Monoterpenoid Alkaloids Research Articles

Antivirulence and antipathogenic activity of Mayan herbal remedies against Pseudomonas aeruginosa

Ethnopharmacological relevanceThe Yucatan Peninsula has a privileged wealth of vascular plants with which various Mayan herbal formulations have been developed. However, studies on their antipathogenic and antivirulence properties are scarce. Aim of the studyIdentify antivirulence properties in Mayan herbal remedies and determine their antipathogenic capacity in burn wounds infected with Pseudomonas aeruginosa. Materials and methodsAn ethnobotanical study was conducted in Mayan communities in central and southern Quintana Roo, Mexico. Furthermore, the antipathogenic capacity of three Mayan herbal remedies was analyzed using an animal model of thermal damage and P. aeruginosa infection. Antivirulence properties were determined by inhibiting phenotypes regulated by quorum sensing (pyocyanin, biofilm, and swarming) and by the secretion of the ExoU toxin. The chemical composition of the most active herbal remedy was analyzed using molecular network analysis. ResultsIt was found that topical administration of the remedy called “herbal soap” (HS) for eleven days maintained 100% survival of the animals, reduced establishment of the bacteria in the burn and prevented its systemic dispersion. Although no curative effect was recorded on tissue damaged by HS treatment, its herbal composition strongly reduced swarming and ExoU secretion. Through analysis of Molecular Networks, it was possible to carry out a global study of its chemical components, and identify the family of oxindole monoterpenoid alkaloids and carboline and tetrahydropyrididole alkaloids. In addition, flavonols, flavan-3-ols, and quinic acid derivatives were detected. ConclusionsThe antipathogenic and antivirulence capacity of ancient Mayan remedies makes them a potential resource for developing new antibacterial therapies to treat burns infected by P. aeruginosa.

Monoterpenoid indole alkaloid adducts and dimers from Melodinus fusiformis

Eight unprecedented monoterpenoid indole alkaloid (MIA) adducts and dimers, melofusinines A–H (1–8), and three undescribed melodinus-type MIA monomers, melofusinines I–K (9–11), together with six putative biogenetic precursors were isolated from the twigs and leaves of Melodinus fusiformis Champ. ex Benth. Compounds 1 and 2 are unusual hybrid indole alkaloids incorporating an aspidospermatan-type MIA with a monoterpenoid alkaloid unit via C–C coupling. Compounds 3–8 feature the first MIA dimers constructed through an aspidospermatan-type monomer and a rearranged melodinus-type monomer with two different types of couplings. Their structures were elucidated by spectroscopic data, single crystal X-ray diffraction, and calculated electric circular dichroism spectra analysis. In addition, dimers 5 and 8 showed significant neuroprotection effects on MPP +-injured primary cortical neurons.

Cover Feature: Total Syntheses of (+)‐Villocarine A, (−)‐Apogeissoschizine, and (+)‐Geissoschizine (Chem. Eur. J. 18/2023)

Geissoschizine is a very important biosynthetic intermediate of monoterpenoid alkaloids in higher plants. In this study, the enantioselective and stereodivergent total syntheses of geissoschizine and two related indole alkaloids (villocarine A and apogeissoschizine) were achieved. The three synthesized natural products are represented as Nishikigoi (varicolored carp), which are also called “swimming jewels” in Japan, and the cascade reaction is represented by their graceful swimming along a river. More information can be found in the Research Article by H. Ishikawa and co-workers (DOI: 10.1002/chem.202300179).

Secondary metabolites from the Mongolian medicine Lomatogonium carinthiacum

Systematic phytochemical investigation on the Mongolian medicinal herb Lomatogonium carinthiacum led to the isolation of 12 monoterpenoids including three new secoiridoids (1, 2 and 4) and one new iridoid glycoside (13), one new monoterpenoid alkaloid (3), and three new sesquiterpenoids (14–16). Comprehensive spectroscopic analysis (including 1D and 2D NMR, and HRESIMS) and quantum chemistry computations (including ECD and NMR calculations) were applied to elucidate their structures. Weak immunosuppressive activities were observed for the new isolates via inhibiting T cell proliferation and cytokine IFN-γ secretion in vitro.

