3-Aryl[1,2,4]triazino[4,3-a]benzimidazol-4(10H)-ones: a new class of selective A1 adenosine receptor antagonists

Radioligand binding assays using bovine cortical membrane preparations and biochemical in vitro studies revealed that various 3-aryl[1,2,4]triazino[4,3-a]benzimidazol-4(10H)-one (ATBI) derivatives, previously reported by us as ligands of the central benzodiazepine receptor (BzR) (Primofiore, G.; et al. J. Med. Chem. 2000, 43, 96-102), behaved as antagonists at the A1 adenosine receptor (A1AR). Alkylation of the nitrogen at position 10 of the triazinobenzimidazole nucleus conferred selectivity for the A1AR vs the BzR. The most potent ligand of the ATBI series (10-methyl-3-phenyl[1,2,4]triazino[4,3-a]benzimidazol-4(10H)-one 12) displayed a Ki value of 63 nM at the A1AR without binding appreciably to the adenosine A2A and A3 nor to the benzodiazepine receptor. Pharmacophore-based modeling studies in which 12 was compared against a set of well-established A1AR antagonists suggested that three hydrogen bonding sites (HB1 acceptor, HB2 and HB3 donors) and three lipophilic pockets (L1, L2, and L3) might be available to antagonists within the A1AR binding cleft. According to the proposed pharmacophore scheme, the lead compound 12 engages interactions with the HB2 site (via the N2 nitrogen) as well as with the L2 and L3 sites (through the pendant and the fused benzene rings). The results of these studies prompted the replacement of the methyl with more lipophilic groups at the 10-position (to fill the putative L1 lipophilic pocket) as a strategy to improve A1AR affinity. Among the new compounds synthesized and tested, the 3,10-diphenyl[1,2,4]triazino[4,3-a]benzimidazol-4(10H)-one (23) was characterized by a Ki value of 18 nM which represents a 3.5-fold gain of A1AR affinity compared with the lead 12. A rhodopsin-based model of the bovine adenosine A1AR was built to highlight the binding mode of 23 and two well-known A1AR antagonists (III and VII) and to guide future lead optimization projects. In our docking simulations, 23 receives a hydrogen bond (via the N1 nitrogen) from the side chain of Asn247 (corresponding to the HB1 and HB2 sites) and fills the L1, L2, and L3 lipophilic pockets with the 10-phenyl, 3-phenyl, and fused benzene rings, respectively.

Linking CoMFA and protein homology models of enzyme-inhibitor interactions: an application to non-steroidal aromatase inhibitors

An approach to compare quantitatively a ligand-based (CoMFA) model and an enzyme active site model was investigated. The active site of the cytochrome P450 human aromatase was constructed by homology modeling techniques and two structurally different non-steroidal aromatase inhibitors were docked into it. A CoMFA model was then developed on a related series of non-steroidal inhibitors by correlating their inhibitory activity (expressed as -log IC50 values) versus only 11 steric descriptors (i.e. Csp3-ligand steric interaction energies). The resulting 3D-QSAR coefficients (11) and the steric field values of the aromatase active site calculated at the same points of the CoMFA lattice (i.e. eleven Csp3-protein steric interaction energies) were pair-wise compared. Specifically, when a positive coefficient was associated with a negative or low ( < 5 kcal/mol) value of the protein steric field or, alternatively, a negative coefficient was associated with a large positive value of the protein steric field we recorded as many matches. When a 3D-QSAR coefficient did not correspond to the protein steric potential in the sense described above we considered that point as a mis-matching point. In our view, in spite of several limitations, such a comparison represents a valuable criterion to evaluate quantitatively how convergent are the results from a 3D-QSAR CoMFA model and a homology-built protein 3D structure.

