QSAR prediction, synthesis, anticancer evaluation, and mechanistic investigations of novel sophoridine derivatives as topoisomerase I inhibitors

Sophoridine, which is derived from the Leguminous plant Sophora alopecuroides L., has certain pharmacological activity as a new anticancer drug. Herein, a series of novel N-substituted sophoridine derivatives was designed, synthesized and evaluated with anticancer activity. Through QSAR prediction models, it was discovered that the introduction of a benzene ring as a main pharmacophore and reintroduced into a benzene in para position on the phenyl ring in the novel sophoridine derivatives improved the anticancer activity effectively. In vitro, 28 novel compounds were evaluated for anticancer activity against four human tumor cell lines (A549, CNE-2, HepG-2, and HEC-1-B). In particular, Compound 26 exhibited remarkable inhibitory effects, with an IC50 value of 15.6 μM against HepG-2 cells, surpassing cis-Dichlorodiamineplatinum (II). Molecular docking studies verified that the derivatives exhibit stronger binding affinity with DNA topoisomerase I compared to sophoridine. In addition, 26 demonstrated significant inhibition of DNA Topoisomerase I and could arrest cells in G0/G1 phase. This study provides valuable insights into the design and synthesis of N-substituted sophoridine derivatives with anticancer activity.

Synthesis of N-Arylcytisine Derivatives Using the Copper-Catalyzed Chan-Lam Coupling

N-Arylcytisine derivatives are quite rare. We report here a practical methodology to obtain these compounds. Using the copper-catalyzed Chan-Lam coupling, we synthesized new N-arylcytisine derivatives at room temperature, in air and using inexpensive phenylboronic acids. Cytisine and 3,5-dihalocytisines can act as substrates, and among the products, the p-Br-derivative 2r was used as a substrate to obtain biaryl derivatives under Pd-coupling conditions; ester 2j was converted into its acid and amide derivatives using classical carbodiimide conditions. This shows that the Chan-Lam cross-coupling reaction can be included as a versatile synthetic tool in the derivatization of natural products.

Near-Infrared Small Molecule as a Specific Fluorescent Probe for Ultrasensitive Recognition of Antiparallel Human Telomere G-Quadruplexes

In the past 10 years, many fluorescent probes have been developed to recognize G-quadruplexes (G4s) since G4s play an important role in biological systems. However, the selectivity and sensitivity of existing probes for G4s limit their further applications. Herein, we design and synthesize a new probe (TOVJ) by introducing 9-vinyljulolidine into TO. The new probe exhibits almost no fluorescence in an aqueous solution. Upon interacting with G4s, especially the antiparallel G4s, the fluorescence intensity was greatly enhanced (maximum 2742-fold) with a large Stokes shift of 198 nm and the maximum emission peak at 694 nm (near-infrared region). TOVJ showed high sensitivity and selectivity to G4s over other DNA topologies (ssDNA/dsDNA), especially to antiparallel G4s. For antiparallel human telomere G4 detection, the limits of detection of Hum24 and 22AG Na⁺ were as low as 164 and 231 pM, respectively. This indicates that TOVJ is a highly sensitive fluorescence sensor that can be effectively used for antiparallel human telomere G4 detection. The result of live-cell imaging showed that TOVJ could enter live cells and locate in the mitochondria.

Design and Synthesis of Matrine Derivatives as Novel Anti-Pulmonary Fibrotic Agents via Repression of the TGFβ/Smad Pathway

A total of 18 matrine derivatives were designed, synthesized, and evaluated for their inhibitory effect against TGF-β1-induced total collagen accumulation in human fetal lung fibroblast MRC-5 cell lines. Among them, compound 3f displayed the most potent anti-fibrotic activity (IC₅₀ = 3.3 ± 0.3 μM) which was 266-fold more potent than matrine. 3f significantly inhibited the fibroblast-to-myofibroblast transition and extracellular matrix production of MRC-5 cells. The TGF-β/small mothers against decapentaplegic homologs (Smad) signaling was also inhibited by 3f, as evidenced by inhibition of cytoplasm-to-nuclear translocation of Smad2/3 and suppression of TGF-β1-induced upregulation of TGF-β receptor type I (TGFβRI). Additionally, 3f exhibited potent inhibitory effects against TGF-β1-induced fibroblasts migration. These data suggested that 3f might be a potential agent for the treatment of idiopathic pulmonary fibrosis via repression of the TGFβ/Smad signaling pathway.

Decarboxylative Annulation of α-Amino Acids with γ-Nitroaldehydes

Indolizidine and quinolizidine derivatives are readily assembled from proline or pipecolic acid and γ-nitroaldehydes by means of a decarboxylative annulation process. These reactions are promoted by simple acetic acid and involve azomethine ylides as reactive intermediates. The method was applied to the synthesis of an epiquinamide analog.

