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Angustilobine and andranginine type indole alkaloids and an uleine-secovallesamine bisindole alkaloid from Alstonia angustiloba

Ku WF, Tan SJ, Low YY, Komiyama K, Kam TS

Phytochemistry, 2011 Dec;72(17):2212-8.

PMID: 21889176 DOI: 10.1016/j.phytochem.2011.08.001

A total of 20 alkaloids were isolated from the leaf and stem-bark extracts of Alstonia angustiloba, of which two are hitherto unknown. One is an alkaloid of the angustilobine type (angustilobine C), while the other is a bisindole alkaloid angustiphylline, derived from the union of uleine and secovallesamine moieties. The structures of these alkaloids were established using NMR and MS analysis. Angustilobine C showed moderate cytotoxicity towards KB cells.

Aspidospermatan-aspidospermatan and eburnane-sarpagine bisindole alkaloids from Leuconotis

Gan CY, Low YY, Robinson WT, Komiyama K, Kam TS

Phytochemistry, 2010 Aug;71(11-12):1365-70.

PMID: 20542302 DOI: 10.1016/j.phytochem.2010.05.015

Leucofoline and leuconoline, representing the first members of the aspidospermatan-aspidospermatan and eburnane-sarpagine subclasses of the bisindole alkaloids, respectively, were isolated from the Malayan Leuconotis griffithii. The structures of these bisindole alkaloids were established using NMR and MS analysis, and in the case of leuconoline, confirmed by X-ray diffraction analysis. Both alkaloids showed weak cytotoxicity towards human KB cells.

Strychnan and secoangustilobine A type alkaloids from Alstonia spatulata. Revision of the C-20 configuration of scholaricine

Tan SJ, Low YY, Choo YM, Abdullah Z, Etoh T, Hayashi M, et al.

J Nat Prod, 2010 Nov 29;73(11):1891-7.

PMID: 21043460 DOI: 10.1021/np100552b

A total of 25 alkaloids were isolated from the leaf and stem-bark extracts of Alstonia spatulata, of which five are new alkaloids of the strychnan type (alstolucines A-E, 1-5) and the other, a new alkaloid of the secoangustilobine A type (alstolobine A, 6). The structures of these alkaloids were established using NMR and MS analysis and, in the case of alstolucine B (2), also confirmed by X-ray diffraction analysis. A reinvestigation of the stereochemical assignment of scholaricine (13) by NMR and X-ray analyses indicated that the configuration at C-20 required revision. Alkaloids 1, 2, 6, 7, 9, 10, and 13 reversed multidrug resistance in vincristine-resistant KB cells.

Leuconicines A-G and (-)-eburnamaline, biologically active strychnan and eburnan alkaloids from Leuconotis

Gan CY, Low YY, Etoh T, Hayashi M, Komiyama K, Kam TS

J Nat Prod, 2009 Dec;72(12):2098-103.

PMID: 20035556 DOI: 10.1021/np900576b

Seven new indole alkaloids of the Strychnos type, leuconicines A-G (1-7), and a new eburnan alkaloid, (-)-eburnamaline (8), were isolated from the stem-bark extract of two Malayan Leuconotis species. The structures of these alkaloids were established using NMR and MS analysis and in the case of 8 also by partial synthesis. Alkaloids 1-5 reversed multidrug resistance in vincristine-resistant KB cells.

Leucophyllidine, a cytotoxic bisindole alkaloid constituted from the union of an eburnan and a new vinylquinoline alkaloid

Gan CY, Robinson WT, Etoh T, Hayashi M, Komiyama K, Kam TS

Org. Lett., 2009 Sep 3;11(17):3962-5.

PMID: 19708704 DOI: 10.1021/ol9016172

A cytotoxic bisindole alkaloid possessing an unprecedented structure constituted from the union of an eburnan half and a novel vinylquinoline alkaloid has been isolated from Leuconotis griffithii. The structure was established by analysis of the spectroscopic data and confirmed by X-ray diffraction analysis. A possible biogenetic pathway to the novel quinolinic coupling partner is presented from an Aspidosperma precursor.