Conformational studies on a synthetic C-terminal fragment of the alpha subunit of G(S) proteins

It has recently been reported that synthetic peptides corresponding to the C-terminal sequence of G alpha, can be used to study the molecular mechanisms of interaction between this protein and G protein coupled receptors (Hamm et al., Science, 1988, Vol. 241, pp. 832-835). A conformational analysis on a 11 amino acids peptide from the G alpha(S) C-terminus, G alpha(S)(384-394) (H-QRMHLRQYELL-OH), was performed by nmr spectroscopy and molecular modeling methods. Two-dimensional nmr spectra, recorded in hexafluoroacetone/water, a mixture with structure stabilizing properties, showed an unusually high number of nuclear Overhauser effects, forming significative pattern to the drawing of a secondary structure. Conformations consistent with experimental NOE distances were obtained through molecular dynamics and energy minimization methods. These calculations yielded two stable conformers corresponding to an alpha-turn and a type III beta-turn involving the last five C-terminal residues. Interestingly, the alpha-turn conformation was found to overlap with good agreement the crystallographic structure of the same fragment in the G alpha(S) protein.

Computer-assisted design, synthesis and biological evaluation of novel pyrrolyl heteroaryl sulfones targeted at HIV-1 reverse transcriptase as non-nucleoside inhibitors

Three pyrrolyl heteroaryl sulfones (ethyl 1-[(1H-benzimidazol-2(3H)one-5-yl)sulfonyl]-1H-pyrrole-2-carboxyla te, ethyl 1-[(1H-benzimidazol-5(6)-yl)sulfonyl]-1H-pyrrole-2-carboxylate and ethyl 1-[(1H-benzotriazol-5(6)-yl)sulfonyl]-1H-pyrrole-2-carboxylate) were designed as novel HIV-1 reverse transcriptase non-nucleoside inhibitors using structure-based computational methods. Although these compounds were inactive in the cell-based assay, they inhibited the target enzyme with micromolar potency (IC50s = 2 microM, 3 microM and 9 microM, respectively).

A galpha(s) carboxyl-terminal peptide prevents G(s) activation by the A(2A) adenosine receptor

The molecular mechanisms of interaction between G(s) and the A(2A) adenosine receptor were investigated using synthetic peptides corresponding to various segments of the Galpha(s) carboxyl terminus. Synthetic peptides were tested for their ability to modulate binding of a selective radiolabeled agonist, [(3)H]2-[4-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxam idoade nosine ([(3)H]CGS21680), to A(2A) adenosine receptors in rat striatal membranes. The Galpha(s) peptides stimulated specific binding both in the presence and absence of 100 microM guanosine-5'-O-(3-thiotriphosphate) (GTPgammaS). Three peptides, Galpha(s)(378-394)C(379)A, Galpha(s)(376-394)C(379)A, and Galpha(s)(374-394)C(379)A, were the most effective. In the presence of GTPgammaS, peptide Galpha(s)(374-394)C(379)A increased specific binding in a dose-dependent fashion. However, the peptide did not stabilize the high-affinity state of the A(2A) adenosine receptor for [(3)H]CGS21680. Binding assays with a radiolabeled selective antagonist, [(3)H]5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo[4, 3-e]-1,2,4-triazolo[1,5-c]pyrimidine ([(3)H]SCH58261), showed that the addition of the Galpha(s) peptide modified the slope of the 5'-N-ethylcarboxamidoadenosine (NECA) competition curve, suggesting modulation of receptor affinity states. In the presence of GTPgammaS, the displacement curve was right-shifted, whereas the addition of Galpha(s)(374-394)C(379)A caused a partial left-shift. Both curves were fitted by one-site models. This same Galpha(s) peptide was also able to disrupt G(s)-coupled signal transduction as indicated by inhibition of the A(2A) receptor-stimulated adenylyl cyclase activity without affecting either basal or forskolin-stimulated enzymatic activity in the same membrane preparations. Shorter peptides from Galpha(s) and Galpha(i1/2) carboxyl termini were not effective. NMR spectroscopy showed the strong propensity of peptide Galpha(s)(374-394)C(379)A to assume a compact carboxyl-terminal alpha-helical conformation in solution. Overall, our results point out the conformation requirement of Galpha(s) carboxyl-terminal peptides to modulate agonist binding to rat A(2A) adenosine receptors and disrupt signal transduction.

