Selectivity Enhancement for trans-2-(2,3-Anthracenedicarboximido)-cyclohexane-derived Diastereomers in HPLC by Using an Ordered Organic Stationary Phase

2-(2,3-anthracenedicarboximido)cyclohexane derivatives (AC) have been known as the evolutionary diastereomerizing reagents for enantiomer discrimination in HPLC with ODS. However, a substantial separation of diastereomers can be observed only at lower temperatures, such as -40 degrees C. Therefore, in this work, poly(octadecyl acrylate)-grafted silica, ODAn was applied as an alternative stationary phase to ODS for the separation of AC-derived diastereomers. As a result, complete separation was achieved even under the conventional condition: for example, methanol as the mobile phase and 0 degrees C as the column temperature. An investigation on the temperature dependency of the selectivity demonstrated that ODAn shows a remarkable increase in selectivity at temperatures below 30 degrees C, which almost agreed with the peak-top temperature of the endothermic peak in a DSC thermogram for ODA35 immersed in a mobile phase. The better separation would be derived from a highly ordered structure of ODAn and a carbonyl-pi interaction with AC-derived diastereomers.

Absolute Stereochemistry of Fungal Beauveriolide III and ACAT Inhibitory Activity of Four Stereoisomers

Fungal beauveriolide III (BeauIII, 1b), a cyclodepsipeptide inhibiting acyl-CoA:cholesterol acyltransferase (ACAT) and showing antiatherogenic activity in mouse models, consists of L-Phe, L-Ala, D-allo-Ile, and 3-hydroxy-4-methyloctanoic acid (HMA) moieties, but the stereochemistry of the HMA part has not until now been fully defined. To determine it, four HMA stereoisomers were synthesized and labeled with (S)-(+)-2-(anthracene-2,3-dicarboximido)-1-propyl trifluoromethane sulfonate (AP-OTf), a chiral fluorescent reagent. The derivatives were separated by HPLC and compared with the natural HMA derivative, which was thereby identified as (3S,4S)HMA in BeauIII. Furthermore, the four beauveriolide III isomers ((3S,4S)BeauIII (23a), (3R,4R)BeauIII (23b), (3R,4S)BeauIII (23c), and (3S,4R)BeauIII (23d)) were synthesized, and it was shown that all the spectral data for 23a were identical with those for natural 1b. Isomers 23a and 23d showed potent inhibitory activity of lipid droplet accumulation in macrophages, while the other two isomers caused weak inhibition. Thus, the 3S configuration of BeauIII is important for this activity. Furthermore, 23a and 23d showed rather specific inhibition against the ACAT1 isozyme.

Chiral discrimination of primary amines by HPLC after labeling with a chiral derivatization reagent,trans-2-(2,3-anthracenedicarboximido)-cyclohexanecarbonyl chloride

Enantiomeric discrimination of chiral primary amines was performed by both reversed-phase HPLC and normal-phase HPLC after labeling with a chiral fluorescent derivatization reagent, (1R,2R)- and (1S,2S)-trans-2-(2,3-anthracenedicarboximido)cyclohexanecarbonyl chloride. Use of HPLC permits separation of diastereomeric derivatives of amines up to C30 which have a primary amino group at the middle of the alkyl chain. The derivatives of primary amines having an anteiso alkyl chain, which has a chiral branched-methyl at the n-3 position of the alkyl chain, were also separated by HPLC, and it was also possible to separate niphatesine D by reversed-phase HPLC after derivatization.

Brachyury homolog (HpTa) is involved in the formation of archenteron and secondary mesenchyme cell differentiation in the sea urchin embryo

Sea urchin Brachyury homolog (HpTa) is expressed exclusively in the vegetal plate and secondary mesenchyme cells in the embryos of sea urchin Hemicentrotus pulcherrimus. In order to gain insights into the role of HpTa during sea urchin development, we designed experiments to perturb the embryo by inducing ectopic overexpression of HpTa by injecting fertilized eggs with HpTa mRNA. The overexpression of HpTa resulted in suppression of the formation of vegetal plate and secondary mesenchyme cells. We assume that the interaction of HpTa with unknown factors is required for the activation of the HpTa target genes, and that the excess amount of HpTa proteins produced from injected HpTa mRNA depletes the co-factors. In consequence, the target genes of HpTa would be repressed by the overexpression of HpTa. We suggest that HpTa is involved in the formation of the vegetal plate and the differentiation of secondary mesenchyme cells.