Synthesis and biological evaluation of matrine derivatives as anti-hepatocellular cancer agents

We delineate herein the synthesis and anti-cancer effects of 15 matrine derivatives. The in vitro growth inhibitory assays showed that most of the prepared compounds exhibited improved anti-proliferative activities towards cancer cells with IC50 17-109 times lower than that of matrine. Compounds CH6 showed the most potent anti-proliferative activities in the four tested cancer cell lines. Moreover, compound CH6 could induce G1 cell cycle arrest and inhibit cell migration in human hepatocellular cancer cell lines Bel-7402 and HepG2 through up-regulation of P21, P27 and E-cadherin and down-regulation of N-cadherin.

Benzo[b]quinolizinium Derivatives Have a Strong Antimalarial Activity and Inhibit Indoleamine Dioxygenase

The heme-containing enzymes indoleamine 2,3-dioxygenase-1 (IDO-1) and IDO-2 catalyze the conversion of the essential amino acid tryptophan into kynurenine. Metabolites of the kynurenine pathway and IDO itself are involved in immunity and the pathology of several diseases, having either immunoregulatory or antimicrobial effects. IDO-1 plays a central role in the pathogenesis of cerebral malaria, which is the most severe and often fatal neurological complication of infection with Plasmodium falciparum. Mouse models are usually used to study the underlying pathophysiology. In this study, we screened a natural compound library against mouse IDO-1 and identified 8-aminobenzo[b]quinolizinium (compound 2c) to be an inhibitor of IDO-1 with potency at nanomolar concentrations (50% inhibitory concentration, 164 nM). Twenty-one structurally modified derivatives of compound 2c were synthesized for structure-activity relationship analyses. The compounds were found to be selective for IDO-1 over IDO-2. We therefore compared the roles of prominent amino acids in the catalytic mechanisms of the two isoenzymes via homology modeling, site-directed mutagenesis, and kinetic analyses. Notably, methionine 385 of IDO-2 was identified to interfere with the entrance of l-tryptophan to the active site of the enzyme, which explains the selectivity of the inhibitors. Most interestingly, several benzo[b]quinolizinium derivatives (6 compounds with 50% effective concentration values between 2.1 and 6.7 nM) were found to be highly effective against P. falciparum 3D7 blood stages in cell culture with a mechanism independent of IDO-1 inhibition. We believe that the class of compounds presented here has unique characteristics; it combines the inhibition of mammalian IDO-1 with strong antiparasitic activity, two features that offer potential for drug development.

[Search of (-)-Cytisine Derivatives as Potential Inhibitors of NF-κB and STAT1]

Design and synthesis ofnew derivatives of (-)-cytisine with a wide spectrum of pharmacological activity, represents the potential therapeutic interest for development of drug candidates for neurodegenerative disorders, inflammatory diseases, and treatment of nicotine addiction. We used HEK293 cell line transiently transfected with N F-κB and STATI luciferase reporter constructs to screen the (-)-cytisine derivatives for their potency to modulate basal and induced NF-κB and STAT1 activity. Currently, NF-κB, STAT1 and components of their signaling pathways are considered as attractive targets for pharmacological intervention, primarily in chronic inflammation, cancer, autoimmune, neurodegenerative and infectious diseases. The library of compounds included the derivatives of (-)-cytisine with amino-, amide-, thio- and carboxamide groups at 3, 5 and 12 position of the starting molecule, as well as some bimolecular derivatives. Our experimental data revealed compounds with moderate activating as well as inhibitory effects for basal NF-κB and STATI activity (IC50 or EC50 values are mainly in the micromolar range). The structure-activity relationship analysis demonstrated that the character of activity (activation or inhibition of NFκ-B and STAT1) is determined by the topology of the substituents at the (-)-cytisine molecule, whereas the nature of the substituents mainly contributes to severity of the effect (introduction of aromatic and adamantyl substituents, as well as thionyl or keto groups are of the principal importance). When evaluating the effect of (-)-cytisine derivatives on activity of NF-κB and STATI, induced by specific agents (TNFα and IFNγ, respectively) we observed that some compounds inhibited basal and stimulated activity of NF-κB and STAT1, another compounds showed the dual effect (an increase of basal- and a decrease of stimulated NF-κB activity) and several compounds increase both basal and induced activity of NF-κB and STAT1. Thus, obtained results suggest that one of the possible mechanisms of biological action of (-)-cytisine derivatives is their ability to influence the components of NF-κB and STAT1-dependent signaling pathways.

Synthesis of isotopically labeled 1,3-dithiane

The 1,3-dithiane is a protected formaldehyde anion equivalent that could serve as a useful labeled synthon. We report a facile synthesis of 1,3-[2-(13)C]- and 1,3-[2-(13)C, 2-(2)H2]dithiane in two steps from [(13)C]- or [(13) C, (2)H3 ]methyl phenyl sulfoxide. We have previously reported the high yield synthesis of [(13)C]methyl phenyl sulfide from [(13)C]MEOH and the oxidation of [(13)C]methyl phenyl sulfide to [(13)C]methyl phenyl sulfoxide. Here, we describe the facile exchange of deuterium from (2) H2 O into [(13)C]methyl phenyl sulfoxide to yield [(13)C, (2)H3]methyl phenyl sulfoxide. Thus, from [(13)C]MEOH and (2)H2O, all possible C2 stable isotopomers of 1,3-dithiane are available. Our synthetic route is also amenable to preparation of radiolabeled 1,3-dithianes.