New C9 -Monoterpenoid Alkaloids Featuring a Rare Skeleton with Anti-Inflammatory and Antiviral Activities from Forsythia suspensa.

Forsyqinlingines C (1) and D (2), two C9 -monoterpenoid alkaloids bearing a rare skeleton, were isolated from the ripe fruits of Forsythia suspensa. Their structures, including absolute configurations, were fully elucidated by extensive spectroscopic data and ECD experiments. The plausible biogenetic pathway for compounds 1 and 2 was also proposed. In vitro, two C9 -monoterpenoid alkaloids showed anti-inflammatory activity performed by the inhibitory effect on the release of β-glucuronidase in rat polymorphonuclear leukocytes (PMNs), as well as antiviral activity against influenza A (H1N1) virus and respiratory syncytial virus (RSV).

Privileged Biorenewable Secologanin-Based Diversity-Oriented Synthesis for Pseudo-Natural Alkaloids: Uncovering Novel Neuroprotective and Antimalarial Frameworks.

Bioprivileged molecules hold great promise for supplementing petrochemicals in sustainable organic synthesis of a diverse bioactive products library. Secologanin, a biorenewable monoterpenoid glucoside with unique structural elements, is the key precursor for thousands of natural monoterpenoid alkaloids. Inspired by its inherent highly congested functional groups, a secologanin-based diversity-oriented synthesis (DOS) strategy for novel pseudo-natural alkaloids was developed. All the reactive units of secologanin were involved in these operation simplicity protocols under mild reaction conditions, including the one-step enantioselective transformation of exocyclic C8, C8/C11, and C8/C9/C10 as well as the chemoenzymatic manipulation of endocyclic C2/C6 via the attack by various nucleophiles. A combinatory scenario of the aforementioned reactions further provided diverse polycyclic products with multiple chiral centers. Preliminary activity screening of these newly constructed molecules led to the discovery of antimalarial and highly potent neuroprotective skeletons. The application of green biorenewable secologanin in diversity-oriented pseudo-natural monoterpenoid alkaloid synthesis might encourage the pursuit of valuable bioactive frameworks.

Biomimetic Synthesis of Iridoid Alkaloids as Novel Leads for Fungicidal and Insecticidal Agents.

Monoterpenoid alkaloids are well known for their broad and excellent biological activities, but their extremely low content and complex chemical structure limit their practical application. This study used the biosynthetic precursor genipin as a basic material to conduct a biomimetic synthesis of iridoid alkaloids. The structures of the iridoid alkaloids were characterized by 1H and 13C NMR spectroscopy and high-resolution mass spectrometry, and their fungicidal and insecticidal activities were evaluated. Bioassay results indicated that iridoid alkaloids possess good to excellent activities against phytopathogenic fungi, diamondback moth, bean aphid, and spider mite. Compound 3s had the most promising activity against three important phytopathogenic fungi Fusarium graminearum (LC50 value of 34.5 μg/mL with a 95% confidence interval of 33.4-35.5 μg/mL), Rhizoctonia solani (18 μg/mL, 15.7-20.8 μg/mL), and Botrytis cinerea (26 μg/mL, 22.4-30.4 μg/mL), thereby emerging as a potential new fungicidal lead. The structure-activity relationship research has shown that the electrical property and steric hindrance sizes of iridoid alkaloids apparently influence fungicidal activity. Moreover, compound 3n exhibited good insecticidal activity against diamondback moth with an LC50 (35.6 μg/mL, 95% confidence interval 19.0-66.6 μg/mL) comparable to that of the commercial insecticide rotenone (35.4 μg/mL, 95% confidence interval 22.2-56.4 μg/mL). This outcome indicates that this compound deserves further study as a potential lead for development of new insecticides.