Modeling of kappa-opioid receptor/agonists interactions using pharmacophore-based and docking simulations

The interaction of the kappa-opioid receptor with arylacetamide and benzomorphan derivatives acting as agonists was modeled through pharmacophore-based and docking calculations. Potentially bioactive conformations of representative ligands (U-50,488 and its benzo-fused analogues 4 and 6 for arylacetamides and MPCB for benzomorphans) were identified by systematic conformational analysis and docked into a 3D model of the kappa-receptor. The obtained complexes, refined by energy-minimization and molecular dynamics, were evaluated for their consistency with structure-activity relationships and site-directed mutagenesis data. The following interactions are hypothesized to govern the ligand-receptor recognition process: (i) a salt bridge between the Asp138 carboxylate and the protonated nitrogen of the bound agonist; (ii) a hydrogen bond donated by the Tyr312 hydroxyl to the carbonyl oxygen of arylacetamides and MPCB; (iii) hydrophobic interactions established by the dichlorophenyl moiety of arylacetamides and the pendant phenyl ring of MPCB with the surrounding side chains of Tyr312, Leu224, Leu295, and Ala298; (iv) a pi-stacking contact between the Tyr312 side chain and the phenyl ring of arylacetamides; (v) a hydrogen bond linking the His291 imidazole ring to the phenolic hydroxy group featured by typical benzomorphans and the arylacetamides 4 and 6.

Structure-based design, synthesis, and biological evaluation of novel pyrrolyl aryl sulfones: HIV-1 non-nucleoside reverse transcriptase inhibitors active at nanomolar concentrations

Pyrrolyl aryl sulfones (PASs) have been recently reported as a new class of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) inhibitors acting at the non-nucleoside binding site of this enzyme (Artico, M.; et al. J. Med. Chem. 1996, 39, 522-530). Compound 3, the most potent inhibitor within the series (EC(50) = 0.14 microM, IC(50) = 0.4 microM, and SI > 1429), was then selected as a lead compound for a synthetic project based on molecular modeling studies. Using the three-dimensional structure of RT cocrystallized with the alpha-APA derivative R95845, we derived a model of the RT/3 complex by taking into account previously developed structure-activity relationships. Inspection of this model and docking calculations on virtual compounds prompted the design of novel PAS derivatives and related analogues. Our computational approach proved to be effective in making qualitative predictions, that is in discriminating active versus inactive compounds. Among the compounds synthesized and tested, 20 was the most active one, with EC(50) = 0.045 microM, IC(50) = 0.05 microM, and SI = 5333. Compared with the lead 3, these values represent a 3- and 8-fold improvement in the cell-based and enzyme assays, respectively, together with the highest selectivity achieved so far in the PAS series.

Non-nucleoside HIV-1 reverse transcriptase inhibitors: synthesis and biological evaluation of novel quinoxalinylethylpyridylthioureas as potent antiviral agents

New heterocyclic derivatives of ethylpyridylthiourea, quinoxalinylethylpyridylthiourea (QXPT) and analogues, inhibited human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) activity and prevented HIV-1 cytopathogenicity in T4 lymphocytes. Several of these novel non-nucleoside RT inhibitors, with a substituted pyrroloquinoxalinone heteroaromatic skeleton, showed inhibitory activity against wild-type RT as well as against mutant RTs containing the single amino acid substitutions L1001, K103N, V106A, Y1811 and Y188L that was much greater than other non-nucleoside inhibitors such as nevirapine. Maximum potency in enzymatic assays was achieved with a fluoropyrroloquinoxaline skeleton linked to the ethylpyridylthiourea moiety (FQXPT). In cell-based assays on different cell lines and on human monocyte-macrophages, 6-FQXPT exhibited EC50 values in the nanomolar range, with a promising selectivity index. Moreover, 6-FQXPT showed synergistic antiviral activity with zidovudine.

