Further experiments on structure-activity relationships among the lycorine alkaloids

Synthetic lycorine analogues, five Amaryllidaceae alkaloids and narciclasine, all structurally related to lycorine, were tested for their ability to inhibit ascorbic acid biosynthesis in vivo. The highest potency observed was displayed by narciclasine followed by compounds having an aromatic C-ring. Derivatives modified at C-1 and/or C-2 were inactive, while the compound with a double bond between these positions is a weak inhibitor. Also lutessine and its deacetyl derivative having an α-methoxyl group bonded to C-4 of the D-ring appeared completely inactive. These results confirm that the presence of an appropriately substituted C-ring is a necessary requirement for optimal ‘response-triggering’ contact between the lycorine derivatives and the specific receptor. Functional groups jutting out from the α-side of the molecule do not allow a good fit with the binding sites.     

Apoptosis-inducing effects of distichamine and narciprimine, rare alkaloids of the plant family Amaryllidaceae

Several of the Amaryllidaceae alkaloids are known for their cytotoxic properties, of which the lycorine group representatives are prominent for potent and cell line specific antiproliferative activities. As a distinct niche within the lycorine group, the phenanthridones, exemplified by narciclasine and pancratistatin, have shown much promise as remarkably selective cytotoxic agents and are presently at various stages of development, with a clinical candidate likely to appear on the market within the next decade. The crinane group of the Amaryllidaceae has also spawned several molecules, such as crinamine and haemanthamine, with promising cytotoxic activities. In the present study, the β-crinane distichamine as well as the phenanthridone narciprimine, both rare constituents of the Amaryllidaceae, are revealed as novel antiproliferative agents. Apoptosis-inducing effects are demonstrated for distichamine in human acute lymphoblastic leukemia (CEM) cells. These findings provide further insights to the structural details of the apoptosis-inducing pharmacophores resident within both series of alkaloids.     

Alkaloids biosynthesis by <Emphasis Type="Italic">Pancratium maritimum</Emphasis> L. shoots in liquid culture

The process of alkaloid biosynthesis by Pancratium maritimum shoot culture, cultivated under submerged conditions, was investigated. Twenty-two compounds of different structural types of the Amaryllidaceae alkaloids (tyramine, narciclasine, galanthamine, haemanthamine, lycorine, pancracine, tazettine and homolycorine types) were detected in the studied samples from biomass and cultural liquid. Dominant compounds in the shoots were of tyramine, lycorine and haemanthamine types, whereas in the culture media were found mainly lycorine type compounds. Based on the multi-metabolic estimation of the alkaloid metabolism and physiological peculiarities, liquid cultures of P. maritimum shoots could be defined as prospective biological systems for producing bioactive molecules with acetylcholinesterase inhibitory and apoptotic activities.     

HPTLC and GC/MS Study of Amaryllidaceae Alkaloids of Two Narcissus Species

In this article, we report on the alkaloid profile and dynamic of alkaloid content and diversity in two Narcissus plants at different stages of development. The alkaloid profile of the two Narcissus species was investigated by GC/MS and HPTLC. Fifty eight Amaryllidaceae alkaloids were detected, and 25 of them were identified in the different organs of N. tazetta and N. papyraceus. The alkaloid 3‐O‐methyl‐9‐O‐demethylmaritidine is tentatively identified here for the first time from the Amaryllidaceae family, and four alkaloids (tazettamide, sternbergine, 1‐O‐acetyllycorine, 2,11‐didehydro‐2‐dehydroxylycorine) are tentatively identified for the first time in the genus Narcissus. The different organs of the two species analyzed showed remarkable differences in their alkaloid pattern, type of biosynthesis, main alkaloid and number of alkaloids. Lycorine‐type alkaloids dominated the alkaloid, metabolism in N. papyraceus, while alkaloids of narciclasine‐, galanthamine‐ and homolycorine‐types were found only in the species N. tazetta L.     

Acetylcholinesterase inhibitory activity of some Amaryllidaceae alkaloids and Narcissus extracts

Amaryllidaceous plants produce pharmacologically active alkaloids, galanthamine being the most interesting for its use in the treatment of Alzheimer's disease as a cholinesterase inhibitor. The aim of this work was to test 23 pure Amaryllidaceae alkaloids and 26 extracts from different species of the genus Narcissus for their acetylcholinesterase inhibitory activity using galanthamine as a reference. Only seven alkaloids, belonging to the galanthamine and lycorine skeleton types, exhibited such an effect, sanguinine being the most active, even more than galanthamine. All the extracts with the highest acetylcholinesterase inhibitory activity contained galanthamine except that of N. assoanus, a lycorine type alkaloid-bearing species.     