Bisindole alkaloids from Tabernaemontana corymbosa

Continued study in bioactive monoterpenoid alkaloids led to the isolation of nine undescribed alkaloids, taberyunines A-I, together with 32 known ones from the aerial parts of Tabernaemontana corymbosa Roxb. ex Wall (Apocynaceae). Among the undescribed alkaloids, taberyunines A-G and H-I were assigned to Aspidosperma-Aspidosperma and Vobasinyl-Ibogan type bisindoles, respectively. Their structures were determined by NMR spectra, MS data and X-ray diffraction. Taberyunine B showed significant cytotoxicity against three cancer cell lines.

Cytotoxic monoterpenoid-type alkaloids from the aerial parts of Melodinus morsei

Three new monoterpenoid alkaloids, melomorines A–C (1–3), along with melohemsine B (4), were isolated from the 70% ethanol extract of the aerial parts of Melodinus morsei. Structural elucidation of all the compounds was performed on the basis of spectral data. All the compounds were tested in vitro for cytotoxic activities. As a result, alkaloids 1, 2, and 4 exhibited cytotoxicities against all the five tested tumor cell lines with IC50 value of less than 20 μM.

New monoterpenoid alkaloids from the aerial parts of Uncaria hirsuta

To investigate the chemical constituents of medicinal plant Uncaria hirsuta, three new monoterpenoid alkaloids, named hirsutanines A–C (1–3), were isolated. Their structures with absolute configurations were elucidated by means of NMR, X-ray diffraction and CD analysis. Compound 3 was the first dimeric monoterpenoid alkaloid obtained from genus Uncaria.

Scaffold Tailoring by a Newly Detected Pictet–Spenglerase Activity of Strictosidine Synthase: From the Common Tryptoline Skeleton to the Rare Piperazino-indole Framework

The Pictet-Spenglerase strictosidine synthase (STR1) has been recognized as a key enzyme in the biosynthesis of some 2000 indole alkaloids in plants, some with high therapeutic value. In this study, a novel function of STR1 has been detected which allows for the first time a simple enzymatic synthesis of the strictosidine analogue 3 harboring the piperazino[1,2-a]indole (PI) scaffold and to switch from the common tryptoline (hydrogenated carboline) to the rare PI skeleton. Insight into the reaction is provided by X-ray crystal analysis and modeling of STR1 ligand complexes. STR1 presently provides exclusively access to 3 and can act as a source to generate by chemoenzymatic approaches libraries of this novel class of alkaloids which may have new biological activities. Synthetic or natural monoterpenoid alkaloids with the PI core have not been reported before.

Improved accumulation of ajmalicine and tetrahydroalstonine in Catharanthus cells expressing an ABC transporter

The biosynthetic pathway of monoterpenoid indole alkaloids in Catharanthus roseus is located throughout various membranes at both the cellular and intercellular levels. ATP-binding cassette (ABC) transporters are known to export vincristine and vinblastine from human cancer cells. It has recently been shown that ABC transporters are also involved in the transport of various monoterpenoid alkaloids in Catharanthus roseus cells. Over-expression of an ABC transporter in this plant might therefore affect the regulation of the alkaloid biosynthetic pathway. CjMDR1, an ABC transporter gene originally isolated from Coptis japonica, was expressed in Catharanthus roseus cell cultures. Cells showing a positive PCR signal of the transgene in both cDNA and genomic DNA samples were subject to transport studies using selected substrates. Unexpectedly, transport of the isoquinoline alkaloid berberine, the main substrate of CjMDR1 transporter in Coptis japonica, was not affected as compared with control and wild-type Catharanthus cells. On the other hand, the endogenous alkaloids ajmalicine and tetrahydroalstonine were accumulated significantly more in Catharanthus roseus cells expressing CjMDR1 in comparison with control lines after feeding these alkaloids.