Toward a unified approach for the lycopodines: synthesis of 10-hydroxylycopodine, deacetylpaniculine, and paniculine

The enantioselective syntheses of 10-hydroxylycopodine, deacetylpaniculine, and paniculine have been accomplished through use of a common intermediate. Key steps in the synthetic sequence toward these lycopodium alkaloids include formation of the tricyclic core via a conformationally accelerated, intramolecular Mannich cyclization and an organocatalyzed, intramolecular Michael addition to form the C(7)-C(12) linkage.

First discovery and stucture-activity relationship study of phenanthroquinolizidines as novel antiviral agents against tobacco mosaic virus (TMV)

A series of phenanthroquinolizidine alkaloids 1-24 were prepared and first evaluated for their antiviral activity against tobacco mosaic virus (TMV). The bioassay results showed that most of these compounds exhibited good to excellent in vivo anti-TMV activity, of which compounds 1, 2, 15 and 16 displayed significantly higher activity than (R)-antofine and commercial Ningnanmycin at the same test condition. The substituents on the phenanthrene moiety play an important role for maintaining high in vivo antiviral activity. The introduction of 6-hydroxyl, which is proposed to interact with TMV RNA, did increased anti-TMV activity. The 14aR-configuration was confirmed to be the preferred antiviral configuration for phenanthroquinolizidine alkaloids. Introduction of hydroxy group at 15-position of phenanthroquinolizidine alkaloids increased activity for S-configuration but decreased activity for R-configuration. Present study provides fundamental support for development and optimization of phenanthroquinolizidine alkaloids as potential inhibitors of plant virus.

Synthesis, characterization and in vitro anti-tumor activities of matrine derivatives

Nineteen previously unreported matrine derivatives were synthesized and characterized using elemental analysis, infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and mass spectrometry. Target compounds 6a-6l and 7a-7c showed stronger inhibitory activities than matrine in the in vitro antitumor tests and inhibited the growth of the Hep7402, B16-F10, A549, and TW03 cell lines. In addition, compound 6i exhibited a potent antitumor activity similar to that of colchicine.

Natural product-inspired cascade synthesis yields modulators of centrosome integrity

In biology-oriented synthesis, the scaffolds of biologically relevant compound classes inspire the synthesis of focused compound collections enriched in bioactivity. This criterion is, in particular, met by the scaffolds of natural products selected in evolution. The synthesis of natural product-inspired compound collections calls for efficient reaction sequences that preferably combine multiple individual transformations in one operation. Here we report the development of a one-pot, twelve-step cascade reaction sequence that includes nine different reactions and two opposing kinds of organocatalysis. The cascade sequence proceeds within 10-30 min and transforms readily available substrates into complex indoloquinolizines that resemble the core tetracyclic scaffold of numerous polycyclic indole alkaloids. Biological investigation of a corresponding focused compound collection revealed modulators of centrosome integrity, termed centrocountins, which caused fragmented and supernumerary centrosomes, chromosome congression defects, multipolar mitotic spindles, acentrosomal spindle poles and multipolar cell division by targeting the centrosome-associated proteins nucleophosmin and Crm1.

Synthesis, structure-activity relationship and biological evaluation of anticancer activity for novel N-substituted sophoridinic acid derivatives

Sophoridine (1), a natural anticancer drug, has been used in China for decades. A series of novel N-substituted sophoridinic acid derivatives were synthesized and evaluated for their cytotoxicity with 1 as the lead. The structure-activity relationship indicated that introduction of an aliphatic acyl on the nitrogen atom might significantly enhance the anticancer activity. Among the compounds, 6b bearing bromoacetyl side-chain afforded a potential effect against four human tumor cell lines (liver, colon, breast, and lung). The mechanism of action of 6b is to inhibit the activity of DNA topoisomerase I, followed by the S-phase arrest and then cause apoptotic cell death, similar to that of its parent 1. We consider 6b promising for further anticancer investigation.

Overcoming multidrug resistance in human lung cancer with novel benzo[a]quinolizin-4-ones

AIM

To investigate the ability of synthetic benzo[a]quinolizin-4-one derivatives to reverse multidrug resistance (MDR) in lung cancer cells.

MATERIALS AND METHODS

A cell line with MDR, A549RT-eto, was established by exposure to 1.5 μM etoposide. Cytotoxic activity was assayed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromine (MTT) method. The mechanism of drug resistance was studied by real-time PCR, Western blot analysis, and flow cytometry. Benzo[a]quinolizin-4-one derivatives were synthesized and tested for cytotoxic activity and ability to modulate MDR.

