Conofolidine, a Natural Plant Alkaloid Causes Apoptosis and Senescence in Cancer Cells

Natural products contribute substantially to anticancer therapy; the plant kingdom provides an important source of molecules. Conofolidine is a novel Aspidosperma-Aspidosperma bisindole alkaloid isolated from the Malayan plant Tabernaemontana corymbosa. Herein, we report conofolidine’s anticancer activity together with that of three other bisindoles - conophylline, leucophyllidine and bipleiophylline against human-derived carcinoma cell lines. Remarkably, conofolidine was able to induce apoptosis (as observed in MDA-MB-468 breast cancer cells) or senescence (as detected in HT-29 colorectal carcinoma cells). Annexin V-FITC/PI, caspase activation and PARP cleavage confirmed the former while positive β-gal staining corroborated the latter. Evident cell cycle perturbations were observed comprising S-phase depletion, accompanied by downregulated CDK2, and cyclins (A2, D1) with p21 upregulation. Confocal imaging of HCT-116 cells revealed induction of aberrant mitotic phenotypes - multi-nucleation, membrane blebbing and DNA-fragmentation. The DNA integrity assessment of HCT-116 and MDA-MB-468 showed irreparable damage identified by increased fluorescent γ-H2AX during the G1 cell cycle phase. Furthermore, γ-H2AX foci were visually validated in HCT-116 and MDA-MB-468 cells using confocal microscopy. Conofolidine increased oxidative stress, preceding apoptosis- and senescence-induction in most carcinoma cell lines as seen by enhanced ROS levels accompanied by NQO1 expression. Collectively, we present conofolidine as a potential anticancer candidate capable of inducing heterogeneous modes of cancer cell death in vitro, encouraging further preclinical evaluation of this natural product

Indole and bisindole alkaloids from Tabernaemontana corymbosa / Nge Choy Eng

A total of 59 alkaloids (1−59) were isolated and characterized from the leaf and stem-bark extracts of the Malayan Tabernaemontana corymbosa Roxb. ex Wall.. Of these, 25 are new alkaloids. Among the new alkaloids, the pentacyclic alkaloids, voatinggine (1) and tabertinggine (2), which are postulated to derive from a common cleavamine-type precursor, the hexacyclic iboga-derived indole, cononuridine 3, the pentacyclic indoles, criofolinine (4) and vernavosine (5) incorporating pyrroloazepine and pyridopyrimidine moieties, respectively, are notable for incorporating novel or intriguing molecular skeletons. Other new alkaloids isolated from this study include a seco-yohimbine (taberisidine, 7), five iboga (conodusines A−E, 8−12), seven Aspidosperma (apocidines A−G, 20−26), three vincamine (conoduzidines A−C, 30−32), one heteroyohimbine [16α-methoxycarbonyl-16,17-dihydro-19-epi-ajmalicine, 34], two iboga-vobasinyl bisindoles, tabernamidines A and B (55, 56) and one Aspidosperma-Aspidosperma bisindole alkaloid (conofolidine, 59). Two of the iboga alkaloids, conodusines B and C (9, 10) and the iboga containing bisindole (tabernamidine B, 56) are notable for the presence of an α-substituted acetyl group at C-20 of the iboga carbon skeleton (naturally-occurring iboga alkaloids with C-20 substitution by ethyl, hydroxyethyl, or acetyl groups, are usually β-oriented). Conofolidine (59) showed pronounced cytotoxicity toward human KB/S, KB/VJ300(−), KB/VJ300(+), PC-3, LNCaP, MCF7, MDA-MB-231, HT-29, and HCT 116 cancer cells (IC50 0.2−5.9 μg/mL)

Diversity and Biosynthetic Potential of Fungi Isolated from St. John’s Island, Singapore

