Pyrrolo- and pyridoazepine alkaloids as chemical markers in Stemona species

LC-MS/MS analysis of didehydrostemofoline from Stemona collinsiae roots extracts in rats plasma and pharmacokinetics profile after oral administration

Stemona collinsiae Craib., Stemonaceae, has been traditionally used as medicinal plants for insecticides, treatment of parasitic worms and various diseases in Southeast Asian countries. Its ethanolic root extract has been postulated for anthelminthic activities which has a potential for development for human gnathostomiasis drug. To investigate the pharmacokinetic profile, liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method for the quantification of didehydrostemofoline in rats' plasma was developed and validated. The chromatographic separation was performed on a C18 column using 1 mM ammonium acetate in water and methanol (50:50, v/v). Tetrahydropalmatine was used as an internal standard. The multiple reaction monitoring mode was used for quantitative analysis. The validated method showed good sensitivity, linearity, precision, and accuracy. The results of stability showed that didehydrostemofoline was stable in the extracted samples in auto-sampler for 24 h and in the plasma samples under room temperature for 24 h, -20 °C for 1 month, and after three freeze-thaw processes. The developed method was applied to the pharmacokinetic study of didehydrostemofoline after oral administration of S. collinsiae root extract. Didehydrostemofoline was rapidly absorbed from the gastrointestinal tract. The time to peak drug concentration was 1.75 ± 0.62 h with maximum drug concentration of 1152.58 ± 271.18 ng/mL. Didehydrostemofoline was rapidly eliminated from the body with terminal half-life of 1.86 ± 0.50 h. Calculated drug clearance of didehydrostemofoline was 96.82 ± 23.51 L/h and volume of distribution was 260.40 ± 96.81 L. The present study provided useful data for understanding drug disposition in the body with dynamic time-course which could be beneficial for further clinical trials.

Oral toxicity of various Stemona collinsiae crude extracts against nymph and adult stages of American cockroach, Periplaneta americana (Dictyoptera: Blattodea)

Stemona collinsiae exhibits insecticidal resistance against various pests and insect vectors. However, insecticidal activity of S. collinsiae roots has not been tested for some insect vectors, including the American cockroach, Periplaneta americana. The synanthropic insect P. americana is a reservoir of pathogenic and non-pathogenic microorganisms and a cause of infectious diseases and cockroach allergy. This important vector transmits microorganisms to animals and humans to cause vector-borne diseases. This research involved detection of the nymphicidal and adulticidal activities of S. collinsiae root extracts against P. americana through oral administration. The effects of hexane, dichloromethane, ethanol, and water crude extracts were tested on final instar nymphs and adult P. americana. After P. americana ingested bait containing hexane and dichloromethane crude extracts, signs of toxicity occurred, such as hind leg shaking, whole-body tremor, immobility, abdomen swelling, and death. At 48 h, the nymphs and adult P. americana that ingested dichloromethane crude extract-containing bait showed corrected mortality of 65%-100% and 20%-100%, respectively. Whereas none of the nymphs and adult P. americana that ingested the water crude extract-containing bait died (0% corrected mortality). When we dissected alimentary canals of the dead P. americana that had ingested dichloromethane and hexane crude extract-containing baits, the foreguts were found to be swollen. TLC analysis showed the dichloromethane and hexane crude extracts contained the alkaloid didehydrostemofoline and unknown fluorescent substances. Phytochemicals from crude extracts were detected in extracts of dissected alimentary canals using thin-layer chromatography, and didehydrostemofoline alkaloid and unknown fluorescent substances were found in cockroaches that ingested dichloromethane- and hexane-containing baits. The cause of death of P. americana may be attributed to alkaloids and synergistic effects of other substances in S. collinsiae root extract. Mechanisms of action might include several pathways involved in nervous system function. Thus, dichloromethane and hexane crude extracts can be developed as alternative active ingredients in a natural insecticide for cockroach control.