RESULTS

A549RT-eto cells had an IC(50) for etoposide of 176 μM, 28-fold higher than parental cells, due to increased levels of MDR1 gene and P-glycoprotein (P-gp), resulting in greater drug efflux. Three benzo[a]quinolizin-4-ones reduced etoposide IC(50) from 176 μM to 22.4 μM -24.7 μM. This resulted from increased drug accumulation without altering P-gp expression at the transcription or translation level.

CONCLUSION

Non-toxic concentrations of benzo[a]quinolizin-4-one derivatives can reverse drug resistance of A549RT-eto by increasing the intracellular drug accumulation.

Michael Elliott's billion dollar crystals and other discoveries in insecticide chemistry

The crowning achievement for Michael Elliott came in 1973 when his most outstanding candidate insecticide from 25 years of research crystallized from hexane solution. The stereochemically pure crystalline compound was the most potent synthetic insecticide ever made until that time, and it was highly selective for insects compared with mammals. It was given the name deltamethrin. Sequential stereospecific crystallization to isolate the most potent epimer and base-catalyzed racemization of the remaining less active isomer could be used to produce deltamethrin efficiently on a large scale; it became the billion dollar crystals. Elliott's discoveries at Rothamsted in England with Norman Janes and David Pulman of resmethrin, permethrin, cypermethrin and ultimately deltamethrin provided crop protection and malaria control for millions of people. Michael also laid the background for lipophilic amide, dithiane and other insecticides and nerve probes that are not involved in pyrethroid cross-resistance. Some aspects of these investigations were best conducted at Berkeley, where Michael studied pyrethrins in 1969, synthetic pyrethroids in 1974 and alternative insecticides in 1986-1988. This review considers Michael's seminal discoveries in insecticide chemistry, with emphasis on his Berkeley years.

Highly enantioselective catalytic dynamic resolution of N-Boc-2-lithiopiperidine: synthesis of (R)-(+)-N-Boc-pipecolic acid, (S)-(-)-coniine, (S)-(+)-pelletierine, (+)-beta-conhydrine, and (S)-(-)-ropivacaine and formal synthesis of (-)-lasubine II and (+)-cermizine C

The catalytic dynamic resolution (CDR) of rac-2-lithio-N-Boc-piperidine using chiral ligand 8 or its diastereomer 9 in the presence of TMEDA has led to the highly enantioselective syntheses of both enantiomers of 2-substituted piperidines using a wide range of electrophiles. The CDR has been applied to the synthesis of (R)- and (S)-pipecolic acid derivatives, (+)-beta-conhydrine, (S)-(+)-pelletierine, and (S)-(-)-ropivacaine and the formal synthesis of (-)-lasubine II and (+)-cermizine C.

Development of an enantioselective route toward the Lycopodium alkaloids: total synthesis of lycopodine

Synthesis of a C(15)-desmethyl tricycle core of lycopodine has been accomplished. Key steps in the synthetic sequence include organocatalytic, intramolecular Michael addition of a keto sulfone and a tandem 1,3-sulfonyl shift/Mannich cyclization to construct the tricyclic core ring system. Synthetic work toward this natural product family led to the development of N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide, an organocatalyst which facilitates enantioselective, intramolecular Michael additions. A detailed mechanistic discussion is provided for both the intramolecular Michael addition and the sulfone rearrangement. Finally, the application of these discoveries to the enantioselective total synthesis of alkaloid lycopodine is described.

Arylalkylamine-, beta-carboline-, quinolizine- and azecine-derived compounds and their in vitro interaction with the ionotropic 5-HT3 receptor: search for new lead structures

Specific serotonin receptor agonists and antagonists are marketed with respect to various diseases, most prominently severe emesis. To identify new chemical classes with affinity for the serotonin 5-HT3 channel, several compounds were synthesized which can be structurally classified as arylalkylamines, azecines, quinolizines and beta-carbolines. These were tested in three models: (1) direct effect on ileum (overall model for contracting or relaxant effect), (2) antiserotoninergic effects on rat ileum (crude serotonin model), (3) inhibitory effect on the 5-HT, receptor channel complex expressed in N1E-115 cells (serotonin-induced [14C]guanidinium influx (specific model)). Key findings and conclusion: Several azecine-type compounds exhibit 5-HT3 receptor channel antagonistic properties at concentrations close to that of tropisetron (used as a positive control) and might serve as potential lead structures for the development of further 5-HT3 channel receptor antagonists.

Epiquinamide: a poison that wasn't from a frog that was

In 2003, we reported the isolation, structure elucidation, and pharmacology of epiquinamide (1), a novel alkaloid isolated from an Ecuadoran poison frog, Epipedobates tricolor. Since then, several groups, including ours, have undertaken synthetic efforts to produce this compound, which appeared initially to be a novel, beta2-selective nicotinic acetylcholine receptor agonist. Based on prior chiral GC analysis of synthetic and natural samples, the absolute structure of this alkaloid was established as (1S,9aS)-1-acetamidoquinolizidine. We have synthesized the (1R*,9aS*)-isomer (epi-epiquinamide) using an iminium ion nitroaldol reaction as the key step. We have also synthesized ent-1 semisynthetically from (-)-lupinine. Synthetic epiquinamide is inactive at nicotinic receptors, in accord with recently published reports. We have determined that the activity initially reported is due to cross-contamination from co-occurring epibatidine in the isolated material.

