Combining 4-aminoquinoline- and clotrimazole-based pharmacophores toward innovative and potent hybrid antimalarials

Antimalarial agents structurally based on novel pharmacophores, synthesized by low-cost synthetic procedures and characterized by low potential for developing resistance are urgently needed. Recently, we developed an innovative class of antimalarials based on a polyaromatic pharmacophore. Hybridizing the 4-aminoquinoline or the 9-aminoacridine system of known antimalarials with the clotrimazole-like pharmacophore, characterized by a polyarylmethyl group, we describe herein the development of a unique class (4a-l and 5a-c) of antimalarials selectively interacting with free heme and interfering with Plasmodium falciparum (Pf) heme metabolism. Combination of the polyarylmethyl system, able to form and stabilize radical intermediates, with the iron-complexing and conjugation-mediated electron transfer properties of the 4(9)-aminoquinoline(acridine) system led to potent antimalarials in vitro against chloroquine sensitive and resistant Pf strains. Among the compounds synthesized, 4g was active in vivo against P. chabaudi and P. berghei after oral administration and, possessing promising pharmacokinetic properties, it is a candidate for further preclinical development.

Clotrimazole scaffold as an innovative pharmacophore towards potent antimalarial agents: design, synthesis, and biological and structure-activity relationship studies

We describe herein the design, synthesis, biological evaluation, and structure-activity relationship (SAR) studies of an innovative class of antimalarial agents based on a polyaromatic pharmacophore structurally related to clotrimazole and easy to synthesize by low-cost synthetic procedures. SAR studies delineated a number of structural features able to modulate the in vitro and in vivo antimalarial activity. A selected set of antimalarials was further biologically investigated and displayed low in vitro toxicity on a panel of human and murine cell lines. In vitro, the novel compounds proved to be selective for free heme, as demonstrated in the beta-hematin inhibitory activity assay, and did not show inhibitory activity against 14-alpha-lanosterol demethylase (a fungal P450 cytochrome). Compounds 2, 4e, and 4n exhibited in vivo activity against P. chabaudi after oral administration and thus represent promising antimalarial agents for further preclinical development.

Design and synthesis of potent antimalarial agents based on clotrimazole scaffold: exploring an innovative pharmacophore

Identification of new molecular scaffolds structurally unrelated to known antimalarials may represent a valid strategy to overcome resistance of P. falciparum (Pf) to currently available drugs. We describe herein the investigation of a new polycyclic pharmacophore, related to clotrimazole, to develop innovative antimalarial agents. This study allowed us to discover compounds characterized by a high in vitro potency, particularly against Pf CQ-resistant strains selectively targeting free heme, which are easy to synthesize by low-cost synthetic strategies.

Discovery of Huperzine A−Tacrine Hybrids as Potent Inhibitors of Human Cholinesterases Targeting Their Midgorge Recognition Sites

We describe herein the development of novel huperzine A-tacrine hybrids characterized by 3-methylbicyclo[3.3.1]non-3-ene scaffolds. These compounds were specifically designed to establish tight interactions, through different binding modes, with the midgorge recognition sites of human acetylcholinesterase (hAChE: Y72, D74) and human butyrylcholinesterase (hBuChE: N68, D70) and their catalytic or peripheral sites. Compounds 5a-c show a markedly improved biological profile relative to tacrine and huperzine A.

Specific targeting highly conserved residues in the HIV-1 reverse transcriptase primer grip region. Design, synthesis, and biological evaluation of novel, potent, and broad spectrum NNRTIs with antiviral activity

Pyrrolobenzoxazepinones (PBOs) represent a new class of human immunodeficiency virus type 1 (HIV-1) nonnucleoside reverse transcriptase (RT) inhibitors (NNRTIs) whose prototype is 5. Molecular modeling studies based on the X-ray structures of HIV-1 RT prompted the synthesis of novel analogues which were tested as anti-HIV agents. The PBO derivatives specifically designed to target the highly conserved amino acid residues within the beta12-beta13 hairpin, namely primer grip, proved to be very potent against the most common mutant enzymes, including the highly resistant K103N mutant strain. Structure-activity relationships (SARs) are discussed in terms of a possible interaction with the RT binding site, depending on the nature of the substituents at C-6. Among the pyrrolobenzoxazepines investigated, 15c appeared to be the most promising NNRTI of the series characterized by potent antiviral activity, broad spectrum, and low cytotoxicity. 15c showed synergistic antiviral activity with AZT.

The pyrrolo-1,5-benzoxazepine, PBOX-6, inhibits the growth of breast cancer cells in vitro independent of estrogen receptor status and inhibits breast tumour growth in vivo

Members of a novel series of pyrrolo-1,5-benzoxazepine (PBOX) compounds have been shown to induce apoptosis in a number of human leukemia cell lines of different haematological lineage, suggesting their potential as anti-cancer agents. In this study, we sought to determine if PBOX-6, a well characterised member of the PBOX series of compounds, is also an effective inhibitor of breast cancer growth. Two estrogen receptor (ER)-positive (MCF-7 and T-47-D) and two ER-negative (MDA-MB-231 and SK-BR-3) cell lines were examined. The 3,4,5-dimethylthiazol-2-yl-2,5-diphenyl-tetrazolium bromide (MTT) assay was used to determine reduction in cell viability. PBOX-6 reduced the cell viability of all four cell lines tested, regardless of ER status, with IC(50) values ranging from 1.0 to 2.3 microM. PBOX-6 was most effective in the SK-BR-3 cells, which express high endogenous levels of the HER-2 oncogene. Overexpression of the HER-2 oncogene has been associated with aggressive disease and resistance to chemotherapy. The mechanism of PBOX-6-induced cell death was due to apoptosis, as indicated by the increased proportion of cells in the pre-G1 peak and poly(ADP-ribose) polymerase (PARP) cleavage. Moreover, intratumoural administration of PBOX-6 (7.5 mg/kg) significantly inhibited tumour growth in vivo in a mouse mammary carcinoma model (p=0.04, n=5, Student's t-test). Thus, PBOX-6 could be a promising anti-cancer agent for both hormone-dependent and -independent breast cancers.

