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Prediction of UV and ESI-MS signal intensities.

All major pharmaceutical companies maintain large collections of compounds that are used either for screening against biological targets or as synthetic precursors. The quality assessment of these compounds is typically done by liquid chromatography combined with mass spectroscopy (LC/MS) and UV purity control. To facilitate the analysis of the analytical data, we have built computational models to predict UV and MS signal intensities under experimental LC/MS conditions. The discriminant partial-least-squares technique was used for classifying compounds into those most likely to yield a MS signal and others where the signal is below the detection limit (94% and 88% correct predictions, respectively). In the case of UV prediction, we compared this statistical linear-regression technique to a knowledge-based approach. A combination of both techniques proved to be the most reliable (96/98% correct predictions of UV-active/ UV-inactive compounds). Both models have been incorporated into the automated compound integrity profiling at F. Hoffmann-La Roche.

Chromogenic Compounds↗

A fluorescent probe for the active site of bovine trypsin.

The compound 2-p-toluidinylnaphthalene-6-(N-beta-ethylamine hydrochloride) sulfonamide (compound III) has a structure that is appropriate for binding to the active site of trypsin. It also has the property of fluorescence when in a nonpolar environment such as when bound to trypsin. Kinetic studies show that compound III competitively inhibits the trypsin-catalyzed hydrolysis of L-alpha-N-Benzoylarginine-p-nitroanilide (L-BAPNA) with a KI' of 3.6 X 10(-4)M at pH 8.1. The fluorescence enhancement of III when bound to bovine trypsin further confirms the existence of a hydrophobic specificity region within the active site of trypsin. The pH dependence of the fluorescence of compound III with trypsin was also determined.

Animals↗

Determination of protein concentration by total organic carbon analysis.

Determination of the carbon concentration in protein solutions by total organic carbon analysis was found to be a sensitive and reliable method for the estimation of protein concentrations. Using a carbon content of 0.53 g/g in protein and of 0.44 g/g in carbohydrate, the concentrations of normal proteins, proteins containing chromophoric groups, and proteins containing carbohydrate could be established. The method appeared to be independent of the nature of the protein and showed complete linearity between 25 and 1000 mg/l (0.5-20 micrograms per assay) when protein was serially diluted. Determination of specific absorption coefficients by measuring both the absorbance of protein solutions at 280 nm and their carbon concentrations gave values which, on the average, coincided within 12% with values reported in the literature. The method may have special applicability in protein purification studies, as it does not require knowledge of molar extinction coefficients beforehand, and also monitors the disappearance of carbon compounds other than protein.

Carbon↗

Prolonged retention of cross-linked trypsin in calcium alginate microspheres.

Trypsin microencapsulated in a calcium alginate matrix was lost quickly through diffusion when the microspheres were placed in an aqueous medium. This problem was overcome by first reacting trypsin with glutaraldehyde to form cross-linkages and then incorporating the enzyme in the alginate microspheres. The performance of the cross-linked trypsin remained optimal at pH 8 while it was found to be more heat-stable and remained highly active even at 80 degrees C. Esters and amides of L-arginine were preferentially hydrolysed by the enzyme indicating that cross-linking did not adversely affect the conformation of the active site. There was a suppression in enzymatic activity when the microspheres were placed in reaction media with an increasing concentration of organic solvent such as ethanol, acetonitrile or isopropanol. However, when returned to a totally aqueous environment, the enzyme resumed its initial tryptic capability. Such a microencapsulated form of cross-linked enzyme may find application in enzyme replacement therapy, optical resolution of racemic compounds as well as organic synthesis in an aqueous-organic environment.

Alginates↗

Gossypol-induced inhibition of plasminogen activator activity in human and ovine acrosomal extract.

The effect of gossypol--a polycyclic compound isolated from cotton seeds--on the plasminogen activator activity of man and ram acrosomal extracts was explored in vitro. The action of gossypol on the plasminogen activator activity was investigated by a spectrophotometric method using the chromogenic substrate S-2251. Gossypol, a known antispermatogenic agent, was found to effectively inhibit human and ovine acrosomal plasminogen activator activity. The inhibition was dose-dependent. Plasminogen activator activity from man and ram extracts was completely inhibited by 350 mumol l-1 and 300 mumol l-1 of gossypol, respectively. In additional experiments, low, non-spermicidal concentrations of gossypol (2.5-40 mumol l-1) were found to significantly inhibit plasmin activity in a dose-dependent manner. The results suggest that inhibition of both acrosomal plasminogen activator and plasmin activity is a possible mechanism by which gossypol exerts its antifertility effect, since the plasminogen activator/plasmin system plays a role in the whole process of ovum fertilization.

