The design, synthesis, and initial evaluation of benzophenone-containing peptides as potential photoaffinity labels of oligosaccharyltransferase

The benzophenone photophore was incorporated into protected tripeptides and tetrapeptides as photoactivatable probes to study the multimeric enzyme oligosaccharyltransferase (OST). These peptides contain the -Asn-X-Thr- sequon which is required for OST-catalyzed N-glycosylation. Two tripeptides, Bz-Asn-Bpa-Thr-NH2 (3b) and Bz-Asn-Lys[N epsilon-(4-Bz)Bz]-Thr-NH2 (4b), were found to be good OST substrates. They were competitive inhibitors versus standard peptide substrate [14C]Bz-Asn-Leu-Thr-NH2 and their Ki values were determined to be 41 +/- 6 microM and 21 +/- 6 microM, respectively, using synthetic (GlcNAc)2-PP-dolichol.

An efficient substitution reaction for the preparation of thyroid hormone analogues

The substitution of the sterically hindered carbon of the potent thyroid hormone agonist, GC-1, was effected by a reaction based on the solvolysis of the benzylic hydroxyl group. The reaction was found to proceed in high yield with a variety of nucleophiles including alcohols, thiols, allyl silanes and electron-rich aromatic compounds, providing a convenient route to the synthesis of new thyroid hormone analogues.

Discovering transthyretin amyloid fibril inhibitors by limited screening

Insoluble protein fibrils, resulting from the self-assembly of a conformational intermediate are implicated to be the causative agent in several human amyloid diseases including familial amyloid polyneuropathy (FAP) and senile systemic amyloidosis (SSA). These diseases are associated with transthyretin (TTR) amyloid fibrils, which appear to form in the acidic partial denaturing environment of a lysosome or endosome. Here we identify several structural classes of small molecules that are capable of inhibiting the TTR conformational changes facilitating amyloid fibril formation. A small molecule inhibitor that stabilizes the normal conformation of a protein is desirable as a promising approach to treat amyloid diseases and to rigorously test the amyloid hypothesis, the apparent causative role of amyloid fibrils in amyloid disease.

Chemical modification and photograft polymerization upon expanded poly(tetrafluoroethylene)

Poly(tetrafluoroethylene) (PTFE) films were surface-modified by employing a reaction solution of benzophenone and sodium hydride in anhydrous dimethylformamide at a temperature of 150 degrees C for 12 h. Electron spectroscopy for chemical analysis (ESCA) showed defluorination, oxygen incorporation, and extensive unsaturation within the treated PTFE surfaces. The suitably of these reduced PTFE films as substrates for graft polymerization was initially assessed via photograft polymerization of the sodium salt of styrenesulfonic acid (SS-Na), which permitted unequivocal surface analysis by the introduction of a new atom, as well as poly(ethylene glycol) monoacrylate (PEG-Ac). All photograpt polymerization was performed employing ultraviolet irradiation with 2,2-dimethoxy-2-phenylacetophenone as an initiator. Photograft polymerization of SS-Na was verified by further reduction of fluorine atomic content and the appearance of new sulfur and sodium atomic peaks on ESCA survey spectra, and that of PEG-Ac was verified by further reduction of fluorine atomic content and increase of atomic percent ratio of O/C from ESCA survey spectra as well as appearance of a new ester peak on high resolution ESCA C 1s spectra. Dynamic water contact angles on reduced and PEG-Ac photograft polymerized films were measured and showed that the PTFE film surface became more hydrophilic after reduction (from 120 to 89 deg) and the reduced film became more hydrophilic after photograft polymerization with PEG-Ac (from 89 to 36 deg). Modification of the complete surface of expanded PTFE (ePTFE), i.e. of the lumenal, outside and pore surfaces, was performed by employing the reaction described above, except at 105 degrees C for 1 day, followed by photograft polymerization of PEG-Ac. ESCA was performed on the superficial surfaces (i.e. the lumen and exterior) as well as on cross-sections of the ePTFE to permit analysis of the pore surfaces. This analysis showed that both the initial surface reduction and subsequent photograft polymerization were successful as indicated from F/C and O/C atomic percent ratios from ESCA survey spectra, from overall peaks shapes of high resolution ESCA C 1s spectra and from generation of new ester peaks on high resolution ESCA C 1s spectra of ePTFE graft polymerized with PEG-Ac, which demonstrated an O/C atomic percent ratio close to that of PEG-Ac homopolymer. Low voltage scanning electron microscopy confirmed minimal morphological damage to the ePTFE microstructure after reduction and graft polymerization. The approach explored thus provides a means for modulation of biological interactions at ePTFE surfaces with only minimal modification of material morphology, with some surface texture appearing on a length scale of 50-100 nm.

Photosensitizing drugs containing the benzophenone chromophore

The nonsteroidal anti-inflammatory agents ketoprofen, tiaprofenic acid, suprofen and tolmetin, together with the anti-hyperlipoproteinemic drug fenofibrate and the anti-arrhythmic amiodarone can be included in the group of benzophenone-derived photosensitizing drugs. They contain a diaryl ketone chromophore and mediate the development of phototoxic reactions. In some cases, photoallergic responses have been reported. These properties have been substantiated in clinical reports, as well as by means of in vivo and in vitro assays. Tolmetin is phototoxic in vitro, however there are no reports on photosensitization by this drug in humans. In general, photochemical and photobiological studies strongly suggest that photosensitization involves formal hydrogen abstraction (either in a single step or via electron transfer followed by proton transfer) by the benzophenone-like chromophore from the excited triplet state. In the case of amiodarone, the radicals generated by photodehalogenation from the triplet are responsible for the photosensitivity side-effects.