Comparative study on the use of ortho-phthalaldehyde, naphthalene-2,3-dicarboxaldehyde and anthracene-2,3-dicarboxaldehyde reagents for alpha-amino acids followed by the enantiomer separation of the formed isoindolin-1-one derivatives using quinine-type chiral stationary phases

Cinchona alkaloid based chiral stationary phases (CSPs) were evaluated and compared for the enantiomer separation of a set of alpha-amino acid derivatives as selectands (SA), using ortho-phthalaldehyde (OPA), naphthalene-2,3-dicarboxaldehyde (NDA) and anthracene-2,3-dicarboxaldehyde (ADA) as reagents in the presence of acetonitrile. Protocols have been developed for the derivatization of most common amino acids in the absence of the usual thiol components (2-mercaptoethanol, mercaptosulphonic acid, sodium sulfite) under acidic and neutral conditions providing the corresponding isoindolin-1-one (phthalimidine) derivatives. They are stable for hours at various reaction conditions compared to thiol or sulfide modified isoindoles resulted by the OPA-thiol reaction type. Among the derivatizing agents, ADA afforded the highest retention factors (k) and for the majority of the analytes also resolution (Rs) and enantioselectivity (alpha) values (i.e. for tryptophan k1 = 23, Rs = 4.93 and alpha = 1.43). Structure variation of the CSPs and selector (SO), respectively indicates that steric arrangement around the binding cleft plays a major role in the enantiodiscriminating events. To provide more detailed information about the derivatization reaction itself, the proposed mechanism for the formation of the OPA derivative (isoindolin-l-one) was further evaluated by deuterium labeling and LC-MS analysis.

Enantiomer separation of a powerful chiral auxiliary, 2-methoxy-2-(1-naphthyl)propionic acid by liquid chromatography using chiral anion exchanger-type stationary phases in polar-organic mode; investigation of molecular recognition aspects

The enantiodiscriminating potential of the weak anion exchange-type quinine-based chiral stationary phases (CSPs) for direct enantiomer separation of racemic 2-methoxy-2-(1-naphthyl)propionic acid (selectand, SA) was studied. The influence of structure variations of the selector (SO) in the carbamate functional group and/or in the C6' position of quinoline moiety on retention and enantioselectivity was investigated. Systematic chromatographic studies were made to gain more insight into the overall chiral recognition mechanism for a given mobile phase. In this context, the tert-butylcarbamoyl quinine and the corresponding diisopropylphenyl-derived selector provided the highest resolution and enantioselectivity under polar-organic conditions with the elution order of (R) before the (S) enantiomer. When the bulkiness of the substituents in the C6' position of the SO was increased, the selectivity was decreased in all cases. Alkylation of the nitrogen atom in the carbamate functionality of the SO resulted in the complete loss of enantiomer separation, confirming the crucial importance of the hydrogen-bond formation involved in the stereodiscriminating events. In addition, ten different mono-, bi-, or trivalent acids, necessary as competitor molecules (counter-ions) of the mobile phase, were screened to judge their influence on retention and overall enantioselectivity. Among them, acetic acid, formic acid, N-acetylglycine, and glycolic acid proved to be the most promising counter-ions with R(S) values of 6.35, 6.81, 8.19, and 7.34, respectively. On the basis of chromatographic data, a tentative molecular recognition model was proposed. Simultaneous ion-pairing and hydrogen bonding, in concert with pi-pi stacking and steric interactions, were expected to be responsible for chiral recognition mechanism. This was partially corroborated by structural and/or conformational analysis of the tert-butylcarbamoyl quinine-2-methoxy-2-(1-naphthyl)propionic acid (SO-SA) complex.

