Influence of solvent and configuration of residues at positions 2 and 3 on distance and mobility of pharmacophore groups at positions 1 and 4 in cyclic enkephalin analogues

The analgesic activity of opioid peptides is mainly connected with their affinity and selectivity for the mu-receptors. The biological activity of cyclic opioid analogues depends on mutual orientation and conformational freedom of aromatic pharmacophore groups at positions 1 and 4. The distance and distance distributions between chromophores at positions 1 [Phe(p-NO(2)), p-nitrophenylalanine] and 4 [Nal, beta-(2-naphthyl)alanine], which constitute an energy donor-acceptor pair, were calculated based on measured fluorescence intensity decays of a donor (Nal). The influence of the solvent and configuration of the residues at position 2 and 3 on donor-acceptor distance distribution and mobility of pharmacophore groups at position 1 and 4 in cyclic enkephalin analogues are discussed.     

Synthesis, biological activity and conformation of enkephalin analogs structurally related to kyotorphin

[D-Arg2,Leu5]Enkephalin and two series of its N-terminal short-chain analogues with a free and modified C-terminal carboxylic group, viz. amides and ethyl esters of tri- and tetrapeptides, were synthesized in solution and by solid-phase method. Their analgesic activity, assayed by the "tail pinch" method following intracisternal and intravenous administration to mice, was compared with activity of enkephalins and morphine. To study the space structure of the synthesized compounds, conformational calculations and fluorescence spectroscopy were applied to measure distance between aromatic nuclei of tyrosine and phenylalanine residues in the two tetrapeptides. Ethyl esters of the tri- and tetrapeptides exceed in analgesic activity the corresponding carboxylic acids and amides. In contrast to the pentapeptide, the tetrapeptide analogues were active upon intravenous administration. Conformational aspects of this series of analogues are discussed in detail; the abrupt increase in activity upon transition from tri- to tetrapeptides does not appear to be related to conformational changes.     

Interaction of aromatic compounds with Photobacterium leiognathi luciferase: fluorescence anisotropy study

The time‐resolved and steady‐state fluorescence techniques were employed to elucidate possible interactions of four aromatic compounds (anthracene, POPOP, MSB and 1,4‐naphthalendiol) with bacterial luciferase. Fluorescence spectra and fluorescence anisotropy decays of these compounds were studied in ethanol, water–ethanol solutions and in the presence of bacterial luciferase. Shifts of fluorescent spectra and differences in rotational correlation times are interpreted in terms of weak (hydrophobic) interactions of the molecules with the enzyme. These interactions suggest the feasibility of intermolecular energy transfer by an exchange resonance mechanism with a collision‐interaction radius as a way of excitation of these compounds in the reaction catalysed by bacterial luciferase. Copyright © 2003 John Wiley & Sons, Ltd.     

Magnesium and biological activity of oxytocin analogues modified on aromatic ring of amino acid in position 2.

For the purpose of evaluating substitution effects in the ortho, meta or para positions of the aromatic ring of tyrosine or phenylalanine in position 2 of oxytocin on uterotonic activity in vitro in the presence and absence of magnesium ions, six new analogues of oxytocin ([D- and L-m-methylphenylalanine2]oxytocin, [D- and L-m-methoxyphenylalanine2]oxytocin and [D- and L-o-methyltyrosine2]-oxytocin) were synthesized and several previously described analogues resynthesized. For the phenylalanine series, it is found that, in the absence of magnesium ions, substitution of the ortho and meta positions leads to loss of intrinsic activity (the analogues are antagonists) in contrast to the para position. In the tyrosine series, only methyl substitution in the meta position has this effect (substitution of ortho position only attenuates the agonistic biological activity). Addition of Mg ions restores to a certain degree the agonistic activity in the case of the o-methylphenylalanine analogue and enhances the agonistic activity of o-methyltyrosine oxytocin. All other analogues keep the original qualities as in the absence of Mg. Molecular modelling calculations of the structure of the above analogues was carried out to help explain these findings of the molecular level.     

Syntheses and antifungal activity of pseudomycin side-chain analogues. Part 1

We have described herein the syntheses of three novel series of aromatic ring containing pseudomycin side-chain analogues. Preliminary biological evaluations of these analogues clearly indicate that it is possible to synthesize rigid pseudomycin side-chain analogues without compromising in vitro antifungal activity.     