Stability testing of the plastics additives 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-ethoxy-2-ethyloxanilide (tinuvin 312) and 2,2'-methylenebis(4-methyl-t-tert-butyl phenol) in aqueous and fatty food simulants

The stability of five additives used in the manufacture of plastics materials intended to be in contact with foodstuffs was tested in two EU aqueous food simulants (3% acidic acid and 15% ethanol), in olive oil and in two alternative fatty food simulants (95% ethanol and isooctane) under various conditions of temperature and time established for migration testing. The additives were the following: 2,4-dihydroxybenzophenone, 2-2'-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-n-octyloxybenzophenone, 2-ethoxy-2-ethyloxanilide and 2,2'-methylenebis(4-methyl-6-tert-butyl phenol). The additives were spiked into the simulants at their anticipated Specific Migration Limit (SML) and submitted to time-temperature conditions used in the migration testing. The test samples were analysed against fresh samples of the additives spiked at the same concentration just before the analysis. All samples were analysed with HPLC, using an ODS2 column and mobile phase of methanol-water or acetonitrile-water. The results were statistically evaluated by applying a two-tailed F-test (at 95% confidence level) to the variances and onetailed t-test (at 90% confidence level) to the means of the control and the test samples. The statistical evaluation of the results showed that the additives were stable in all simulants within the statistical allowances. Only the 2.2'-methylenebis(4-methyl-6-tert-butyl phenol) showed a loss of about 20% in olive oil and 17% in 3% aqueous acetic acid. The results of the study will be used by the Commission, DG III-C-I. to help to determine whether legislative restrictions in the additives Directive should be applied to the finished material or article (QM) or to migration to simulants (SML).

Magnetic field effects on the behavior of radicals in protein and DNA environments

We have examined the behavior of radical pairs derived by hydrogen abstraction of triplet benzophenone and some of its derivatives from bovine serum albumin, human serum albumin and calf thymus DNA. They have been investigated by means of nanosecond laser flash photolysis techniques. The dynamics of radical pair behavior are shown to be sensitive to external magnetic fields; these effects are interpreted using the established model for the influence of magnetic fields on radical pairs in micellar aggregates, in which intersystem crossing of the radical pair is slowed by the external magnetic field. Our results indicate that proteins and DNA can confine the radicals for a sufficiently long period of time for spin evolution to be affected by external fields. In proteins the radical pair retains its geminate character (i.e. remains confined) for about 0.5-1 microsecond. Interestingly, the magnetic field effects observed in proteins and in DNA seem to occur in distinct timescales; for example, for 2,3,4,5,6-pentafluorobenzophenone bound to DNA, the magnetic field alters the radical reactivity only over times < or = 50 ns, suggesting poor confinement. The timescale for these effects can be increased by promoting Coulombic attraction between DNA and the radical precursor. Electron transfer interactions play a role in the case of DNA.

Glucuronidation of entacapone, nitecapone, tolcapone, and some other nitrocatechols by rat liver microsomes

PURPOSE

Nitrocatechol COMT inhibitors are a new class of bioactive compounds, for which glucuronidation is the most important metabolic pathway. The objective was to characterize the enzyme kinetics of nitrocatechol glucuronidation to improve the understanding and predicting of the pharmacokinetic behavior of this class of compounds.

METHODS

The glucuronidation kinetics of seven nitrocatechols and 4-nitrophenol, the reference substrate for phenol UDP-glucuronosyltransferase activity, was measured in liver microsomes from creosote-treated rats and determined by non-linear fitting of the experimental data to the Michaelis-Menten equation. A new method that combined densitometric and radioactivity measurement of the glucuronides separated by HPTLC was developed for the quantification.

RESULTS

Apparent K(m) values for the nitrocatechols varied greatly depending on substitution pattern being comparable with 4-nitrophenol (0.11 mM) only in the case of 4-nitrocatechol (0.19 mM). Simple nitrocatechols showed two-fold Vmax values compared with 4-nitrophenol (68.6 nmol min-1 mg-1), while all disubstituted catechols exhibited much lower glucuronidation rate. Vmax/K(m) values were about 10 times higher for monosubstituted catechols compared to disubstituted ones. The kinetic parameters for COMT inhibitors were in the following order: K(m) nitecapone > > entacapone > tolcapone; Vmax nitecapone > entacapone > tolcapone; Vmax/K(m) tolcapone > nitecapone > entacapone.

CONCLUSIONS

Nitrocatechols can in principle be good substrates of UGTs. However, substituents may have a remarkable effect on the enzyme kinetic parameters. The different behaviour of nitecapone compared to the other COMT inhibitors may be due to its hydrophilic 5-substituent. The longer elimination half-life of tolcapone in vivo compared to entacapone could not be explained by glucuronidation kinetics in vitro.

Rescue of a mutant G-protein by substrate-assisted catalysis

Signaling by guanine-nucleotide-binding proteins (G-proteins) occurs when they are charged with GTP, while hydrolysis of the bound nucleotide turns the signaling off. Despite a wealth of biochemical and structural information, the mechanism of GTP hydrolysis by G-proteins remains controversial. We have employed substrate-assisted catalysis as a novel approach to study catalysis by G-proteins. In these studies, we have used diaminobenzophenone-phosphonoamidate-GTP, a unique GTP analog bearing the functional groups that are missing in the GTPase-deficient [Leu227]G(s alpha) mutant. This mutant, found in various human tumors, fails to hydrolyze GTP for an extended period. In contrast, the GTP analog is hydrolyzed by this mutant and by the wild-type enzyme at the same rate. On the other hand, modification of G(s alpha) by cholera toxin, which catalyses ADP-ribosylation of Arg201 of G(s alpha), decreased the rates of hydrolysis of both GTP and its analog by 95%. These results attest to the specificity of the GTP analog as a unique substrate for the [Leu227]G(s alpha) mutant and to the essential role of Gln227 in GTP hydrolysis. Furthermore, the finding that the GTP analog was hydrolyzed at the same rate as GTP by the wild-type enzyme, favors a model in which formation of a pentavalent transition state intermediate, presumably stabilized by the catalytic glutamine, is not the rate-limiting step of the GTPase reaction.