Selective cytochrome P450 3A4 inhibitory activity of Amaryllidaceae alkaloids

A library of natural and semi-synthetic Amaryllidaceae alkaloids was screened for cytochrome P450 3A4 (CYP3A4) inhibitory activity. Of the crinane, lycorane and galanthamine representatives examined two semi-synthetic silylated lycorane analogues, accessed via a chemoselective silylation strategy from lycorine, and the natural compound narciclasine exhibited low micromolar activities. Important pharmacological features uncovered include the lack of CYP3A4 inhibitory activity seen for galanthamine and the selective activity that is seen with narciclasine over pancratistatin.     

Biogeographical Patterns and Phenological Changes in Lapiedra martinezii Lag. Related to Its Alkaloid Diversity

The aim of this work was to investigate the alkaloid patterns of Lapiedra martinezii and their relation to biogeography and phenology focused in a phylogenetic comparison. Plants from 14 populations of L. martinezii, covering almost its entire distribution area, were subjected to morphological, ecological, and phytochemical analysis. Experiments for different alkaloid‐type content are proposed as a new tool for analysis of plant distribution. Several plants were transplanted for weekly observation of their phenological changes, and alkaloids from different plant organs were extracted, listed, and compared. The alkaloid pattern of L. martinezii comprises 49 compounds of homolycorine, lycorine, tazettine, haemantamine, and narciclasine types. The populations located in the north and south margins of the distribution area displayed alkaloid patterns different from those of the central area. Changes in these patterns during their phenological cycle may be related to a better defence for plant reproduction. L. martinezii is an old relict plant, and it has maintained some of the more primitive morphological features and alkaloid profiles of the Mediterranean Amaryllidaceae. The variations in alkaloid content observed could be interpreted in a phylogenetic sense, and those found in their phenological changes, in an adaptive one.     

Insight to the antifungal properties of Amaryllidaceae constituents

BackgroundFungal pathogenesis continues to be a burden to healthcare structures in both developed and developing nations. The gradual and irreversible loss of efficacies of existing antifungal medicines as well as the emergence of drug-resistant strains have contributed largely to this scenario. There is therefore a pressing need for new drugs from diverse structural backgrounds with improved potencies and novel modes of action to fortify or replace contemporary antifungal schedules.AimAlkaloids of the plant family Amaryllidaceae exhibit good growth inhibitory activities against several fungal pathogens. This review focuses on the mechanistic aspects of these antifungal activities. It achieves this by highlighting the molecular targets as well as structural features of Amaryllidaceae constituents which serve to enhance such action.MethodsDuring the information gathering stage extensive use was made of the three database platforms; Google Scholar, SciFinder and Scopus. In most instances articles were accessed directly from journals licensed to the University of KwaZulu-Natal. In the absence of such proprietary agreements the respective corresponding authors were approached directly for copies of papers.ResultsAlthough several classes of molecules from the Amaryllidaceae have been probed for their antifungal effects, it is the key constituents lycorine and narciclasine which have together afforded the most profound mechanistic insights. These may be summarized as follows: (i) effects on the fungal cell wall and cell membrane; (ii) effects on morphology such as budding and hyphal growth; (iii) effects on fungal organelles such as ribosomes; (iv) effects on macromolecules such as DNA, RNA and proteins and; (v) identification of the active sites for these constituents.ConclusionThe key feature in the antifungal effects of Amaryllidaceae alkaloids is the inhibition of protein synthesis. This involved the inhibition of peptide bond formation by binding to yeast ribosomes via the 60S subunit. Related effects involved the inhibition of both DNA and RNA synthesis. These adverse effects were reflected morphologically on both the fungal cell wall and cell membrane. Such observations should prove useful in the chemotherapeutic arena should efforts shift towards the development of a clinical candidate.     