Biologically active aspidofractinine alkaloids from Kopsia singapurensis

Subramaniam G, Hiraku O, Hayashi M, Koyano T, Komiyama K, Kam TS

J Nat Prod, 2008 Jan;71(1):53-7.

PMID: 18078327

Ten new indole alkaloids of the aspidofractinine type, in addition to several recently reported indole alkaloids and 20 other known alkaloids, were obtained from the leaf and stem-bark extract of the Malayan Kopsia singapurensis, viz., kopsimalines A-E (1-5), kopsinicine (6), kopsofinone (7), and kopsiloscines H-J (8-10). The structures of these alkaloids were determined using NMR and MS analysis. Kopsimalines A (1), B (2), C (3), D (4), and E (5) and kopsiloscine J (10) were found to reverse multidrug-resistance in vincristine-resistant KB cells, with 1 showing the highest potency.

Biologically active aspidofractinine, rhazinilam, akuammiline, and vincorine alkaloids from Kopsia

Subramaniam G, Hiraku O, Hayashi M, Koyano T, Komiyama K, Kam TS

J Nat Prod, 2007 Nov;70(11):1783-9.

PMID: 17939738

Eleven new indole alkaloids, in addition to the previously reported rhazinal (1), and 14 other known alkaloids, were obtained from the Malayan Kopsia singapurensis, viz., kopsiloscines A-F (2-7), 16-epikopsinine (8), kopsilongine- N-oxide (9), 16-epiakuammiline (10), aspidophylline A (11), and vincophylline (12). The structures of these alkaloids were determined using NMR and MS analyses. Rhazinal (1), rhazinilam (17), and rhazinicine (18) showed appreciable cytotoxicity toward drug-sensitive as well as vincristine-resistant KB cells, while kopsiloscines A (2), B (3), and D (5) and aspidophylline A (11) were found to reverse drug-resistance in drug-resistant KB cells.

Leuconoxine, kopsinitarine, kopsijasmine, and kopsinone derivatives from Kopsia

Lim SH, Sim KM, Abdullah Z, Hiraku O, Hayashi M, Komiyama K, et al.

J Nat Prod, 2007 Aug;70(8):1380-3.

PMID: 17608533

Four new indole alkaloids were obtained from two Kopsia species, 6-oxoleuconoxine (1) from the leaf extract of K. griffithii and kopsinitarine E (2), kopsijasminine (3), and kopsonoline (4) from the stem-bark extract of K. teoi. The structures of these alkaloids were determined using NMR and MS analysis. Kopsijasminine (3) showed moderate activity in reversing multidrug resistance in vincristine-resistant KB cells.

Biologically active indole alkaloids from Kopsia arborea

Lim KH, Hiraku O, Komiyama K, Koyano T, Hayashi M, Kam TS

J Nat Prod, 2007 Aug;70(8):1302-7.

PMID: 17665953

Nine new indole alkaloids, rhazinoline (1), 19(S)-methoxytubotaiwine (2), 19(R)-methoxytubotaiwine (3), kopsamidine A (4), kopsamidine B (5), kopsinidine A (6), kopsinidine B (7), paucidactine C (8), and pericine N-oxide (9), in addition to several recently reported novel indoles and 34 other known ones, were obtained from the stem-bark extract of the Malayan Kopsia arborea. The structures were determined using NMR and MS analysis. Valparicine (12) showed pronounced cytotoxic effects against KB and Jurkat cells (IC(50) 13.0 and 0.91 microM, respectively).

Lumusidines A-D and villalstonidine F, macroline-macroline and macroline-pleiocarpamine bisindole alkaloids from Alstonia macrophylla

Lim SH, Low YY, Subramaniam G, Abdullah Z, Thomas NF, Kam TS

Phytochemistry, 2013 Mar;87:148-56.

PMID: 23200029 DOI: 10.1016/j.phytochem.2012.11.005

Lumusidines A-D, bisindole alkaloids of the macroline-macroline type, and one of the macroline-pleiocarpamine type, villalstonidine F, were isolated from the stem-bark extract of Alstonia macrophylla (Apocynaceae). The structures and absolute configurations of these alkaloids were established using NMR, MS, and X-ray diffraction analyses.

