Arboricine and arboricinine, unusual tetracyclic indole regioisomers from Kopsia

Systematic appraisals of naturally occurring alkaloids from medicinal plants

Alkaloids are a complex class of biologically active compounds with a broad spectrum of health-related applications. Particularly the alkaloids of indole, steroidal, terpenoids, isoquinoline, and bisbenzylisoquinoline have been extensively investigated. Ultimately, substantial advancement has been highlighted in the investigation of chemical constituents and the therapeutic benefits of plant alkaloids, particularly during the last ten years. A total of 386 alkaloids have been isolated from over 40 families, including Apocynaceae, Annonaceae, Rubiaceae, Menispermaceae, Ranunculaceae, Buxaceae, Papaveraceae, Magnoliaceae, Rutaceae and Phyllanthaceae. This paper will investigate several alkaloids that have been isolated from botanical medicines as well as offer an in-depth analysis of their cytotoxic properties.

A comprehensive review on phytochemistry and pharmacology of genus Kopsia: monoterpene alkaloids - major secondary metabolites

Kopsia belongs to the family Apocynaceae, which was originally classified as a genus in 1823. Kopsia consists of medicinal plants that can be traditionally used to treat rheumatoid arthritis, pharyngitis, tonsillitis, and dropsy. More than one hundred and twenty-five publications have been documented relating to the phytochemical and pharmacological results, but a systematic review is not available. The goal of this study is to compile almost all of the secondary metabolites from the plants of genus Kopsia, as well as the coverage of their pharmacological research. The document findings were conducted via reliable sources, including Web of Science, Sci-Finder, Science Direct, PubMed, Google Scholar, and publishers, while four words “Kopsia”, “monoterpene alkaloids”, “Phytochemistry” and “Pharmacology” are key factors to search for references. Most Kopsia secondary metabolites were collected. A total of four hundred and seventy-two, including four hundred and sixty-six monoterpene alkaloids, five triterpenoids, and one sterol, were summarized, along with their resource. Kopsia monoterpene alkaloids presented in various skeletons, but aspidofractinines, eburnamines, and chanofruticosinates are the three major backbones. Mersinines and pauciflorines are new chemical classes of monoterpene alkaloids. With the rich content of monoterpene alkaloids, Kopsia constituents were also the main objects in pharmacological studies since the plant extracts and isolated compounds were proposed for anti-microbial, anti-inflammatory, anti-allergic, anti-diabetic, anti-manic, anti-nociceptive, acetylcholinesterase (AChE) inhibitory, cardiovascular, and vasorelaxant activities, especially cytotoxicity.

Monoterpene alkaloids (466 isolated compounds) are major components, and anticancer activity is characteristic of Kopsia constituents.

Methyl chanofruticosinate type alkaloids from the aerial parts of Kopsia lancibracteolata Merr

A chemical investigation on the 70% ethanol extract from the leaves and stems of Kopsia lancibracteolata Merr. resulted in the isolation of three new methyl chanofruticosinate type alkaloids, 12-hydroxyl prunifoline A (1), 12-hydroxyl prunifoline C (2), and N(4)-oxide prunifoline D (3). Structural elucidation of all the compounds was performed by spectral methods such as 1D- and 2D-NMR, IR, UV, and HR-ESI-MS. The isolated alkaloids were tested in vitro for cytotoxic potential against five tumor cell lines (BGC-823, HepG2, MCF-7, SGC-7901, and SK-MEL-2). As a result, alkaloid 3 exhibited significant cytotoxic activity against all tested tumor cell lines with IC₅₀ values from 7.2 to 8.9 μM.

Cytotoxic and antibacterial aspidofractinine alkaloids from Kopsia hainanensis

The ethanol extract of the twigs and leaves of Kopsia hainanensis afforded six new aspidofractinine alkaloids, kopsiahainanins A-F (1-6), among which alkaloids 1 and 2 possessed a lactone bridge with novel regiochemistry. The structures of the isolated compounds were established based on 1D and 2D (¹H¹H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. The isolated compounds were tested in vitro for cytotoxic activity against seven tumor cell lines and antibacterial activities against two Gram-positive bacteria and five Gram-negative bacteria. As a result, alkaloids 1 and 2 exhibited cytotoxic activities (IC₅₀ values <20 μM) against all tested tumor cell lines and significant antibacterial properties (MIC values from 0.12 to 0.26 mM).

Alkaloids with Immunosuppressive Activity from the Bark of Pausinystalia yohimbe

Ten new alkaloids (1-10), including two pairs of enantiomeric mixtures (5a,b and 6a,b), and 15 known analogues (11-25) were obtained from the bark of Pausinystalia yohimbe. The structures of 1-25 were established by spectroscopic methods, and the absolute configurations of compounds 1-10 were resolved by X-ray diffraction and ECD data analyses. The in vitro immunosuppressive activities of selected isolates were tested. Compounds 11 and 16 exhibited moderate inhibition with IC₅₀ values of 16.8 and 27.6 μM against ConA-induced T lymphocyte proliferation and 13.5 and 40.5 μM against LPS-induced B lymphocyte proliferation, respectively.