Specific targeting of hepatitis C virus NS3 RNA helicase. Discovery of the potent and selective competitive nucleotide-mimicking inhibitor QU663

Hepatitis C virus (HCV) infection is an emerging global epidemic, and no effective cure is yet available. Interferon-alpha (INFalpha) and pegylated INFs, in combination or otherwise with ribavirin, have proven to be effective in no more than 50% of chronically infected patients. New and better therapeutic strategies are therefore needed. HCV nonstructural protein 3 (NS3) RNA helicase (h) is a promising target for developing new therapeutics. QU663 was discovered as a potent new selective inhibitor of the helicase reaction of HCV NS3 (K(i) = 0.75 microM), competing with the nucleic acid substrate without affecting ATPase function, even at high concentrations. QU663 is one of a new generation of small-molecule nucleotide-mimicking inhibitors which are potential anti-HCV agents. A thorough molecular modeling study was carried out to explain the molecular basis of NS3h inhibition by QU663. The resulting three-dimensional interaction model is discussed.

Pyrrolo[1,5]benzoxa(thia)zepines as a new class of potent apoptotic agents. Biological studies and identification of an intracellular location of their drug target

We have recently developed five novel pyrrolo-1,5-benzoxazepines as proapoptotic agents. Their JNK-dependent induction of apoptosis in tumor cells suggested their potential as novel anticancer agents. The core structure of the apoptotic agent 6 was investigated, and the SARs were expanded with the design and synthesis of several analogues. To define the apoptotic mechanism of the new compounds and the localization of their drug target, two analogues of 6 were designed and synthesized to delineate events leading to JNK activation. The cell-penetrating compound 16 induced apoptosis in tumor cells, while its nonpenetrating analogue, 17, was incapable of inducing apoptosis or activating JNK. Plasma membrane permeabilization of tumor cells resulted in 17-induced JNK activation, suggesting that the pyrrolo-1,5-benzoxazepine molecular target is intracellular. Interestingly, compound 6 displayed cytotoxic activity against a panel of human tumor cell lines but demonstrated negligible toxicity in vivo with no effect on the animals' hematology parameters.

Development of Molecular Probes for the Identification of Extra Interaction Sites in the Mid-Gorge and Peripheral Sites of Butyrylcholinesterase (BuChE). Rational Design of Novel, Selective, and Highly Potent BuChE Inhibitors†

Tacrine heterobivalent ligands were designed as novel and reversible inhibitors of cholinesterases. On the basis of the investigation of the active site gorge topology of butyrylcholinesterase (BuChE) and acetylcholinesterase (AChE) and by using flexible docking procedures, molecular modeling studies formulated the hypothesis of extra interaction sites in the active gorge of hBuChE, namely, a mid-gorge interaction site and a peripheral interaction site. The design strategy led to novel BuChE inhibitors, balancing potency and selectivity. Among the compounds identified, the heterobivalent ligand 4m, containing an amide nitrogen and a sulfur atom at the 8-membered tether level, is one of the most potent and selective BuChE inhibitors described to date. The novel inhibitors, bearing postulated key features, validated the hypothesis of the presence of extra interaction sites within the hBuChE active site gorge.

Novel Atypical Antipsychotic Agents: Rational Design, an Efficient Palladium-Catalyzed Route, and Pharmacological Studies

Using rational drug design to develop atypical antipsychotic drug candidates, we generated novel and metabolically stable pyrrolobenzazepines with an optimized pK(i) 5-HT(2A)/D(2) ratio. 5a, obtained by a new palladium-catalyzed three-step synthesis, was selected for further pharmacological and biochemical investigations and showed atypical antipsychotic properties in vivo. 5a was active on conditioned avoidance response at 0.56 mg/kg, it had low cataleptic potential and proved to be better than ST1899, clozapine, and olanzapine, representing a new clinical candidate.

Selective induction of apoptosis by the pyrrolo-1,5-benzoxazepine 7-[[dimethylcarbamoyl]oxy]-6-(2-naphthyl)pyrrolo-[2,1-d] (1,5)-benzoxazepine (PBOX-6) in Leukemia cells occurs via the c-Jun NH2-terminal kinase-dependent phosphorylation and inactivation of Bcl-2 and Bcl-XL