Benzophenone-3,3',4,4'-tetracarboxylic acid dihydrate

The title compound, C17H10O9,2H2O, crystallizes in the centrosymmetric space group P2(1)/a but does not exhibit strong eight-membered cyclic dimer hydrogen bonds about centers of symmetry or otherwise. A richly three-dimensional hydrogen-bonding network is observed, however, which arises from 19 hydrogen bonds per asymmetric unit; it includes a 14-membered cyclic dimer about about a center of symmetry and hydrogen-bonding rings of 18 and 30 members involving the acid molecule and a water molecule, both also about centers of symmetry. The carboxyl H and O atoms are ordered in each of the carboxyl groups. The configuration of the benzophenone core is quite similar to that in benzophenone itself and the configuration of the adjacent carboxyl groups is quite similar to that in phthalic acid and naphthalene-2,3-dicarboxylic acid.

Formation of microscale gradients of protein using heterobifunctional photolinkers

Gradients of biological molecules on a microscale have been postulated to elicit cellular responses, such as migration. However, it has been difficult to prepare such gradients for experimental testing. A means for producing such gradients has been developed using a heterobifunctional photolinking agent with laser light activation. The photolinking agent synthesized includes an N-hydroxysuccinimide group and a photoreactive benzophenone (BP) separated by a tetraethylene glycol (TEG) spacer. The presence of the tetraethylene glycol spacer renders the photolinker hydrophilic, a desirable trait for conjugation in aqueous solutions. The linker was then conjugated to R-phycoerythrin (R-PE), a fluorescent protein. The resulting photolinker-R-phycoerythrin conjugate (BP-TEG-PE) was then immobilized onto a polystyrene surface by laser irradiation on a motorized stage. By varying exposure time of the sample to the beam, the amount of BP-TEG-PE immobilized on the surface was changed over an order of magnitude over a distance of 250 microns. This method can be applied to prepare gradients of proteins that elicit biological responses, such as extracellular matrix proteins or growth factors, and to study the biological effects of such gradients.

Photodermatitis from ketoprofen with cross-reactivity to fenofibrate and benzophenones

The aim of this study was to evaluate the possibility of cross-reactivity between ketoprofen, fenofibrate and benzophenones because of their structural similarities. Seven patients presenting photodermatitis from ketoprofen underwent patch and photopatch tests. Ketoprofen, fenofibrate, benzophenone 3, benzophenone 10, benzophenone 4, personal medications and topical creams were tested. All patients had positive patch or photopatch tests to ketoprofen and fenofibrate, four patients had positive UVA photopatch tests to benzophenone 3, and two to benzophenone 10. Patients presenting photosensitization to ketoprofen may also have cross-reactivity to fenofibrate and some benzophenones.

Selective photoaffinity labeling of the inositol polyphosphate binding C2B domains of synaptotagmins

Synaptotagmin (Syt) II, a synaptic vesicle protein containing two copies of highly conserved protein kinase C homology regions known as the C2A and C2B domains, acts as a Ca2+ sensor and provides both phospholipid and inositol polyphosphate (IPn) recognition domains important in endo- and exocytosis. Four photoaffinity analogues of IP3, IP4, and IP6 containing a P-1- or P-2-linked 4-benzoyldihydrocinnamidyl (BZDC) photophore were used to label glutathione S-transferase (GST) fusion constructs of the Syt II-C2A and C2B domains. The P-2-linked [3H]BZDC-IP6 showed efficient, IP6-displaceable labeling of the GST-Syt II-C2B. The rank order of photocovalent modification paralleled the order of competitive displacement: IP6 (P-2-linked) > IP4 > IP3. The P-1-linked [3H]BZDC-IP6 failed to label the C2B domains. The GST-Syt III-C2B domain, which lacks IP6 binding affinity, also failed to undergo labeling by P-2-linked [3H]BZDC-IP6. When mixtures of the 32-amino acid basic peptide corresponding to the essential IPn binding region of the Syt II-C2B domain and GST-Syt II-C2B were labeled by a stoichiometric amount of P-2-linked [3H]BZDC-IP6, the two polypeptides showed equivalent affinity for the photolabel. Although the CD spectrum of this 32-mer at two pH values showed a random coil, the photoaffinity analogue of IP6 appeared to induce a binding-compatible structure in the short peptide.

Benzophenone photoprobes for phosphoinositides, peptides and drugs

Benzophenones (BP) and related aryl ketone photophores have become established as the photoactivatable group of choice for high-efficiency covalent modification of hydrophobic regions of binding proteins, including enzymes and receptors that recognize peptide hormones, (oligo) nucleotides and nucleosides, phosphoinositides, inositol polyphosphates and a wide variety of therapeutic molecules. This review presents the advantages of BP as photoaffinity labels and provides specific examples from the last 3 years of applications of BP-containing ligands used in biochemistry.

High-performance liquid chromatographic assay for common sunscreening agents in cosmetic products, bovine serum albumin solution and human plasma

This paper reports the development of a reversed-phase high-performance liquid chromatographic assay for quantifying five of the most common sunscreen agents, namely 2-ethylhexyl-p-dimethyl aminobenzoate (Escalol 507), 2-ethylhexyl-p-methoxycinnamate (Parsol MCX); 4-tert.-butyl-4'-methoxydibenzoylmethane (Parsol 1789), 2-hydroxy-4-methoxybenzophenone-3 (oxybenzone) and 2-ethylhexyl-salicylate (octylsalicylate). The assay permits analysis of the sunscreen agents in formulations and in biological fluids, including bovine serum albumin (BSA) solution, a common additive to in vitro skin diffusion cell receptor fluids, as well as human plasma. Separation was achieved using an ODS C154 column with a methanol-water (88:12) mobile phase. The analytes were detected by ultraviolet light absorption at a wavelength of 315 nm. The assay was linear with minimum detectable limits, calculated as greater than 3-times the baseline noise level: for oxybenzone and Escalol 507, 0.05 microgram/ml; for Parsol 1789 and Parsol MCX, 0.1 microgram/ml; for octylsalicylate, 1 microgram/ml. Recoveries from both plasma and 2% BSA were within the range 89-107%. The inter- and intra-day coefficients of variation for the five agents were not more than 4% at the upper end of the linear range and not more than 10% at the lower end. Preliminary stability studies of the sunscreen agents in a commercial product and in two diffusion cell receptor fluids were also conducted.