Ibogan, Aspidosperman, Vincamine, and Bisindole Alkaloids from a Malayan Tabernaemontana corymbosa: Iboga Alkaloids with C-20α Substitution

Nge CE, Chong KW, Thomas NF, Lim SH, Low YY, Kam TS

J Nat Prod, 2016 05 27;79(5):1388-99.

PMID: 27077800 DOI: 10.1021/acs.jnatprod.6b00129

Ten new indole alkaloids (1-10) 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 Tabernaemontana corymbosa. The structures of these alkaloids were determined based on analysis of the NMR and MS data and, in five instances (1, 3, 5, 6, 8), confirmed by X-ray diffraction analysis. Two of the iboga alkaloids, conodusines B (2) and C (3), and the iboga-containing bisindole tabernamidine B (10) are notable for the presence of an α-substituted acetyl group at C-20 of the iboga carbon skeleton. The iboga alkaloid (+)-conodusine E (5) had MS and NMR data that were identical to those of (-)-ervatamine I, recently isolated from Ervatamia hainanensis. Establishment of the absolute configuration of (+)-conodusine E (5) was based on analysis of the ECD data, correlation with (-)-heyneanine, and X-ray analysis, which showed that (+)-5 belongs to the same enantiomeric series as exemplified by (-)-coronaridine. The configuration at C-20' of the previously reported Tabernaemontana 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.

Arborisidine and Arbornamine, Two Monoterpenoid Indole Alkaloids with New Polycyclic Carbon-Nitrogen Skeletons Derived from a Common Pericine Precursor

Wong SP, Chong KW, Lim KH, Lim SH, Low YY, Kam TS

Org. Lett., 2016 Apr 1;18(7):1618-21.

PMID: 27033525 DOI: 10.1021/acs.orglett.6b00478

Two new monoterpene indole alkaloids, characterized by previously unencountered natural product skeletons, viz., arborisidine (1), incorporating indolizidine and cyclohexanone moieties fused to an indole unit, and arbornamine (2), incorporating an unprecedented 6/5/6/5/6 "arbornane" skeleton (distinct from the eburnan or tacaman skeleton), were isolated from a Malayan Kopsia arborea. The structures of the alkaloids were determined based on analysis of the NMR and MS data. Possible biogenetic pathways to these alkaloids from a common pericine precursor (3) are presented.

Vobatensines A-F, Cytotoxic Iboga-Vobasine Bisindoles from Tabernaemontana corymbosa

Sim DS, Teoh WY, Sim KS, Lim SH, Thomas NF, Low YY, et al.

J Nat Prod, 2016 Apr 22;79(4):1048-55.

PMID: 26918761 DOI: 10.1021/acs.jnatprod.5b01117

Six new bisindole alkaloids of the iboga-vobasine type, vobatensines A-F (1-6), in addition to four known bisindoles (8-11), were isolated from a stem bark extract of a Malayan Tabernaemontana corymbosa. The structures of these alkaloids were determined based on analysis of the spectroscopic data and in the case of vobatensines A (1), B (2), and 16'-decarbomethoxyvoacamine (8) also confirmed by partial syntheses. Nine of these alkaloids (1-5, 8-11) showed pronounced in vitro growth inhibitory activity against human KB, PC-3, LNCaP, HCT 116, HT-29, MCF7, MDA-MB-231, and A549 cancer cells.

Arboridinine, a Pentacyclic Indole Alkaloid with a New Cage Carbon-Nitrogen Skeleton Derived from a Pericine Precursor

Wong SP, Gan CY, Lim KH, Ting KN, Low YY, Kam TS

Org. Lett., 2015 Jul 17;17(14):3628-31.

PMID: 26183592 DOI: 10.1021/acs.orglett.5b01757

A new monoterpene indole alkaloid characterized by an unprecedented pentacyclic cage skeleton, arboridinine (1), was isolated from a Malaysian Kopsia species. The structure and absolute configuration of the alkaloid were determined based on NMR, MS, and X-ray diffraction analysis. A possible biogenetic pathway from a pericine precursor is presented.