Chiral discrimination of secondary alcohols by both1H-NMR and HPLC after labeling with a chiral derivatization reagent, 2-(2,3-anthracenedicarboximide)cyclohexane carboxylic acid

Enantiomeric discrimination of chiral secondary alcohols was performed by both reversed-phase HPLC and 1H-NMR after labeling with a chiral fluorescent derivatization reagent, 2-(2,3-anthracenedicarboximide)cyclohexanecarboxylic acid. It was possible to discriminate by HPLC the chirality of alcohols up to C30 having a chiral hydroxyl group at the middle of the straight alkyl chain, and, by 1H-NMR, alcohols up to C16. For alcohols having one straight alkyl and one isoalkyl group with the same carbon numbers at both sides of a hydroxyl group, it was possible to discriminate the chiralities of alcohols up to C19 by both 1H-NMR and HPLC. The 1H-NMR methods also made it possible to determine absolute configurations empirically.

Investigations of molecular recognition aspects related to the enantiomer separation of 2-methoxy-2-(1-naphthyl)propionic acid using quinine carbamate as chiral selector: An NMR and FT-IR spectroscopic as well as X-ray crystallographic study

The chiral recognition mechanism of a cinchona alkaloid-based chiral stationary phase (CSP) showing high enantiomer discrimination potential for 2-methoxy-2-(1-naphthyl)propionic acid (MalphaNP acid) was investigated. Conformational and structural analyses of the 1:1 complexes of 9-O-(tert-butylcarbamoyl) quinine selector (SO) and MalphaNP acid (selectand, SA) were carried out employing NMR spectroscopy in solution, Fourier-transform infrared (FT-IR) spectroscopy, and solid-state X-ray diffraction analysis. Intramolecular NOEs of a soluble analogue of the CSP afforded the conformational states of the free and complexed form of the selector. The (1)H-NMR spectra revealed that the free form of the SO constitutes anti-open as well as anti-closed and/or syn-closed conformers. Upon complexation with the (S)-MalphaNP acid enantiomer to form the more stable diastereomeric associate, a conformational transition of the selector takes place, resulting in the synthesis of the anti-open conformer nearly exclusively. FT-IR spectra reveal that, besides the primary ion-pairing interaction, stereoselective hydrogen bonding stabilizes the more stable complex via the amide hydrogen of the SO. X-ray diffraction analysis of 9-O-(tert-butylcarbamoyl)quinine and (S)-MalphaNP acid complex further revealed the occurrence of a bidentate H-bond-mediated ionic interaction between SO and SA as well as the lack of pi-pi interaction in the 1:1 complex, and corroborated the conclusions derived from spectroscopic and chromatographic studies.

Sea urchin insulator protects lentiviral vector from silencing by maintaining active chromatin structure

Suppressed expression of transgenes in vivo is the major obstacle in the gene therapy. For the long-term expression, we utilized a chromatin insulator from sea urchin arylsulfatase (Ars) gene locus (Ars insulator, ArsI), which has been shown to epigenetically regulate gene expression across species. ArsI was able to prevent silencing of the transgene in a myeloid cell line, HL-60, and a murine embryonic stem cell line, CCE, in an orientation-dependent manner, but not in Huh-7, K562 and MCF-7 cells, indicating that the effect of ArsI on gene silencing was cell type dependent. Although anti-silencing effect of ArsI was almost equivalent to that of chicken beta-globin insulator, incorporation of ArsI into lentiviral vector had little effect on the virus titer compared with chicken beta-globin insulator. Clonal analysis of transduced HL-60 cells revealed that ArsI protects the lentiviral vector from position effects regardless of its orientation. Furthermore, chromatin immunoprecipitation assays revealed that a high acetylation level was observed in the promoter of the insulated vector, whereas that of ArsI was independent of its anti-silencing capacity. In addition to it having little deteriorative effect on the virus titer, the identified anti-silencing effect of ArsI suggested its possibility for application in gene therapy.