Evolution of multi-component anion relay chemistry (ARC): construction of architecturally complex natural and unnatural products

Efficient construction of architecturally complex natural and unnatural products is the hallmark of organic chemistry. Anion relay chemistry (ARC)-a multi-component coupling protocol-has the potential to provide the chemist with a powerful synthetic tactic, enabling efficient, rapid elaboration of structurally complex scaffolds in a single operation with precise stereochemical control. The ARC tactic can be subdivided into two main classes, comprising the relay of negative charge either through bonds or through space, the latter with aid of a transfer agent. This review will present the current state of through-space anion relay, in conjunction with examples of natural and unnatural product syntheses that illustrate the utility of this synthetic method.

Enantioselective total synthesis of lycopodine

The first enantioselective total synthesis of lycopodine has been completed. Key steps include a highly diastereoselective organocatalyzed cyclization of a keto sulfone to establish the key C7 and C8 stereocenters and a tandem 1,3-sulfonyl shift/intramolecular Mannich cyclization to form the tricyclic core.

Enantioselective rhodium-catalyzed [2+2+2] cycloaddition of alkenyl isocyanates and terminal alkynes: application to the total synthesis of (+)-lasubine II

The use of TADDOL-based phosphoramidite ligands on rhodium allows for the incorporation of terminal alkynes in the [2+2+2] cycloaddition with alkenyl isocyanates. Terminal aliphatic alkynes provide bicyclic lactams, while the use of aryl alkynes provides complementary access to vinylogous amides. Product selectivity seems to be governed by a combination of electronics and sterics, with smaller and/or more electron-deficient substituents favoring lactam formation. The use of homologous alkenyl isocyanates leads to an expedient asymmetric total synthesis of the alkaloid lasubine II.

Identification of Inhibitors for Mycobacterial Protein Tyrosine Phosphatase B (MptpB) by Biology-Oriented Synthesis (BIOS)

Protein phosphatases have recently emerged as important targets for research in chemical biology and medicinal chemistry, and new classes of phosphatase inhibitors are in high demand. BIOS (biology-oriented synthesis) employs the criteria of relevance to nature and biological prevalidation for the design and synthesis of compound collections. In an application of the BIOS principle, an efficient solid-phase synthesis of highly substituted indolo[2,3-a]quinolizidines by using a vinylogous Mannich-Michael reaction in combination with phosgene- or acid-mediated ring closure was developed. Screening of this library for phosphatase inhibitors yielded a new inhibitor class for the Mycobacterium tuberculosis phosphatase MptpB.

The First Synthesis of the ABC-Ring System of ‘Upenamide

The first synthetic route to the spirooxaquinolizidinone core (ABC core) of the macrocyclic marine alkaloid 'upenamide (1) has been developed. All five stereocenters were introduced with complete stereocontrol. The hydroxyl group at C-11 was introduced by a regio- and stereoselective SeO(2)-mediated allylic oxidation. The spirocyclic skeleton was formed by a stannous chloride induced deacetalization-bicyclization procedure. Further stereocenters were introduced by an enzymatic desymmetrization and by incorporation of an (S)-malic acid derived building block.

Practical total syntheses of epiquinamide enantiomers

Short and practical syntheses of epiquinamide and its enantiomer were accomplished with high overall yields and high stereoselectivity from readily available starting materials.

Sch35966 is a potent, selective agonist at the peripheral cannabinoid receptor (CB2) in rodents and primates

BACKGROUND AND PURPOSE

The peripheral cannabinoid receptor (CB(2)) is expressed on peripheral immune cells and is thought to have a role in the immunosuppressive effects of cannabinoids. Historically, there have been few potent, CB(2)-selective agonists to assess the contribution of CB(2) to this phenomenon. The studies presented here describe the synthesis of 8,10-bis[(2,2-dimethyl-1-oxopropyl)oxy]-11-methyl-1234-tetrahydro-6H-benzo[beta]quinolizin-6-one (Sch35966), which binds with low nanomolar potency to CB(2) in both primates and rodents.

EXPERIMENTAL APPROACH

The affinity, potency and efficacy of Sch35966 and other cannabinoid ligands at CB(2) was assessed using competition binding assays vs [(3)H]CP55,940, [(35)S]GTPgammaS exchange, cAMP accumulation and cell chemotaxis assays.

KEY RESULTS

We showed that Sch35966 has >450-fold selectivity for CB(2) binding vs the central cannabinoid receptor (CB(1)) in primates (humans and cynomolgus monkeys) and rodents (rats and mice). Sch35966 is an agonist as it effectively inhibited forskolin-stimulated cAMP synthesis in CHO-hCB(2) cells, stimulated [(35)S]GTPgammaS exchange and directed chemotaxis in cell membranes expressing CB(2). In all species examined, Sch35966 was more potent, more efficacious and more selective than JWH-015 (a commonly used CB(2)-selective agonist).