Vindoline Formation in Shoot Cultures of Catharanthus roseus is Synchronously Activated with Morphogenesis Through the Last Biosynthetic Step

The Madagascar periwinkle (Catharanthus roseus) produces the monoterpenoid alkaloid vindoline, which requires a specialized cell organization present only in the aerial tissues. Vindoline content can be affected by photoperiod and this effect seems to be associated with the morphogenetic capacity of branches; this association formed the basis of the study reported here. Vindoline-producing in vitro shoot cultures were exposed either to continuous light or a 16-h photoperiod regime. New plantlet formation and alkaloid biosynthesis were analysed throughout a culture cycle. In cultures under the photoperiod, the formation of new plantlets occurred in a more synchronized fashion as compared to those under continuous light. The accumulation of vindoline in cultures under the photoperiod occurred in co-ordination with plantlet formation, in contrast to cultures under continuous light, and coincided with a peak of activity of deacetylvindoline acetyl CoA acetyltransferase (DAT), the enzyme that catalyses the last step in vindoline biosynthesis. When new plantlet formation was blocked in cultures under the photoperiod by treatment with phytoregulators, vindoline synthesis was also reduced via an effect on DAT activity. No association between plantlet formation and other biosynthetic enzymes, such as tryptophan decarboxylase (TDC) and deacetoxyvindoline 4-hydroxylase (D4H), was found. Effects of light treatment on vindoline synthesis were not mediated by ORCA-3 proteins (which are involved in the induction of alkaloid synthesis in response to elicitation), suggesting that the presence of a different set of regulatory proteins. The data suggest that vindoline biosynthesis is associated with morphogenesis in shoot cultures of C. roseus.

Promoter analysis of the Catharanthus roseus geraniol 10-hydroxylase gene involved in terpenoid indole alkaloid biosynthesis

Geraniol 10-hydroxylase (G10H) is an important enzyme in the biosynthetic pathway of monoterpenoid alkaloids found in diverse plant species. The Catharanthus roseus G10H controls the first committed step in biosynthesis of terpenoid indole alkaloids (TIA). The C. roseus G10H promoter sequence was isolated by a PCR-based genome walking method. Sequence analysis revealed that the G10H promoter contains several potential eukaryotic regulatory elements involved in regulation of gene expression. The major transcription start site of the promoter was mapped to an adenine 31 bp downstream of the TATA-box. For functional characterization, transcriptional fusions between the G10H promoter fragments with 5′ or 3′ deletions and the GUS reporter gene were generated and their expressions were analyzed in a tobacco protoplast transient expression assay. Deletion of the promoter down to − 318 bp had little effect on GUS activity. However, further deletion of the promoter to position − 103 resulted in approximately 5-fold reduction of GUS activity. Gain-of-function experiments revealed the presence of three potential transcriptional enhancers located in regions between − 191 and − 147, − 266 and − 188, and − 318 and − 266, respectively. The G10H promoter was capable of conferring stable GUS expression in transgenic tobacco plants and C. roseus hairy roots. In transgenic tobacco seedlings GUS expression was tissue-specific, restricted to leaf and actively growing cells around the root tip, and not detected in the hypocotyls, root cap and older developing areas of the root. The GUS expression in both transgenic C. roseus hairy roots and tobacco seedlings were responsive to fungal elicitor and methyljasmonate. Compared to other known promoters of TIA pathway genes, the G10H promoter contains unique binding sites for several transcription factors, suggesting that the G10H promoter may be regulated by a different transcriptional cascade.