Novel bisbenzamidines and bisbenzimidazolines as noncompetitive NMDA receptor antagonists.

A series of novel bisbenzamidines and bisbenzimidazolines with different linkers connecting the aromatic groups was tested in vitro for NMDA receptor antagonist activity. IC50 values for these compounds ranged from 1.2 to >200 microM. The bisbenzamidine with a homopiperazine ring as the central linker was found to be the most potent NMDA receptor antagonist among all the pentamidine analogues tested so far.     

1-(1-Arylethylidene)thiosemicarbazide derivatives: a new class of tyrosinase inhibitors

A series of 1-(1-arylethylidene)thiosemicarbazide compounds and their analogues were synthesized and characterized by 1H NMR, MS. Their tyrosinase inhibitory activities were investigated by an assay based on the catalyzing ability of tyrosinase for the oxidation of L-DOPA, comparing with 4-methoxycinnamic acid and arbutin. The results showed that (1) all the synthesized compounds could perform a significant inhibitory activity for tyrosinase; (2) for these compounds, the main active moiety interacting with the center of tyrosinase would be thiosemicarbazo group; (3) the inhibitory activity was close related with thiosemicarbazide moieties and the groups attached on the aromatic ring.     

Phenylcyclohexene and phenylcyclohexadiene substituted compounds having retinoid antagonist activity

Retinoids are natural and synthetic analogues of the hormone retinoic acid. Systemic retinoid agonist therapy is usually associated with toxic side effects, such as mucocutaneous toxicity, which may be alleviated by the use of topical retinoid antagonists. We report the synthesis and biological activity of a new series of potent, RAR-specific antagonists substituted with phenylcyclohexene and phenylcyclohexadiene groups.     

Comparative structure-activity relationships of benztropine analogues at the dopamine transporter and histamine H(1) receptors

Benztropine (BZT) and its analogues inhibit dopamine uptake and bind with moderate to high affinity to the dopamine transporter (DAT). However, many of these compounds, in contrast to other monoamine uptake inhibitors, lack cocaine-like behavioral effects and fail to potentiate the effects of cocaine. The BZT analogues also exhibit varied binding affinities for muscarinic M(1) and histamine H(1) receptors. In this study, a comparative analysis was conducted of pharmacophoric features with respect to the activities of BZT analogues at the DAT and at the histamine H(1) receptor. The BZT analogues showed a wide range of histamine H(1) receptor (K(i)=16-37,600 nM) and DAT (K(i)=8.5-6370 nM) binding affinities. A stereoselective histamine H(1)-antagonist pharmacophore, using a five-point superimposition of classical antagonists on the template, cyproheptadine, was developed. A series of superimpositions and comparisons were performed with various analogues of BZT. In general, smaller substituents were well tolerated on the aromatic rings of the diphenyl methoxy group for both the DAT and H(1) receptor, however, for the H(1) receptor, substitution at only one of the aromatic rings was preferred. The substituents at the 2- and N-positions of the tropane ring were preferred for DAT, however, these groups seem to overlap receptor essential regions in the histamine H(1) receptor. Molecular models at the DAT and the histamine H(1) receptor provide further insight into the structural requirements for binding affinity and selectivity that can be implemented in future drug design.     

A spectroscopic and molecular modeling study on novel pseudopeptides exhibiting biological activity.

A series of pseudopeptides, containing two fluorophores, such as naphthalene (N) and indole (I), and exhibiting interesting biological activity as tachykinin receptor antagonists, were investigated by electronic absorption, CD and steady-state fluorescence experiments. In polar solvents (e.g. methanol), bioactivity is coupled with a stacked, charge-separated complex between I and N, the amount of which depends on the stereochemical features and conformational mobility of the central scaffold in the molecules examined. This agrees with the idea that dipolar charged, spatially close, aromatic moieties are important topochemical elements in the mechanism of action of these receptor antagonists. Molecular mechanics calculations allowed us to build up hypothetical, low-energy conformations of a few representative pseudopeptides, whose structural features are consistent with the experimental findings.     