3-Aryl-[1,2,4]triazino[4,3-a]benzimidazol-4(10H)-ones: tricyclic heteroaromatic derivatives as a new class of benzodiazepine receptor ligands

A series of 3-substituted [1,2,4]triazino[4,3-c]benzimidazoles V were prepared and tested at the central benzodiazepine receptor (BzR). These compounds were designed as rigid analogues of the previously described N-benzylindolylglyoxylylamide derivatives IV. The title compounds V showed an affinity which depended directly on the presence of the N(10)-H group and an aromatic ring at position 3. Some of them elicited a 2- or 3-fold higher affinity with respect to that of the indolylglyoxylylamide derivatives IV (R = H). The GABA ratio and [(35)S]-tert-butylcyclophosphorothionate binding data revealed an efficacy profile of partial inverse agonists/antagonists for compounds 1c,e,f,j,k, and of a partial agonist for 2c. This last compound proved to be effective in antagonizing pentylenetetrazole-induced seizures in mice. Attempts were made to interpret the structure-affinity relationships of compounds V in the light of possible tautomeric equilibria involving the ligands.

Pyrroloquinoxaline derivatives as high-affinity and selective 5-HT(3) receptor agonists: synthesis, further structure-activity relationships, and biological studies

The synthesis, pharmacological evaluation, and structure-activity relationships (SARs) of a series of novel pyrroloquinoxalines and heteroaromatic-related derivatives are described. The new pyrroloquinoxaline-related ligands were tested in rat cortex, a tissue expressing high density of 5-HT(3) receptors, and on NG108-15 cells and exhibited IC(50) values in the low nanomolar or subnanomolar range, as measured by the inhibition of [(3)H]zacopride binding. The SAR studies detailed herein delineated a number of structural features required for improving affinity. Some of the ligands were employed as "molecular yardsticks" to probe the spatial dimensions of the lipophilic pockets L1, L2, and L3 in the 5-HT(3) receptor cleft, while the 7-OH pyrroloquinoxaline analogue was designed to investigate hydrogen bonding with a putative receptor site H1 possibly interacting with the serotonin hydroxy group. The most active pyrroloquinoxaline derivatives showed subnanomolar affinity for the 5-HT(3) receptor. In functional studies ([(14)C]guanidinium accumulation test in NG108-15 hybrid cells, in vitro) most of the tested compounds showed clear-cut 5-HT(3) agonist properties, while some others were found to be partial agonists. Several heteroaromatic systems, bearing N-substituted piperazine moieties, have been explored with respect to 5-HT(3) affinity, and novel structural leads for the development of potent and selective central 5-HT(3) receptor agonists have been identified. Preliminary pharmacokinetic studies indicate that these compounds easily cross the blood-brain barrier (BBB) after systemic administration with a brain/plasma ratio between 2 and 20, unless they bear a highly hydrophilic group on the piperazine ring. None of the tested compounds showed in vivo anxiolytic-like activity, but potential analgesic-like properties have been possibly disclosed for this new class of 5-HT(3) receptor agonists.

Pyrrolobenzoxazepinone derivatives as non-nucleoside HIV-1 RT inhibitors: further structure-activity relationship studies and identification of more potent broad-spectrum HIV-1 RT inhibitors with antiviral activity

Pyrrolobenzoxazepinone (PBO) derivatives represent a new class of human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase (RT) inhibitors (NNRTs) whose prototype is (+/-)-6-ethyl-6-phenylpyrrolo[2,1-d][1,5]benzoxazepin-7(6H)- one (6). Docking studies based on the three-dimensional structure of RT prompted the synthesis and biological evaluation of novel derivatives and analogues of 6 featuring a meta-substituted phenyl or a 2-thienyl ring at C-6 and a pyridine system in place of the fused-benzene ring to yield pyrrolopyridooxazepinones (PPOs). Compared with the lead 6 and nevirapine, several of the synthesized compounds (PBOs 13a-d and PPOs 13i-k) displayed higher inhibitory activity against wild-type RT and clinically relevant mutant RTs containing the single amino acid substitutions L100I, K103N, V106A, Y181I, and Y188L. The most potent inhibitors were further evaluated for in vitro antiviral activity on lymphocytes and monocyte-macrophages, for cytotoxicity on a panel of cell lines, and for potential synergistic antiviral activity with AZT. Pharmacokinetic studies performed on 13b, 13c, and 13i showed that these compounds achieve high concentrations in the brain. The results of the biological and pharmacokinetic experiments suggest a potential clinical utility of analogues such as 13b-d, 13i, and 13j, in combination with nucleoside RT inhibitors, against strains of HIV-1 bearing those mutations that confer resistance to known NNRTI.