Ibogan, tacaman, and cytotoxic bisindole alkaloids from tabernaemontana. Cononusine, an iboga alkaloid with unusual incorporation of a pyrrolidone moiety

Lim KH, Raja VJ, Bradshaw TD, Lim SH, Low YY, Kam TS

J Nat Prod, 2015 May 22;78(5):1129-38.

PMID: 25919190 DOI: 10.1021/acs.jnatprod.5b00117

Six new indole alkaloids, viz., cononusine (1, a rare example of an iboga-pyrrolidone conjugate), ervaluteine (2), vincamajicine (3), tacamonidine (4), 6-oxoibogaine (5), and N(4)-chloromethylnorfluorocurarine chloride (6), and two new vobasinyl-iboga bisindole alkaloids, ervatensines A (7) and B (8), in addition to other known alkaloids, were isolated from the stem-bark extract of the Malayan Tabernaemontana corymbosa. The structures of these alkaloids were established on the basis of NMR and MS analyses and, in one instance (7), confirmed by X-ray diffraction analysis. Vincamajicine (3) showed appreciable activity in reversing multidrug resistance in vincristine-resistant KB cells (IC50 2.62 μM), while ervatensines A (7) and B (8) and two other known bisindoles displayed pronounced in vitro growth inhibitory activity against human KB cells (IC50 < 2 μM). Compounds 7 and 8 also showed good growth inhibitory activity against A549, MCF-7, MDA-468, HCT-116, and HT-29 cells (IC50 0.70-4.19 μM). Cell cycle and annexin V-FITC apoptosis assays indicated that compounds 7 and 8 inhibited proliferation of HCT-116 and MDA-468 cells, evoking apoptotic and necrotic cell death.

Concise synthesis of the vasorelaxant alkaloids schwarzinicines A and B

Lee FK, Krishnan P, Muhamad A, Low YY, Kam TS, Ting KN, et al.

Nat Prod Res, 2021 Mar 22.

PMID: 33749454 DOI: 10.1080/14786419.2021.1903005

A concise synthesis of the 1,4-diarylbutanoid-phenethylamine alkaloids, schwarzinicines A (1) and B (2), recently isolated from Ficus schwarzii, is reported. Key steps include a Claisen condensation to assemble the 1,4-diaryl-2-butanone intermediate, followed by a reductive amination to furnish the core skeleton of the target compounds. The overall synthetic yields of 1 and 2 were 9.1% and 3.5%, respectively. Synthetic (-)-1, (+)-1 and (±)-1 exhibited comparable vasorelaxation as natural schwarzinicine A on rat isolated aortic rings, suggesting that the observed vasorelaxant effects were not influenced by the chirality at C-2.

Lycopodium Alkaloids: Lycoplatyrine A, an Unusual Lycodine-Piperidine Adduct from Lycopodium platyrhizoma and the Absolute Configurations of Lycoplanine D and Lycogladine H

Yeap JS, Lim KH, Yong KT, Lim SH, Kam TS, Low YY

J Nat Prod, 2019 02 22;82(2):324-329.

PMID: 30698428 DOI: 10.1021/acs.jnatprod.8b00754

Three new Lycopodium alkaloids comprising two lycodine-type alkaloids (1, 2) and one fawcettimine alkaloid (3), in addition to 16 known alkaloids, were isolated from Lycopodium platyrhizoma. The structures of these alkaloids were elucidated based on analysis of their NMR and MS data. Lycoplatyrine A (1) represents an unusual lycodine-piperidine adduct. The structures and absolute configurations of lycoplanine D (hydroxy-des- N-methyl-α-obscurine, 10) and lycogladine H (11) were confirmed by X-ray diffraction analysis.

Conolodinines A-D, Aspidosperma- Aspidosperma Bisindole Alkaloids with Antiproliferative Activity from Tabernaemontana corymbosa

Sim DS, Navanesan S, Sim KS, Gurusamy S, Lim SH, Low YY, et al.

J Nat Prod, 2019 04 26;82(4):850-858.

