Quantum chemical investigation on solvation of Ginkgolides

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Ginkgolides: selective acetylations,translactonization, and biological evaluation

Protocols for selective acetylation of the hydroxyl groups of ginkgolide C have been developed. These acetylations have given rise to various ginkgolide C acetates and iso-ginkgolide C acetates, the latter having a rearranged skeleton resulting from translactonization. These acetyl derivatives, as well as ginkgolides A and B acetates have been investigated for their ability to bind to a cloned platelet-activating factor (PAF) receptor.     

Identification and the retention index of bilobalide and ginkgolides using capillary gas chromatography

Ginkgo biloba L. is known to contain the unique terpene trilactone compounds bilobalide and ginkgolides. Capillary gas chromatography is used for the quantitative identification of bilobalide and the main ginkgolides (ginkgolide A, B, and C). The retention indices of these compounds are also determined. Retention indices of bilobalide and ginkgolide A, B, and C substitute the use of their standards at their routine identification. Our procedure does not require temperature-programmed operation.     

The pharmacokinetics study of ginkgolide A,B and the effect of food on bioavailability after oral administration of ginkgolide extracts in beagle dogs

Ginkgolides are the primarily active components in Ginkgo products that are popular worldwide. However, few studies have evaluated the bioavailability of ginkgolides and the effects of food on it after oral administration of ginkgolides. In this article, pharmacokinetics and absolute bioavailability of the primary components in ginkgolide extracts were evaluated in beagle dogs. For the first time, we showed that the fed dogs had significantly increased area under the concentration–time curve and peak concentration relative to the fasted dogs based on the data from both the prototype form and total lactones of ginkgolide A (GA) and ginkgolide B (GB). In terms of the free form of the prototype ginkgolides, the absolute bioavailabilities of GA and GB were 34.8 and 5.2% in the fasted dogs, respectively, which significantly increased to an average of 78.6 and 17.0%, respectively, in the fed dogs. In terms of acidified total lactones, the absolute bioavailabilities of GA and GB were 7.5 and 14.5% in the fed dogs, and the percentages declined to 4.1 and 3.7% in the fasted dogs, respectively. It was suggested that administration of ginkgolides after meals could promote the in vivo exposure and the bioavailability of GA and GB, and hence potentially enhance therapeutic outcomes.     

LC-ESI-MS Determination of Bilobalide and Ginkgolides in Canine Plasma

A sensitive and selective method using liquid chromatography with electrospray ionization mass spectrometric detection was developed for the quantification of bilobalide and ginkgolides in canine plasma. The analytes were extracted with diethyl ether-dichloromethane-isopropanol (6:3:1, v/v) after spiking the samples with daidzein (internal standard). The lower limit of quantification (LLOQ) of the method was 2.5 μg L⁻¹ for ginkgolide B and 10.0 μg L⁻¹ for bilabolide, ginkgolide A and ginkgolide C. The accuracy of the method was within 15% of the actual values over a wide range of plasma concentrations. The intra-day and inter-day precision was better than 15% (R.S.D.). Finally, the LC-ESI-MS method was successfully applied to study the pharmacokinetics of ginkgolides and bilabolide after administration of Ginkgo biloba extracts to dogs.     

Lactone-free ginkgolides via regioselective DIBAL-H reduction

The lactone rings of ginkgolide A are converted into corresponding tetrahydrofuran moieties via DIBAL-H reduction followed by deoxygenation of the formed lactols with Et3SiH-BF3.Et2O to produce a series of lactone-free ginkgolides.     