Micelle-bound conformations of neurohypophyseal hormone analogues modified with a Cα-disubstituted residue: NMR and molecular modelling studies

In this study, by applying a combined approach of NMR measurements and molecular modelling, the conformations and the interactions with membrane-like environment of five arginine vasopressin (AVP) or oxytocin (OT) analogues modified with Cα-disubstituted cis-1-amino-4-phenylcyclohexane-1-carboxylic acid in position 2 have been determined. In addition, the AVP analogues were prepared in N-acylated forms with various bulky acyl groups. All of the peptides studied interacted with the mixed dodecylphosphocholine:sodium dodecyl sulphate micelle, providing a model of biological membrane. A different polarities of the AVP- and OT-like peptides resulted in their different position relative to the micelle surface. Thus, the arrangement of the former was nearly perpendicular, whereas the latter was rather parallel to the micelle's surface. Moreover, the results of our studies have shown that the binding sites for antagonists may be overlapped with that for agonists, as well as it may be quite different. Nevertheless, the aromatic–aromatic contacts represent the most important interactions for antagonists, whereas the hydrophilic interactions seem to be crucial for agonists.     

Exploration of a new series of PAR1 antagonists

Two series of new PAR1 antagonists have been identified. The first incorporates a cinnamoylpiperidine motif and the second a cinnamoylpyridine pattern. The synthesis, biological activity and structure–activity relationship of these compounds are presented. In each series, one analog showed potent in vivo antithrombotic activity in a rat AV shunt model, with up to 53% inhibition at 1.25 mpk iv for compound 30.     

14-membered cyclic opioids related to dermorphin and their partially retro-inverso modified analogues. I. Synthesis and biological activity.

As a continuation of our program to study structure-activity relationships of opiate peptides, we report the syntheses and biological activities of a series of 14-membered cyclic dermorphin analogues closely related to enkephalin analogue Tyr-c[D-A2bu-Gly-Phe-Leu] incorporating a phenylalanine at the third position in place of glycine. In addition to two parent dermorphin analogues Tyr-c[D-A2bu-Phe-Phe-(L and D)-Leu], four stereoisomeric retro-inverso modified analogues Tyr-c[D-A2bu-Phe-gPhe-(S and R)-mLeu] with a reversed amide bond between residues four and five, and Tyr-c[D-Glu-Phe-gPhe-(L and D)-rLeu] with two reversed amide bonds between residues four and five, and between residue five and the side chain of residue two have been synthesized. The results from the guinea pig ileum (GPI) and mouse vas deferens (MVD) assays show that all analogues are superactive at either one or both opiate receptors and in general display higher activities as compared to the corresponding enkephalin analogues with a glycine at the third position. Results from the in vitro biological assays and conformational analysis using 1H-NMR spectroscopy (adjoining paper) will provide useful information to understand the role of the Phe3 aromatic side chain in dermorphin, and that of the Phe4 aromatic side chain in enkephalin, on opiate activity since these cyclic dermorphin analogues contain two Phe residues at both the third and fourth positions.     

Anti-oxidant activities of curcumin and related enones

The natural product curcumin (diferuloylmethane, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), obtained from the spice turmeric, exhibits numerous biological activities including anti-cancer, anti-inflammatory, and anti-angiogenesis activities. Some of these biological activities may derive from its anti-oxidant properties. There are conflicting reports concerning the structural/electronic basis of the anti-oxidant activity of curcumin. Curcumin is a symmetrical diphenolic dienone. A series of enone analogues of curcumin were synthesized that included: (1) curcumin analogues that retained the 7-carbon spacer between the aryl rings; (2) curcumin analogues with a 5-carbon spacer; and (3) curcumin analogues with a 3-carbon spacer (chalcones). These series included members that retained or were devoid of phenolic groups. Anti-oxidant activities were determined by the TRAP assay and the FRAP assay. Most of the analogues with anti-oxidant activity retained the phenolic ring substituents similar to curcumin. However, a number of analogues devoid of phenolic substituents were also active; these non-phenolic analogues are capable of forming stable tertiary carbon-centered radicals.     