Ca2+-dependent binding of calcyclin to muscle tropomyosin

The interaction of calcyclin with tropomyosin and tropomyosin-actin was studied with fluorescence titrations and photo-reactive crosslinking experiments. Titrations of pyreneiodoacetamide-labeled tropomyosin alone or with actin showed binding of calcyclin to tropomyosin with muM dissociation constants when Ca2+ was present. UV irradiation of mixtures of calcyclin and gizzard beta beta-tropomyosin labeled with benzophenone-iodoacetamide at Cys36, with or without actin, produced crosslinks between tropomyosin chains and calcyclin monomers only in the presence of Ca2+. These data provide direct evidence for a Ca+2-dependent tropomyosin-calcyclin interaction at or near Cys36 of tropomyosin and indicate that calcyclin binding to tropomyosin-actin does not cause tropomyosin dissociation.

Photolysis of retinol in liposomes and its protection with tocopherol and oxybenzone

In this work the stabilities of retinol in methanolic solutions and liposomal suspensions exposed to UV light were compared using absorbance spectroscopy and the ability of alpha-tocopherol and the sunscreen additive, oxybenzone, to reduce the rate of retinol decomposition assessed. Retinol in methanol decolorized almost completely within a few minutes of exposure to a 6 W 350 nm wavelength lamp. From the concentration dependence of the reaction rates it appears that retinol activated by light can decomposed either directly or after collision with a second retinol molecule. Several reaction products are formed. alpha-Tocopherol solutions were unaffected by 350 nm light but they did darken when irradiated with 250 nm wavelength light. Addition of alpha-tocopherol or removal of oxygen from the retinol in methanol solutions reduced only slightly the rates of retinol photolysis. When dispersed in water within liposomes made of equimolar egg phosphatidylcholine (PC) and cholesterol, up to six-fold increases in the decomposition rate of the retinol were observed. The reaction rate could be reduced but only slightly by increasing the ratio of PC to retinol. A mechanism that explains the concentration dependence of the retinol photolysis is that the reduction in reaction rate on diluting the retinol concentration within a given liposome was due to the prevention of the reaction between one light-activated retinol molecule with another within the same liposome. Incorporation of oxybenzone into the liposomes reduced the reaction rates. The results suggested that most of the protection in this case arises through the oxybenzone closet to the light source absorbing the light, thereby preventing it reaching retinol much further into the sample. Incorporation of alpha-tocopherol into the liposomes could also reduce substantially the photolysis rate of co-entrapped retinol. The mechanism of protection in this case appears to be via the tocopherol quenching activated retinol molecules. The close proximity of the tocopherol to the retinol within a single liposome has shown to be important in this case. Only slight protection of retinol in one liposome by tocopherol in another was observed under the conditions studied. This means that the protection by tocopherol will still be observed if the liposome dispersions are diluted considerably or if only thin samples are exposed to light.

Behaviour of Chimassorb 81 in the recycling process of agricultural films used as soil covers

Two different films, low density polyethylene (LDPE) and an ethylene-vinyl acetate copolymer (EVA), used as agricultural soil covers were studied. The films were recycled five and ten times respectively, and both the tensile strength and the content of Chimassorb 81, a UV-stabilizer, were analysed in each cycle. Losses of 17.44% in tensile strength and 23.69% (Thermic film) and 13.22% (EVA) in the concentration of Chimassorb 81 were found after five recycling cycles. The extraction of Chimassorb 81 from the film is optimized. As these films can be recycled for the same application or even for use as food-contact materials, the standard migration tests with established simulants have been carried out. The results obtained are discussed.

Exploratory laser flash photolysis study of free radical reactions and magnetic field effects in melatonin chemistry

Melatonin is an excellent free radical scavenger, reacting with tert-butoxyl and cumyloxyl radicals with rate constants of 3.4 x 10(7) and 6.7 x 10(7) M-1s-1, respectively. Reaction with benzophenone triplet occurs with a near-diffusion-controlled rate constant of 7.6 x 10(9) M-1s-1 in acetonitrile and probably involves charge transfer. When the radical pair formed by reaction of benzophenone triplet and melatonin is sequestered in a micelle, it is subject to extensive magnetic field effects that can be readily interpreted by the radical pair model.

Influence of combined AC-DC magnetic fields on free radicals in organized and biological systems. Development of a model and application of the radical pair mechanism to radicals in micelles

The effect of an alternating current (AC) magnetic field (MF) on radical behavior is identical to that exerted by a direct current (DC) field of the same instantaneous strength provided that the frequency is low enough in comparison with radical pair dynamics. This criterion is easily met by environmental fields. In general, combined AC/DC fields will lead to increased radical concentrations and oscillating free radical concentrations. Interestingly, the frequency of oscillation for radical concentration seldom follows exactly the pattern of the external AC component of the MF. Even the simple case of an AC-only field at 60 Hz can lead to oscillations in radical concentrations at 120 Hz. The concentration time dependence patterns can be even more complex when the singlet and triplet levels of the radical pair are not degenerate. Further, the effects can change dramatically depending upon the absolute and relative values of the AC and DC components, thus providing a possible explanation for MF windows for certain effects reported experimentally. Effects on the average radical concentration are probably relevant only for fields higher than about 0.1 gauss. Oscillating radical concentrations may influence signal transduction processes or other cellular mechanisms; at the present time there is not enough knowledge available to establish a reasonable threshold for these types of effects. This contribution aims at providing a solid foundation to guide the experimentalist in the design of meaningful experiments on the possible role of MF perturbations of radical chemistry on biological response.