Morphological and chemical variation of Stemona tuberosa from southern China - Evidence for heterogeneity of this medicinal plant species

The occurrence of bioactive alkaloids and tocopherols was studied in 15 different provenances of Stemona tuberosa Lour. collected in southern China, to examine chemical variation of individuals that show notable differences in flower characteristics. Morphological variations stimulated examination of chemical characteristics of these individuals. Methanolic root extracts of 15 individuals of S. tuberosa were comparatively assessed with HPLC-UV-DAD/ELSD. Five of seven compounds were co-chromatographically identified. Two compounds were isolated and their structure elucidated using NMR and MS. Amounts of alkaloids and tocopherols were determined using HPLC-UV-DAD/ELSD with the external standard method. Five alkaloids, tuberostemonine (1), tuberostemonine A (2), neotuberostemonine (3), tuberostemonine N (4), stemoninine (5) and two 3,4-dehydrotocopherol derivatives were identified. Within S. tuberosa alkaloid accumulation tends either towards tuberostemonine (1) or stemoninine (5). All individuals show a notable co-occurrence of compounds 1 or 5 and 3,4-dehydro-δ-tocopherol (6). These results coincide with differences in flower morphology of S. tuberosa. Stemona tuberosa, as defined in the Flora of China, shows a remarkable variation in flower morphology and additionally in the accumulation of alkaloids. The obtained data show the need for future species delimitation to either species or subspecies level.

Insecticidal activity of Stemona collinsiae root extract against Parasarcophaga ruficornis (Diptera: Sarcophagidae)

In Thai indigenous knowledge, Stemona plant has traditionally been used as insecticide on plantations. Recently, S. collinsiae extract was showed to be an anti-feedant and growth inhibitor and to exert strong insecticidal activity. Here, the insecticidal activity of S. collinsiae root extract against Parasarcophaga ruficornis is studied. The larvicidal and pupicidal activities of the ethanolic root extract of S. collinsiae were tested using contact toxicity tests, and adulticidal activity was tested using the topical contact toxicity and sugar bait methods The ethanolic extract at concentration ranging of 0.3-320mg/larva for the direct contact toxicity test and from 0.3 to 3.2mg/cm²/larva for the secondary contact toxicity test showed 3.0-51.0 and 1.0-94.0% corrected mortality, respectively. Against third-instar larvae, the LD₅₀ concentrations of the ethanolic extract were 31.7±0.0mg/larva and 1.4±0.0mg/cm²/larva for direct and secondary contact toxicity tests, respectively. Pupae were not eliminated at all concentrations of the ethanolic extract. Against adult flies, which were killed via oral administration, the LD₅₀ concentration of the ethanolic extract was 0.145±0.070g extract/g glucose. Thus, the ethanolic extract of S. collinsiae was capable of eliminating P. ruficornis in larval and adult stages via topical and ingestion administration, respectively.

Tuberostemonine N, an active compound isolated from Stemona tuberosa, suppresses cigarette smoke-induced sub-acute lung inflammation in mice

OBJECTIVE

Our previous study demonstrated that a Stemona tuberosa extract had significant effects on cigarette smoking (CS)-induced lung inflammation in mice. The present study evaluated the potential of tuberostemonine N (T.N) to prevent airway inflammation and suppress airway responses in a CS-induced in vivo COPD model.

METHODS

T.N was isolated from the root of ST and analyzed using 1D and 2D NMR. The purity of T.N was accessed using HPLC-ELSD analysis. C57BL/6 mice in this study were whole-body exposed to mainstream CS or room air for 4 weeks, and T.N (1, 5 and 10 mg/kg body wt.) was administered to mice via intraperitoneal (i.p.) injection before CS exposure. The number of inflammatory cells, including neutrophils, macrophages and lymphocytes, and the amount of proinflammatory cytokines and chemokines were accessed from bronchoalveolar lavage fluid (BALF) to investigate the anti-inflammatory effects of T.N. Average alveoli size was also measured using histological analyses.

RESULTS

Cellular profiles and histopathological analyses revealed that the infiltration of peribronchial and perivascular inflammatory cells decreased significantly in the T.N-treated groups compared to the CS-exposed control group. T.N significantly inhibited the secretion of proinflammatory cytokines and chemokines in BALF and decreased alveoli size in lung tissue.

CONCLUSIONS

These data suggest that T.N exerts anti-inflammatory effects against airway inflammation, and T.N may be a novel therapeutic agent for lung diseases, such as COPD.