Geraniol 10-hydroxylase , a cytochrome P450 enzyme involved in terpenoid indole alkaloid biosynthesis

Geraniol 10-hydroxylase (G10H) is a cytochrome P450 monooxygenase involved in the biosynthesis of iridoid monoterpenoids and several classes of monoterpenoid alkaloids found in a diverse range of plant species. Catharanthus roseus (Madagascar periwinkle) contains monoterpenoid indole alkaloids, several of which are pharmaceutically important. Vinblastine and vincristine, for example, find widespread use as anti-cancer drugs. G10H is thought to play a key regulatory role in terpenoid indole alkaloid biosynthesis. We purified G10H from C. roseus cells. Using degenerate PCR primers based on amino acid sequence information we cloned the corresponding cDNA. The encoded CYP76B6 protein has G10H activity when expressed in C. roseus and yeast cells. The stress hormone methyljasmonate strongly induced G10h gene expression coordinately with other terpenoid indole alkaloid biosynthesis genes in a C. roseus cell culture.

Expression of two consecutive genes of a secondary metabolic pathway in transgenic tobacco: molecular diversity influences levels of expression and product accumulation.

We have created a population of transgenic tobacco plants carrying cDNAs encoding two consecutive enzymes from early stages in monoterpenoid alkaloid biosynthesis in Catharanthus roseus. The cDNAs, encoding tryptophan decarboxylase (tdc) and strictosidine synthase (str1) together with a selectable marker gene, were introduced on a single transforming plasmid into tobacco leaves by particle bombardment. Analysis of 150 independent transgenic plants at the DNA and RNA levels demonstrated a range of integration events and steady-state transcript levels for the tdc and str1 transgenes. Southern blot analysis indicated that the tdc and str1 transgenes were integrated at least once in all 150 transformants giving a 100% co-integration frequency of the two unselected genes carried on the same plasmid. A comparison of Southern and northern data suggested that in 26% of the plants, both tdc and str1 transgenes were silenced, 41% demonstrated a preferential silencing of either the tdc or the str1 transgene, with the remaining 33% of the plants expressing both transgenes. We observed no clear correlation between the number of integration events of a specific transgene and the levels of accumulated transcript. Twenty plants representing the range of molecular diversity in the transgenic population were selected for further analysis. Seeds were collected from self-fertilised transformants and germinated on medium containing kanamycin. Seedlings were harvested after 7 weeks and TDC and STR1 enzymatic assays were carried out. We observed a 24- and 110-fold variation in levels of TDC and STR1 activities, respectively. Our data correlate molecular diversity with biochemistry and accumulation of end-product and provide a detailed molecular and biochemical characterization of transgenic plants transformed with a single plasmid carrying two genes of secondary metabolism.

The biosynthesis of monoterpenoid indole alkaloids from strictosidine

The differential incorporation of doubly labelled strictosidine and vincoside into several indole alkaloids belonging to the Corynanthe(3α and 3β series), Aspidosperma, and Iboga types in three plant families has been studied, and it has been demonstrated that only strictosidine is incorporated while vincoside is metabolically inert in these plants with regard to alkaloid formation. During the conversion of strictosidine into the 3β-indole alkaloids, the hydrogen atom at the 3-position is lost, while it is retained during the biosynthesis of the 3α alkaloids. The chemical synthesis of [7-3H]secologanin, an important intermediate for further work in the biosynthesis of monoterpenoid alkaloids, is also described.

Venoterpine - a new monoterpenoid alkaloid from the fruits of [formula omitted] R.Br.

Venoterpine - a new monoterpenoid alkaloid from the fruits of [formula omitted] R.Br.

A new monoterpenoid alkaloid from Jasminum species and from Ligustrum novoguineense (family Oleaceae)

Jasminine, C11H12N2O3, a new monoterpenoid alkaloid isolated from several Jasminum species and from Ligustrum novoguineense Lingelsheim, has been shown to be (11), with the preferred conformation indicated in (IIa).

Alkaloid Studies—XXXII : Studies on skytanthus acutus meyen. The structure of the monoterpenoid alkaloid skytanthine

Investigation of a Chilean member of the Apocynaceae family, Skytanthus acutus Meyen, has led to the isolation of a new monoterpenoid alkaloid which we have named skytanthine. The isolation and structure elucidation of this alkaloid (VII) is described.