarbonyl-5'-chlorobenzylidene)-3-butenylamine (10) were observed. The reaction of a variety of imines with TMSOTf or TiCl(4) led to the formation of different heterocycles including iminodibenzo[b,f][1,5]diazocines, hexahydropyrido[1, 2-c]quinazolin-6-ones, tetrahydropyrrolo[1,2-c]quinazolin-5-ones, 2-arylpiperidines, and 2-arylpyrrolidines. Tetrahydropyrrolo[1, 2-c]quinazolin-5-one 54, obtained via this new methodology, was used as an intermediate in the synthesis of the tricyclic ring system (65) of the martinellines.

Amines↗
PubMed2000

Reactivity toward deamidation of asparagine residues in beta-turn structures.

Mimetics of beta-turn structures in proteins have been used to calibrate the relative reactivities toward deamidation of asparagine residues in the two central positions of a beta-turn and in a random coil. N-Acetyl-Asn-Gly-6-aminocaproic acid, an acyclic analog of a beta-turn mimic undergoes deamidation of the asparaginyl residue through a succinimide intermediate to generate N-acetyl-Asp-N-Gly-6-aminocaproic acid (6-aminocaproic acid, hereafter Aca) and N-acetyl-L-iso-aspartyl (isoAsp)-Gly-Aca (pH 8.8, 37 degrees C) approximately 3-fold faster than does the cyclic beta-turn mimic cyclo-[L-Asn-Gly-Aca] with asparagine at position 2 of the beta-turn. The latter compound, in turn, undergoes deamidation approximately 30-fold faster than its positional isomer cyclo-[Gly-Asn-Aca] with asparagine at position 3 of the beta-turn. Both cyclic peptides assume predominantly beta-turn structures in solution, as demonstrated by NMR and circular dichroism characterization. The open-chain compound and its isomer N-acetyl-Gly-Asn-Aca assume predominantly random coil structures. The latter isomer undergoes deamidation 2-fold slower than the former. Thus the order of reactivity toward deamidation is: asparagine in a random coil approximately 3x(asparagine) in position 2 of a beta-turn approximately 30x (asparagine) in position 3 of a beta-turn.

Amino Acid Sequence↗
PubMed1998

Synthesis and evaluation of peptidyl Michael acceptors that inactivate human rhinovirus 3C protease and inhibit virus replication.

Human rhinovirus, the chief cause of the common cold, contains a positive-sense strand of RNA which is translated into a large polyprotein in infected cells. Cleavage of the latter to produce the mature viral proteins required for replication is catalyzed in large part by a virally encoded cysteine proteinase (3Cpro) which is highly selective for -Q approximately GP- cleavage sites. We synthesized peptidyl derivatives of vinylogous glutamine or methionine sulfone esters (e.g., Boc-Val-Leu-Phe-vGln-OR: R = Me, 1; R = Et, 2) and evaluated them as inhibitors of HRV-14 3C protease (3Cpro). Compounds 1 and 2 and several related tetra- and pentapeptide analogues rapidly inactivated 3Cpro with submicromolar IC50 values. Electrospray mass spectrometry confirmed the expected 1:1 stoichiometry of 3Cpro inactivation by 1, 2, and several other analogues. Compound 2 also proved to be useful for active site titration of 3Cpro, which has not been possible heretofore because of the lack of a suitable reagent. In contrast to 1, 2, and congeners, peptidyl Michael acceptors lacking a P4 residue have greatly reduced or negligible activity against 3Cpro, consistent with previously established structure-activity relationships for 3Cpro substrates. Hydrolysis of the P1 vinylogous glutamine ester to a carboxylic acid also decreased inhibitory activity considerably, consistent with the decreased reactivity of acrylic acids vs acrylic esters as Michael acceptors. Incorporating a vinylogous methionine sulfone ester in place of the corresponding glutamine derivative in 1 also reduced activity substantially. Compounds 1 and 2 and several of their analogues inhibited HRV replication in cell culture by 50% at low micromolar concentrations while showing little or no evidence of cytotoxicity at 10-fold higher concentrations. Peptidyl Michael acceptors and their analogues may prove useful as therapeutic agents for pathologies involving cysteine proteinase enzymes.

3C Viral Proteases↗
PubMed1997

Butitaxel analogues: synthesis and structure-activity relationships.

N-Acyl analogues 8, 9, and 12-26 of butitaxel (3) were prepared in one or two steps from amines 5 and 6 through Schotten-Baumann acylation. Seventeen novel analogues, consisting of aliphatic carbamates, alicyclic amides, and heteroaromatic amides, were synthesized. They were evaluated for their in vitro ability to stimulate the formation of microtubules, their cytotoxicity toward B16 melanoma cells, and their solubility in water. The most potent analogue found in this study was N-debenzoyl-N-(2-thenoyl)butitaxel (20), possessing ca. 2-fold better tubulin assembly properties and cytotoxic activity against B16 melanoma cells than paclitaxel. Compound 20 was ca. 25 times more water soluble than paclitaxel.

Animals↗
PubMed1997

Effect of stereochemistry on the transport of Aca-linked beta-turn peptidomimetics across a human intestinal cell line.

Transcellular transport is one of the most important barriers facing the development of new therapeutic agents. However, little is known about the specific effects of structure and particularly stereochemistry on cell permeability. An attractive in vitro model has been developed for the direct assessment of cell transport, using the immortalized human epithelial cell line, Caco-2. The present study assesses the effects of stereochemistry on transport in a commonly used beta-turn model system. Thus, L,L- and L,D-Ala-Ala were cyclized with aminocaproic acid, resulting in macrocycles in which the dipeptides correspond to the i + 1 and i + 2 positions of a beta-turn. The transport of these dipeptides across a Caco-2 cell monolayer was determined, along with corresponding acyclic models (L,L- and L,D-CH3CH2C(O)-Ala-Ala-n-Pr). The transport studies were carried out in the presence and absence of verapamil, a known inhibitor of the apically polarized efflux system present in Caco-2 cells. Both apical-->basolateral and basolateral-->apical transport were measured. Measurements made in the presence of verapamil showed that the cyclic peptides experienced a ca. 4-5-fold difference in intrinsic flux depending on stereochemistry, with the L,D isomer being transported at a higher rate. These differences disappeared in the acyclic cases examined (permeability coefficient ratios of the L,D/L,L isomers were 1.04-1.13). These observations are discussed in terms of the conformations and hydrogen-bonding characteristics of the compounds as determined by NMR spectroscopy.

Biological Transport↗
PubMed1995

Novel cytotoxic 3'-(tert-butyl) 3'-dephenyl analogs of paclitaxel and docetaxel.

3'-(tert-Butyl) 3'-dephenyl analogs of paclitaxel were synthesized from 10-deacetylbaccatin III and oxazolidinecarboxylic acid 7 followed by acylation of intermediate amines 10 and 11. Oxazolidinecarboxylic acid 7 was prepared in five steps and in good overall yield from L-tert-leucine. Twelve analogs were synthesized and evaluated for their in vitro ability to stimulate the formation of microtubules and for their cytotoxicity against B16 melanoma cells. Amide, carbamate, urea, and thiourea congeners were prepared. The most potent derivatives found in this study are the docetaxel analog 13, the N-[(tert-amyloxy)carbonyl] analog 17, and the 3'-phenylurea and 3'-tert-butylurea derivatives 20 and 23. Six of these analogs were shown to be ca. 90 times more soluble in water than paclitaxel and ca. 4-5 times more water-soluble than docetaxel.

Antineoplastic Agents, Phytogenic↗