Suppression of IL-2 production and proliferation of CD4(+) T cells by tuberostemonine O

Tuberostemonine stereoisomers are natural alkaloids found in Stemona tuberosa, that are known to have anti-inflammatory and anti-infective properties. Tuberostemonine alkaloids inhibit inflammation by suppressing the expression of inflammatory mediators such as cyclooxygenase and nitric oxide synthase. However, the direct immunomodulatory properties of tuberostemonine alkaloids in T cells have not been elucidated so far. In this study, the activities in T cells of tuberostemonine N (TbN) and a novel alkaloid, tuberostemonine O (TbO), isolated from S. tuberosa, were investigated. Although TbN did not have a significant effect on cytokine production in splenic T cells, TbO selectively suppressed interleukin (IL)-2 production. Moreover, TbO, but not TbN, significantly inhibited IL-2 production by primary CD4(+) T cells and delayed the T-cell proliferation in a dose-dependent manner. Addition of excess recombinant IL-2 restored the decreased cell-division rates in TbO-treated CD4(+) T cells to control levels. Collectively, these findings suggest that the immunomodulatory effects of TbO occurred by the suppression of IL-2 expression and IL-2-induced T-cell proliferation, suggesting a potential beneficial role of tuberostemonine alkaloids for the control of chronic inflammatory and autoimmune diseases caused by hyperactivated T cells.

Stemona tuberosa prevented inflammation by suppressing the recruitment and the activation of macrophages in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Stemona tuberosa (ST) is a traditional herbal medicine used for the treatment of various respiratory diseases in eastern Asia.

AIM OF THE STUDY

We investigated the anti-inflammatory effects of a ST water extract in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages and in cigarette smoke (CS)-induced lung inflammation mouse models.

MATERIALS AND METHODS

RAW 264.7 macrophages were treated with the ST extract and stimulated by LPS. The expressions of pro-inflammatory mediators were evaluated by using nitric oxide (NO) assay, enzyme-linked immunosorbent assay and Western blot analysis. After the C57BL/6 mice were exposed to CS, they were administrated with the ST extract. The accumulated inflammatory cells in the bronchoalveolar lavage fluid (BALF) were counted. Also, real-time polymerase chain reaction and hematoxylin and eosin staining were performed in lung tissues.

RESULTS

The ST extract treatment reduced the production of NO via blocking the expressions of cyclooxygenase-2 and inducible nitric oxide synthase protein in RAW 264.7 macrophages. In addition, ST extract treatment decreased the secretions of inflammatory cytokines and regulated NF-κB activation by inhibiting the phosphorylation of IκB and the mitogen-activated protein kinase pathway. Also, ST extract administration to mice reduced the infiltrations of macrophages into BALF and the histological inflammatory changes in lung tissues. Furthermore, administration of the ST extract regulated the levels of tumor necrosis factor-α, interleukin (IL)-6, IL-1β, monocyte chemoattractant protein-1 and matrix metalloproteinases-12 in the lungs.

CONCLUSION

These findings suggested that ST extract attenuated pulmonary inflammatory responses by inhibiting the expression of diverse inflammatory mediators in vivo and in vitro.

Stemona Alkaloids: Biosynthesis, Classification, and Biogenetic Relationships

Stemona alkaloids form a unique class, which can be attributed to hemiterpenoid pyrrolidine- and monoterpenoid pyrrolidine-class alkaloids originated from L-ornithine and glutamic acid. By the end of 2013, approximately 183 Stemona alkaloids had been isolated from nature. The literature on Stemona alkaloids in the realms of chemical structure, synthesis, and bioactivities has been elegantly summarized and reviewed. We thus summarize in this review the biosynthesis, structural classification, and the intrinsic, biogenetic relationships of Stemona alkaloids. Based on the comprehensive consideration of biogenetic pathways and chemical features, the 183 Stemona alkaloids are classified into two classes (hemiterpenoid pyrrolidine- and monoterpenoid pyrrolidine) and fourteen types.

Effect of Stemona spp. against Rhipicephalus microplus

Stemona plants have been traditionally used against various insects in Thailand and Southeast Asian countries. The acaricidal efficacy of 9 species of Stemona grown in Thailand was evaluated against dairy cattle tick, Rhipicephalus microplus using adult immersion test and in vivo evaluation on infested calves. From the ten Stemona root extracts used in this study, S. collinsiae of a concentration 250 mg/ml possessed the highest activity. In vivo study revealed that S. collinsiae extract could significantly reduce the attached ticks on calf skin compared to the control and promoted not significantly different efficacy from flumethrin, a common pyrethroid used in dairy farms. No side effect was found on calves during the experiment. The results confirmed traditional use of S. collinsiae as a better source of insecticide than other species and could be used as guidance for further development of S. collinsiae as a herbal acaricide.