Probing the bimolecular interactions of parathyroid hormone with the human parathyroid hormone/parathyroid hormone-related protein receptor. 1. Design, synthesis and characterization of photoreactive benzophenone-containing analogs of parathyroid hormone

Parathyroid hormone (PTH) regulates calcium and phosphate metabolism through a G-protein-coupled receptor which is shared with PTH-related protein (PTHrP). Therefore, structure-activity studies of PTH and PTHrP with their common receptor provide an unusual opportunity to examine the structural elements in the two hormones and their common receptor which are involved in the expression of biological activity. Our approach to studying the nature of the bimolecular interface between hormone and receptor is to use a series of specially designed photoreactive benzophenone- (BP-) containing PTH analogs in "photoaffinity scanning" of the PTH/PTHrP receptor. In this report we describe a series of BP-containing agonists and antagonists which have been synthesized by solid-phase methodology and characterized physiocochemically and biologically. Each of the 12 analogs contains a single BP moiety at a different defined position. Examples of BP-containing agonists prepared and studied in human osteogenic sarcoma Saos-2/B-10 cells are [Nle8,18,Lys13(epsilon-pBZ2),L-2-Nal23,Tyr34]bPTH(1-34 )NH2(K13)(Kb = 13 nM; Km = 2.7 nM) and [Nle8,18,L-Bpa23,Tyr34[bPTH(1-34)NH2(L-Bpa23) (Kb = 42 nM; Km = 8.5 nM). Another BP-containing analog, [Nle8,18,D-2-Nal12,Lys13(epsilon-pBZ2),L-2-Nal23 ,Tyr34]bPTH(7-34)NH2, was a potent antagonist (Kb = 95 nM; Ki = 72 nM). The amino acids substituted by residues carrying the BP moiety span the biologically active domain of the hormone (Phe7, Gly12, Lys13, Trp23, and Lys26). Analysis of photo-cross-linked conjugates of PTH/PTHrP receptor with BP-containing PTH analogs should help to identify the "contact points" between ligand and receptor.

Acid hydrolysis of diazepam. Kinetic study of the reactions of 2-(N-methylamino)-5-chlorobenzophenone, with HCl in MeOH-H2O

In the acid hydrolysis of diazepam (1), several unusual products, apart from 2-(N-methylamino)-5-chlorobenzophenone (2) and glycine, were isolated. On the assumption that some of those products could arise from further degradation of 2, the reaction of this compound with 0.5-2 M HCl was studied, in 1:1 MeOH-H2O, at 60 and 80 degrees C. Several unexpected products were isolated from the reaction of 2 with HCl, namely, 2-amino-5-chlorobenzophenone (3), 2-(N,N-dimethylamino)-5-chlorobenzophenone (4), 2-(N-methylamino)-3,5-dichlorobenzophenone (5), 2-amino-3,5-dichlorobenzophenone (6), 2,4-dichloro-10-methyl-9,10- acridinone (7), and 2,4-dichloro-9,10-acridinone (8). The methyl transfers, the chlorination, and the cyclization reactions that give rise to products 3-8 are unexpected under the present reaction conditions. The rate of reaction of 2, as well as the rate of formation of compounds 3-6, was measured at several HCl concentrations.

Type I benzophenone-mediated nucleophilic reaction of 5'-amino-2',5'-dideoxyguanosine. A model system for the investigation of photosensitized formation of DNA-protein cross-links

5'-Amino-2',5'-dideoxyguanosine has been synthesized in order to investigate the intramolecular reactivity of an amino group toward the guanine radical produced by type I photosensitization mechanism. Benzophenone-mediated photosensitization of 5'-amino-2',5'-dideoxyguanosine in aerated aqueous solution results in the formation of a predominant cyclic nucleoside together with an unstable nucleoside precursor. The two modified nucleosides have been isolated by reverse phase high performance liquid chromatography and characterized by spectroscopic measurements including 13C and 1H NMR, fast atom bombardment mass spectroscopy, and UV absorption. The stable photoproduct has been identified as 9-oxa-2,4-diazabicyclo[4.2.1]non-2-en-7-ol, 3-amino- (1R-exo), whereas its precursor has been assigned as acetic acid, [(7-hydroxy-9-oxa-2,4-diazabicyclo[4.2.1]non-2-en-3-yl)amino]oxo- (1R-exo). A reaction mechanism, involving nucleophilic addition of the sugar amino group to guanine radical intermediates, is proposed to explain the formation of the two photoproducts.

Tethered benzophenone reagents for the synthesis of photoactivatable ligands

A new radiolabeled, bifunctional photoaffinity cross-linking reagent, N-succinimidyl p-benzoyl-[2,3-3H2]dihydrocinnamate, has been synthesized in high yield and with high specific activity. This reagent can be used to append the benzophenone photophore to amino groups of small molecules, such as O-aminoalkylinositol polyphosphates and polypeptides. The resulting tritiated photoaffinity labels can be purified and manipulated in ambient light and can be activated at 360 nm.

Photoaffinity labeling of methyl farnesoate epoxidase in cockroach corpora allata

The last enzyme in the biosynthetic pathway to juvenile hormone III in the corpora allata of hemimetabolous insects is methyl farnesoate epoxidase, a cytochrome P450 monooxygenase. Assays with intact glands incubated in vitro and with gland homogenates have identified a series of 1,5-disubstituted imidazoles as potent inhibitors of the enzyme. We have designed, synthesized and tested two imidazoles, diazirine-Ice T and benzophenone-Ice T, in which a radiolabeled and photoactivatable diazirine or benzophenone group was introduced to label the hydrophobic substrate binding site of the enzyme. Our results show that these bifunctional compounds inhibit JH III synthesis by intact glands as well as methyl farnesoate epoxidation by gland homogenates. Moreover both compounds selectively label a protein of ca. 55 kDa in corpora allata of the cockroach, Diploptera punctata. These photoaffinity labels, which use an imidazole to coordinate to the heme iron and a photoreactive group to modify the hydrophobic substrate binding pocket, are specific and effective probes for the molecular analysis of methyl farnesoate epoxidase.