Global physicochemical properties as activity discriminants for the mGluR1 subtype of metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) are important as candidate therapeutic targets for many neurological disorders. In the present work, the focus has been on the mGluR1 subtype, where agonists have a proconvulsant profile while antagonists exert anticonvulsant activity. Identification of molecular determinants for the inhibition of mGluR1 provides a new avenue for the discovery and development of novel anticonvulsant drugs. Spatial configuration of key groups alone cannot explain activation selectivity at this specific receptor subtype. In fact, all known agonists and antagonists acting at mGluR1 can accommodate the same critical moieties in a similar geometric arrangement that corresponds to the extended conformation of glutamate. Therefore, other factors must account for the differences in activation. This study presents the results of an analysis of a large suite of steric, topological, electrostatic, and thermodynamic molecular properties calculated for a representative set of potent mGluR1 agonists and antagonists. Global steric parameters and the total nonpolar area provide discrimination between the mGluR1 agonists and antagonists considered in the present work. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 2018–2027, 2001     

Synthetic collagen heterotrimers: structural mimics of wild-type and mutant collagen type I

Collagen type I is an AAB heterotrimer assembled from two alpha1 chains and one alpha2 chain. Missense mutations in either of these chains that substitute a glycine residue in the ubiquitous X-Y-Gly repeat with a bulky amino acid leads to osteogenesis imperfecta (OI) of varying severity. These mutations have been studied in the past using collagen-like peptide homotrimers as a model system. However, homotrimers, which by definition will contain glycine mutations in all the three chains, do not accurately mimic the mutations in their native form and result in an exaggerated effect on stability and folding. In this article, we report the design of a novel model system based upon collagen-like heterotrimers that can mimic the glycine mutations present in either the alpha1 or alpha2 chains of type I collagen. This design utilizes an electrostatic recognition motif in three chains that can force the interaction of any three peptides, including AAA (all same), AAB (two same and one different), or ABC (all different) triple helices. Therefore, the component peptides can be designed in such a way that glycine mutations are present in zero, one, two, or all three chains of the triple helix. With this design, we for the first time report collagen mutants containing one or two glycine substitutions with structures relevant to native forms of OI. Furthermore, we demonstrate the difference in thermal stability and refolding half-life times between triple helices that vary only in the frequency of glycine mutations at a particular position.     

Ginkgolide

The ginkgolides are along with bilobalide and some flavonoids the most important active agents of the maidenhair tree (Ginkgo biloba). They derive from the terpenoid biosynthetic pathway, and are established by cyclisation of geranylgeranyl diphosphate, oxidative functionalization and scaffold rearrangements. Elias J. Corey and Michael T. Crimmins published prominent total syntheses of ginkgolide B. In the 1950s, Willmar Schwabe III developed an extract of the dried leaves, which is rich in ginkgolides, bilobalide and flavonoids. It is used for the symptomatic treatment of memory disorders, absent‐mindedness, dizziness, tinnitus and dementia.     

Homology modeling of a human glycine alpha 1 receptor reveals a plausible anesthetic binding site

The superfamily of ligand-gated ion channels (LGICs) has been implicated in anesthetic and alcohol responses. Mutations within glycine and GABA receptors have demonstrated that possible sites of anesthetic action exist within the transmembrane subunits of these receptors. The exact molecular arrangement of this transmembrane region remains at intermediate resolution with current experimental techniques. Homology modeling methods were therefore combined with experimental data to produce a more exact model of this region. A consensus from multiple bioinformatics techniques predicted the topology within the transmembrane domain of a glycine alpha one receptor (GlyRa1) to be alpha helical. This fold information was combined with sequence information using the SeqFold algorithm to search for modeling templates. Independently, the FoldMiner algorithm was used to search for templates that had structural folds similar to published coordinates of the homologous nAChR (1OED). Both SeqFold and Foldminer identified the same modeling template. The GlyRa1 sequence was aligned with this template using multiple scoring criteria. Refinement of the alignment closed gaps to produce agreement with labeling studies carried out on the homologous receptors of the superfamily. Structural assignment and refinement was achieved using Modeler. The final structure demonstrated a cavity within the core of a four-helix bundle. Residues known to be involved in modulating anesthetic potency converge on and line this cavity. This suggests that the binding sites for volatile anesthetics in the LGICs are the cavities formed within the core of transmembrane four-helix bundles.     