Acrosome↗

Heparin, carboxyl-reduced sulfated heparin, and Trestatin A sulfate. Antiproliferative and anticoagulant activities.

Human smooth muscle cells were used to investigate the antiproliferative activities of sulfated carbohydrates. The antiproliferative potencies of coarse heparin fractions prepared by ultrafiltration increased with the mean molecular-weight, whereas the anticoagulant activities of a high-molecular-weight fraction had submaximal values. Furthermore, the dependence of antiproliferative activity on sulfate content is discussed. Carboxyl-reduction of heparin abolished both antiproliferative and anticoagulant activities. Sulfation of this compound yielded CRS-heparin with restored antiproliferative potency but devoid of antithrombin III-mediated anticoagulant activity. Sulfation of the pseudo-nonasaccharide, Trestatin A, yielded a compound having the highest antiproliferative activity, so far observed for a low-molecular-weight compound, and having only weak anticoagulant properties.

Anticoagulants↗

Comparative in vitro investigation of prothrombin complex concentrates.

Three commercial prothrombin complex concentrates (PCC) were compared in vitro. Differences in the activities or contents, respectively, of the PCC factors FII, FVII, FIX, FX and the proteins C, S, and Z (antigen) in particular were found. Global tests of activated factors did not reveal marked differences between the products. Neither free thrombin nor elevated levels of activated FX were detected. In contrast, analyses of FVIIa, of residual amidolytic activities, and of concentrations of unwanted ingredients demonstrated considerable differences between the products. While antithrombin III was detected only in two of three concentrates, heparin was found in all PCCs but in markedly different concentrations. Although the homogeneity of the products has been clearly improved in comparison with former comparative investigations, the products can be distinguished by their compound profile and by a couple of in vitro assays.

Biological Products↗

1-Thio-beta-D-galactofuranosides: synthesis and evaluation as beta-D-galactofuranosidase inhibitors.

Beta-D-galactofuranosidase is a good chemotherapeutic target for the design of inhibitors, since beta-D-galactofuranose is a constituent of important parasite glycoconjugates but is not present in the host mammals. With this aim, we have synthesized for the first time alkyl, benzyl and aryl 1-thio-beta-D-galactofuranosides by condensation of penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols, in the presence of SnCl4as catalyst. The complete chemical and spectroscopical characterization of these compounds showed that the reaction was stereoselective. Debenzoylation with sodium methoxide afforded the beta-S-galactofuranosides in high yield. The thioglycosides were tested as inhibitors of the beta-D-galactofuranosidase of Penicillium fellutanum, using for the first time 4-nitrophenyl-beta-D-galactofuranoside as chromogenic substrate. The 4-aminophenyl-1-thio-beta-D-galactofuranoside, obtained by catalytic hydrogenation of the nitrophenyl derivative, was the best inhibitor being then an adequate ligand for the preparation of an affinity phase aimed at the isolation of beta-d-galactofuranosidases from different sources. Also the inhibitory activity of d-galactono-1, 4-lactone was shown.

Chromogenic Compounds↗

Development of a dynamic model for real-time determination of membrane-bound acetylcholinesterase activity upon perfusion with inhibitors and reactivators.

Quantitative predictions of the course of acetylcholinesterase (AChE) activity, following interference of inhibitors and reactivators, are usually obscured by the time-dependent changes of all reaction partners. To mimic these dynamics we developed an in vitro model. Immobilized human erythrocyte ghosts in a bioreactor were continuously perfused while AChE activity was monitored by a modified Ellman method. The perfusion system consisted of two HPLC pumps with integrated quaternary low-pressure gradient formers that were programmed by a computer using commercial HPLC software. The combined eluates passed a particle filter (Millex-GS, 0.22 microm) containing a thin layer of erythrocytes that was immersed in a temperature-controlled water bath. The effluent passed a flow cell in a UV-vis detector, the signal of which was digitized, written to disc and calculated with curve fitting programs. AChE activity decreased by 3.4% within 2.5 h. The day-to-day variation of the freshly prepared bioreactor using the same enzyme source was +/-3.3%. Residual activity of 0.2% marked the limit of quantification. Following perfusion with paraoxon, pseudo first-order rate constants of inhibition were established that did not differ from results obtained in conventional assays. The same holds true for reactivation with obidoxime. The set-up presented allows freely programmable time-dependent changes of up to eight solvents to mimic pharmacokinetic profiles without accumulation of products. Due to some hysteresis in the system, reaction half-lives should be >3 min and concentration changes in critical compounds should exceed half-lives of 5 min. Otherwise, the system offers much flexibility and operates with high precision.