TLC-Image Analysis of Non-Chromophoric Tuberostemonine Alkaloid Derivatives in Stemona Species

A simple, selective, precise, and accurate thin-layer chromatographic (TLC) image analytical method was developed and validated for simultaneous quantification of the major components in the root extracts of Stemona. tuberosa (tuberostemonine, tuberostemonine N and neotuberostemonine)), and S. phyllantha (tuberostemonine and tuberostemonine A). The analysis was performed by TLC on silica gel 60 F254 aluminum plates using a mixture of dichloromethane: ethyl acetate: methanol: ammonium hydroxide (50:45:4:1) as mobile phase. Post-derivatization was employed by dipping the TLC plate into Dragendorff's reagent to visualize the spots. Image analysis of the scanned TLC plate was performed to detect the contents of tuberostemonine derivatives. The polynomial regression data for the calibration plots showed good linear relationships within the concentration range of 2–7 μg/spot. The method gave satisfactory precision, accuracy, selectivity and could simultaneously quantify tuberostemonine, tuberostemonine A, tuberostemonine N and neotuberostemonine. Dried powdered roots of S. tuberosa grown in Thailand contained 1.31 + 0.28, 1.63 + 0.18 and 1.24 + 0.27% tuberostemonine, tuberostemonine N, and neotuberostemonine (dry weight), respectively, while S. phyllantha roots contained 1.39 + 0.14% tuberostemonine and 0.39 + 0.08 % tuberostemonine A (dry weight). The proposed method was simple, inexpensive, and more accessible to apply for many local authorities and small laboratories.

The diversity of Stemona stilbenoids as a result of storage and fungal infection

In relation to their biogenetic origin, 68 Stemona stilbenoids have been grouped into four structural types and are listed in order of increasing substitution pattern. Besides different hydroxylations and methoxylations, the rare C-methylations of the aromatic rings represent a typical chemical feature of these compounds. The formation of phenylbenzofurans constitutes another important chemical character separating Stemona species into two groups consistent with morphological and DNA data. Fungal infection leads to an increasing accumulation of stilbenes, dihydrostilbenes, and phenylbenzofurans with unsubstituted A-rings, suggesting the ecological role of these compounds as phytoalexins. Further oxygenations and methylations of both rings are interpreted as a result of aging or the drying processes. Bioautographic tests on TLC plates and germ-tube inhibition assays in microwells against four different fungi exhibited antifungal activities for almost all stilbenoids tested. Some derivatives also showed effects against yeasts and bacteria. Further activities may also be seen as dormancy-inducing factors of Stemona species occurring in periodically dry habitats. A leucotriene biosynthesis inhibition assay using 15 stilbenoids showed interesting structure-activity relationships, with more potent effects of some compounds than the commercial 5-lipoxygenase inhibitor zileuton being observed. Potential neuroprotective activities have been reported for three dihydrostilbene glucosides against 6-hydroxydopamine-induced neurotoxicity in human neuroblastoma SH-SY5Y cells.

HPLC Analysis of Stemokerrine and Oxystemokerrine in the Thai Medicinal Plant

A HPLC-UV method was developed and validated for determination of stemokerrine and oxystemokerrine in Stemona kerrii roots. The chromatographic separation was performed on a Hypersil BDS C18-column eluted with methanol: 50 mM ammonium acetate solution using a gradient system with a flow rate of 1 mL/min and detection at 300 nm. Stemokerrine and oxystemokerrine showed a linear relationship within the range of 0.5-100 μg/mL. The method was shown to be precise with a RSD <2%. The average percent recovery of stemokerrine was 101.6% and for oxystemokerrine 99.5%. Two samples of S. kerrii were analyzed and the average contents of stemokerrine and oxystemokerrine were 0.2 and 0.05%, w/w, respectively. The present work will provide a useful standardization method for S. kerrii raw materials for further pharmaceutical development.

HPLC quantitative analysis of insecticidal didehydrostemofoline and stemofoline in Stemona collinsiae root extracts

INTRODUCTION

Stemona spp. have been traditionally used as natural pesticides and medicinal plants. Stemona collinsiae Craib has been of interest for its insecticidal activity, which has been supported by many scientific research studies. The roots contain didehydrostemofoline and stemofoline alkaloids as active components.