Overexpression of the Bcl-2 proto-oncogene in tumor cells confers resistance against chemotherapeutic drugs. In this study, we describe how the novel pyrrolo-1,5-benzoxazepine compound 7-[[dimethylcarbamoyl]oxy]-6-(2-naphthyl)pyrrolo-[2,1-d] (1,5)-benzoxazepine (PBOX-6) selectively induces apoptosis in Bcl-2-overexpressing cancer cells, whereas it shows no cytotoxic effect on normal peripheral blood mononuclear cells. PBOX-6 overcomes Bcl-2-mediated resistance to apoptosis in chronic myelogenous leukemia (CML) K562 cells by the time- and dose-dependent phosphorylation and inactivation of antiapoptotic Bcl-2 family members Bcl-2 and Bcl-XL. PBOX-6 also induces Bcl-2 phosphorylation and apoptosis in wild-type T leukemia CEM cells and cells overexpressing Bcl-2. This is in contrast to chemotherapeutic agents such as etoposide, actinomycin D, and ultraviolet irradiation, whereby overexpression of Bcl-2 confers resistance against apoptosis. In addition, PBOX-6 induces Bcl-2 phosphorylation and apoptosis in wild-type Jurkat acute lymphoblastic leukemia cells and cells overexpressing Bcl-2. However, Jurkat cells containing a Bcl-2 triple mutant, whereby the principal Bcl-2 phosphorylation sites are mutated to alanine, demonstrate resistance against Bcl-2 phosphorylation and apoptosis. PBOX-6 also induces the early and transient activation of c-Jun NH2-terminal kinase (JNK) in CEM cells. Inhibition of JNK activity prevents Bcl-2 phosphorylation and apoptosis, implicating JNK in the upstream signaling pathway leading to Bcl-2 phosphorylation. Collectively, these findings identify Bcl-2 phosphorylation and inactivation as a critical step in the apoptotic pathway induced by PBOX-6 and highlight its potential as an effective antileukemic agent.

Pyrrolo[1,3]benzothiazepine-Based Serotonin and Dopamine Receptor Antagonists. Molecular Modeling, Further Structure−Activity Relationship Studies, and Identification of Novel Atypical Antipsychotic Agents

Recently we reported the pharmacological characterization of the 9,10-dihydropyrrolo[1,3]benzothiazepine derivative (S)-(+)-8 as a novel atypical antipsychotic agent. This compound had an optimum pK(i) 5-HT(2A)/D(2) ratio of 1.21 (pK(i) 5-HT(2A) = 8.83; pK(i) D(2) = 7.79). The lower D(2) receptor affinity of (S)-(+)-8 compared to its enantiomer was explained by the difficulty in reaching the conformation required to optimally fulfill the D(2) pharmacophore. With the aim of finding novel atypical antipsychotics we further investigated the core structure of (S)-(+)-8, synthesizing analogues with specific substituents; the structure-activity relationship (SAR) study was also expanded with the design and synthesis of other analogues characterized by a pyrrolo[2,1-b][1,3]benzothiazepine skeleton, substituted on the benzo-fused ring or on the pyrrole system. On the 9,10-dihydro analogues the substituents introduced on the pyrrole ring were detrimental to affinity for dopamine and for 5-HT(2A) receptors, but the introduction of a double bond at C-9/10 on the structure of (S)-(+)-8 led to a potent D(2)/5-HT(2A) receptor ligand with a typical binding profile (9f, pK(i) 5-HT(2A)/D(2) ratio of 1.01, log Y = 8.43). Then, to reduce D(2) receptor affinity and restore atypicality on unsaturated analogues, we exploited the effect of specific substitutions on the tricyclic system of 9f. Through a molecular modeling approach we generated a novel series of potential atypical antipsychotic agents, with optimized 5HT(2A)/D(2) receptor affinity ratios and that were easier to synthesize and purify than the reference compound (S)-(+)-8. A number of SAR trends were identified, and among the analogues synthesized and tested in binding assays, 9d and 9m were identified as the most interesting, giving atypical log Y scores respectively 4.98 and 3.18 (pK(i) 5-HT(2A)/D(2) ratios of 1.20 and 1.30, respectively). They had a multireceptor affinity profile and could be promising atypical agents. Compound 9d, whose synthesis is easier and whose binding profile is atypical (log Y score similar to that of olanzapine, 3.89), was selected for further biological investigation. Pharmacological and biochemical studies confirmed an atypical antipsychotic profile in vivo. The compound was active on conditioned avoidance response at 1.1 mg/kg, a dose 100-times lower than that required to cause catalepsy (ED(50) >90 mg/kg), it induced a negligible increase of prolactin serum levels after single and multiple doses, and antagonized the cognitive impairment induced by phencyclidine. In conclusion, the pharmacological profile of 9d proved better than clozapine and olanzapine, making this compound a potential clinical candidate.

Inhibition of G1 cyclin-dependent kinase activity during growth arrest of human astrocytoma cells by the pyrrolo-1,5-benzoxazepine, PBOX-21

The present study examines the molecular mechanisms by which a member of a novel series of pyrrolo-1,5-benzoxazepines, PBOX-21, induces G1 arrest in 1321N1 cells. PBOX-21-induced G1 arrest is preceded by both a decrease in CDK2 kinase activity, which is critical for the G1/S transition, and a downregulation in cyclin D(3) protein expression levels, suggesting that these two events may be crucially involved in the mediation of the cell cycle arrest. The decrease in CDK2 activity may be due to an observed decrease in CDK2 protein levels following PBOX-21 treatment. Coinciding with the arrest is a reduction in the activity of CDK4, due to either the observed PBOX-21 induced downregulation in CDK4 expression, or a reduction in complex formation between cyclin D(3)-CDK4 leading to a decrease in the levels of active cyclin D(3)-CDK4 complexes with kinase activity. The level of CDK6 activity was also seen to be reduced following PBOX-21 treatment, also possibly due to a reduction in complex formation with cyclin D(3). However, this reduction in CDK6 kinase activity was not seen until after PBOX-21-induced G1 arrest has reached its maximum, and therefore may be viewed as a consequence of, and a method of maintaining the PBOX-21-induced arrest, rather than a cause. Also in parallel with the G1 arrest elicited by PBOX-21 is an upregulation in the universal CDK inhibitor, p21. Furthermore, the retinoblastoma protein (Rb), a substrate of CDK2 and CDK6, whose phosphorylation is necessary for cell cycle progression, becomes hypophosphorylated. These results indicate that PBOX-21 exerts its growth inhibitory effects through the modulation of the expression and activity of several key G1 regulatory proteins.