Synthesis and biological activities of angiotensin II and Sarmesin analogues containing cyclohexylalanine

Analogues of angiotensin II with cyclohexylalanine (Cha) at position 4 or 8, and analogues of the competitive (type II) angiotensin antagonist [Sar1,Tyr(Me)4]ANG II (Sarmesin) with Cha at position 8, have been prepared by the solid phase method and purified by reversed-phase HPLC. Analogues of ANG II with Cha at position 8 in which the position 1 residue was substituted with sarcosine (Sar) or amino-isobutyric acid (Aib) or was deleted (Des), were slowly reversing (Type I) antagonists with "pA2" values in the rat isolated uterus assay of approximately 8.5. The additional substitution of Tyr(Me) for Tyr at position 4 of these peptides gave reversible competitive (Type I/II) antagonists with pA2 values of 6.7, 5.8, and less than 5, while substitution of Phe for Tyr gave pA2 values of 7.4, 6.7, and less than 5, respectively. All 19 peptides synthesized in this study had low intrinsic agonist activity in the rat isolated uterus assay except for the type I antagonists [Sar1, Cha8]ANG II (7%), [Aib1, Cha8]ANG II (12%) and [Des1, Cha8]ANG II (20%). These data illustrate that the substitution of Cha at position 8 of ANG II analogues produces potent antagonists; however, Type I antagonists retain significant agonist activity whereas Type I/II antagonists do not. In contrast, substitution of Cha at position 4 in a variety of ANG II analogues resulted in severely diminished biological activity, illustrating that the presence of an aromatic ring quadrupole at position 4 is obligatory for receptor binding and activity.     

Design,synthesis, and docking of highly hypolipidemic agents: Schizosaccharomyces pombe as a new model for evaluating α-asarone-based HMG-CoA reductase inhibitors

A series of α-asarone-based analogues was designed by conducting docking experiments with published crystal structures of human HMG-CoA reductase. Indeed, synthesis and evaluation of this series showed a highly hypocholesterolemic in vivo activity in a murine model, as predicted by previous docking studies. In agreement with this model, the polar groups attached to the benzene ring could play a key role in the enzyme binding and probably also in its biological activity, mimicking the HMG-moiety of the natural substrate. The hypolipidemic action mechanism of these compounds was investigated by developing a simple, efficient, and novel model for determining HMG-CoA reductase inhibition. The partial purification of the enzyme from Schizosaccharomyces pombe allowed for testing of α-asarone- and fibrate-based analogues, resulting in positive and significant inhibitory activity.     

Conformations and interactions of excited states. II. Polystyrene, polypeptides, and proteins

Previous fluorescence and phosphorescence studies of aromatic model compounds have been extended to polymers: “atactic” and isotactic polystyrene, seven aromatic poly-(amino acids), and two proteins. We have confirmed previous observations that both forms of polystyrene exhibit strong excimer fluorescence emission at room temperature but not at 77°K. Of the poly(amino acids) (all observed in helix-supporting solvents), poly-L -phenylalanine, poly(α-benzyl-L -aspartic acid), and poly-1-benzyl-L -histidine likewise show excimer emission at room temperature but not at 77°K., while poly-L -tyrosine, poly-L -tryptophan, poly(γ-benzyl-L -glutamic acid), and poly-S-benzyl-L -cysteine exhibit no excimer emission at either temperature. The aromatic residues of bovine serum albumin exhibit only “normal” fluorescence, but, lysozyme appears to be unique among proteins in showing excimer-like tryptophan emission in the native state; its luminescence becomes “normal” upon denaturation. It appears very probable that none of these polymers has a ground-state conformation in which the aromatic groups have face-to-face orientations appropriate for excimer interaction. It is concluded that at room temperature absorption of light can cause local “melting” of regular (usually helical) structures and thus, in some polymers, permit the attainment of a face-to-face arrangement of aromatic rings within the radiative lifetime of their excited singlet states. In certain other polymers (for reasons not clear at present), and in all polymers at 77°K., this does not occur. This concept is extended to provide a bettor basis for understanding the mechanism of formation of the photodimer of thy mine in irradiated DNA.     

Structure activity relationship studies on Amb639752: toward the identification of a common pharmacophoric structure for DGKα inhibitors

Abstract

A series of analogues of Amb639752, a novel diacylglycerol kinase (DGK) inhibitor recently discovered by us via virtual screening, have been tested. The compounds were evaluated as DGK inhibitors on α, θ, and ζ isoforms, and as antagonists on serotonin receptors. From these assays emerged two novel compounds, namely 11 and 20, which with an IC₅₀ respectively of 1.6 and 1.8 µM are the most potent inhibitors of DGKα discovered to date. Both compounds demonstrated the ability to restore apoptosis in a cellular model of X-linked lymphoproliferative disease as well as the capacity to reduce the migration of cancer cells, suggesting their potential utility in preventing metastasis. Finally, relying on experimental biological data, molecular modelling studies allow us to set a three-point pharmacophore model for DGK inhibitors.