CONCLUSIONS AND IMPLICATIONS

Taken together, the data show that Sch35966 is a potent and efficacious CB(2)-selective agonist in rodents and primates.

Straightforward methodology for the enantioselective synthesis of benzo[a]- and indolo[2,3-a]quinolizidines

An enantioselective two-step route to substituted benzo[a]- and indolo[2,3-a]quinolizidines has been developed. It consists of (i) a stereoselective cyclocondensation of a racemic or prochiral delta-oxo(di)ester with either (S)-(3,4-dimethoxyphenyl)alaninol or (S)-tryptophanol in a process involving a dynamic kinetic resolution and/or the differentiation of enantiotopic or diastereotopic ester groups, and (ii) a subsequent stereocontrolled cyclization on the aromatic ring taking advantage of the masked N-acyl iminium ion present in the resulting oxazolopiperidone lactams.

Synthesis and pharmacology of site-specific cocaine abuse treatment agents: restricted rotation analogues of methylphenidate

A series of threo-1-aza-3 or 4-substituted-5-phenyl[4.4.0]decanes (quinolizidines), which were envisioned as restricted rotational analogues (RRAs) of methylphenidate (MP), was synthesized and tested for inhibitory potency against [(3)H]WIN35,428, [3H]citalopram, and [3H]nisoxetine binding to the dopamine, serotonin, and norepinephrine transporters, respectively. Two different synthetic schemes were used; a Wittig reaction or acylation (followed by an intramolecular condensation) was a key feature of each scheme. The unsubstituted RRA, threo(trans)-1-aza-5-phenyl[4.4.0]decane (12a), was equipotent to unconstrained threo-MP against [(3)H]WIN35,428 binding. The extra ring in these RRAs (which reduces the conformational freedom) and the orientation and polarity of substituents at the 4-position on this extra ring are of critical importance to the biological activity. Generally, the RRAs paralleled the corresponding unconstrained MP derivatives in binding affinity to the three transporters. The results suggest that the conformation of MP in which the carbonyl group of the methyl ester is H-bonded to the piperidinyl N-H may be the bioactive form of the molecule.

One-Pot, Multicomponent Route to Pyrazoloquinolizinones

[reaction: see text] An efficient synthesis of 5a-hydroxy-4,5,5a,6,7,8-hexahydropyrazolo[4,3-c]quinolizin-9-ones based on the three-component condensation of 5-aminopyrazoles, aromatic aldehydes, and cyclic 1,3-diketones is described. The multicomponent reaction is performed under strongly basic conditions applying controlled microwave heating in a sealed vessel and involves an unusual base-mediated ring-opening/recyclization of the cyclic 1,3-diketone moiety.

General synthesis of pyrroloquinolizidines: synthesis of an unnatural homologue of the pyrroloindolizidine myrmicarin alkaloid 215B

A general synthesis approach to pyrroloquinolizidines (3,4,5,5a,6,7,8-heptahydropyrrolo[2,1,5-de]quinolizines) via a münchnone 1,3-dipolar cycloaddition is reported. The approach was applied to the synthesis of an unnatural pyrroloquinolizidine homologue of myrmicarin 215B.

Asymmetric synthesis of ring functionalized trans-2,6-disubstituted piperidines from N-sulfinyl delta-amino beta-keto phosphonates. total synthesis of (-)-myrtine

Sulfinimine-derived N-sulfinyl delta-amino beta-ketophosphonates are transformed via the enaminones to the phosphoryl dihydropyridones that selectively give trans-2,6-disubstituted 1,2,5,6-tetrahydropyridines on organocuprate addition and dephosphorylation.

Novel Quinolizidinyl Derivatives as Antiarrhythmic Agents

Eighteen analogues of lidocaine, mexiletine, and procainamide were synthesized, replacing their aminoalkyl chains with the rigid and cumbersome quinolizidine nucleus. The target compounds were tested for antiarrhythmic, inotropic, and chronotropic effects on isolated guinea pig (gp) heart tissues and to assess calcium antagonist activity. Most compounds exhibited from moderate to high antiarrhythmic activity, and compounds 7, 9, and 19 were more active and potent than quinidine and lidocaine, while producing only modest inotropic, chronotropic, and vasorelaxant effects. These compounds were studied on spontaneously beating Langendorff-perfused gp heart. While quinidine and amiodarone produced a dose-dependent prolongation of all the ECG intervals, compounds 7, 9, and 19, even at concentrations 10-20 times higher than EC50 for the antiarrhythmic activity, only moderately prolonged the PR and QT intervals, leaving unchanged the QRS complex. Ether 7 deserves further investigations due to its interesting cardiovascular profile.