Pharmacophore model for bile acids recognition by the FPR receptor

Formyl-peptide receptors (FPRs) belong to the family A of the G-protein coupled receptor superfamily and include three subtypes: FPR, FPR-like-1 and FPR-like-2. They have been involved in the control of␣many inflammatory processes promoting the recruitment and infiltration of leukocytes in regions of inflammation through the molecular recognition of chemotactic factors. A large number of structurally diverse chemotypes modulate the activity of FPRs. Newly identified antagonists include bile acids deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA). The molecular recognition of these compounds at FPR receptor was computationally investigated using both ligand- and structure-based approaches. Our findings suggest that all antagonists bind at the first third of the seven helical bundles. A closer inspection of bile acid interaction reveals a number of unexploited anchor points in the binding site that may be used to aid the design of new potent and selective bile acids derivatives at FPR.     

An efficient etherification of Ginkgol biloba extracts with fewer side effects in a micro-flow system

In this study, etherification of ginkgolide B and dimethylaminoethyl chloride hydrochloride was investigated as a model reaction in a micro-flow system (MFS), providing the resulting ethers in high yield with fewer side effects. Meanwhile, this novel process in MFS worked well for other ginkgolides from Ginkgol biloba and halides, giving moderate yields.     

Screening of 5-HT1A receptor antagonists using molecularly imprinted polymers

Molecular imprinting produces network polymers with recognition sites for imprint molecules. The high binding affinity and selectivity in conjunction with the polymers' physical robustness positions molecular imprinted polymers (MIPs) as candidates for use as preliminary screens in drug discovery. As such, MIPs can serve as crude mimics of native receptors. In an effort to evaluate the relationship between MIPs and native receptors, imprinted polymers for WAY-100635, an antagonist of the serotonin (5-HT) receptor subtype 5-HT1A were prepared. The resulting MIP P(WAY) was evaluated as an affinity matrix in the screening of serotonin receptor antagonists with known affinities for the native receptor. Rough correlations in affinity between the synthetic P(WAY) and native receptor 5-HT1A were found. These findings provide some support for the analogy between MIPs and native receptors and their possible use as surrogates.     

Design,synthesis and biological activity of rigid cannabinoid CB1 receptor antagonists

The design, synthesis and biological activities of potent pyrazole-based tricyclic CB1 receptor antagonists (2) are described. The key synthetic step involves the ring closure of the lithiated alpha, gamma-keto ester adduct (4). The optimal nitroderivative (28) in this series exhibits a high CB1 receptor affinity (pKi=7.2) as well as very potent antagonistic activity (pA2=8.8) in vitro. The regioselectivity of the pyrazole ring closure is shown to depend strongly on the aromatic substitution pattern of the applied arylhydrazine.     

Synthesis and biological evaluation of novel phenothiazine derivatives as non-peptide arginine vasopressin V2 receptor antagonists

A series of novel phenothiazine derivatives was synthesized and tested for arginine vasopressin receptor antagonist activity. They were synthesized as novel arginine vasopressin receptor antagonists from phenothiazine as a scaffold via successive acylation, reduction and acylation reactions. Their structures were characterized by 1HNMR, 13CNMRandHRMS, and biological activitywas evaluated by in vitro and in vivo studies. The in vitro binding assay indicated that several compounds are potent selective V2 receptor antagonists. Compounds with promising binding affinity to V2 receptors were selected to conduct the in vivo diuretic studies on Sprague-Dawley rats. Among them, 1n, 1r, 1t and 1v exhibited excellent diuretic activity, especially 1r and 1v. Therefore, 1r and 1v are potent novelAVP V2receptor antagonist candidates.     

Nonpeptide arginine vasopressin antagonists for both V1A and V2 receptors: synthesis and pharmacological properties of 4-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)benzanili de derivatives and 4'-(5,6-dihydro-4H-thiazolo[5,4-d][1]benzoazepine-6-carbonyl)benzanilid e derivatives