Synthesis and pharmacological evaluation of potent and highly selective D3 receptor ligands: inhibition of cocaine-seeking behavior and the role of dopamine D3/D2 receptors

The synthesis, pharmacological evaluation, and structure-activity relationships (SARs) of a series of novel arylalkylpiperazines structurally related to BP897 (3) are described. In binding studies, the new derivatives were tested against a panel of dopamine, serotonin, and noradrenaline receptor subtypes. Focusing mainly on dopamine D(3) receptors, SAR studies brought to light a number of structural features required for high receptor affinity and selectivity. Several heteroaromatic systems were explored for their dopamine receptor affinities, and combinations of synthesis, biology, and molecular modeling, were used to identify novel structural leads for the development of potent and selective D(3) receptor ligands. Introduction of an indole ring linked to a dichlorophenylpiperazine system provided two of the most potent and selective ligands known to date (D(3) receptor affinity in the picomolar range). The intrinsic pharmacological properties of a subset of potent D(3) receptor ligands were also assessed in [(35)S]-GTPgammaS binding assays. Evidence from animal studies, in particular, has highlighted the dopaminergic system's role in how environmental stimuli induce drug-seeking behavior. We therefore tested two novel D(3) receptor partial agonists and a potent D(3)-selective antagonist in vivo for their effect in the cocaine-seeking behavior induced by reintroduction of cocaine-associated stimuli after a long period of abstinence, and without any further cocaine. Compound 5 g, a nonselective partial D(3) receptor agonist with a pharmacological profile similar to 3, and 5p, a potent and selective D(3) antagonist, reduced the number of active lever presses induced by reintroduction of cocaine-associated stimuli. However, 5q, a highly potent and selective D(3) partial agonist, did not have any effect on cocaine-seeking behavior. Although brain uptake studies are needed to establish whether the compounds achieve brain concentrations comparable to those active in vitro on the D(3) receptor, our experiments suggest that antagonism at D(2) receptors might significantly contribute to the reduction of cocaine craving by partial D(3) agonists.

Neuronal high-affinity sodium-dependent glutamate transporters (EAATs): targets for the development of novel therapeutics against neurodegenerative diseases

L-Glutamate is the major excitatory neurotransmitter in mammalian central nervous system, and excitatory amino acid transporters (EAATs) are essential for terminating synaptic excitation and for maintaining extracellular glutamate concentration below toxic levels. Although the structure of these channel-like proteins has not been yet reported, their membrane topology has been hypothesised based on biochemical and protein sequence analyses. In the case of an inadequate clearance from synaptic cleft and from the extrasynaptic space, glutamate behaves as a potent neurotoxin, and it may be related to several neurodegenerative pathologies including epilepsy, ischemia, amyotrophic lateral sclerosis, and Alzheimer disease. The recent boom of glutamate is demonstrated by the enormous amount of publications dealing with the function of glutamate, with its role on modulation of synaptic transmission throughout the brain, mainly focusing: i). on the structure of its receptors, ii). on molecular biology and pharmacology of Glu transporters, and iii). on the role of glutamate uptake and reversal uptake in several neuropathologies. This review will deal with the recent and most interesting published results on Glu transporters membrane topology, Glu transporters physiopathological role and Glu transporters medicinal chemistry, highlighting the guidelines for the development of potential neuroprotective agents targeting neuronal high-affinity sodium-dependent glutamate transporters.

Synthesis of new molecular probes for investigation of steroid biosynthesis induced by selective interaction with peripheral type benzodiazepine receptors (PBR)

In the present study, we have synthesized and tested novel pyridopyrrolo- and pyrrolobenzoxazepine derivatives, as novel and selective peripheral type benzodiazepine receptor (PBR) ligands, and their ability to modulate steroid biosynthesis has been investigated. A subset of new ligands bind the PBR (rat brain and testis) with picomolar affinity, representing the most potent ligands that have been identified to date, and elicited effects on endogenous rate of steroidogenesis in MA10 Leydig cells, having similar potency and effect as PK11195. Several compounds, differently substituted at C-7, were used as molecular yardsticks to probe the spatial dimension of the lipophilic pocket L4 in the receptor binding site.

Non-nucleoside HIV-1 reverse transcriptase (RT) inhibitors: past, present, and future perspectives

Along with nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) have gained a definitive and important place in the treatment of HIV-1 infections, and are in rapid development. These compounds can be grouped into two classes: the first generation NNRTIs, mainly discovered by random screening, and the second generation NNRTIs, developed as a result of comprehensive strategies involving molecular modelling, rationale-based drug synthesis, biological and pharmacokinetic evaluations. The recent boom of NNRTIs is mainly due to their antiviral potency, high specificity and low toxicity. The rapid emergence of drug-resistant HIV-1 strains induced by the first generation drugs is a disadvantage bypassed, in part, by the broad spectrum second generation NNRTIs. Starting from the first generation, this review will focus on the second generation NNRTIs dealing with the recent and most interesting published results, highlighting the guidelines for the development of a third generation of NNRTIs.