5-Alkyl-2-(alkylthio)-6-(2,6-dihalophenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones: novel potent and selective dihydro-alkoxy-benzyl-oxopyrimidine derivatives

Molecular modeling analysis of compounds belonging to the recently published series of dihydro-alkoxy-benzyl-oxopyrimidines (DABOs), such as S-DABOs and DATNOs, gave support to the design of new 2, 6-disubstituted benzyl-DABO derivatives as highly potent and specific inhibitors of the HIV-1 reverse transcriptase (RT). To follow up on the novel DABO derivatives, we decided to investigate the effect of electron-withdrawing substituents in the benzyl unit of the S-DABO skeleton versus their anti-HIV-1 activity. Such chemical modifications impacted the inhibitory activity, especially when two halogen units were introduced at positions 2 and 6 in the phenyl portion of the benzyl group bound to C-6 of the pyrimidine ring. Various 5-alkyl-2-(alkyl(or cycloalkyl)thio)-6-(2, 6-dichloro(or 2,6-difluoro)phenylmethyl)-3, 4-dihydropyrimidin-4(3H)-ones were then synthesized and tested as anti-HIV-1 agents in both cell-based and enzyme (recombinant reverse transcriptase, rRT) assays. Among the various mono- and disubstituted phenyl derivatives, the most potent were those containing a 6-(2,6-difluorophenylmethyl) substituent (F-DABOs), which showed EC50's ranging between 40 and 90 nM and selectivity indexes up to >/=5000. An excellent correlation was found between EC50 and IC50 values which confirmed that these compounds act as inhibitors of the HIV-1 RT. The structure-activity relationships of the newly synthesized pyrimidinones are presented herein.

Geometrically and conformationally restrained cinnamoyl compounds as inhibitors of HIV-1 integrase: synthesis, biological evaluation, and molecular modeling

Various cinnammoyl-based structures were synthesized and tested in enzyme assays as inhibitors of the HIV-1 integrase (IN). The majority of compounds were designed as geometrically or conformationally constrained analogues of caffeic acid phenethyl ester (CAPE) and were characterized by a syn disposition of the carbonyl group with respect to the vinylic double bond. Since the cinnamoyl moiety present in flavones such as quercetin (inactive on HIV-1-infected cells) is frozen in an anti arrangement, it was hoped that fixing our compounds in a syn disposition could favor anti-HIV-1 activity in cell-based assays. Geometrical and conformational properties of the designed compounds were taken into account through analysis of X-ray structures available from the Cambridge Structural Database. The polyhydroxylated analogues were prepared by reacting 3,4-bis(tetrahydropyran-2-yloxy)benzaldehyde with various compounds having active methylene groups such as 2-propanone, cyclopentanone, cyclohexanone, 1,3-diacetylbenzene, 2, 4-dihydroxyacetophenone, 2,3-dihydro-1-indanone, 2,3-dihydro-1, 3-indandione, and others. While active against both 3'-processing and strand-transfer reactions, the new compounds, curcumin included, failed to inhibit the HIV-1 multiplication in acutely infected MT-4 cells. Nevertheless, they specifically inhibited the enzymatic reactions associated with IN, being totally inactive against other viral (HIV-1 reverse transcriptase) and cellular (RNA polymerase II) nucleic acid-processing enzymes. On the other hand, title compounds were endowed with remarkable antiproliferative activity, whose potency correlated neither with the presence of catechols (possible source of reactive quinones) nor with inhibition of topoisomerases. The SARs developed for our compounds led to novel findings concerning the molecular determinants of IN inhibitory activity within the class of cinnamoyl-based structures. We hypothesize that these compounds bind to IN featuring the cinnamoyl residue C=C-C=O in a syn disposition, differently from flavone derivatives characterized by an anti arrangement about the same fragment. Certain inhibitors, lacking one of the two pharmacophoric catechol hydroxyls, retain moderate potency thanks to nonpharmacophoric fragments (i.e., a m-methoxy group in curcumin) which favorably interact with an "accessory" region of IN. This region is supposed to be located adjacent to the binding site accommodating the pharmacophoric dihydroxycinnamoyl moiety. Disruption of coplanarity in the inhibitor structure abolishes activity owing to poor shape complementarity with the target or an exceedingly high strain energy of the coplanar conformation.