High pressure nmr study of dihydrofolate reductase from a deep-sea bacterium Moritella profunda

We have investigated the effect of pressure and temperature on the structural and thermodynamic stability of a protein dihydrofolate reductase from a deep-sea bacterium Moritella profunda in its folate-bound form in the pressure range between 3 and 375 MPa and the temperature range between -5 and 30 degrees C. The on-line cell variable pressure 1H NMR spectroscopy has been used to analyze the chemical shift and signal intensity in one-dimensional 1H NMR spectra. Thermodynamic analysis based on signal intensities from protons in the core part indicates that the thermodynamic stability of Moritella profunda DHFR is relatively low over the temperature range between -5 and 30 degrees C (deltaG0=15.8 +/- 4.1 kJ/mol at 15 degrees C), but is well adapted to the living environment of the bacterium (2 degrees C and 28 MPa), with the maximum stability around 5 degrees C (at 0.1 MPa) and a relatively small volume change upon unfolding (deltaV= 66 +/- 19 ml/mol). Despite the relatively low overall stability, the conformation in the core part of the folded protein remains intact up to approximately 200 MPa, showing marked stability of the core of this protein.

Highly Potent Chiral Labeling Reagents for the Discrimination of Chiral Alcohols*

Highly sensitive chiral labeling reagents, (1R,2R)- and (1S,2S)-2-(2,3-anthracenedicarboximido)cyclohexanecarboxylic acids [(1R,2R)- and (1S,2S)-A] and (1R,2R)- and (1S,2S)-2-(2,3-naphthalenedicarboximido)cyclohexanecarboxylic acids [(1R,2R)- and (1S,2S)-A'], were prepared. Reagent A has enabled us to discriminate the enantiomers of anteiso fatty alcohols up to C9 methyl branching by 1H NMR, and both reagents A and A' have allowed up to C16 methyl branching at the 10(-15) molar level by fluorescence detected reversed-phase HPLC.

Determination of the absolute configurations of the anteiso acid moieties of glycoglycerolipid S365A isolated from Corynebacterium aquaticum

The absolute configurations of the two acid moieties, 12-methyltetradecanoate and 14-methylhexadecanoate, of glycoglycerolipid S365A isolated from Corynebacterium aquaticum were determined by an HPLC analysis after their conversion with the chiral fluorescent labeling reagents, (1S,2S)- and (1R,2R)-2-(2,3-anthracenedicarboximido)cyclohexanol. Both anteiso acids had the S configuration.

Fluorimetric analysis of lipase hydrolysis of intermediate- and long-chain glycerides

For the purpose of deducing the digestive behavior of dietary fat in the digestive organs, a fluorimetric method for the measurement of hydrolysis by porcine pancreatic lipase was performed using intermediate- and long- acyl chain glycerides as substrates. Insoluble glycerides constituted by C10-C16 acyl chains were mechanically dispersed in 100% buffer and hydrolyzed by porcine pancreatic lipase. After the reaction, fatty acid released by the enzyme was extracted and its carboxyl group was fluorescently labeled with 9-bromomethylacridine. The 9-acridinylmethyl derivative of the fatty acid was separated and determined by HPLC. The sensitivity of this method was about 1000 times higher than that of the titrimetric method. Only 0.5 ng of porcine pancreatic lipase was sufficient for one routine assay. This assay method was successfully applied to investigate the enzymatic properties of porcine pancreatic lipase with respect to dietary lipids. The effects of some physiological factors concerned with lipid digestion, such as bile salt and colipase, on the lipase hydrolysis were also examined. The method established in the present study could contribute to a highly sensitive assay of some hydrolases containing lipase with regard to insoluble substrates.

Native-like tertiary structure formation in the alpha-domain of a hen lysozyme two-disulfide variant

Structure formation in two species of the two-disulfide variant of hen lysozyme was investigated by means of CD spectroscopy, disulfide exchange measurement, and 1H-NMR spectroscopy. One species, 2SS [6-127, 30-115], which contained the two disulfide bonds found in the alpha-domain of authentic lysozyme, had amounts of secondary and tertiary structures, and bacteriolytic activity comparable to those of authentic lysozyme, and showed a cooperative thermal unfolding. By contrast, the other species, 2SS [64-80, 76-94], which contained the beta-domain disulfide bond as well as the inter-domain one, had a limited amount of secondary structure and little tertiary structure. Disulfide-exchange did not occur for 2SS [6-127, 30-115], whereas it occurred for 2SS [64-80, 76-94], indicating that the protein main-chain fold coupled with the formation of two disulfide bonds is relatively stable for the former variant, while unstable for the latter. 1H-NMR spectra of 2SS [6-127, 30-115] showed that native-like local environment is present within the region that corresponds to the alpha-domain, while it is absent within the region that corresponds to the beta or inter-domain. These results indicate that the alpha-domain of hen lysozyme can be an independent folding domain at equilibrium. Although the bipartite nature in the structure formation of hen lysozyme is similar to that reported for alpha-lactalbumin, differences exist between the disulfide-intermediates of the two proteins in terms of the structural domain that accomplishes tertiary structure.