Acetylcholinesterase↗

Modest in vivo exposure to solar wavelengths induces a visible absorbing chromophore in Skh-1 mouse epidermis.

BACKGROUND/PURPOSE: In the previous work, we correlated epidermal hyperplasia with increased epidermal absorption in the 250-400 nm region. During a recent review of that work, the apparent formation of a chromophore, with absorption slightly longer than 400 nm, in the epidermis of irradiated animals was noted. In this study, we have extended the transmission measurement to include the 250-800 nm region. METHODS: Age-matched Skh-1 hairless mice were separated into three groups. One group was irradiated with 6.3 J/cm(2) (0.9 minimal erythemal dose; MED) of solar simulating ultraviolet radiation (SSUVR) five times/week for 2 weeks, then increased to 1.1 MED (7.1 J/cm(2)) for two additional weeks (20-day group). A second 10-day group, added halfway through the protocol, was irradiated with 0.9 MED five times/week for 2 weeks. The control group received no UV irradiation. Routine H&E staining and epidermal absorption spectral analysis were carried out on biopsy specimens from each animal. RESULTS: This work confirms the development or enhancement of a visible chromophore with a maximum absorption at ca 412 nm. This peak appears to be radiation dose dependent. It can be discerned in both the groups, albeit more prominently in the 20-day animals. The absorption is sufficiently strong to impart a yellow to reddish appearance to skin viewed in full spectrum visible light. CONCLUSIONS: Accumulation of such a chromophore in humans may contribute to the coloration of chronically exposed skin. The absorption strength and wavelength location of the peak is strongly suggestive of a heme-like compound. We are currently conducting experiments to further characterize this chromophore.

Absorption↗

Spectrophotometric study of several sensitive reagents for serum iron.

A comparison of three sensitive ligands for iron is described. All show varying degrees of enhancement of values by copper, an element that is the primary interference encountered in serum assays for iron. Two of three tested reagents, 2,4-bis(5,6-diphenyl-1,2,4-triazin-3-yl) pyridine tetrasulfonate and Ferene S are not current clinical chemistry choices whereas ferrozine is widely used. The described study presents spectral characterization of the copper interference with all three ligands. The virtual complete removal of this interference, by the masking actions of either thioglycolic acid, neocuproine or thiourea, is also described . Evidence will be presented that contradicts a previously proposed mechanism for the action of thioglycolic acid which suggests that copper is prevented from dissociating from its protein-binding site by this compound. The preparation of a protein-free filtrate as the matrix in which to generate the color reaction is described, and alternative procedures discussed in brief.

Benzenesulfonates↗

A microtiter colorimetric assay for the HIV-1 protease.

We have developed a novel colorimetric assay for the HIV-1 protease that is suitable for high-throughput screening of inhibitors. This assay utilizes two nonenzymatic reaction steps, which are carried out in succession following enzymatic hydrolysis of a synthetic peptide. The first step involves a carbamylation reaction between cyanate and the nascent alpha amino group resulting from enzymatic hydrolysis. The second step involves a carbamidodiacetyl reaction between 2,3-butanedione monoxime (diacetylmonoxime) and the de novo carbamido compound. The entire assay can be performed in a microtiter plate and is amenable to automation. In addition, this peptidolysis assay is readily adaptable to other proteolytic enzymes and their substrates.

Amino Acid Sequence↗

Matrix metalloproteinase inhibitors containing a (carboxyalkyl)amino zinc ligand: modification of the P1 and P2' residues.

Systematic modification of the presumed P1 side chain in a series of (carboxyalkyl)amino-based inhibitors of matrix metalloproteinases enabled identification of the 2-(1,3-dihydro-1,3-dioxo-2H-benz[f]isoindol-2-yl)ethyl group as a preferred substituent imparting potent inhibition of the enzymes collagenase and gelatinase. It was subsequently found that the P2'-P3' residues in this series could be replaced by small non-peptide residues, while maintaining inhibitory potency. The imide group in this series of compounds can undergo autocatalytic hydrolysis under neutral conditions.

Amino Acid Sequence↗

An internally quenched fluorogenic substrate of prohormone convertase 1 and furin leads to a potent prohormone convertase inhibitor.

