Biomedical subjects

Paul R Carlier

Publications and source records attributed to Paul R Carlier.

At least 19 recordsLinked to original sources

PubMed2006

Enantioselective synthesis of diversely substituted quaternary 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones.

Benzodiazepines are privileged scaffolds in medicinal chemistry, but enantiopure examples containing quaternary stereogenic centers are extremely rare. We demonstrate that installation of the di(p-anisyl)methyl (DAM) group at N1 of 1,4-benzodiazepin-2-ones and 1,4-benzodiazepine-2,5-diones derived from enantiopure proteinogenic amino acids allows retentive replacement of the C3-proton via a deprotonation/trapping protocol. A wide variety of carbon and nitrogen electrophiles function well in this reaction, providing the corresponding quaternary benzodiazepines with excellent enantioselectivity. Deprotonation/trapping experiments on a pair of diastereomeric 1,4-benzodiazepine-2,5-diones provide evidence for a key role of conformational chirality in these enantioselective reactions. Acidic removal of the DAM group is fast and high-yielding and can be performed selectively in the presence of a N-Boc indole. Thus the synthesis of quaternary benzodiazepines with diverse N1 functionality can now be accomplished.

Alkylation↗

PubMed2006

Effect of 2,6-disubstituted aryl groups on acyclic conformation: preference for an antiperiplanar orientation of the geminal and vicinal hydrogens.

Multiple X-ray crystallographic and 1H NMR spectroscopic studies demonstrate that 2,6-disubstituted aryl groups exert a strong effect on acyclic conformation, inducing the geminal and vicinal hydrogens on the adjacent sp3-sp3 C-C bond to adopt an antiperiplanar orientation. Twenty-one examples comprising nitrile, ketone, and dithiane aldols are provided. A search of the Cambridge Structural Database uncovered an additional 11 examples of this effect. This preference causes some unanticipated remote effects on acyclic conformations: in anti-nitrile aldols, this effect causes 2,6-disubstituted aryls to generally prefer a gauche, rather than antiperiplanar, relationship to the largest vicinal groups. X-ray crystallography, 1H-1H NOESY spectroscopy, and computation demonstrate that minimization of allylic 1,3-strain and syn-pentane-like interactions work together in establishing this conformational preference.

Journal Article↗

PubMed2006

Alkylene tether-length dependent gamma-aminobutyric acid type A receptor competitive antagonism by tacrine dimers.

Bis(7)-tacrine was previously demonstrated as an antagonist of gamma-aminobutyric acid type A (GABA(A)) receptors. In this study, the effects of a series of alkylene-linked tacrine dimers on GABA(A) receptors were examined. In radioligand binding assay, the analogues differed in binding affinity for GABA(A) receptors, and potency monotonically increased as the tether was shortened from nine to two methylenes. Bis(2)-tacrine, the shortest tacrine dimer, could displace [(3)H]muscimol from rat brain membranes with an IC(50) of 0.48 microM, which was 11, 13 and 525 times more potent than the GABA(A) receptor antagonist (+)-bicuculline, bis(7)-tacrine and tacrine, respectively. In whole-cell patch-clamp recordings, these dimeric tacrine analogues competitively antagonized GABA-induced inward current with a rank order of potency of bis(2)-tacrine>bicuculline>bis(7)-tacrine>bis(9)-tacrine>tacrine, and the potency of bis(2)-tacrine was 11, 18 and 487 times higher than that of (+)-bicuculline, bis(7)-tacrine and tacrine, respectively. Bis(2)-tacrine shifted the GABA concentration-response curve to the right in a parallel manner, and the inhibition was voltage-independent between -80 and +20 mV. It can be concluded that the shorter the alkylene linkage in tacrine dimers the stronger the binding affinity and higher the antagonistic effect on the GABA(A) receptor will be.

Alkylation↗

PubMed2006

Antidepressant-like effects of novel triple reuptake inhibitors, PRC025 and PRC050.