Two folded conformers of ubiquitin revealed by high-pressure NMR

High-pressure 15N/1H two-dimensional NMR spectroscopy has been utilized to study conformational fluctuation of a 76-residue protein ubiquitin at pH 4.5 at 20 degrees C. The on-line variable pressure cell technique is used in conjunction with a high-field NMR spectrometer operating at 750 MHz for 1H in the pressure range between 30 and 3500 bar. Large, continuous and reversible pressure-induced 1H and 15N chemical shifts were observed for 68 backbone amide groups, including the 7.52 ppm 15N shift of Val70 at 3500 bar, indicating a large-scale conformational change of ubiquitin with pressure. On the basis of the analysis of sigmoid-shaped pressure shifts, we conclude that ubiquitin exists as an equilibrium mixture of two major folded conformers mutually converting at a rate exceeding approximately 10(4) s(-1) at 20 degrees C at 2000 bar. The second conformer exists at a population of approximately 15% (DeltaG(0) = 4.2 kJ/mol) and is characterized with a significantly smaller partial molar volume (DeltaV(0) = -24 mL/mol) than that of the well-known basic native conformer. The analysis of 1H and 15N pressure shifts of individual amide groups indicates that the second conformer has a loosened core structure with weakened hydrogen bonds in the five-stranded beta-sheet. Furthermore, hydrogen bonds of residues 67-72 belonging to beta5 are substantially weakened or partially broken, giving increased freedom of motion for the C-terminal segment. The latter is confirmed by the significant decrease in 15N[1H] nuclear Overhauser effect for residues beyond 70 at high pressure. Since the C-terminal carboxyl group constitutes the reactive site for producing a multi-ubiquitin structure, the finding of the second folded conformer with a substantially altered conformation and mobility in the C-terminal region will shed new light on the reaction mechanism of ubiquitin.

High-pressure NMR study of the complex of a GTPase Rap1A with its effector RalGDS. A conformational switch in RalGDS revealed from non-linear pressure shifts

Unusually large non-linear 1H and 15N nuclear magnetic resonance chemical shifts against pressure have been detected for individual amide groups of the Ras-binding domain of Ral guanine dissociation stimulator (GDS). The non-linear response is largest in the region of the protein remote from the Rap1A-binding site, which increases by about two-fold by the complex formation with its effector protein Rap1A. The unusual non-linearity is explained by the increasing population of another conformer (N'), lying energetically above the basic native conformer (N), at higher pressure. It is considered likely that the conformational change from N to N' in the Ras-binding domain of RalGDS works as a switch to transmit the effector signal further to molecules of different RalGDS-dependent signaling pathways.

Filling a cavity dramatically increases pressure stability of the c-Myb R2 subdomain

Cavities or packing defects in proteins may generally be related with the dynamics and function of a protein. In the c-Myb R2 subdomain, its single cavity has been shown to be crucial for its DNA recognition. Cavities are also considered important in determining the pressure stability of a protein. In the present work, high-pressure proton nuclear magnetic resonance ((1)H NMR) spectroscopy at 750 MHz is used to study the effect of a cavity-filling mutation (V103L) on the stability of the c-Myb R2 subdomain in the pressure range between 1 and 3,700 bar at 5 degrees C. A dramatic increase in the pressure stability of the c-Myb R2 subdomain is attained, from which we estimate the cavity size to be 35.3 A(3), in good agreement with literature values. We also evaluated the increase in thermodynamic stability DeltaG(0)(1bar) from 5.35 kJ/mol to 7.34 kJ/mol by the mutation, giving a clear example of the effect of a cavity on the global stability of a globular protein.