Photochemistry of acetylenic ketones in micellar solutions as studied by product-yield-detected ESR and transient absorption techniques

The electron spin resonance (ESR) spectra of the transient radical pairs in the photoreduction of 1,5-diphenyl-1,4-pentadiyn-3-one(I) and 1,3-diphenyl-2-propyn-1-one(II) in sodium dodecyl sulfate (SDS) micellar solutions have been obtained by using the product-yield-detected ESR (PYESR) technique. The PYESR spectra, detected by tracing the microwave effect on the spin-adduct yield as functions of the magnetic field, show the ESR spectra of the ketyl radical of the ketone and SDS radical as the components of the radical pairs. In addition, the growth and the decay processes of the radical pair were observed through detecting the effect of microwave pulse as functions of the delay period between a laser pulse and the off and on time, respectively, of a microwave pulse. The absorption spectra of transient species have also been obtained by using the laser flash photolysis technique. Through the analysis of these data and molecular orbital calculations, the role of acetylenic groups in the photoreactivity of acetylenic ketones is discussed.

Balmoralmycin, a new angucyclinone, and two related biosynthetic shunt products containing a novel ring system

A new angucyclinone, named balmoralmycin (1), was isolated as an inhibitor of protein kinase C-alpha (PKC-alpha) from the Streptomyces strain P6417. Chemical screening of extracts of the same strain resulted in the detection of two decaketides with unusual structural features (2 and 3). Both compounds belong to a recently described structural class of secondary metabolites which arises from engineered biosynthesis of a recombinant Streptomyces strain. The isolation of compounds of this class from a wild-type strain has never been reported before.

Zeneca ZD6169 and its analogs from a novel series of anilide tertiary carbinols: in vitro KATP channel opening activity in bladder detrusor

The potassium (K+) channel opening activity of Zeneca ZD6169 and one of its pyridylsulfonyl analogs from the anilide tertiary carbinol series was ascertained. Their mechanoinhibitory effects on the myogenic activity of the guinea pig bladder detrusor muscle were measured in a set of functional assays. Elevating the K+ concentration in the tissue bath from 15 to 80 mmol/l increased the IC50 value of ZD6169 from 1.61 +/- 0.22 223 +/- 37 mumol/l. This result suggests that ZD6169 may act as a K+ channel opener. Similar to the prototypic ATP-sensitive K+ (KATP) channel opener cromakalim, the K+ channel openers from the anilide tertiary carbinol series displayed stereoselective mechanoinhibitory activity only in the test protocol in which the detrusor was stimulated with 15 mmol/l KCl. Being the active enantiomer, ZD6169 has an activity more than 30-fold higher than the less active enantiomer. ZD6169 at 10 mumol/l hyperpolarized the guinea pig detrusor membrane potential by 6.1 +/- 1.2 mV and increased the whole cell KATP current in isolated guinea pig smooth muscle cells by 34.9 +/- 7.9 pA. This is comparable to the increase of 26.8 +/- 5.0 pA obtained with 10 mumol/l of lemakalim, the active enantiomer of cromakalim. The K+ channel opening activity of ZD6169 and the pyridylsulfonyl analog was competitively antagonized by the KATP channel blocker glibenclamide in the guinea pig detrusor with a pA2 value of 7.2. This activity, however, was unaffected by blockers of small and large conductance Ca-dependent K+ channels, such as apamin and charybdotoxin, respectively. The present study showed that Zeneca ZD6169 and its analog from the anilide tertiary carbinol series are K+ channel openers that activate KATP channels in vitro to relax bladder detrusors.

Hydroxylamine analogs of 2,6-di-t-butylphenols: dual inhibitors of cyclooxygenase and 5-lipoxygenase or selective 5-lipoxygenase inhibitors

The preparation of hydroxylamine analogs of 2,6-di-tert-butylphenols (DTBP) and the inhibition of cyclooxygenase (CO) and 5-lipoxygenase (5-LO) by these compounds is discussed.

[Anti-arrhythmia action of amidinohydrazone substituted benzophenones. 6. Parenteral drug forms of (Z)-2-amino-5-chlorobenzophenone amidinohydrazone acetate (G 256)]

The combination of lyophilized G 256 and a solvent ampoule is recommended as an optimal variant for the application of the compound. In the lyophilized substance both the hydrolysis and the isomerisation are reduced so it is stable enough for the required period of usability.

Pyridazine analogs of piperidinylbenzophenone immunomodulators. 70th communication: syntheses and reactions of pyridazines

Starting from conveniently accessible halogen-substituted phenyl pyridazinyl ketones, a series of piperidinyl-substituted diazabenzophenones was prepared. The new compounds were screened for immunomodulatory activity.

Benzophenone photophores in biochemistry

The photoactivatable aryl ketone derivatives have been rediscovered as biochemical probes in the last 5 years. The expanding use of benzophenone (BP) photoprobes can be attributed to three distinct chemical and biochemical advantages. First, BPs are chemically more stable than diazo esters, aryl azides, and diazirines. Second, BPs can be manipulated in ambient light and can be activated at 350-360 nm, avoiding protein-damaging wavelengths. Third, BPs react preferentially with unreactive C-H bonds, even in the presence of solvent water and bulk nucleophiles. These three properties combine to produce highly efficient covalent modifications of macromolecules, frequently with remarkable site specificity. This Perspectives includes a brief review of BP photochemistry and a selection of specific applications of these photoprobes, which address questions in protein, nucleic acid, and lipid biochemistry.