Three Distinct Reactions of 3,4-Dihydroisoquinolines with Azlactones: Novel Synthesis of Imidazoloisoquinolin-3-ones, Benzo[a]quinolizin-4-ones, and Benzo[d]azocin-4-ones

A facile and direct synthetic entry to tricyclic imidazoloisoquinolin-3-ones and benzo[a]quinolizin-4-ones is reported based on the ring annulation of 1-unsubstituted and 1-substituted dihydroisoquinolines with azlactones under neutral conditions in a one-step procedure. Bicyclic 2,3-dihydrobenzo[d]azocin-4-ones were also prepared using simple azlactone and 1-substituted dihydroisoquinolines in a one-pot reaction. [reaction: see text]

Chiral Oxazolopiperidone Lactams: Versatile Intermediates for the Enantioselective Synthesis of Piperidine-Containing Natural Products

Phenylglycinol-derived oxazolopiperidone lactams are exceptionally versatile building blocks for the enantioselective construction of structurally diverse piperidine-containing natural products and bioactive compounds. These lactams are readily available in both enantiomeric series by cyclocondensation of the chiral amino alcohol with a delta-oxo acid derivative and allow the substituents to be introduced at the different ring positions in a regio- and stereocontrolled manner, providing access to enantiopure polysubstituted piperidines bearing virtually any type of substitution pattern, and also quinolizidines, indolizidines, perhydroquinolines, hydroisoquinolines, as well as complex indole alkaloids. Of particular interest are cyclocondensation reactions with racemic or prochiral delta-oxo (di)acid derivatives in processes involving dynamic kinetic resolution and/or differentiation of enantiotopic or diastereotopic ester groups, as they directly lead to lactams that already incorporate the carbon substituents on the heterocyclic ring. The use of (S)-3,4-dimethoxyphenylalaninol or (S)-tryptophanol in the above cyclocondensation reactions expands the potential and the scope of the methodology, providing a straightforward route to enantiopure benzo[a]- and indolo[2,3-a]quinolizidines.

Comparative Studies on the DNA-Binding Properties of Linear and Angular Dibenzoquinolizinium Ions

The interaction of the linear dibenzo[b,g]quinolizinium (5a) and the angular dibenzo[a,f]quinolizinium (6) with DNA was studied in detail in order to evaluate the influence of the shape of polycyclic quinolizinium ions on their DNA-binding properties. First, the synthesis and the thermally induced dimerization of 5a were reinvestigated because the preparation and isolation of the bromide salt of 5a according to literature procedures turned out to be problematic. The dibenzo[b,g]quinolizinium bromide [5a(Br)] tends to dimerize in solution with a highly selective and unprecedented formation of the corresponding anti-head-to-head dimer. Nevertheless, it was observed that careful exclusion of bromide ions from the reaction mixture suppresses the formation of the dimer. Moreover, the dimer may be transformed to the monomer by a remarkably rapid photoinduced electron-transfer reaction with 1-methoxynaphthalene. The association of 5a and 6 with nucleic acids was investigated by spectrophotometric and spectrofluorimetric DNA titrations, CD and LD spectroscopy, DNA thermal denaturation studies, and competition-dialysis techniques. Both dibenzoquinolizinium ions 5a and 6 exhibit an intercalative mode of binding to double-stranded DNA with moderate binding constants (K = 1-7 x 10(5) M(-1)) and a slight preference for association with GC-rich DNA regions. The structures of the intercalation complexes were calculated by molecular modeling methods. Competition-dialysis studies reveal that the isomers 5a and 6 bind selectively to triple-helical DNA (poly[dA]-poly[dT]2) as compared to selected synthetic and native double-stranded nucleic acids. Notably, the selectivity of the linear dibenzo[b,g]quinolizinium 5a toward triplex DNA is higher than the one of the angular derivative 6. In contrast, the DNA thermal denaturation studies reveal a higher stabilization of triple-helical DNA in the presence of 6 (DeltaTm3-->2 = 28 degrees C at r = 0.5) as compared to the stabilization by 5a (DeltaTm3-->2 = 14 degrees C at r = 0.5). This comparison emphasizes the importance of the extended pi system for the interaction of annelated quinolizinium ions with DNA. Moreover, the comparison between 5a and 6 demonstrates the significant influence of the shape of the pi system on the duplex- and triplex-stabilizing properties of the dibenzoquinolizinium ions.

The synthesis and nicotinic binding activity of (±)-epiquinamide and (±)-C(1)-epiepiquinamide

The synthesis of (+/-)-epiquinamide 1 and (+/-)-C(1)-epiepiquinamide 2 based on the use of a Curtius rearrangement to introduce the C(1) amino residue is reported. In a competition binding assay for [(3)H]epibatidine binding to rat brain membranes neither (+/-)-1 nor (+/-)-2 showed any significant level of nicotinic activity.

Total Synthesis of Clavepictines A and B and Pictamine

[Structure: see text] A short route for assembling clavepictines A and B and pictamine is described, which features elaboration of its trisubstituted piperidine moiety via condensation of a beta-keto sulfone with an l-alanine-derived bromide and subsequent alkylative cyclization and construction of its quinolizidine skeleton via a diastereoselective intramolecular conjugate addition. The possible stereochemical course for this conjugate addition is discussed.

