Synthesis and structure–activity relationships of cassiarin A as potential antimalarials with vasorelaxant activity

Facile synthesis of isoquinolines and isoquinoline N-oxides via a copper-catalyzed intramolecular cyclization in water

A highly efficient method for the facile access of isoquinolines and isoquinoline N-oxides via a Cu(i)-catalyzed intramolecular cyclization of (E)-2-alkynylaryl oxime derivatives in water has been developed. This protocol was performed under simple and mild conditions without organic solvent, additives or ligands. By switching on/off a hydroxyl protecting group of oximes, the selective N-O/O-H cleavage could be triggered, delivering a series of isoquinolines and isoquinoline N-oxides, respectively, in moderate to high yields with good functional group tolerance and high atom economy. Moreover, the practicality of this method was further demonstrated by the total synthesis of moxaverine in five steps.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

First total synthesis of ampullosine, a unique isoquinoline alkaloid isolated from Sepedonium ampullosporum, and of the related permethylampullosine

A straightforward and convenient approach toward the first total synthesis of ampullosine, a structurally unique 3-methylisoquinoline alkaloid isolated from Sepedonium ampullosporum, is reported. Access to the related O-methyl ampullosine methyl ester from a common intermediate is also disclosed. The synthetic sequence toward the natural product comprised a Kolbe-type carboxylation of 3,5-dihydroxybenzoic acid and further esterification of the diacid, followed by masking of one of the phenols through selective ester reduction and subsequent acetonide formation. Installation of the three-carbon atom required for the 3-methylpyridine ring was performed by triflation of the remaining free phenol and a Pd-catalyzed Suzuki–Miyaura reaction with potassium E-propenyltrifluoroborate. Deprotection of the acetonide, followed by partial oxidation of the benzylic alcohol to the salicylaldehyde, O-methylation of the free phenol and hydrazonation of the resulting ortho-anisaldehyde derivative gave a hydrazone-based 1-azatriene. This was further subjected to 6π-azaelectrocyclization to afford permethylampullosine (11 steps, 14% overall yield), whereas exhaustive demethylation with AlI₃ generated in situ gave ampullosine (12 steps, 3.2% global yield).

The first total synthesis of ampullosine, a unique isoquinoline isolated from Sepedonium ampullosporum, is reported. The related permethylampullosine was also synthesized.

Chemical Constituents and Bioactivities of Several Indonesian Plants Typically Used in Jamu

This article reviews the chemical constituents and bioactivities of several Indonesian plants typically used in Jamu prescriptions in Indonesia. Jamu is Indonesia traditional medicine: it consists of either a single ingredient or a mixture of several medicinal plants. One plant family always used in Jamu is Zingiberaceae (ginger), such as Curcuma domestica/C. longa, C. xanthorrhizae, C. heyneana, C. zedoaria, C. aeruginosa, Zingiber aromaticum, Alpinia galanga. We also report other commonly used plant families such as Justicia gendarussa and Cassia siamea, whose activities have been extensively explored by our department.

Inverse docking based screening and identification of protein targets for Cassiarin alkaloids against Plasmodium falciparum

Various reports have shown Cassiarin alkaloids, selective in vitro activities against various strains of Plasmodium falciparum with low cytotoxicity, which indicates their possible candidature as antimalarial drug. However, poor recognition of their protein targets and molecular binding behaviour, certainly limits their exploration as antimalarial drug candidature. To address this, we utilises inverse screening, based on three different docking methodologies in order to find their most putative protein targets. In our study, we screened 1047 protein structures from protein data bank, which belongs to 147 different proteins. Our investigation identified 16 protein targets for Cassiarins. In few cases of identified protein targets, the binding site was poorly studied, which encouraged us to perform comparative sequence and structural studies with their homologous proteins, like as in case of Kelch motif associated protein, Armadillo repeats only protein and Methionine aminopeptidase 1b. In our study, we also found Tryptophanyl-tRNA synthetase and 1-Deoxy-D-Xylose-5-phosphate reductoisomerase proteins are the most common targets for Cassiarins.