Activation of the c-Jun N-terminal kinase (JNK) signaling pathway is essential during PBOX-6-induced apoptosis in chronic myelogenous leukemia (CML) cells

The mitogen-activated protein (MAP) kinase family is activated in response to a wide variety of external stress signals such as UV irradiation, heat shock, and many chemotherapeutic drugs and leads to the induction of apoptosis. A novel series of pyrrolo-1,5-benzoxazepines have been shown to potently induce apoptosis in chronic myelogenous leukemia (CML) cells, which are resistant to many chemotherapeutic agents. In this study we have delineated part of the mechanism by which a representative compound known as PBOX-6 induces apoptosis. We have investigated whether PBOX-6 induces activation of MAP kinase signaling pathways in CML cells. Treatment of K562 cells with PBOX-6 resulted in the transient activation of two JNK isoforms, JNK1 and JNK2. In contrast, PBOX-6 did not activate the extracellular signal-regulated kinase (ERK) or p38. Apoptosis was found to occur independently of the small GTPases Ras, Rac, and Cdc42 but involved phosphorylation of the JNK substrates, c-Jun and ATF-2. Pretreatment of K562 cells with the JNK inhibitor, dicoumarol, abolished PBOX-6-induced phosphorylation of c-Jun and ATF-2 and inhibited the induced apoptosis, suggesting that JNK activation is an essential component of the apoptotic pathway induced by PBOX-6. Consistent with this finding, transfection of K562 cells with the JNK scaffold protein, JIP-1, inhibited JNK activity and apoptosis induced by PBOX-6. JIP-1 specifically scaffolds JNK, MKK7, and members of the mixed-lineage kinase (MLK) family, implicating these kinases upstream of JNK in the apoptotic pathway induced by PBOX-6 in K562 cells.

Caspase-3 is not essential for DNA fragmentation in MCF-7 cells during apoptosis induced by the pyrrolo-1,5-benzoxazepine, PBOX-6

Effector caspases-3, -6 and -7 are responsible for producing the morphological features associated with apoptosis, such as DNA fragmentation. The present study demonstrates that a member of a novel series of pyrrolo-1,5-benzoxazepines, PBOX-6, induces apoptosis in MCF-7 cells, which lack caspase-3. Apoptosis was accompanied by DNA fragmentation and the activation of caspase-7, but not caspases-3 and -6. Inhibition of caspase-7 activity reduced the extent of apoptosis induced, indicating that activation of caspase-7 is involved in the mechanism by which PBOX-6 induces apoptosis in MCF-7 cells. This study suggests that caspase-3 is not necessarily essential for DNA fragmentation and the morphological changes associated with apoptosis.

Pyrrolo[1,3]benzothiazepine-based atypical antipsychotic agents. Synthesis, structure-activity relationship, molecular modeling, and biological studies

The prototypical dopamine and serotonin antagonist (+/-)-7-chloro-9-(4-methylpiperazin-1-yl)-9,10-dihydropyrrolo[2,1-b][1,3]benzothiazepine (5) was resolved into its R and S enantiomers via crystallization of the diastereomeric tartaric acid salts. Binding studies confirmed that the (R)-(-)-enantiomer is a more potent D(2) receptor antagonist than the (S)-(+)-enantiomer, with almost identical affinity at the 5-HT(2) receptor ((S)-(+)-5, log Y = 4.7; (R)-(-)-5, log Y = 7.4). These data demonstrated a significant stereoselective interaction of 5 at D(2) receptors. Furthermore, enantiomer (S)-(+)-5 (ST1460) was tested on a panel of receptors; this compound showed an intriguing binding profile characterized by high affinity for H(1) and the alpha(1) receptor, a moderate affinity for alpha(2) and D(3) receptors, and low affinity for muscarinic receptors. Pharmacological and biochemical investigation confirmed an atypical pharmacological profile for (S)-(+)-5. This atypical antipsychotic lead has low propensity to induce catalepsy in rat. It has minimal effect on serum prolactin levels, and it has been selected for further pharmacological studies. (S)-(+)-5 increases the extracellular levels of dopamine in the rat striatum after subcutaneous administration. By use of 5 as the lead compound, a novel series of potential atypical antipsychotics has been developed, some of them being characterized by a stereoselective interaction at D(2) receptors. A number of structure-activity relationships trends have been identified, and a possible explanation is advanced in order to account for the observed stereoselectivity of the enantiomer of (+/-)-5 for D(2) receptors. The molecular structure determination of the enantiomers of 5 by X-ray diffraction and molecular modeling is reported.

Characterization of the 1H-cyclopentapyrimidine-2,4(1H,3H)-dione derivative (S)-CPW399 as a novel, potent, and subtype-selective AMPA receptor full agonist with partial desensitization properties

(S)-CPW399 (2b) is a novel, potent, and subtype-selective AMPA receptor full agonist that, unlike (S)-willardiine and related compounds, in mouse cerebellar granule cells, stimulated an increase in [Ca(2+)](i), and induced neuronal cell death in a time- and concentration-dependent manner. Compound 2b appears to be a weakly desensitizing, full agonist at AMPA receptors and therefore represents a new pharmacological tool to investigate the role of AMPA receptors in excitotoxicity and their molecular mechanisms of desensitization.

The stereoselective targeting of a specific enzyme-substrate complex is the molecular mechanism for the synergic inhibition of HIV-1 reverse transcriptase by (R)-(-)-PPO464: a novel generation of nonnucleoside inhibitors