Synthesis and pharmacological evaluation of novel 9- and 10-substituted cytisine derivatives. Nicotinic ligands of enhanced subtype selectivity

We report the synthesis and pharmacological properties of several cytisine derivatives. Among them, two 10-substituted derivatives showed much higher selectivities for the alpha4beta2 nAChR subtype in binding assays than cytisine. The 9-vinyl derivative was found to have a very similar agonist activity profile to that of cytisine.

A Versatile Approach for the Asymmetric Syntheses of (1R,9aR)-Epiquinamide and (1R,9aR)-Homopumiliotoxin 223G

[reaction: see text] Using 5b as a common intermediate, the first asymmetric synthesis of (-)-epiquinamide (4) and a formal asymmetric synthesis of (-)-homopumiliotoxin 223G (2) is described. A key feature of our approach is the flexible introduction of a functionalized C(4) side chain to (S)-3-benzyloxyglutarimide 7 in a regio- and diastereoselective manner. Utilization of a tandem Swern oxidation-Grignard addition strategy efficiently prevented racemization. An unexpected NaN(3)-promoted methanesulfonic acid elimination yielded 17, a reaction which could be useful for the syntheses of 8-dehydrodesmethylpumiliotoxins such as alkaloid 235C (3).

Expedient synthesis and structure-activity relationships of phenanthroindolizidine and phenanthroquinolizidine alkaloids

The total synthesis of alkaloids phenanthroindolizidine 1a, tylophorine 1b, and phenanthroquinolizidine 1c, has been achieved in 46%, 49%, and 42% overall yield, respectively, starting from the corresponding phenanthrene-9-carboxaldehyde. Compound exhibited potent inhibition activity in three human cancer cell lines, with IC(50) values ranging from 104 to 130 nM. The structure-activity relations of these alkaloids and some of their synthetic intermediates against the three cell lines were also described.

Anion Relay Chemistry: An Effective Tactic for Diversity Oriented Synthesis

An effective one-flask multicomponent linchpin coupling protocol employing the concept of anion relay chemistry (ARC) was developed. This concept calls for addition of an anion (5) to an epoxide (6), bearing on a distal carbon a trialkyl silyl group and an anion stabilizing group (ASG), to furnish upon epoxide ring opening oxyanion 7. Addition of HMPA or other polar solvents to trigger a solvent controlled 1,4-Brook rearrangement then leads to a new distal anion (8), which in turn is available to react with a variety of second electrophiles.

Parallel Synthesis of 3-Amino-4H-Quinolizin-4-ones, Fused 3-Amino-4H-Pyrimidin-4-ones, and Fused 3-Amino-2H-Pyran-2-ones

On the basis of the enaminone methodology, libraries of 3-amino-4H-quinolizin-4-ones, fused 3-amino-4H-pyrimidin-4-ones, and fused 3-amino-2H-pyran-2-ones were synthesized by the solid-phase and by the solution-phase parallel synthesis. The solution-phase approach turned out to be advantageous over the solid-phase approach. The solution-phase synthesis afforded, in most cases, analytically pure products in high yields, whereas the solid-phase approach gave products in poor yields and in low purity.

4-Aminoquinoline quinolizidinyl- and quinolizidinylalkyl-derivatives with antimalarial activity

A set of quinolizidinyl and quinolizidinylalkyl derivatives of 4-amino-7-chloroquinoline and of 9-amino-6-chloro-2-methoxyacridine were prepared and tested in vitro against CQ-sensitive (D-10) and CQ-resistant (W-2) strains of Plasmodium falciparum. All compounds but one exerted significant antimalarial activity. Some of the quinolizidine derivatives were from 5 to 10 times more active than chloroquine on the CQ-resistant strain. No toxicity against mammalian cells was observed.

A Six-Step Asymmetric Synthesis of (+)-Hyperaspine

[reaction: see text] The ladybird alkaloid, (+)-hyperaspine, has been synthesized in a concise and highly stereoselective manner. The total synthesis was accomplished in six steps and 21% overall yield.

Stereocontrolled Synthesis of the DE Ring System of the Marine Alkaloid Upenamide

[reaction: see text] A stereocontrolled synthesis of the DE fragment (2) of the marine alkaloid upenamide (1) is described. The synthesis proceeds in 12 steps from caprolactone (10) and 20-25% overall yield.

Concise Synthesis of (±)-Cytisine via Lithiation of N-Boc-bispidine

[reaction: see text] (+/-)-Cytisine has been synthesized in 19% overall yield via a six-step approach from commercially available materials. Key features of this new strategy are as follows: (i) initial construction of the bispidine core, (ii) lithiation-transmetalation-allylation of an N-Boc-bispidine, and (iii) a Pd/C-mediated dihydropyridone oxidation-N-debenzylation process.