Cnidimonins A-C, Three Types of Hybrid Dimer from Cnidium monnieri: Structural Elucidation and Semisynthesis

Three pairs of racemic dimers, (±)-cnidimonins A-C (1-3), were isolated from the fruits of Cnidium monnieri. They represent novel hybrid-dimerization patterns of coumarin skeleton with structurally diverse units (flavonol, benzofuran, and chromone) via an unprecedented terminal chiral carbon of prenyl. The absolute configurations of the enantiomers were determined by electronic circular dichroism (ECD). To investigate their bioactivities in depth, (±)-cnidimonins A-C (1-3) were synthesized. The racemic mixture (±)-1 exhibited stronger antiviral activity against HSV-1 (IC₅₀: 1.23 μM) than its corresponding optically pure enantiomers.

Highly efficient and facile fabrication of monodispersed Au nanoparticles using pullulan and their application as anticancer drug carriers

This work presented a simple, rapid, green and efficient approach to the synthesis of gold nanoparticles using pullulan as a reducing/stabilizing/capping agent for drug delivery systems to increase the safety and efficacy of these systems. Monodispersed AuNPs@pullulan with prolonged stability were fully characterized by UV-VIS, FTIR, TEM, EDX, TGA and zeta potential analyses. A mechanism of AuNPs formation was proposed in which pullulan created reducing species for the reduction of Au³⁺ to AuNPs (Au⁰) that resulted in the formation of spherical AuNPs@pullulan with an average size of approximately 11±5nm, while the hydroxyl groups of pullulan were oxidized to carboxylate compounds. Novel cassiarin A chloride derivatives (3d and 3i) as candidate anticancer drugs were successfully loaded onto AuNPs@pullulan through electrostatic interactions. AuNPs@pullulan-3d (IC₅₀=6.0±0.1μM) and AuNPs@pullulan-3i (5.2±0.1μM) exhibited a 10.2-fold and 7.1-fold higher cytotoxicity against KATO-III cells than free compounds 3d (60.9±0.6μM), 3i (37.1±0.2μM) and cisplatin (64.5±0.9μM), respectively. AuNPs@pullulan exhibited high cellular uptake, biocompatibility and non-cytotoxicity to normal cells. Therefore, AuNPs@pullulan-3d or AuNPs@pullulan-3i have the potential to be developed for treatment of gastric cancer.

Synthesis of Natural Product-like Polyheterocycles via One-Pot Cascade Oximation, C-H Activation, and Alkyne Annulation

An efficient protocol for the direct transformation of chroman-4-ones to tricyclic fused pyridines with the skeleton of cassiarins, a family of alkaloids with antimalarial activity, was developed. Also, a general strategy for modular construction of polyheterocycles with diverse natural product-like skeletons was developed by using ketone-alkyne bifunctional substrates. These reactions involved a one-pot cascade oximation of ketones, rhodium-catalyzed C-H activation, and intermolecular/intramolecular alkyne annulations under mild conditions with high atom, step, and redox economy.

Alstiphyllanines I-O, ajmaline type alkaloids from Alstonia macrophylla showing vasorelaxant activity

Seven new ajmaline type alkaloids, alstiphyllanines I-O (1-7) were isolated from the leaves of Alstonia macrophylla together with six related alkaloids (8-13). Structures and stereochemistry of 1-7 were fully elucidated and characterized by 2D NMR analysis. A series of alstiphyllanines I-O (1-7) as well as the known ajmaline type alkaloids (8-13) showed that they relaxed phenylephrine (PE)-induced contractions against rat aortic ring. Among them, vincamedine (10) showed potent vasorelaxant activity, which may be mediated through inhibition of Ca(2+) influx through voltage-dependent Ca(2+) channels (VDCs) and/or receptor-operated Ca(2+) channels (ROCs) as well as partially mediated the NO release from endothelial cells. The presence of substituents at both N-1 and C-17 may be important to show vasorelaxation activity.