The human immunodeficiency virus type 1 (HIV-1) nonnucleoside reverse transcriptase (RT) inhibitor pyrrolopyridooxazepinone (PPO) derivative, (+/-)-PPO294, was shown to be active toward wild type and mutated HIV-1 RT and to act synergistically in combination with 3'-azido-3'-deoxythymidine (Campiani, G., Morelli, E., Fabbrini, M., Nacci, V., Greco, G., Novellino, E., Ramunno, A., Maga, G., Spadari, S., Caliendo, G., Bergamini, A., Faggioli, E., Uccella, I., Bolacchi, F., Marini, S., (1999) J. Med. Chem. 42, 4462-4470). The (+/-)-PPO294 racemate was resolved into its pure enantiomers, and the absolute configuration was determined by x-ray analysis. Only one enantiomer, (R)-(-)-PPO464, displayed antiviral activity against both the wild type and the K103N mutant HIV-1 RT and was found to interact exclusively with the reaction intermediate formed by RT complexed with both the DNA and the nucleotide substrates. Being the first compound of its class to display this behavior, (R)-(-)-PPO464 is the representative of a novel generation of nonnucleoside inhibitors. (R)-(-)-PPO464 showed significant synergism when tested in combination with other RT inhibitors and efficiently inhibited viral replication when tested against the laboratory strain HIV-1 IIIB or against either wild type or multidrug-resistant clinical isolates. Pharmacokinetic studies in mice and rats showed a more favorable profile for (R)-(-)-PPO464 than for the corresponding racemate. (R)-(-)-PPO464 was also found to easily cross the blood-brain barrier. The coadministration of the HIV-1 protease inhibitor ritonavir increased the bioavailability of (R)-(-)-PPO464, having little effect on its plasma and brain elimination rates.

Pyrrolo-1,5-benzoxazepines: a new class of apoptotic agents

Some members of a series of novel pyrrolo-1,5-benzoxazepines (PBOXs) potently induce apoptosis in a number of human cancerous cell lines including HL-60 cells and the drug-resistant chronic myelogenous leukaemia cell line, K562. The apoptotic induction seems to be independent of the mitochondrial peripheral-type benzodiazepine receptor (PBR), which binds these PBOXs with high affinity, due to a lack of correlation between their affinities for the receptor and their apoptotic potencies and their high apoptotic activity in PBR-deficient cells. PBOX-6, a potent member of the series, induces a transient activation of c-Jun N-terminal kinase (JNK) in a dose-dependent manner, which correlates with induction of apoptosis. Expression of a cytoplasmic inhibitor of the JNK signal transduction pathway, Jip-1, prevents JNK activity and significantly reduces the extent of apoptosis induced by PBOX-6. This demonstrates the requirement for JNK in the cellular response to this apoptotic agent. In addition, PBOX-6 activates caspase-3-like proteases in K562 and HL-60 cells. The caspase-3 inhibitor, Z-Asp-Glu-Val-Asp-fluoromethylketone (z-DEVD-fmk), blocks caspase-3-like protease activity in both cell types but only prevents PBOX-6-induced apoptosis in HL-60 cells, suggesting that the requirement for caspase-3-like proteases in the apoptotic pathway is dependent on the cell type.

Quinoxalinylethylpyridylthioureas (QXPTs) as potent non-nucleoside HIV-1 reverse transcriptase (RT) inhibitors. Further SAR studies and identification of a novel orally bioavailable hydrazine-based antiviral agent

Quinoxalinylethylpyridylthioureas (QXPTs) represent a new class of human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) whose prototype is 6-FQXPT (6). Docking studies based on the three-dimensional structure of RT prompted the synthesis of novel heteroarylethylpyridylthioureas which were tested as anti-HIV agents. Several compounds proved to be potent broad-spectrum enzyme inhibitors and significantly inhibited HIV-1 replication in vitro. Their potency depends on the substituents and the nature of the heterocyclic skeleton linked to the ethyl spacer, and structure-activity relationships are discussed in terms of the possible interaction with the RT binding site. Although the new QXPTs analogues show potent antiviral activity, none of the compounds tested overcome the pharmacokinetic disadvantages inherent to ethylpyridylthioureidic antiviral agents, which in general have very low oral bioavailability. Through an integrated effort involving synthesis, docking studies, and biological and pharmacokinetic evaluation, we investigated the structural dependence of the poor bioavailability and rapid clearance within the thioureidic series of antivirals. Replacing the ethylthioureidic moiety with a hydrazine linker led to a new antiviral lead, offering promising pharmacological and pharmacokinetic properties in terms of antiviral activity and oral bioavailability.

Pyrrolo-1,5-benzoxazepines induce apoptosis in chronic myelogenous leukemia (CML) cells by bypassing the apoptotic suppressor bcr-abl

Expression of the transforming oncogene bcr-abl in chronic myelogenous leukemia (CML) cells is reported to confer resistance against apoptosis induced by many chemotherapeutic agents such as etoposide, ara-C, and staurosporine. In the present study some members of a series of novel pyrrolo-1,5-benzoxazepines potently induce apoptosis, as shown by cell shrinkage, chromatin condensation, DNA fragmentation, and poly(ADP-ribose) polymerase (PARP) cleavage, in three CML cell lines, K562, KYO.1, and LAMA 84. Induction of apoptosis by a representative member of this series, PBOX-6, was not accompanied by either the down-regulation of Bcr-Abl or by the attenuation of its protein tyrosine kinase activity up to 24 h after treatment, when approximately 50% of the cells had undergone apoptosis. These results suggest that down-regulation of Bcr-Abl is not part of the upstream apoptotic death program activated by PBOX-6. By characterizing the mechanism in which this novel agent executes apoptosis, this study has revealed that PBOX-6 caused activation of caspase 3-like proteases in only two of the three CML cell lines. In addition, inhibition of caspase 3-like protease activity using the inhibitor z-DEVD-fmk blocked caspase 3-like protease activity but did not prevent the induction of apoptosis, suggesting that caspase 3-like proteases are not essential in the mechanism by which PBOX-6 induces apoptosis in CML cells. In conclusion, this study demonstrates that PBOX-6 can bypass Bcr-Abl-mediated suppression of apoptosis, suggesting an important potential use of these compounds in the treatment of CML.