Adaptation to a wide variety of habitats allows fungi to develop unique abilities to produce diverse secondary metabolites with diverse bioactivities. In this study, 30 Ascomycetes fungi isolated from St. John’s Island, Singapore were investigated for their general biosynthetic potential and their ability to produce antimicrobial secondary metabolites (SMs). All the 30 fungal isolates belong to the Phylum Ascomycota and are distributed into 6 orders and 18 genera with Order Hypocreales having the highest number of representative (37%). Screening for polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) genes using degenerate PCR led to the identification of 23 polyketide synthases (PKSs) and 5 nonribosomal peptide synthetases (NRPSs) grouped into nine distinct clades based on their reduction capabilities. Some of the identified PKSs genes share high similarities between species and known reference genes, suggesting the possibility of conserved biosynthesis of closely related compounds from different fungi. Fungal extracts were tested for their antimicrobial activity against S. aureus, Methicillin-resistant S. aureus (MRSA), and Candida albicans. Bioassay-guided fractionation of the active constituents from two promising isolates resulted in the isolation of seven compounds: Penilumamides A, D, and E from strain F4335 and xanthomegnin, viomellein, pretrichodermamide C and vioxanthin from strain F7180. Vioxanthin exhibited the best antibacterial activity with IC50 values of 3.0 μM and 1.6 μM against S. aureus and MRSA respectively. Viomellein revealed weak antiproliferative activity against A549 cells with an IC50 of 42 μM. The results from this study give valuable insights into the diversity and biosynthetic potential of fungi from this unique habitat and forms a background for an in-depth analysis of the biosynthetic capability of selected strains of interest with the aim of discovering novel fungal natural products

Voatinggine and Tabertinggine, Pentacyclic Indole Alkaloids Derived from an Iboga Precursor via a Common Cleavamine-Type Intermediate

Two new indole alkaloids, voatinggine (1) and tabertinggine (2), which are characterized by previously unencountered natural product skeletons, were isolated from a Malayan <i>Tabernaemontana</i> species. The structures and absolute configuration of these alkaloids were determined using NMR and MS analysis, and X-ray diffraction analysis. A possible biogenetic pathway to these novel alkaloids from an iboga precursor, and via a common cleavamine-type intermediate, is presented

A Hexacyclic, Iboga-Derived Monoterpenoid Indole with a Contracted Tetrahydroazepine C‑Ring and Incorporation of an Isoxazolidine Moiety, a <i>Seco</i>-Corynanthean, an <i>Aspidosperma-Aspidosperma</i> Bisindole with Anticancer Properties, and the Absolute Configuration of the Pyridopyrimidine Indole Alkaloid, Vernavosine

Examination of the EtOH extract of the Malayan <i>Tabernaemontana corymbosa</i> resulted in the isolation of three new alkaloids, viz., cononuridine (<b>1</b>), an unusual hexacyclic, iboga-derived, monoterpenoid indole characterized by contraction of the tetrahydroazepine C-ring and incorporation of an additional isoxazolidine ring, taberisidine (<b>2</b>), a <i>seco</i>-corynanthean alkaloid, and conofolidine (<b>3</b>), an <i>Aspidosperma</i>-<i>Aspidosperma</i> bisindole that showed pronounced in vitro growth inhibitory activity against an array of human cancer cell lines, including KB, vincristine-resistant KB, PC-3, LNCaP, MCF7, MDA-MB-231, HT-29, and HCT 116 cells. The structures and absolute configurations of <b>1</b> and <b>3</b> and the absolute configuration of the novel pyridopyrimidine indole alkaloid vernavosine (<b>4</b>) were confirmed by X-ray diffraction analysis. A reasonable biosynthesis route to cononuridine starting from an iboga precursor is presented

Criofolinine and Vernavosine, New Pentacyclic Indole Alkaloids Incorporating Pyrroloazepine and Pyridopyrimidine Moieties Derived from a Common Yohimbine Precursor

Two new indole alkaloids characterized by previously unencountered natural product skeletons, viz., criofolinine (<b>1</b>), incorporating a pyrroloazepine motif within a pentacyclic ring system, and vernavosine (<b>2</b>, isolated as its ethyl ether derivative <b>3</b>, which on hydrolysis regenerated the putative precursor alkaloid <b>2</b>), incorporating a pyridopyrimidine moiety embedded within a pentacyclic carbon framework, were isolated from a Malayan <i>Tabernaemontana</i> species. The structures and absolute configuration of these alkaloids were determined on the basis of NMR and MS analysis and confirmed by X-ray diffraction analysis

Ibogan, Aspidosperman, Vincamine, and Bisindole Alkaloids from a Malayan <i>Tabernaemontana corymbosa</i>: Iboga Alkaloids with C‑20α Substitution