New skeletons and new concepts in Amaryllidaceae alkaloids

The Amaryllidaceae alkaloids, represent a group of isoquinoline alkaloids, which are produced almost solely by members of the Amaryllidaceae family. The alkaloids of this family have attracted considerable amount of interest due to some important pharmacological activities they were shown to possess. In the last decade, our phytochemical studies on four Galanthus (Amaryllidaceae) species of Turkish origin have yielded quite a number of new alkaloids with diverse structures. Among these alkaloids, gracilines and plicamines constitute two new subgroups for the Amaryllidaceae alkaloids. The gracilines contain an incorporated 10b,4a-ethanoiminodibenzo[b,d]pyrane skeleton. The plicamines are dinitrogenous compounds, where the oxygen atom in position 7 of a tazettine skeleton is replaced by a nitrogen atom substituted by a pendant 4-hydroxyphenethyl moiety. One of the new alkaloids, galanthindole, which possesses a nonfused indole ring, unlike the already known subgroups of Amaryllidaceae alkaloids, may be considered as the prototype of a third new subgroup of the Amaryllidaceae alkaloids. Additionally, two known isoquinoline alkaloids which do not possess one of the established skeletons of the Amaryllidaceae alkaloids, namely ( − )-capnoidine and (+)-bulbocapnine, have been isolated from a Turkish Galanthus species. Totally, 21 new, 20 known alkaloids and 2 known lignans have been characterized. In this review, the isolation and structure elucidation of these compounds with interesting chemical structures are described.     

Alkaloid patterns in Leucojum aestivum shoot culture cultivated at temporary immersion conditions

The alkaloid patterns in Leucojum aestivum L. shoot culture cultivated at temporary immersion conditions were investigated using gas chromatography-mass spectrometry. 18 alkaloids were identified, and galanthamine, hamayne and lycorine were dominant. The L. aestivum 80 shoot culture, cultivated at temporary immersion conditions, is a prospective biological matrix for obtaining wide range Amaryllidaceae alkaloids, showing valuable biological and pharmacological activities. The temperature of cultivation influenced enzyme activities, catalyzing phenol oxidative coupling of 4′-O-methylnorbelladine and formation of the different groups Amaryllidaceae alkaloids. Decreasing the temperature of cultivation of L. aestivum 80 shoot culture led to activation of para-ortho’ phenol oxidative coupling (formation of galanthamine type alkaloids) and inhibited ortho-para’ and para-para’ phenol oxidative coupling (formation of lycorine and haemanthamine types alkaloids).     

Alkaloids of Haemanthus kalbreyeri

The roots of Haemanthus kalbreyeri contain a new phenanthridone alkaloid, kalbretorine, and a new glucosyloxy alkaloid, kalbreclasine. Additionally, six known alkaloids, viz. haemanthamine, haemanthidine, hippadine, lycorine, narciclasine and pratorimine, previously reported from other Amaryllidaceous plants have now been isolated also from this species. Kalbretorine produced marked inhibition of growth and viability of S-180 tumour cells. Kalbreclasine caused significant mitogenic activation of splenic lymphocytes characteristic of immuno stimulants.     

Cytotoxic activities of Amaryllidaceae alkaloids against gastrointestinal cancer cells

The treatment of many diseases is highly dependent on natural products and natural products can also be used as design templates for future anticancer drugs. Thirteen Amaryllidaceae alkaloids possessing α-crinane, β-crinane, galantamine, lycorine and tazettine-type skeleton have been isolated in our laboratory, and their cytotoxicity against p53-mutated gastrointestinal cancer cells were evaluated. At the same time, healthy small intestine cells were used to determine overall toxicity against noncancerous cells. In this study, we demonstrated that haemanthamine, haemanthidine and lycorine showed strong cytotoxicity against p53-mutated Caco-2 and HT-29 colorectal adenocarcinoma cells as quantified in terms of IC₅₀ values. We for the first time observed approximately 20 times higher IC₅₀values against normal intestine epithelial cells FHs-74 Int after haemanthamine and lycorine treatment when compared with Caco-2 and HT-29 cancer cells. In conclusion, our data indicate that α-C2 bridged haemanthamine may be perspective anticancer drug candidate for further semisynthetic modification and structure-activity relationship study.     

Plants of the ‘Libellus de Medicinalibus Indorum Herbis’ from Mexico, 1552. Zephyranthes fosteri (Amaryllidaceae) Alkaloids

The Libellus de Medicinalibus Indorum Herbis (Booklet of Indian Medicinal Plants) is the first book of medicinal plants written in the American continent. It was first published in 1939 as ‘An Aztec Herbal’. One of the depicted plants is Huetzcanixochitl (laughing flower) interpreted as Zephyranthes fosteri (Amaryllidaceae). No chemical or pharmacological studies are reported for this species; so, we decide to investigate it. The GC/MS of the bulbs and aerial parts extracts indicated that they contain Amaryllidaceae alkaloids, among them: lycorine, 3-O-acetylpowelline, and norlycoramine. An unknown major alkaloid was isolated and identified by ¹H, ¹³C-NMR and MS, as 3′-demethoxy-6-epimesembranol ( 1 ). The methanolic extract, the alkaloid fraction, and compound 1 inhibited acetylcholinesterase in vitro. Mesembrine alkaloids are found in Sceletium species (Aizoaceae). Several are known as serotonin recapture inhibitors and have been proposed as potential antidepressant drugs. The presence of 1 suggests that Z. fosteri was probably used in pre-Columbian times in Mexico as a ‘stimulant and euphoriant’, alike Sceletium tortuosum by several ethnic groups in South Africa.     