Most currently prescribed antidepressants act by selectively increasing the synaptic availability of serotonin or norepinephrine, or through action on both serotonin and norepinephrine. However, most therapies require several weeks of treatment before improvement of symptoms is observed and not all patients respond to antidepressant treatment. One strategy that has emerged in new antidepressant development is the use of triple reuptake inhibitors, which inhibit reuptake of serotonin, norepinephrine, and dopamine. These compounds have been hypothesized to have a more rapid onset of activity and better efficacy over single or dual reuptake inhibitor antidepressants in part due to the addition of the dopamine component. We have developed novel compounds that are analogs of venlafaxine, of which two, racemic PRC025 ((2SR, 3RS)-N,N-dimethyl-3-cyclohexyl-3-hydroxy-2-(2'-naphthyl)propylamine) and PRC050 ((2RS,3RS)-N-methyl-3-hydroxy-2-(2'-naphthyl)-3-phenylpropylamine), are highly potent at human serotonin, norepinephrine, and dopamine transporters and inhibit the reuptake of serotonin, norepinephrine, and dopamine into rat brain synaptosomes. These compounds were tested in animal models used to evaluate potential antidepressants: the forced swim test in rats and the tail suspension test in mice. In the forced swim test, both PRC025 and PRC050 reduced the time spent immobile and increased the time spent swimming, comparable to the effects seen with imipramine, a tricyclic antidepressant. In addition, both PRC025 and PRC050 were effective in reducing the time spent immobile in the tail suspension test, again with effects comparable to imipramine. Therefore it appears that our compounds may possess antidepressant activity and represent a new class of triple reuptake inhibitors.

Animals↗

PubMed2006

Complexes of alkylene-linked tacrine dimers with Torpedo californica acetylcholinesterase: Binding of Bis5-tacrine produces a dramatic rearrangement in the active-site gorge.

The X-ray crystal structures were solved for complexes with Torpedo californica acetylcholinesterase of two bivalent tacrine derivative compounds in which the two tacrine rings were separated by 5- and 7-carbon spacers. The derivative with the 7-carbon spacer spans the length of the active-site gorge, making sandwich interactions with aromatic residues both in the catalytic anionic site (Trp84 and Phe330) at the bottom of the gorge and at the peripheral anionic site near its mouth (Tyr70 and Trp279). The derivative with the 5-carbon spacer interacts in a similar manner at the bottom of the gorge, but the shorter tether precludes a sandwich interaction at the peripheral anionic site. Although the upper tacrine group does interact with Trp279, it displaces the phenyl residue of Phe331, thus causing a major rearrangement in the Trp279-Ser291 loop. The ability of this inhibitor to induce large-scale structural changes in the active-site gorge of acetylcholinesterase has significant implications for structure-based drug design because such conformational changes in the target enzyme are difficult to predict and to model.

Acetylcholinesterase↗

PubMed2006

Protonated 2-methyl-1,2-epoxypropane: a challenging problem for density functional theory.

Protonated epoxides feature prominently in organic chemistry as reactive intermediates. Herein, we describe 10 protonated epoxides using B3LYP, MP2, and CCSD/6-311++G calculations. Relative to CCSD, B3LYP consistently overestimates the C2-O bond length. Protonated 2-methyl-1,2-epoxypropane is the most problematic species studied, where B3LYP overestimates the C2-O bond length by 0.191 angstroms. Seventeen other density functional methods were applied to this protonated epoxide; on average, they overestimated the CCSD bond length by 0.2 angstroms. We present a range of data that suggest the difficulty for DFT methods in modeling the structure of the titled protonated epoxide lies in the extremely weak C2-O bond, which is reflected in the highly asymmetric charge distribution between the two ring carbons. Protonated epoxides featuring more symmetrical charge distribution and cyclic homologues featuring less ring strain are treated with greater accuracy by B3LYP. Finally, MP2 performed very well against CCSD, deviating in the C2-O bond length at most by 0.009 angstroms; it is, therefore, recommended when computational resources prove insufficient for coupled cluster methods.

Electrons↗

PubMed2005

Highly enantioselective synthesis of rigid, quaternary 1,4-benzodiazepine-2,5-diones derived from proline.

[reaction: see text] Proline-derived 1,4-benzodiazepine-2,5-diones are extremely useful scaffolds in medicinal chemistry. In this paper, we describe a protocol for retentive C3 alkylation of these materials, thus accomplishing the direct synthesis of enantiopure quaternary 1,4-benzodiazepine-2,5-diones. The high enantioselectivities (up to 99.5%) are attributed to memory of chirality.

Benzodiazepinones↗

PubMed2005

Crystal packing mediates enantioselective ligand recognition at the peripheral site of acetylcholinesterase.