OBJECTIVE

To develop and validate a HPLC method for the quantitative analysis of didehydrostemofoline and stemofoline in S. collinsiae root extracts.

METHODOLOGY

HPLC was carried out using a Hypersil BDS C₁₈-column eluted with methanol:1 m m ammonium acetate (55:45) with a flow rate of 1 mL/min and detection at 295 nm. Method validation was performed to assure its linearity, precision, accuracy and limits of detection and quantitation.

RESULTS

Didehydrostemofoline and stemofoline showed a linear relationship within the range of 0.5-432.4 and 0.5-188.4 µg/mL, respectively. The method was shown to be precise with RSD < 2%. The average recovery of didehydrostemofoline and stemofoline were 98.80 and 99.97%, respectively. Eight samples of S. collinsiae root extracts were analysed and the average contents of didehydrostemofoline and stemofoline were 0.78 and 0.048% w/w, respectively.

CONCLUSION

The HPLC method developed was appropriate for the analysis of didehydrostemofoline and stemofoline in S. collinsiae root extracts. This work would be useful as a guide for the standardisation of S. collinsiae root extract raw materials and their products as natural pesticides.

Structural relationships of stemona alkaloids: assessment of species-specific accumulation trends for exploiting their biological activities

On the basis of a comparison of 42 Stemona samples, representing eight different species collected and cultivated in Thailand, species-specific accumulation trends of Stemona alkaloids were analyzed. An overview was achieved by comparative HPLC analyses of methanolic crude extracts of underground parts coupled with diode array or evaporative light scattering detectors. All major compounds were isolated and their structures elucidated by NMR and MS analyses. Protostemonine- and stichoneurine-type derivatives dominated, from which the latter characterize S. tuberosa and S. phyllantha accumulating species-specific isomers of tuberostemonine (3). The widespread S. curtisii and S. collinsiae clearly deviate by protostemonine-type derivatives dominated by stemofoline (10) and/or didehydrostemofoline (11). Further diversification within this structural type results from a mutual accumulation of derivatives with a pyrrolo- or pyridoazepine nucleus, leading to chemical variability in S. curtisii and S. aphylla.

Phytochemical studies on Stemona aphylla: isolation of a new stemofoline alkaloid and six new stemofurans

A new stemofoline alkaloid, (2'S)-hydroxy-(11S,12R)-dihydrostemofoline (3), new stemofurans M-R (8-13), and known compounds stemofoline (1), (2'S)-hydroxystemofoline (2), stemofuran E (4), stemofuran F (5), stemofuran J (6), and stilbostemin F (7) have been isolated from the root extracts of Stemona aphylla. The structures and relative configurations of these new compounds have been determined by spectroscopic data interpretation and from semisynthetic studies. These natural and semisynthetic alkaloids were tested for acetylcholinesterase inhibitory activities and were found to be 10-20 times less active than 1',2'-didehydrostemofoline itself. Stemofurans 4, 6, 8, 11, and 13 were tested for their antibacterial and antifungal activities. Three of these showed antibacterial activities against MRSA with MIC values of 15.6 μg/mL.

Stemona alkaloids, from traditional Thai medicine, increase chemosensitivity via P-glycoprotein-mediated multidrug resistance

P-glycoprotein-mediated drug efflux can cause a multidrug resistance (MDR) phenotype that is associated with a poor response to cancer chemotherapy. Through bioassay-guided fractionation, active Stemona alkaloids were isolated from the roots of Stemona aphylla and S. burkillii. The chemical structures of isolated alkaloids were confirmed by HPLC, LC-MS and NMR as stemocurtisine and oxystemokerrine from S. aphylla, and stemofoline from S. burkillii. The isolated alkaloids were evaluated for synergistic growth inhibitory effect with cancer chemotherapeutic agents including vinblastine, paclitaxel and doxorubicin of KB-V1 cells (MDR human cervical carcinoma with P-gp expression), but not in KB-3-1 cells (drug sensitive human cervical carcinoma, which lack P-gp expression). Verapamil was employed as a comparative agent. The results showed that among these three isolated alkaloids; stemofoline exhibited the most potent effect in vitro in the reversal of P-gp-mediated MDR. Treatment with stemofoline at the various concentrations up to 72 h was able to significantly increase sensitivity of anticancer drugs including vinblastine, paclitaxel and doxorubicin in dose- and time-dependent manner in KB-V1 cells. The result obtained from this study indicated that Stemona alkaloids may play an important role as a P-gp modulator as used in vitro and may be effective in the treatment of multidrug-resistant cancers. This is the first report of new pharmacological activity of Stemona alkaloids, which could be a new potential MDR chemosensitizer.