N'-Phenylindol-3-ylglyoxylohydrazide derivatives: synthesis, structure-activity relationships, molecular modeling studies, and pharmacological action on brain benzodiazepine receptors

A series of N'-phenylindol-3-ylglyoxylohydrazides, isosters of the N-benzylindol-3-ylglyoxylamide derivatives previously described by us, were synthesized and tested for their ability to displace [3H]Ro 15-1788 from bovine brain membranes. These compounds were designed with the aim of obtaining products which could exert an in vivo activity, thanks to a higher hydrosolubility and consequently a better bioavailability. Affinity was restricted to the derivatives unsubstituted in the 5 position of the indole nucleus (1, 6, 9, 12, 15, 18, 23, and 26), with Ki values ranging from 510 to 11 nM. The most active compounds (6, 9, 23, and 29) proved to be effective in antagonizing pentylenetetrazole-induced seizures. Molecular modeling studies were performed to rationalize the lack of affinity of hydrazides with a chloro or a nitro group in the 5 position of the indole nucleus. It was hypothesized that the conformational preference of the hydrazide side chain, characterized by a gauche disposition of lone pairs and substituents about the N-N bond, prevents all hydrazides from binding to the receptor similarly to other classes of indole analogues previously investigated. The potency of 5-H hydrazides was attributed to a binding mode which is not feasible for 5-Cl and 5-NO2 counterparts. This theoretical model of ligand-receptor interaction permitted a more stringent interpretation of structure-affinity relationships of hydrazides and of recently described benzylamide derivatives (Da Settimo et al. J. Med. Chem. 1996, 39, 5083-5091).

Synthesis and biological evaluation of 5H-indolo [3,2-b][1,5]benzothiazepine derivatives, designed as conformationally constrained analogues of the human immunodeficiency virus type 1 reverse transcriptase inhibitor L-737,126

In the presence of sodium hydride, reaction of aryl-disulphides with ethyl esters of indole-2-carboxylic acids furnished ethyl 3-arylthioindole-2-carboxylates, which were cyclized intramolecularly to afford 5H-indolo[3,2-b][1,5]benzothiazepin-6(7H)-ones or hydrolysed in alkaline medium to give 3-arylthioindole-2-carboxylic acids. These acids, also obtained by the action of aryldisulphides on indole-2-carboxylic acids, afforded tetracyclic 5H-indolo [3,2-b][1,5]benzothiazepin-6(7H)-ones upon treatment with EDCI-DMAP. Transformation of cyclic sulphides into the required sulphones was achieved by treatment with hydrogen peroxide or with m-chloroperbenzoic acid. The title derivatives are conformationally constrained analogues of the potent human immunodeficiency virus type 1 (HIV-1) reverse transcriptase inhibitor 3-benzene-sulphonyl-5-chloroindole-2-carboxamide (L-737, 126). Although the indolobenzothiazepine derivatives, as well as the indolyl aryl sulphones used for their synthesis, were endowed with anti-HIV-1 activities in the submicromolar and micromolar range, none of them proved more potent than L-737,126.