PMID: 30869890 DOI: 10.1021/acs.jnatprod.8b00919

Examination of the EtOH extract of the leaves of the Malayan Tabernaemontana corymbosa resulted in the isolation of four new (1-4) and two known bisindole alkaloids (5, 6) of the Aspidosperma- Aspidosperma type. The structures of these alkaloids were determined based on analysis of the spectroscopic data (NMR and HRESIMS). X-ray diffraction analyses of the related bisindole alkaloids conophylline (5) and conophyllinine (6) established the absolute configurations. Treatment of the bisindole alkaloid conophylline (5) with benzeneselenic anhydride gave, in addition to the known bisindole polyervinine (7) previously isolated from another Malayan Tabernaemontana, another bisindole product, 8, an isolable tautomer of 7. X-ray diffraction analyses yielded the absolute configurations of both bisindoles and in addition showed that polyervinine (7) exists primarily as the neutral dione structure. The bisindoles (1-8) and the related conophylline-type bisindoles (9-13) 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, A549, HT-29, and HCT 116 cells, with IC50 values for the active compounds in the 0.01-5 μM range.

Transformations of Ferric Chloride-Generated Stilbene Cation Radicals. The Effect of Aromatic Substitution and a Comparison with Anodic Oxidation

Hong FJ, Chong KW, Low YY, Thomas NF, Kam TS

Chem Asian J, 2015 Oct;10(10):2207-20.

PMID: 26097065 DOI: 10.1002/asia.201500488

A systematic study on the FeCl3-induced oxidation of 1,2-diarylalkenes was carried out with the focus on the variation of product type as a function of aromatic substitution, as well as to compare the reactivity of stilbene cation radicals generated via Fe(III) oxidation with those generated by anodic oxidation. The aromatic substituents were found to fall into three main categories, namely those that give rise to tetralins and/or dehydrotetralins, those that give products possessing pallidol and ampelopsin F-type carbon skeletons, and last, those that give rise to trimeric products, indanes, and dehydrotetralins/tetralins. The latter are those stilbenes with a para-methoxy substituent in one ring and a para- or meta-EWG (CF3, NO2, Cl, F) in the other, and represent the most prominent departure when compared with the behavior of the same stilbenes under the conditions of anodic oxidation. Reaction pathways to rationalize the formation of the different products are presented.

Fulltext The natural alkaloid Jerantinine B has activity in acute myeloid leukemia cells through a mechanism involving c-Jun

Alhuthali HM, Bradshaw TD, Lim KH, Kam TS, Seedhouse CH

BMC Cancer, 2020 Jul 07;20(1):629.

PMID: 32635894 DOI: 10.1186/s12885-020-07119-2

BACKGROUND: Acute myeloid leukemia (AML) is a heterogenous hematological malignancy with poor long-term survival. New drugs which improve the outcome of AML patients are urgently required. In this work, the activity and mechanism of action of the cytotoxic indole alkaloid Jerantinine B (JB), was examined in AML cells.

METHODS: We used a combination of proliferation and apoptosis assays to assess the effect of JB on AML cell lines and patient samples, with BH3 profiling being performed to identify early effects of the drug (4 h). Phosphokinase arrays were adopted to identify potential driver proteins in the cellular response to JB, the results of which were confirmed and extended using western blotting and inhibitor assays and measuring levels of reactive oxygen species.

RESULTS: AML cell growth was significantly impaired following JB exposure in a dose-dependent manner; potent colony inhibition of primary patient cells was also observed. An apoptotic mode of death was demonstrated using Annexin V and upregulation of apoptotic biomarkers (active caspase 3 and cleaved PARP). Using BH3 profiling, JB was shown to prime cells to apoptosis at an early time point (4 h) and phospho-kinase arrays demonstrated this to be associated with a strong upregulation and activation of both total and phosphorylated c-Jun (S63). The mechanism of c-Jun activation was probed and significant induction of reactive oxygen species (ROS) was demonstrated which resulted in an increase in the DNA damage response marker γH2AX. This was further verified by the loss of JB-induced C-Jun activation and maintenance of cell viability when using the ROS scavenger N-acetyl-L-cysteine (NAC).

CONCLUSIONS: This work provides the first evidence of cytotoxicity of JB against AML cells and identifies ROS-induced c-Jun activation as the major mechanism of action.

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