Phytochemical investigations of Stemona curtisii and synthetic studies on stemocurtisine alkaloids

The isolation of two new Stemona alkaloids, 1-hydroxyprotostemonine and stemocurtisine N-oxide, and a new benzofuran, stemofuran L, from the root extracts of Stemona curtisii is reported. The major known alkaloids from this plant extract, stemocurtisine, stemocurtisinol, and oxyprotostemonine, were also isolated along with oxystemokerrine N-oxide. The nonalkaloid components of this extract included a new benzofuran derivative, stemofuran L, the known stemofurans F, J, and K, dihydro-γ-tocopherol, and stigmasterol. Stemocurtisine and stemocurtisinol were converted to their respective N-oxides by oxidation. Stemocurtisine was converted to a tetracyclic derivative by oxidative cleavage of the γ-butyrolactone ring, while stemocurtisinol gave a novel lactam derivative by oxidative cleavage of the C-4 side chain under basic conditions. The acetylcholinesterase inhibitory activities of some known and new alkaloids and their derivatives are also reported. All were 10-20 times less active as acetylcholinesterase inhibitors than the pyrrolo[1,2-a]azepine Stemona alkaloids stemofoline and 1',2'-didehydrostemofoline. None of the stemofuran compounds showed significant antibacterial or antifungal activities.

Antitussive and central respiratory depressant effects of Stemona tuberosa

AIMS OF THE STUDY

Stemona alkaloids with distinctly different chemical skeletons are recently reported as the active components in the antitussive herb Baibu derived from the root-tubers of Stemona tuberosa. This study aims to determine if alkaloids of this herb contribute equally to the antitussive functions, act on the same sites of cough reflex, and play any role in inducing central respiratory depressant effects.

MATERIALS AND METHODS

Antitussive potency of four major alkaloids was evaluated on guinea pigs with citric acid aerosol to induce cough. The action sites of the alkaloids on cough reflex pathway were tested with electrical stimulation of the superior laryngeal nerve in guinea pigs. The central respiratory effects of croomine were also tested on guinea pigs.

RESULTS

Croomine, neotuberostemonine and stemoninine showed similar antitussive potency, while tuberostemonine showed much weaker antitussive potency. Neotuberostemonine, tuberostemonine and stemoninine acted on the peripheral cough reflex pathway, while croomine acted on the central part. Croomine also showed obvious central respiratory depressant effects.

CONCLUSIONS

The four major Stemona alkaloids in Stemona tuberosa do not contribute equally to antitussive potency in guinea pigs. Neotuberostemonine, tuberostemonine and stemoninine target on peripheral cough reflex pathway. Croomine acts on central sites in the cough reflex pathway and demonstrates central respiratory depressant effects, which can partly account for the adverse reactions reported for the herb.

Pandanus alkaloids in Stemonaceae: finding of a plausible biogenetic origin of Stemona alkaloids

The isolation of (Z,Z)-pandanamine (1) and its corresponding isomers (Z,E)-pandanamine (2) and (E,E)-pandanamine (3) from Stichoneuron calcicola of the family Stemonaceae is of outstanding chemosystematic importance. This alkaloid was previously only known from the family Pandanaceae, where it was accompanied by a series of pyrrolidines, collectively called Pandanus alkaloids. The pyrrolidines pandamarilactonines A (4), B (5), C (6), and D (7) were also detected in the present study, most likely representing artificial cyclization products of pandanamine (1-3) formed by acidic conditions during chromatographic separation on silica gel. Similar structures were found in various Stemona alkaloids, suggesting a close relationship between the two plant families. Structurally, pandanamine (1-3) can be regarded as a direct precursor of croomine (8), originally isolated from Croomia, a genus closely related to Stichoneuron, but later also found in various Stemona species. The co-occurrence of pandanamine (1-3), croomine (8), and stichoneurin (9) in the family Stemonaceae represents a sound argument for a new interpretation of the biogenetic origin of Stemona alkaloids and at the same time substantiates the removal of the family from the order Dioscoreales and its inclusion into Pandanales, as already suggested by DNA sequencing.