Synthesis, structure-activity relationships, and molecular modeling studies of N-(indol-3-ylglyoxylyl)benzylamine derivatives acting at the benzodiazepine receptor

A number of N-(indol-3-ylglyoxylyl)benzylamine derivatives were synthesized and tested for [3H]flunitrazepam displacing activity in bovine brain membranes. Some of these derivatives (9, 12, 14, 15, 17, 27, 34, 35, 38, 41, and 45) exhibited high affinity for the benzodiazepine receptor (BzR) with Ki values ranging from 67 to 11 nM. The GABA ratio and [35S]-tert-butylbicyclophosphorothionate binding data, determined for the most active compounds, showed that they elicit an efficacy profile at the BzR which depends on the kind of substituent present on the phenyl ring of the benzylamine moiety. Moreover, lengthening (propylamine derivatives 1-3) and shortening (aniline derivatives 46-54) of the distance between the phenyl ring and the amide group of the side chain gave compounds with a drastically lower binding potency. The biological results are discussed in the light of a recently proposed pharmacophore model and compared, by molecular modeling studies, with those obtained from effective BzR ligands.

Synthesis, biological activity, and SARs of pyrrolobenzoxazepine derivatives, a new class of specific "peripheral-type" benzodiazepine receptor ligands

The "peripheral-type" benzodiazepine receptor (PBR) has been reported to play a role in many biological processes. We have synthesized and tested a novel series of PBR ligands based on a pyrrolobenzoxazepine skeleton, in order to provide new receptor ligands. Several of these new compounds proved to be high affinity and selective ligands for PBR, and benzoxazepines 17f and 17j were found to be the most potent ligands for this receptor to have been identified to date. The SAR and the molecular modeling studies detailed herein delineated a number of structural features required for improving affinity. Some of the ligands were employed as "molecular yardsticks" to probe the spatial dimensions of the lipophilic pockets L1 and L3 in the PBR cleft and to determine the effect of occupation of L1 and L3 with respect to affinity, while other C-7 modified analogues provided information specifically on the hydrogen bonding with a putative receptor site H1. The new pyrrolobenzoxazepines were tested in rat cortex, a tissue expressing high density of mitochondrial PBR, and exhibited IC50 and Ki values in the low nanomolar or subnanomolar range, as measured by the displacement of [3H]PK 11195 binding. A subset of the highest affinity ligands was also found to have high affinities for [3H]PK 11195 and [3H]Ro 5-4864 binding in rat adrenal mitochondria. All the ligands in this subset are stimulators of steroidogenesis having similar potency and extent of stimulation as PK 11195 and Ro 5-4864 of steroidogenesis in the mouse Y-1 adrenocortical cell line.

Pyrrolobenzothiazepinones and pyrrolobenzoxazepinones: novel and specific non-nucleoside HIV-1 reverse transcriptase inhibitors with antiviral activity

Two novel classes of pyrrolobenzothiazepinones and pyrrolobenzoxazepinones were investigated as potential anti-AIDS drugs. These compounds were found to inhibit HIV-1 reverse transcriptase (RT) enzyme in vitro and to prevent HIV-1 cytopathogenicity in T4 lymphocytes, without appreciable activity on HIV-2 cytopathic effects, and against HBV as well as calfthymus DNA alpha-polymerase. Their potency is influenced by substituents at position 6 and on the fused aromatic ring. Specifically, small lipophilic substituents at C-6 were preferred, whereas substitutions on the benzo-fused ring were found to be detrimental to activity, with respect to the unsubstituted compounds. Modification of the pie-system at C-6 is well tolerated, although the replacement of the benzo-fused with a [2,3]naphtho-fused ring leads to a less active compound. Maximum potency and specificity is achieved with a phenyl and an ethyl group at position 6 of the pyrrolobenzoxazepinone system. In the enzymatic assay the oxazepinone derivative (+/-)-6-ethyl-6-phenylpyrrolo[2,1-d][1,5] benzoxazepin-7(6H)-one 16e (IC50 = 0.25 microM) was found to be more potent than nevirapine (IC50 = 0.5 microM), tested in the same experimental conditions using rC.dG as a template-primer. In cell culture assay benzoxazepine 16e was active against HIV-1, both wild type and AZT-sensitive, and HIV-1 (IIIB) strains, but not against HIV-2. In enzyme assay although 16e inhibited HIV-1 RT, it was inactive against the nevirapine-resistant recombinant RT Y181C at 50 microM. Molecular modeling studies suggest that these derivatives present a 3D pharmacophoric arrangement similar to that of other non-nucleoside inhibitors such as nevirapine.