Ten new indole alkaloids (<b>1</b>–<b>10</b>) comprising five ibogan, two aspidosperman, one vincamine, and two bisindole alkaloids, in addition to 32 known alkaloids, were isolated from the stem-bark extract of a Malayan <i>Tabernaemontana corymbosa</i>. The structures of these alkaloids were determined based on analysis of the NMR and MS data and, in five instances (<b>1</b>, <b>3</b>, <b>5</b>, <b>6</b>, <b>8</b>), confirmed by X-ray diffraction analysis. Two of the iboga alkaloids, conodusines B (<b>2</b>) and C (<b>3</b>), and the iboga-containing bisindole tabernamidine B (<b>10</b>) are notable for the presence of an α-substituted acetyl group at C-20 of the iboga carbon skeleton. The iboga alkaloid (+)-conodusine E (<b>5</b>) had MS and NMR data that were identical to those of (−)-ervatamine I, recently isolated from <i>Ervatamia hainanensis</i>. Establishment of the absolute configuration of (+)-conodusine E (<b>5</b>) was based on analysis of the ECD data, correlation with (−)-heyneanine, and X-ray analysis, which showed that (+)-<b>5</b> belongs to the same enantiomeric series as exemplified by (−)-coronaridine. The configuration at C-20′ of the previously reported <i>Tabernaemontana</i> bisindole alkaloid 19′-oxotabernamine (renamed tabernamidine B) required revision based on the present results. Several of the bisindoles showed pronounced in vitro growth inhibitory activity against drug-sensitive and vincristine-resistant KB cells

A Hexacyclic, Iboga-Derived Monoterpenoid Indole with a Contracted Tetrahydroazepine C‑Ring and Incorporation of an Isoxazolidine Moiety, a <i>Seco</i>-Corynanthean, an <i>Aspidosperma-Aspidosperma</i> Bisindole with Anticancer Properties, and the Absolute Configuration of the Pyridopyrimidine Indole Alkaloid, Vernavosine

Examination of the EtOH extract of the Malayan <i>Tabernaemontana corymbosa</i> resulted in the isolation of three new alkaloids, viz., cononuridine (<b>1</b>), an unusual hexacyclic, iboga-derived, monoterpenoid indole characterized by contraction of the tetrahydroazepine C-ring and incorporation of an additional isoxazolidine ring, taberisidine (<b>2</b>), a <i>seco</i>-corynanthean alkaloid, and conofolidine (<b>3</b>), an <i>Aspidosperma</i>-<i>Aspidosperma</i> bisindole that showed pronounced in vitro growth inhibitory activity against an array of human cancer cell lines, including KB, vincristine-resistant KB, PC-3, LNCaP, MCF7, MDA-MB-231, HT-29, and HCT 116 cells. The structures and absolute configurations of <b>1</b> and <b>3</b> and the absolute configuration of the novel pyridopyrimidine indole alkaloid vernavosine (<b>4</b>) were confirmed by X-ray diffraction analysis. A reasonable biosynthesis route to cononuridine starting from an iboga precursor is presented

Cytotoxic Vobasine, Tacaman, and Corynanthe-Tryptamine Bisindole Alkaloids from <i>Tabernaemontana</i> and Structure Revision of Tronoharine

Seven new indole alkaloids (<b>1</b>–<b>7</b>) comprising four vobasine, two tacaman, and one corynanthe-tryptamine bisindole alkaloid were isolated from the stem-bark extract of a Malayan <i>Tabernaemontana</i>. Two of the new vobasine alkaloids (<b>1</b>, <b>3</b>), as well as 16-epivobasine (<b>15</b>) and 16-epivobasenal (<b>17</b>), showed appreciable cytotoxicity toward KB cells (IC₅₀ ca. 5 μg/mL). The structure of the known <i>Tabernaemontana</i> alkaloid tronoharine (<b>8</b>) was revised based on newly acquired NMR data, as well as X-ray diffraction analysis

Cytotoxic Vobasine, Tacaman, and Corynanthe-Tryptamine Bisindole Alkaloids from <i>Tabernaemontana</i> and Structure Revision of Tronoharine

Seven new indole alkaloids (<b>1</b>–<b>7</b>) comprising four vobasine, two tacaman, and one corynanthe-tryptamine bisindole alkaloid were isolated from the stem-bark extract of a Malayan <i>Tabernaemontana</i>. Two of the new vobasine alkaloids (<b>1</b>, <b>3</b>), as well as 16-epivobasine (<b>15</b>) and 16-epivobasenal (<b>17</b>), showed appreciable cytotoxicity toward KB cells (IC₅₀ ca. 5 μg/mL). The structure of the known <i>Tabernaemontana</i> alkaloid tronoharine (<b>8</b>) was revised based on newly acquired NMR data, as well as X-ray diffraction analysis