Recently, alkylene-linked heterodimers of tacrine (1) and 5-amino-5,6,7,8-tetrahydroquinolinone (2, hupyridone) were shown to exhibit higher acetylcholinesterase (AChE) inhibition than either monomeric 1 or 2. Such inhibitors are potential drug candidates for ameliorating the cognitive decrements in early Alzheimer patients. In an attempt to understand the inhibition mechanism of one such dimer, (RS)-(+/-)-N-9-(1,2,3,4-tetrahydroacridinyl)-N'-5-[5,6,7,8-tetrahydro-2'(1'H)-quinolinonyl]-1,10-diaminodecane [(RS)-(+/-)-3] bisoxalate, the racemate was soaked in trigonal Torpedo californica AChE (TcAChE) crystals, and the X-ray structure of the resulting complex was solved to 2.30 A resolution. Its structure revealed the 1 unit bound to the "anionic" subsite of the active site, near the bottom of the active-site gorge, as seen for the 1/TcAChE complex. Interestingly, only the (R)-enantiomer of the 2 unit was seen in the peripheral "anionic" site (PAS) at the top of the gorge, and was hydrogen-bonded to the side chains of residues belonging to an adjacent, symmetry-related AChE molecule covering the gorge entrance. When the same racemate was soaked in orthorhombic crystals of TcAChE, in which the entrance to the gorge is more exposed, the crystal structure of the corresponding complex revealed no substantial enantiomeric selectivity. This observation suggests that the apparent enantiomeric selectivity of trigonal crystals of TcAChE for (R)-3 is mainly due to crystal packing, resulting in preferential binding of one enantiomeric inhibitor both to its "host" enzyme and to its neighbor in the asymmetric unit, rather than to steric constraints imposed by the geometry of the active-site gorge.

Acetylcholinesterase↗

PubMed2005

Experimental and computational studies of ring inversion of 1,4-benzodiazepin-2-ones: implications for memory of chirality transformations.

We recently reported the enantioselective syntheses of quaternary 1,4-benzodiazepin-2-ones via memory of chirality. The success of this method depends on formation of conformationally chiral enolates that racemize very slowly under the reaction conditions. As a prelude to undertaking experimental and computational studies on the racemization of these enolates, we have studied the ring-inversion process of the parent 1,4-benzodiazepin-2-ones. In this paper, we use dynamic and 2D-EXSY NMR to characterize inversion barriers. Using DFT calculations, we reproduce the experimental results with high accuracy (within 1-2 kcal/mol). Structural parameters obtained from DFT calculations provide valuable insights into the important effect of the N1 substituent on the ring-inversion barrier and shed light on the mechanism of the memory of chirality method. These measurements and calculations provide a foundation for future studies of benzodiazepine enolates and will be valuable in the design of new memory of chirality reactions.

Benzodiazepinones↗

PubMed2005

Novel dimeric acetylcholinesterase inhibitor bis7-tacrine, but not donepezil, prevents glutamate-induced neuronal apoptosis by blocking N-methyl-D-aspartate receptors.

The neuroprotective properties of bis(7)-tacrine, a novel dimeric acetylcholinesterase (AChE) inhibitor, on glutamate-induced excitotoxicity were investigated in primary cultured cerebellar granule neurons (CGNs). Exposure of CGNs to 75 mum glutamate resulted in neuronal apoptosis as demonstrated by Hoechst staining, TUNEL, and DNA fragmentation assays. The bis(7)-tacrine treatment (0.01-1 mum) on CGNs markedly reduced glutamate-induced apoptosis in dose- and time-dependent manners. However, donepezil and other AChE inhibitors, even at concentrations of inhibiting AChE to the similar extents as 1 mum bis(7)-tacrine, failed to prevent glutamate-induced excitotoxicity in CGNs; moreover, both atropine and dihydro-beta-erythroidine, the cholinoreceptor antagonists, did not affect the anti-apoptotic properties of bis(7)-tacrine, suggesting that the neuroprotection of bis(7)-tacrine appears to be independent of inhibiting AChE and cholinergic transmission. In addition, ERK1/2 and p38 pathways, downstream signals of N-methyl-d-aspartate (NMDA) receptors, were rapidly activated after the exposure of glutamate to CGNs. Bis(7)-tacrine inhibited the apoptosis and the activation of these two signals with the same efficacy as the coapplication of PD98059 and SB203580. Furthermore, using fluorescence Ca(2+) imaging, patch clamp, and receptor-ligand binding techniques, bis(7)-tacrine was found effectively to buffer the intracellular Ca(2+) increase triggered by glutamate, to reduce NMDA-activated currents and to compete with [(3)H]MK-801 with an IC(50) value of 0.763 mum in rat cerebellar cortex membranes. These findings strongly suggest that bis(7)-tacrine prevents glutamate-induced neuronal apoptosis through directly blocking NMDA receptors at the MK-801-binding site, which offers a new and clinically significant modality as to how the agent exerts neuroprotective effects.