Application of the radical pair mechanism to free radicals in organized systems: can the effects of 60 Hz be predicted from studies under static fields?

The influence of 60-Hz magnetic fields on free radical reactions can be quantitatively predicted from the knowledge of the effect of static fields on free radical behavior. Studies of radical reactions in micellar systems show that the behavior under a 60-Hz field is identical to that under a static field at any given point in time.

Benzophenone-sensitized lipid peroxidation in linoleate micelles

Benzophenone-photosensitized peroxidation in linoleic acid micelles (Type I reaction) has been investigated and quantum yields of both sensitizer photolysis and lipid peroxidation have been obtained. Benzophenone as well as its derivative, benzophenone-4'-heptyl-4-pentanoic acid (BHPA) have been utilized as sensitizers in this study. A quantum yield of 1.2 for hydroperoxide formation, compared with a benzophenone disappearance quantum yield of 0.41 (in the same linoleate micellar solution) was obtained; yields of 1.3 and 0.6 were found for comparable systems in which BHPA was the sensitizer. Although such data are consistent with the peroxidation mechanism of chain reaction, it is necessary to know the yields of initiating species to arrive at chain reaction lengths in these systems. Such yields have been determined by flash photolysis. The dependencies of sensitizer photolysis and hydroperoxide yields on linoleate concentration have also been determined in order to elucidate the effects of micelle formation or molecular organization on the peroxidative process. Additionally, for comparison in a saturated surfactant (lipid) system hydrogen abstraction was investigated by photolysis techniques in sodium dodecyl sulfate alone using these two sensitizers.

Solid-phase synthesis of O-mannosylated peptides: two strategies compared

A comparison of the O-glycosylation of resin-bound assembled peptides with the incorporation of glycosylated amino acids using established chemistry is presented. Fmoc/tert-butyl-based protecting groups were used for the peptidic moieties in conjunction with acetyl sugar protection. Koenigs-Knorr glycosylations were carried out using protected bromomannose derivatives, the acceptor being threonine or serine, either in solution or within a resin-bound peptide. The characterisation of microgram quantities of glycopeptides by the use of glycosidases in combination with mass spectrometry is also described.

Glycosylated derivatives of benzophenone, benzhydrol, and benzhydril as potential venous antithrombotic agents

A series of glycosylated derivatives of benzophenone, benzhydrol, and benzhydril has been synthesized and evaluated for potential activity as venous antithrombotic agents. Studies on structure-activity relationships revealed that compounds having an electron-withdrawing group in the benzhydril or benzhydrol moiety, and specifically those having the beta-D-xylopyranosyl structure in the sugar moiety, were good antithrombotic agents in a rat model of venous thrombosis.

Structure-based discovery of inhibitors of thymidylate synthase

A molecular docking computer program (DOCK) was used to screen the Fine Chemical Directory, a database of commercially available compounds, for molecules that are complementary to thymidylate synthase (TS), a chemotherapeutic target. Besides retrieving the substrate and several known inhibitors, DOCK proposed putative inhibitors previously unknown to bind to the enzyme. Three of these compounds inhibited Lactobacillus casei TS at submillimolar concentrations. One of these inhibitors, sulisobenzone, crystallized with TS in two configurations that differed from the DOCK-favored geometry: a counterion was bound in the substrate site, which resulted in a 6 to 9 angstrom displacement of the inhibitor. The structure of the complexes suggested another binding region in the active site that could be exploited. This region was probed with molecules sterically similar to sulisobenzone, which led to the identification of a family of phenolphthalein analogs that inhibit TS in the 1 to 30 micromolar range. These inhibitors do not resemble the substrates of the enzyme. A crystal structure of phenolphthalein with TS shows that it binds in the target site in a configuration that resembles the one suggested by DOCK.

[Antiarrhythmia active amidinohydrazone substituted benzophenones. 5. The stability of (Z)-2-amino-5-chlorobenzophenone amidinohydrazone acetate in solution]

The aqueous solution of the title compound can be used for injection for one year if it is stored at room temperature and under light protection. Under these conditions 8% of the E-isomer are produced. The reaction is reversible at day light. Red coloured products of decomposition are formed by long lasting influence of light. At higher temperatures or at sterilisation several products of decomposition are formed which structure is elucidated. For these decomposition a scheme is proposed.

[Antiarrhythmic active amidinohydrazones of substituted benzophenones. 4. The photoisomerization of (Z)- and (E)-2-amino-5-chlorobenzophenone amidinohydrazones and the corresponding (E)-N-phenylamidinohydrazone]

The title compounds undergo a photoisomerization by irradiation. If the E-isomers are irradiated by light of a wavelength of an absorption maximum typical for them, they can be converted quantitatively to the corresponding Z-isomers. In case that the synthesis of analogs of the title compounds give only one configurational isomer, sometimes the missing one can be obtained by photoisomerization.

Interaction of gelsolin with covalently cross-linked actin dimer

One of the two actin molecules in the ternary actin-gelsolin complex was selectively cross-linked to gelsolin when benzophenonemaleimide-actin (BPM-actin) was used [Doi, Y., Banba, M., & Vertut-Doi (1991a) Biochemistry 30, 5769-5777]. Here, we examine the interaction between gelsolin and BPM-actin dimer in which BPM-actin is covalently conjugated to unlabeled actin by p-phenylenedimaleimide (pPDM). BPM-actin dimer having an apparent molecular mass of 115 kDa is photo-cross-linked to gelsolin (90 kDa) more effectively than BPM-actin monomer in the presence of Ca2+, forming a cross-linked actin dimer-gelsolin (1:1) complex with a molecular mass of 210 kDa. The tight direct association of the dimer to gelsolin is shown by the titration of gelsolin with the fluorescently labeled dimer and by the higher concentration of phosphatidylinositol 4,5-bisphosphate required to inhibit the formation of BPM-dimer complex with gelsolin than that of BPM-monomer complex. However, an attempt to cross-link the two actin molecules in the ternary actin-gelsolin (2:1) complex by pPDM fails. The results argue that the topography of the two actin molecules in the actin-gelsolin (2:1) complex is similar, but not identical, to that of the barbed end of an actin filament.