Indole alkaloids from the aerial parts of Kopsia fruticosa and their cytotoxic, antimicrobial and antifungal activities

A chemical investigation on the 80% EtOH extract of the aerial parts of Kopsia fruticosa led to five new indole alkaloids, kopsifolines G-K (1-5), and one known alkaloid, kopsifoline A (6). Structural elucidation of all the compounds were performed by spectral methods such as 1D and 2D (¹H-¹H COSY, HMQC, and HMBC) NMR spectroscopy, in addition to high resolution mass spectrometry. The isolated components were evaluated in vitro for cytotoxic activities against seven tumor cell lines, antimicrobial activities against two Gram-positive bacteria and five Gram-negative bacteria, and antifungal activities against five pathogens. As a result, alkaloids 3-5 exhibited some cytotoxicity against all of seven tested tumor cell lines (HS-1, HS-4, SCL-1, A431, BGC-823, MCF-7, and W480) with IC₅₀ values of 11.8-13.8, 10.3-12.5, and 7.3-9.5 μM, respectively. Alkaloids 3-5 also possessed significant antimicrobial and antifungal activities which was reported for the first time for the alkaloids isolated from Kopsia genus.

Application of the Asymmetric Pictet-Spengler Reaction in the Total Synthesis of Natural Products and Relevant Biologically Active Compounds

Tetrahydroisoquinolines are the framework of numerous natural products predominantly alkaloids, an important and one of the most wide spread families of naturally occurring compounds in the plant kingdom. Tetrahydroisoquinolines are commonly constructed through an old reaction, the so-called Pictet−Spengler Reaction (PSR). In this reaction, a β-aryl ethylamine undergoes an acid mediated condensation with a suitable aldehyde or ketone, followed by ring closure. In this review, we aim to highlight the applications of the asymmetric variant of this old name reaction in the total synthesis of natural products, chiefly, alkaloids, which exhibit significant biological properties.

Cytotoxic aspidofractinine alkaloids from Kopsia hainanensis

Five new aspidofractinine-type alkaloids, kopsiahainins A-E (1-5), were isolated from a 80% EtOH extract of the leaves and stems of Kopsia hainanensis. Structural elucidation of all the compounds were performed by spectral methods such as 1D- and 2D-NMR, IR, UV, and HR-ESI-MS. Alkaloids 3 and 4 exhibited some cytotoxic activity against all of six tested tumor cell lines (BGC-823, HepG2, MCF-7, SGC-7901, SK-MEL-2, and SK-OV-3) with IC₅₀ values of 7.3-9.5μM and 9.2-10.6μM, respectively.

Monoterpene Indole Alkaloids from the Twigs of Kopsia arborea

The phytochemistry of Kopsia arborea Blume has received considerable attention, which has resulted in the isolation of a number of new unusual indole alkaloids with intriguing structures. In this study, a new eburnane-type alkaloid, phutdonginin (1), together with eight known alkaloids: 19-OH-(-)-eburnamonine (2), melodinine E (3), kopsinine (4), kopsilongine (5), kopsamine (6), (-)-methylenedioxy-11,12-kopsinaline (7), decarbomethoxykopsiline (8), and vincadifformine (9), were isolated from the twigs of K. arborea. Their structures were characterized extensively by 1D and 2D NMR spectroscopy and HR-ESI-MS. All compounds were submitted to TLC screening for acetylcholinesterase inhibitory activities. Only kopsamine and decarbomethoxykopsiline showed AChE inhibition with MIR values of 12.5 and 6.25 μg, respectively, compared with galanthamine (positive control, 0.004 μg). In addition, compounds 1 and 2 inhibited moderate antibacterial activity against E. coli TISTR 780 with the MIC value of 32 μg/mL.

Grandilodines A-C, biologically active indole alkaloids from Kopsia grandifolia

Three new indole alkaloids (1-3), named grandilodines A-C, and five known ones were obtained from the Malayan Kopsia grandifolia. The structures were established using NMR and MS analyses and, in the case of 1 and 2, were confirmed by X-ray diffraction analyses. Alkaloids 1, 3, and lapidilectine B (8) were found to reverse multidrug resistance in vincristine-resistant KB cells.

Leucoridines A-D, cytotoxic Strychnos-Strychnos bisindole alkaloids from Leuconotis

Four new bisindole alkaloids of the Strychnos-Strychnos type, leucoridines A-D (1-4), were isolated from the stem-bark extract of Leuconotis griffithii. Alkaloids 1-4 showed moderate cytotoxicity against drug-sensitive and vincristine-resistant human KB cells.

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

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

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.

Rhazinilam and quebrachamine derivatives from Yunnan Kopsia arborea

Three new rhazinilam-derived alkaloids, kopsiyunnanines C1, C2, and C3, and a new quebrachamine-type alkaloid, kopsiyunnanine D, which possess an unusual methoxymethyl or ethoxymethyl function, were isolated from the aerial parts of Yunnan Kopsia arborea. This is the first report of the presence of these functions in natural alkaloids. The structures and absolute configurations of the alkaloids were determined by spectroscopic methods and confirmed by semisynthesis.

Methyl chanofruticosinate alkaloids from Kopsia arborea

Six alkaloids belonging to the methyl chanofruticosinate group, viz., prunifolines A-F, in addition to six other known methyl chanofruticosinate alkaloids, were isolated from the leaf extract of Kopsia arborea. The structures were determined using NMR and MS analysis and comparison with known related compounds.

Biologically active aspidofractinine alkaloids from Kopsia singapurensis

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

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.