Pyrrolo-1,5-benzoxazepines induce apoptosis in HL-60, Jurkat, and Hut-78 cells: a new class of apoptotic agents

Some, but not all, of a series of novel pyrrolo-1,5-benzoxazepines (PBOXs) induce apoptosis as shown by cell shrinkage, chromatin condensation, and DNA fragmentation in three human cell lines, HL-60 promyelocytic, Jurkat T lymphoma, and Hut-78 s.c. lymphoma cells. This chemical selectivity, together with the lack of apoptotic activity against rat Leydig cells, argues against a general cell poisoning effect. PBOX-6, a potent member of the series, caused activation of a member of the caspase-3 family of proteases. In addition, the caspase-3-like inhibitor z-DEVD-fmk, but not the caspase-1-like inhibitor z-YVAD-fmk prevented PBOX-6-induced apoptosis, suggesting that caspase 3-like proteases are involved in the mechanism by which PBOX compounds induce apoptosis. The release of cytochrome c into the cytosol in HL-60 cells in response to PBOX-6 suggests that this cellular response may be important in the mechanism by which PBOX-6 induces apoptosis. However, reactive oxygen intermediates do not play a key role in PBOX-6-induced apoptosis because neither the free radical scavenger TEMPO nor the antioxidant N-acetylcysteine had any effect on PBOX-6-induced apoptosis. The apoptotic induction seems independent of the mitochondrial peripheral-type benzodiazepine receptor (PBR) that binds these pyrrolobenzoxazepines with high affinity, due to the lack of correlation between their affinities for the receptor and their apoptotic potencies, their high apoptotic activity in PBR-deficient cells such as Jurkats, and their lack of apoptotic induction in PBR-rich rat Leydig cells. These PBOXs also can overcome nuclear factor-kappaB-mediated resistance to apoptosis. This suggests an important potential use of these compounds in drug-resistant cancers.

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.

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.

Thiazolothiazepine inhibitors of HIV-1 integrase

A series of thiazolothiazepines were prepared and tested against purified human immunodeficiency virus type-1 integrase (HIV-1 IN) and viral replication. Structure-activity studies reveal that the compounds possessing the pentatomic moiety SC(O)CNC(O) with two carbonyl groups are in general more potent against purified IN than those containing only one carbonyl group. Substitution with electron-donating or -withdrawing groups did not enhance nor abolish potency against purified IN. By contrast, compounds with a naphthalene ring system showed enhanced potency, suggesting that a hydrophobic pocket in the IN active site might accommodate an aromatic system rather than a halogen. The position of sulfur in the thiazole ring appears important for potency against IN, as its replacement with an oxygen or carbon abolished activity. Further extension of the thiazole ring diminished potency. Compounds 1, 19, and 20 showed antiviral activity and inhibited IN within similar concentrations. These compounds inhibited IN when Mn(2+) or Mg(2+) was used as cofactor. None of these compounds showed detectable activities against HIV-1 reverse transcriptase, protease, virus attachment, or nucleocapsid protein zinc fingers. Therefore, thiazolothiazepines are potentially important lead compounds for development as inhibitors of IN and HIV replication.

New antipsychotic agents with serotonin and dopamine antagonist properties based on a pyrrolo[2,1-b][1,3]benzothiazepine structure

The development of a synthetic approach to the novel pyrrolo[2, 1-b][1,3]benzothiazepine and its derivatives and their biological evaluation as potential antipsychotic drugs are described. In binding studies these compounds proved to be potent 5-HT2, D2, and D3 receptor ligands. The more potent benzothiazepine (+/-)-3b was resolved into its enantiomers by using HPLC techniques. In vitro testing confirmed that (-)-3b is a more potent D2 receptor ligand, maintaining high affinity for 5-HT2 receptors. In contrast, the (+)-3b enantiomer presents a 35 times higher affinity for 5-HT2 than for dopamine D2 receptors with a similar dopamine D1 receptor affinity to that of (-)-3b. Overall, (+)-3b shows an "atypical" neuroleptic binding profile, while (-)-3b has a more "classical" profile. Furthermore pharmacological and biochemical testing displayed that the novel benzothiazepine (+/-)-3b is able to increase the extracellular levels of dopamine in the rat striatum and causes a dose-related suppression of apomorphine-induced locomotor activity. At low doses (+/-)-3b does not induce catalepsy, showing atypical antipsychotic properties similar to those of olanzapine. These heterocyclic compouds represent new leads for the development of novel antipsychotic drugs with atypical properties.

Synthesis and anticholinesterase activity of huperzine A analogues containing phenol and catechol replacements for the pyridone ring

Based upon modeling results obtained using the crystal structure of huperzine A in complex with acetylcholinesterase (AChE), two novel analogues of this potent AChE inhibitor were designed with phenol or catechol rings replacing the pyridone ring. From the modeling studies, the catechol analogue appeared capable of replacing one of the crystallographic waters bridging huperzine with Tyr 130 and Glu 199 of AChE. The synthesis of these materials by use of a palladium catalyzed bicycloannulation strategy is detailed together with the results of AChE inhibition assays.

Antiproliferative action of pyrrolobenzoxazepine derivatives in cultured cells: absence of correlation with binding to the peripheral-type benzodiazepine binding site

Three novel peripheral-type benzodiazepine binding site (PBBS) ligands, NF 182, 213 and 262, along with the classically used PBBS ligands, PK 11195 and Ro5-4864, were found to inhibit, at micromolar concentrations and in dose-dependent manner, the proliferation of rat C6 glioma and human 1321N1 astrocytoma, without being cytotoxic. This antiproliferative effect is mediated by arrest in the G1 phase of the cell cycle and does not appear to be mediated by a specific interaction of these ligands with the peripheral-type benzodiazepine binding site.