Arginine vasopressin (AVP) has a dual action mainly in the periphery, i.e., vasoconstriction and water reabsorption via V1A and V2 receptors; it may play a role in a number of diseases, including congestive heart failure (CHF), hypertension, renal disease, edema, and hyponatremia. We have attempted to develop a new series of orally active AVP antagonists for both V1A and V2 receptors based on the hypothesis that the blockade of both V1A and V2 receptors might be beneficial to CHF patients. In this report, a series of compounds structurally related to 4'-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6- carbonyl)benzanilide and 4'-(5,6-dihydro-4H- thiazolo[5,4-d][1]benzoazepine-6-carbonyl)benzanilide were synthesized and examined for AVP antagonist activity for both V1A and V2 receptors. As a result, it was found that the 4'-(1,4,5,6-tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbon yl)-2- phenylbenzanilide derivatives showed potent binding affinity for both V1A and V2 receptors. Especially, 4'-(2-methyl-1,4,5,6- tetrahydroimidazo[4,5-d][1]benzoazepine-6-carbonyl)-2-phe nylbenzanilide monohydrochloride (18, YM087 = conivaptan hydrochloride) exhibited potent binding affinity and AVP antagonist activity, after intravenous administration, for both V1A and V2 receptors. Furthermore, YM087 exhibited the most potent oral activity for the V2 receptor. Details of the synthesis and pharmacological properties of this series are presented.     

Capillary electrophoresis using immobilized whole cells with overexpressed endothelin receptor for specific ligand screening

A new capillary electrophoresis method using immobilized cells as the stationary phase has been developed. The power of this method is demonstrated by the separation and identification of endothelin antagonists on a capillary column coated by the transfected Chinese hamster ovary (CHO) cells with overexpressing endothelin receptors. The screening results are validated by functional assays suppressing the increase of intracellular calcium concentration induced by endothelin-1. Instead of making efforts in isolating protein receptors, the easily prepared whole-cell capillary column provides a superior tool on the basis of ligand/receptor affinity for a rapid screening of potent drug candidates from compound libraries.     

Structure-activity relationships of 2-(benzothiazolylthio)acetamide class of CCR3 selective antagonist

The structure activity relationships of novel selective CCR3 receptor antagonists, 2-(benzothiazolylthio)acetamimde derivatives were described. A lead structure (1a) was discovered from the screening of the focused library that was based on the structure of our dual antagonists for the human CCR1 and CCR3 receptors. Derivatization of 1a including incorporation of substituent(s) into each benzene ring of the benzothiazole and piperidine side chain resulted in the identification of potent and selective compounds (1b, r, s) exhibiting nano-molar binding affinity (IC(50)s: 1.5-3.0 nM) and greater than 800-fold selectivity for the CCR3 receptor over the CCR1 receptor.     

Molecular dynamics study-based mechanism of nefiracetam-induced NMDA receptor potentiation

Plastic changes in the brain required for memory formation and long-term learning are dependent on N-methyl-d-aspartic acid (NMDA) receptor signaling. Nefiracetam reportedly boosts NMDA receptor functions as a basis for its nootropic properties. Previous studies suggest that nefiracetam potentiates the NMDA receptor activation, as a more potent co-agonist for glycine binding site than glycine, though the underlying mechanisms remain elusive. Here, using BSP-SLIM method, a novel binding site within the core of spiral β-strands-1-5 of LBD-GLUN1 has been predicted in glycine-bound GLUN1 conformation in addition to the glycine pocket in Apo-GLUN1. Within the core of spiral β-strands-1-5 of LBD-GLUN1 pocket, all-atom molecular dynamics simulation revealed that nefiracetam disrupts Arg523-glycine-Asp732 interaction resulting in open GLUN1 conformation and ultimate diffusion of glycine out of the clamshell cleft. Open GLUN1 conformation coerces other intra-chain domains and proximal inter-chain domains to sample inactivate conformations resulting in closure of the transmembrane gate via a novel gauche trap on threonine 647 (chi-1 dihedral (χ₁) = −45° instead of +45°). Docking of nefiracetam into the glycine pocket reversed the gauche trap and meditates partial opening of the TMD gate within a time-scale of 100 ns as observed in glycine-only state. All these results suggest that nefiracetam can favorably complete with glycine for GLUN1-LBD in a two-step process, first by binding to a novel site of GLUN1-LBD-NMDA receptor followed by disruption of glycine-binding dynamics then replacing glycine in the GLUN1-LBD cleft.