Based upon the observed cleavage of various peptidyl substrates by the recombinant prohormone convertases PC1 and furin, an intramolecularly quenched fluorogenic peptidyl substrate, (o-aminobenzoyl)-Lys-Glu-Arg-Ser-Lys-Arg-Ser-Ala-Leu-Arg-Asp-(3-nitro)Ty r-Ala, was synthesized. In spite of the distance (approx. 33 A) separating the fluorescent donor/acceptor pair, the highly fluorescent o-aminobenzoyl group is efficiently quenched by long-range resonance energy transfer to the (3-nitro)Tyr moiety. Both recombinant human PC1 and human furin recognize and cleave specifically this substrate at the expected Arg-Ser site in a sensitive manner. The Km values for human PC1 and human furin were 17 microM and 30 microM respectively, with Vmax. values of 6.4 microM/h and 18 microM/h. These values differ significantly from those obtained when using a 7-amino-4-methylcoumarin-containing pentapeptidyl substrate where, for similar Km values, the Vmax. values were much lower. The peptide sequence was used to synthesize another peptide incorporating a ketomethylene arginyl pseudopeptide bond. This compound proved to be a potent competitive inhibitor of both human PC1 and human furin, displaying Ki values of 7.2 microM and 2.4 microM respectively.

Amino Acid Sequence↗

Pharmacology of low molecular weight heparins.

The investigations on LMW heparins that are reviewed in this article demonstrate that there is no relationship between the specific anti-Factor Xa activity and the release of HTGL activity after intravenous or subcutaneous administration to man. The measurement of anti-Factor Xa-like activity in patients treated with unfractionated or with LMW heparin was validated in whole blood samples obtained from the fingertip using Heptest reagents. Administration of high doses of LMW heparin twice daily resulted in a small but significant accumulation in healthy persons. The half-life of anti-Factor Xa-like activity increased after repeated administration, indicating that glycosaminoglycans or other compounds are released by LMW heparin into the bloodstream. The studies indicated that the improved pharmacologic properties may induce fewer side effects than unfractionated heparin and that patients with contraindications to unfractionated heparin or oral anticoagulants may be given long-term treatment with LMW heparin.

Animals↗

A continuous assay of myristoyl-CoA:protein N-myristoyltransferase for proteomic analysis.

Protein N-myristoylation is an important lipid modification that affects the activity and membrane-binding properties of crucial proteins belonging to signal transduction cascades. The aim of this work was to develop a rapid and easy diagnostic method to check for (i) effective N-myristoylation of any given protein and (ii) easy proteome annotation. The N-myristoylation reaction was coupled to that of pyruvate dehydrogenase, and NADH was continuously detected spectrophotometrically. This method was optimized for and applied to full-length Saccharomyces cerevisiae and Arabidopsis thaliana N-myristoyltransferases and two A. thaliana enzyme derivatives. The data were validated by comparison with a previously described discontinuous assay, modification of the chemical nature of the substrates, and use of specific inhibitors. The kinetics of N-myristoylation were determined in vitro with various compounds including a full-length polypeptide substrate, a small G protein of the RAB family already known to be N-myristoylated in vivo. This automated assay can be used for proteomic studies to determine the N-myristoylation state of any protein.

Acyl Coenzyme A↗

Requirement for reducing agents in deoxyribonucleic acid strand scisson by the purified chromophore of auromomycin.

By methanol extraction and high-pressure liquid chromatography a nonprotein chromophore has been obtained from the antitumor protein antibiotic auromomycin (AUR) which possesses the cytotoxic and the in vivo and in vitro deoxyribonucleic acid (DNA) strand scission activities of the parent material. The rate of DNA strand breakage by the purified chromophore is markedly stimulated by reducing compounds (maximally at approximately 0.1 mM dithiothreitol), but DNA strand scission activity is lost upon pretreatment of the chromophore with these agents. Apoprotein specifically protects against such inactivation but blocks the activity of both the stimulated and unstimulated reactions, presumably by complexing the chromophore and making it less available to the target DNA. Dithiothreitol-dependent scission of DNA by chromophore is faster and more complete at 0 degrees C than at 37 degrees C. The reaction at 0 degrees C is almost entirely dependent on the presence of a reducing compound. Although 2-mercapto-ethanol does not stimulate the reaction of either AUR or its chromophore at 37 degrees C, it has a significant stimulatory effect at 0 degrees C.

Anti-Bacterial Agents↗