[Anti-arrhythmic action of some amidinohydrazone substituted benzophenones. 1. Synthesis of new amidinohydrazone and N-phenylamidinohydrazone substituted benzophenones]

The title compounds are synthesized as a rule by condensation of substituted benzophenones and derivatives of aminoguanidine in the presence of up to 2.5 moles of an anorganic acid. They can be obtained alternatively via corresponding hydrazones, thiosemicarbazones or methylthiothiocarbonylhydrazones.

Analysis of photoacoustic waveforms using the nonlinear least squares method

Pulsed-laser photoacoustics is a technique which measures photoinduced enthalpic and volumetric changes on the nano- and microsecond timescales. Analysis of photoacoustic data generally requires deconvolution for a sum of exponentials, a procedure which has been developed extensively in the field of time-resolved fluorescence decay. Initial efforts to adapt an iterative nonlinear least squares computer program, utilizing the Marquardt algorithm, from the fluorescence field to photoacoustics indicated that significant modifications were needed. The major problem arises from the wide range of transient decay times which must be addressed by the photoacoustic technique. We describe an alternative approach to numerical convolution with exponential decays, developed to overcome the problems. Instead of using an approximation method (Simpson's rule) for evaluating the convolution integral, we construct a continuous instrumental response function by quadratic fitting of the discrete data and evaluate the convolution integral directly, without approximations. The success and limitations of this quadratic-fit convolution program are then demonstrated using simulated data. Finally, the program is applied to the analysis of experimental data to compare the resolution capabilities of two commercially available transducers. The advantages of a broadband, heavily damped transducer are shown for a standard organic photochemical system, the quenching of the triplet state of benzophenone by 2,5-dimethyl-2,4-hexadiene.

Acetylcholinesterase inhibition by pitofenone: a spasmolytic compound

Pitofenone, a spasmolytic compound, inhibited the acetylcholinesterase activity from bovine erythrocytes and from electric eel. It is a potent inhibitor of this enzyme from the two sources, with Ki values of 36 and 45 microM, respectively. Of the five compounds structurally related to pitofenone, only those containing a piperidine moiety show acetylcholinesterase inhibition. All these inhibitions are reversible, linear, and noncompetitive in nature. A qualitative correlation between the anticholinesterase and the corresponding antimuscarinic activity for some of these compounds was apparent. Good separation of these two effects would be a desirable feature for newer muscarinic antagonists.

Analysis of benzophenones by gas chromatography/Fourier transform-infrared spectrometry

A gas chromatograph/Fourier transform-infrared spectrometric analysis of benzophenones, as hydrolyzed products of benzodiazepine, was evaluated and the vapor phase spectra obtained were compared with those measured in the condensed phase. Each infrared spectrum obtained in the vapor phase showed a much greater difference in comparison to differences found in those in the condensed phase, especially in the fingerprint region. The identification of 14 benzophenones by their infrared spectra in the vapor phase was possible. The detection limits for these benzophenones were between 50-100 ng with high signal-to-noise ratios. The vapor phase spectra of the benzophenones were unique and the analytical method allowed the differentiation of closely related classes of drugs, such as benzophenones.

Further studies on ultraviolet-absorbing hydrogels for intraocular lenses: relationship between concentration of a polymerizable benzophenone, absorption, and extractability

A tendency to reduce the use of benzophenone absorbers is currently evident in the manufacture of the UV-absorbing IOLs, mainly because the cutoff wavelengths are inferior to those provided by benzotriazoles. In principle, by incorporating large amounts of benzophenones it may be possible to achieve high cutoff wavelengths. A covalently bondable benzophenone UV absorber, Cyasorb UV-2098, was incorporated in poly(2-hydroxyethyl methacrylate) (PHEMA) in increasing concentrations, and certain associated phenomena were investigated. At 4% w/w absorber content, the nonhydrated polymers turned partially opaque. In water-swollen hydrogels, opacification occurred at a lower absorber content (2% w/w). By using extraction techniques and gas chromatography, we also found that up to 8% w/w of the absorber remained unpolymerized and could leach out from any material containing less than 5% w/w absorber. In samples with higher initial content of absorber, the amount of unreacted, leachable absorber was significantly higher (25% to 30%). Based on this study model (hydrogel/Cyasorb UV-2098), we concluded that benzophenone absorbers cannot provide cutoff wavelengths higher than those provided by benzotriazoles.

Benzophenone dicarboxylic acid antagonists of leukotriene B4. 2. Structure-activity relationships of the lipophilic side chain

A series of lipophilic benzophenone dicarboxylic acid derivatives were found to inhibit the binding of the potent chemotaxin leukotriene B4 (LTB4) to its receptor on intact human neutrophils. Activity at the LTB4 receptor was determined by using a [3H]LTB4-binding assay. The structure-activity relationship for the lipophilic side chain was systematically investigated. Compounds with n-alkyl side chains of varying lengths were prepared and tested. Best inhibition of [3H]LTB4 binding was observed with the n-decyl derivative. Analogues with alkyl chains terminated with an aromatic ring showed improved activity. The 6-phenylhexyl side chain was optimal. Substitution on the terminal aromatic ring was also evaluated. Methoxyl, methylsulfinyl, and methyl substituents greatly enhanced the activity of the compound. For a given substituent, the para isomer had the best activity. Thus the nature of the lipophilic side chain can greatly influence the ability of the compounds to inhibit the binding of LTB4 to its receptor on intact human neutrophils. The most active compound from this series, 84 (LY223982), bound to the LTB4 receptor with an affinity approaching that of the agonist.