Novel and highly potent 5-HT3 receptor agonists based on a pyrroloquinoxaline structure

The synthesis and the biological evaluation of a series of novel pyrroloquinoxaline derivatives are described. In binding studies several compounds proved to be potent and selective 5-HT3 receptor ligands. The most active pyrroloquinoxalines, 11d and 11e, showed a subnanomolar affinity for 5-HT3 receptor and were able to functionally discriminate the central and peripheral 5-HT3 receptor, being agonists and antagonists, respectively. In functional studies ([14C]-guanidinium accumulation test in NG 108-15 cells, in vitro) most of the synthesized compounds showed clear-cut 5-HT3 agonist properties. In in vivo studies on the von Bezold-Jarisch reflex test (a peripheral interaction model) the behavior of the tested compounds ranged from agonist to antagonist, while clear agonist properties were obtained with 12a on cortical acetylcholine release in freely moving rats. Pharmacokinetic studies with 11e and 12c indicate that the compounds easily cross the blood-brain barrier (BBB) after systemic administration with a brain/plasma ratio of 17.5 and 37.5, respectively. Thus compounds 11e and 12c represent the most potent central 5-HT3 agonists identified to date that are able to cross the blood-brain barrier.

Diltiazem-like calcium entry blockers: a hypothesis of the receptor-binding site based on a comparative molecular field analysis model

A series of 26 pyrrolo[2,1-c][1,4]benzothiazines, which have been already synthesized and reported to show calcium antagonist activity in both radioligand-binding assays and functional studies, were investigated using the comparative molecular field analysis (CoMFA) paradigm. Due to the lack of experimental structural data on these derivatives, the minimum energy conformers obtained by molecular mechanics calculations were used in the subsequent study. Structures were aligned following an alignment criterion based on the pharmacophoric groups of the studied compounds. The predictive ability of the CoMFA model was evaluated using a test set consisting of three representative compounds. The best 3D-quantitative structure-activity relationship model found yields significant cross-validated, conventional, and predictive r2 values equal to 0.703, 0.970, and 0.865, respectively, the average absolute error of predictions being 0.26 log unit. The predictive capability of this model was also tested on a further test set of molecules consisting of diltiazem and nine pyrrolo[2,1-d][1,5]benzothiazepines endowed with calcium antagonist activity. The accurate results obtained also in this case revealed the robustness of the model. On the basis of the same alignment, the structural moieties of the studied calcium entry blockers which are thought to contribute to the biological activity were identified, and a possible receptor-binding site for all these compounds is presented taking into account the information derived from the analysis of the steric and electrostatic CoMFA contour maps.

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.

Cardiovascular characterization of pyrrolo[2,1-d][1,5]benzothiazepine derivatives binding selectively to the peripheral-type benzodiazepine receptor (PBR): from dual PBR affinity and calcium antagonist activity to novel and selective calcium entry blockers

The synthesis and cardiovascular characterization of a series of novel pyrrolo[2,1-d][1,5]-benzothiazepine derivatives (54-68) are described. Selective peripheral-type benzodiazepine receptor (PBR) ligands, such as PK 11195 and Ro 5-4864, have recently been found to possess low but significant inhibitory activity of L-type calcium channels, and this property is implicated in the cardiovascular effects observed with these compounds. In functional studies both PK 11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxa mide) and Ro 5-4864 (4'-chlorodiazepam) did not display selectivity between cardiac and vascular tissue. Therefore, several 7-(acyloxy)-6-arylpyrrolo[2,1-d][1,5]benzothiazepines, potent and selective peripheral-type benzodiazepine receptor ligands recently developed by us (3, 7-20), were subjected to calcium channel receptor binding assay. Some of these compounds showed an unexpected potency in displacing the binding of [3H]nitrendipine from L-type calcium channels, much higher than that reported for PK 11195 and Ro 5-4864 and equal to or higher than that of reference calcium antagonists such as verapamil and (+)-cis-diltiazem. Specifically, in rat cortex homogenate, our prototypic PBR ligand 7-acetoxy-6-(p-methoxyphenyl)pyrrolo[2,1-d][1,5]benzothiazepine (3) showed an IC50 equal to 0.13 nM for inhibition of [3H]nitrendipine binding. Furthermore, in functional studies this compound displayed a clear-cut selectivity for cardiac over vascular tissue. Comparison of calcium antagonist activity on guinea pig aorta strips with the negative inotropic activity, determined by using isolated guinea pig left atria, revealed that 3 displayed higher selectivity than the reference (+)-cis-diltiazem. Thus, the pyrrolobenzothiazepine 3 might represent a new tool for characterizing the relationship between the PBR and cardiac function. Furthermore, we have also investigated the structural dependence of binding to PBR and L-type calcium channels, and this study allowed us to identify a new class of potent calcium channel blockers selective for cardiac over vascular tissue, with no affinity for PBR. A number of structure-activity relationship trends have been identified, and a possible explanation is advanced in order to account for the observed differences in selectivity. Three structural features, namely, (i) the saturation of the C(6)-C(7) double bond, with a consequent higher molecular flexibility, (ii) the presence of a substituent in the benzofused ring, and (iii) a basic side chain at C-10 of the pyrrolobenzothiazepine ring system, were found to be responsible for potent L-type calcium channel antagonism and clear-cut selectivity for cardiac over vascular tissue. Among the synthesized compounds the pyrrolobenzothiazepine 62 was found to be the most promising selective calcium channel blocker. Additionally, the molecular structure determination of the key intermediate 48 by X-ray diffraction, molecular modeling, and NMR analysis is reported.