The Amaryllidaceae alkaloids haemanthamine,haemanthidine and their semisynthetic derivatives as potential drugs

Plants of the Amaryllidaceae family, have a wide distribution through both tropical and sub-tropical regions of the world. They have also a long and notable place in the history of traditional and Western medicine. Amaryllidaceae alkaloids are a structurally diverse group of plant metabolites with a wide range of biological properties including antimalarial, antitumor, antimicrobial, antiviral, enzyme inhibitory, antioxidant, anticonvulsant and antifungal activities. Among them, the haemanthamine-type alkaloids, which have the 5,10b-ethanophenanthridine skeleton as the core structure, represented by haemanthamine and haemanthidine, have received considerable attention, since they have been reported to possess antitumor properties. The present review aims to summarize comprehensively the research that has been published on the Amaryllidaceae alkaloids haemanthamine and haemanthidine.

     

Glucosyloxy alkaloids from Pancratium biflorum

From fluids of flower stems and bulbs, and from extracts of roots of Pancratium biflorum, collected at different stages of growth, three new glucosyloxy alkaloids, viz. hordenine-4-O-β-d-glucoside, lycorine-1-O-β-d-glucoside and pseudolycorine-1-O-β-d-glucoside, have been isolated and characterized. Additionally, three proto alkaloids, β-phenethylamine, tyramine and hordenine, together with four true alkaloids, lycorine, pseudolycorine, pretazettine and tazettine, encountered before in other memebrs of the Amaryllidaceae, have now been isolated also from this species. Ontogenic variations of alkaloidal constituents have been observed. The ability of the alkaloidal constituents to complex with divalent metal ions and phytosterols has been examined with a view to evaluating their significance in plant biochemistry.     

Oxocrinine and other alkaloids from Crinum americanum

From bulbs of Crinum americanum oxocrinine, an intermediate in the biosynthesis of Amaryllidaceae alkaloids, was isolated for the first time. In addition, the plant contains crinine, flexinine, O-acetylcrinine, lycorine, hippadine, pratorinine, pratorimine, pratosine, ungeremine and trisphaeridine. The alkaloids were identified by spectroscopic evidence, chemical transformations and partial syntheses.     

Two non-hydroxylated alkaloids in Crinum augustum

Several alkaloids were isolated from Crinum augustum grown in Assiut, Egypt. Two were identified as lycorine and buphanisine. In addition two new non-hydroxylated alkaloids of identical molecular formula C₁₇H₁₉NO₄ were investigated by spectroscopic methods. The gross structure of the first, termed augustine, belongs to the 1,2-epoxy-5, 10-b-ethanophenanthridine-type. In contrast the second could not be related to any of the known alkaloid types of the Amaryllidaceae.     

Effects of sucrose and plant growth regulators on acetylcholinesterase inhibitory activity of alkaloids accumulated in shoot cultures of Amaryllidaceae

The influence of sucrose (30, 60, 90 and 120 g/L), activated charcoal (5 and 10 g/L), and various levels of several plant growth regulators (6-benzyladenine, naphthalene-1-acetic acid, 2,4-dichlorophenoxyacetic acid, and picloram) on organogenesis (bulb and root development) and the accumulation of alkaloid and galanthamine in shoot cultures of three Amaryllidaceae species (Narcissus pseudonarcissus, Galanthus elwesii, and Leucojum aestivum) was investigated in a full-factorial experiment. Alkaloid extracts were analyzed by gas chromatography–mass spectrometry, leading to the quantification of galanthamine and to the identification of other alkaloids. The different extracts were then subjected to an Ellman test to evaluate the inhibitory activity of acetylcholinesterase. The highest contents of galanthamine [0.02–0.1% dry weight (DW) depending on the plant species] were always accompanied with a high level of acetylcholinesterase inhibition (>30%). However, some samples containing low amounts of galanthamine (0.005% DW) showed high inhibitory activities (40–80%). These findings demonstrate the presence of Amaryllidaceae alkaloids that have not yet been identified as having anti-acetylcholinesterase activity.