Vasorelaxant activity of indole alkaloids from Tabernaemontana dichotoma

The aim of this study was to search for bioactive natural products from medicinal plants targeting vasorelaxant activity and we found the methanol extract from bark of Tabernaemontana dichotoma showed vasorelaxant activity on rat aorta. We isolated eight indole alkaloids including 10-methoxyalstonerine (1), a new macroline type indole alkaloid, from bark of T. dichotoma. These were respectively identified as 10-methoxyaffinisine (2), lochnerine (3), cathafoline (4), (-)-alstonerine (5), 19,20-dehydro-10-methoxytalcarpine (6), alstonisine (7), and alstonal (8) based on spectroscopic analysis. Among them, sarpagine type (2 and 3), akuammiline type (4), and macroline oxindole type (7 and 8) showed potent vasorelaxant activity. Mechanism of action on vasorelaxant activity of 10-methoxyaffinisine (2), cathafoline (4), and alstonisine (7) was clarified. Effects of 10-methoxyaffinisine (2), cathafoline (4), and alstonisine (7) were partially mediated the NO release from endothelial cells. Furthermore, 10-methoxyaffinisine (2) and alstonisine (7) attribute to the inhibitory effect of VDC and ROC, and cathafoline (4) have inhibitory effect on Ca(2+) influx via ROC. In addition, 10-methoxyaffinisine (2) as a major compound from bark of T. dichotoma showed hypotensive effect on normotensive rats in vivo.

Vasorelaxant effect of isoquinoline derivatives from two species of Popowia perakensis and Phaeanthus crassipetalus on rat aortic artery

Five bisbenzyl isoquinolines (1-5), three benzyl isoquinolines (6-8), four isoquinoline alkaloids (9-12), and two unclassified compounds (13 and 14) from Popowia perakensis and Phaeanthus crassipetalus were evaluated for their vasorelaxant effect on rat aortic arteries. In aortic rings pre-contracted with phenylephrine (PE, 0.3 μM), some of the bisbenzyl isoquinoline alkaloids, benzyl isoquinoline alkaloids, and isoquinoline alkaloids showed clearly vasorelaxant effects at 30 μM. The action of (-)-limacine (4) was deduced to be mediated through the increased release of NO from endothelial cells, and that of pecrassipine A (7) and backebergine (12) partly mediated by NO release. Further, the action of pecrassipine A (7) and backebergine (12) may be attributed to their inhibition of the voltage-dependent Ca(2+) channel and receptor-operated Ca(2+) channel.

Concise synthesis of 5-methoxy-6-hydroxy-2-methylchromone-7-O- and 5-hydroxy-2-methylchromone-7-O-rutinosides. Investigation of their cytotoxic activities against several human tumor cell lines

The synthesis of two novel 2-methylchromone-7-O-rutinosides is reported, and the in vitro biological activities of these compounds and their synthetic precursors have been investigated on the basis of their cytotoxicity against several human tumor cell lines. The synthesis features early stage assembly of the acidic labile glycosidic bond between sugar and 2-methylchromone aglycon under phase transfer catalyzed glycosidation conditions, whereas all the other standard glycosylation conditions specific to a wide array of rutinosyl donors bearing different anomeric leaving groups (e.g., SPh, OC(NH)CCl(3), Br, OH groups) failed to furnish any detectable products.

Vasodilator effect of Cassiarin A, a novel antiplasmodial alkaloid from Cassia siamea, in rat isolated mesenteric artery

The aim of this study was to investigate the vasorelaxant effect induced by cassiarin A, a novel antiplasmodial alkaloid from Cassia siamea, in rings cut from rat superior mesenteric arteries. In rings precontracted with phenylephrine, cassiarin A induced a concentration-dependent relaxation. This relaxation was attenuated: 1) after removal of the endothelium or after pretreatment of rings with 100 microM of N(G)-nitro-L-arginine (nitric oxide synthase inhibitor) or 10 microM of 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one (guanylyl cyclase inhibitor), but not after pretreatment with 10 microM of indomethacin (cyclooxygenase inhibitor); and 2) after pretreatment of preparations with either a nonselective or selective inhibitor of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels [1 mM of tetraethylammonium or 100 nM of iberiotoxin, respectively]. The cassiarin A-induced relaxation was also attenuated by these BK(Ca) inhibitors in endothelium-denuded preparations. The cassiarin A-induced relaxation was not altered by treatment with the ATP-sensitive K(+)-channel inhibitor glibenclamide (10 microM) or with the voltage-dependent K(+)-channel inhibitor 4-aminopyridine (1 mM). In isolated mesenteric artery rings, cassiarin A tended to increase nitric oxide (NO) levels. These results suggest that in the rat mesenteric artery, cassiarin A-induced relaxation may be mediated by endothelial NO and may occur partly via BK(Ca)-channel activation.