Modification of the potent peptide FK888 with unusual aminoacids: effects on activity on neurokinin receptors

We report on the synthesis and the pharmacological properties of a new series of tachykinin antagonists based on the peptide N2-[(4R)-4-hydroxy-1-[(1-methyl-1H-indol-3-yl) carbonyl]-L-prolyl]-N-methyl-N-(phe-nylmethyl)-3-(2-naphthyl)-L-al aninamide (FK888) modified on the (2-naphthyl)-L-alanine and the [(1-methyl-1H-indol-3-yl)carbonyl] moieties. The compounds were tested on guinea pig ileum for NK-1, rat colon for NK-2 and rat portal vein for NK-3 receptors. The two most potent peptides of this series, 1b and 2b, were selective for the NK-2 receptor (pA2 = 7.5 and 7.3, respectively).

A concerted study using binding measurements, X-ray structural data, and molecular modeling on the stereochemical features responsible for the affinity of 6-arylpyrrolo[2,1-d][1,5]benzothiazepines toward mitochondrial benzodiazepine receptors

The 7-(acyloxy)-6-arylpyrrolo[2,1-d][1,5]benzothiazepine derivatives have been recently proposed as a new class of ligands specific for the mitochondrial benzodiazepine receptor (Fiorini et al. J. Med. Chem. 1994, 37, 1427-1438) (Greco et al. J. Med. Chem. 1994, 37, 4100-4108). In this paper we report the X-ray crystallographic structures of three potent (1-3) and two inactive (4 and 5) previously described benzothiazepines, as well as binding affinity constants for two newly assayed analogs in which the acyloxy side chain was replaced by a methoxy group (6) or removed (7). Structure-affinity relationships and molecular mechanics calculations performed using crystal structures as references have led to a revised 3D pharmacophore model accounting for all the data available up until now. Interestingly, the hypothetical receptor-bound conformations of 1-3 display a considerable degree of similarity with their crystal geometries. Additional calculations have confirmed that the poor affinities of benzothiazepines bearing an aroyloxy group (4 and 5) should be ascribed to the steric and/or electronic features of the side chain aryl moieties rather than to unfavorable conformational properties.

Synthesis and in vitro activities of highly potent and selective tripeptide antagonists of the neurokinin NK-1 receptor

We report on the synthesis and the pharmacological properties of a new series of tachykinin antagonists based on the tripeptide Ac-Thr-D-Trp(CHO)-Phe-N(Me)-Bzl (1, FR113680) partly modified on the C-terminal amide part. Stereochemistry around the benzilic carbon, as well as nitrogen substitution was investigated. Selected compounds were tested on guinea pig ileum for NK-1, rat colon and rat portal vein for NK-2 and NK-3 receptors, respectively. Two of these peptides were shown to have higher tachykinin antagonist activity (pA2 > 8.8) and selectivity for NK-1 receptors compared with compound 1 taken as reference (Table 2). In addition we investigated the stability of compounds 2 and 3 on guinea pig plasma and liver homogenate.

Synthesis of 3-(2'-furoyl)indole derivatives as potential new ligands at the benzodiazepine receptor, structurally more restrained analogues of indoleglyoxylylamides

A number of furoylindoles were synthesized with the aim of obtaining structurally more restrained analogues of the previously described indoleglyoxylylamides, which are high affinity ligands at the benzodiazepine receptor. In these new compounds, the oxygen atom of the oxalyl CO(2) is inserted into the rigid furan ring. However, unlike the glyoxylylamides, they proved to be incapable of interacting with the benzodiazepine receptor. To rationalize these results, molecular electrostatic potentials were calculated; these indicated a positive electrostatic potential region for the furan oxygen, which thus prevents the formation of a hydrogen bond necessary for interaction with the receptor. Nevertheless, these findings confirmed that the CO(2) of the indoleglyoxylylamide derivatives represents one of the principal points of interaction with the receptor site for these kinds of ligands, as previously hypothesized by us.