Animals↗

PubMed2004

Development of bivalent acetylcholinesterase inhibitors as potential therapeutic drugs for Alzheimer's disease.

At present the only FDA-approved therapy for Alzheimer's disease involves the administration of acetylcholinesterase inhibitors, to alleviate the cholinergic deficit associated with this disease. However, none of the approved drugs is ideal in efficacy or tolerability. One possible strategy to improve selectivity and potency is to design drugs that can simultaneously bind to the catalytic and peripheral anionic sites of AChE. In this review we will describe the development of dimeric AChE inhibitors, from the early observations of high inhibition potency by bis-quaternary inhibitors, to the structure-based design of dimers based on tacrine, huperzine A, galanthamine, and polyamines.

Alzheimer Disease↗

PubMed2003

Enantioselective synthesis of "quaternary" 1,4-benzodiazepin-2-one scaffolds via memory of chirality.

Glycine-derived 1,4-benzodiazepine-2-ones such as diazepam are chiral by virtue of the boat-shaped conformation of the diazepine ring and exist as a racemic mixture of conformational enantiomers. However, the presence of a chiral center at C-3 of the benzodiazepine perturbs this equilibrium and preferentially stabilizes one ring conformer. We report that N-i-Pr 1,4-benzodiazepine-2-ones derived from (S)-Ala and (S)-Phe can be deprotonated and alkylated in 86-99% ee, despite the fact that the original chiral center is destroyed in the deprotonation step. We attribute this highly enantioselective alkylation to the chiral memory of the benzodiazepine ring. This protocol provides easy access to the previously unexplored "quaternary" 1,4-benzodiazepine-2-ones.

Benzodiazepinones↗

PubMed2003

Configurational stability of chiral lithiated cyclopropylnitriles: a density functional study.

Chiral, configurationally stable lithiated nitriles would be valuable intermediates for asymmetric carbon-carbon bond-forming reactions. To gain insight into the design of such species, Walborsky's attempted enantioselective deprotonation/trapping reactions of a chiral cyclopropylnitrile were studied computationally up to the MP2(fc)/6-31+G* and B3LYP/6-31+G* levels. Investigation of cyclopropylnitrile/LiNH(2) deprotonation transition structures demonstrated a significant (20-23 kcal/mol) kinetic preference for N-lithiation, and a facile (4-6 kcal/mol barrier) "conducted tour" racemization pathway for the N-lithiated nitrile product. Addition of a model directing group (formyl) to the beta-carbon of the cyclopropyl ring is predicted to significantly favor C-lithiation over N-lithiation, both kinetically and thermodynamically. Thus, chiral beta-Lewis base substituted cyclopropylnitriles may serve as precursors to chiral, configurationally stable organolithium reagents.

Journal Article↗

PubMed2003

Acetylcholinesterase complexed with bivalent ligands related to huperzine a: experimental evidence for species-dependent protein-ligand complementarity.

Acetylcholinesterase (AChE) inhibitors improve the cognitive abilities of Alzheimer patients. (-)-Huperzine A [(-)-HupA], an alkaloid isolated from the club moss, Huperzia serrata, is one such inhibitor, but the search for more potent and selective drugs continues. Recently, alkylene-linked dimers of 5-amino-5,6,7,8-tetrahydroquinolinone (hupyridone, 1a), a fragment of HupA, were shown to serve as more potent inhibitors of AChE than (-)-HupA and monomeric 1a. We soaked two such dimers, (S,S)-(-)-bis(10)-hupyridone [(S,S)-(-)-2a] and (S,S)-(-)-bis(12)-hupyridone [(S,S)-(-)-2b] containing, respectively, 10 and 12 methylenes in the spacer, into trigonal TcAChE crystals, and solved the X-ray structures of the resulting complexes using the difference Fourier technique, both to 2.15 A resolution. The structures revealed one HupA-like 1a unit bound to the "anionic" subsite of the active-site, near the bottom of the active-site gorge, adjacent to Trp84, as seen for the TcAChE/(-)-HupA complex, and the second 1a unit near Trp279 in the "peripheral" anionic site at the top of the gorge, both bivalent molecules thus spanning the active-site gorge. The results confirm that the increased affinity of the dimeric HupA analogues for AChE is conferred by binding to the two "anionic" sites of the enzyme. Inhibition data show that (-)-2a binds to TcAChE approximately 6-7- and > 170-fold more tightly than (-)-2b and (-)-HupA, respectively. In contrast, previous data for rat AChE show that (-)-2b binds approximately 3- and approximately 2-fold more tightly than (-)-2a and (-)-HupA, respectively. Structural comparison of TcAChE with rat AChE, as represented by the closely related mouse AChE structure (1maa.pdb), reveals a narrower gorge for rat AChE, a perpendicular alignment of the Tyr337 ring to the gorge axis, and its conformational rigidity, as a result of hydrogen bonding between its hydroxyl group and that of Tyr341, relative to TcAChE Phe330. These structural differences in the active-site gorge explain the switch in inhibitory potency of (-)-2a and 2b and the larger dimer/(-)-HupA potency ratios observed for TcAChE relative to rat AChE. The results offer new insights into factors affecting protein-ligand complementarity within the gorge and should assist the further development of improved AChE inhibitors.

Acetylcholinesterase↗

PubMed2002

Immobilized enzymes as catalytically-active tools for nanofabrication.

One efficient strategy for creating nanostructures on surfaces is to use the catalytic properties of a surface molecule. This strategy benefits from the amplification and chemical specificity inherent in catalysis. We describe a demonstration of the key step of such a strategy: the surface trapping of a product generated by a nanometer-scale patch of surface-bound enzyme. Nanografting was used to create a approximately 70-nm patch of carboxylic acid groups surrounded by antibiofouling oligio(ethyleneoxide) groups on the surface of a gold ball. A catalytic site was prepared by immobilization of acetylcholine esterase to the carboxylic acid patch, and a product trap was prepared by scratching a small hole in the antibiofouling surface to reveal the gold surface. Two hours after addition of acetylthiocholine, the trap was filled. This demonstrated that the enzyme had catalyzed a reaction and that the product had been used to modify the surface film.

Acetylcholinesterase↗

PubMed2002

Catalytic asymmetric synthesis of protected tryptophan regioisomers.

Tryptophan 1 (Trp) is superior to all other naturally occurring peptide residues in its ability to bind cations (the cation-pi interaction). In an effort to expand the toolbox of Trp-like amino acids, in this note we report catalytic asymmetric syntheses of Trp regioisomers 2a-e, where the alanine unit is attached not to C-3 of indole but to C-2, C-4, C-5, C-6, or C-7. Excellent asymmetric induction is obtained in each case (generally >97% ee). Ab initio calculations suggest that the indole nuclei of 2a-e will bind Na(+) with the same affinity as that of Trp.

Catalysis↗

PubMed2002

Discovery of non-zwitterionic GABA(A) receptor full agonists and a superagonist.

Numerous previous studies of GABA(A) receptor ligands have suggested that GABA(A) receptor agonists must be zwitterionic and feature an intercharge separation similar to that of GABA (approx. 4.7-6A). In this communication we demonstrate that appropriately functionalized GABA amides are partial, full, or superagonists, despite their non-zwitterionic structure.

Amides↗

PubMed2002

Effective computational modeling of constitutional isomerism and aggregation states of explicit solvates of lithiated phenylacetonitrile.

We present the first calculations which accurately account for the position of metalation and aggregation state of lithiated nitriles. Solvation is found to be a key determinant of structure. Five known solvates of lithiated phenylacetonitrile were examined computationally to determine the minimum level of theory required to reproduce the observed X-ray and multinuclear NMR structures. In all cases Hartree-Fock 3-21G energies of explicit solvates calculated at PM3 geometries correctly predict the observed N-lithiated constitutional isomer. Selected density functional theory (B3LYP/6-31+G*//PM3) energy calculations reproduce this trend. We also show that 3-21G//PM3 calculations which do not include explicit solvent molecules, or which include water as a model for diethyl ether, may lead to incorrect predictions of the preferred constitutional isomer. 3-21G//PM3 energies also adequately account for observed aggregation states of the TMEDA, diethyl ether, and THF solvates. Finally, calculations of THF-solvated monomers up to the B3LYP/6-31+G*//B3LYP/6-31+G level indicate a significant (6.8 kcal/mol) preference for N-lithiation.

Journal Article↗