New alkaloids of the sarpagine group from Rauvolfia serpentina hairy root culture

Phytochemistry and biological activities of corynanthe alkaloids

Medicinal plants constitute a source for designing clinically useful drugs targeting diseases through various mechanisms. Plant secondary metabolites can be used as lead compounds of drugs. Corynanthe alkaloids are highly abundant natural bioactive substances of various core structures possessing important properties such as nerve excitation and antimalarial and analgesic effects. In this review, we summarize and review the state-of-the-art corynanthe-type alkaloid research focusing on phytochemistry, pharmacology, and structural chemistry. Approximately 120 articles reporting 231 alkaloids classified into simple corynanthe, yohimbine, oxindole corynanthe, mavacurane, sarpagine, akuammiline, strychnos, and ajmaline-type groups were compiled. Relevant biological properties discussed include antiviral, antibacterial, anti-inflammatory, antimalarial, muscle-relaxant, vasorelaxant, and analgesic activities and activities affecting the main nervous and cardiac systems, as well as NF-κB inhibitory and Na⁺-glucose cotransporter inhibitory properties. This review provides insights and a reference for future studies, thus paving the way for the discovery of drugs based on corynanthe alkaloids.

New Monoterpenoid Indole Alkaloids from Tabernaemontana crassa Inhibit β-Amyloid42 Production and Phospho-Tau (Thr217)

Eleven monoterpenoid indole alkaloids, including three new ones, tabercrassines A-C (1-3), were isolated from the seeds of Tabernaemontana crassa. Tabercrassine A (1) is an ibogan-ibogan-type bisindole alkaloid which is formed by the polymerization of two classic ibogan-type monomers through a C3 unit aliphatic chain. Their structures were established by extensive analysis of HRESIMS, NMR, and ECD spectra. Cellular assays showed that alkaloids 1-3 all reduce Aβ42 production and inhibit phospho-tau (Thr217), a new biomarker of Alzheimer's disease [AD] associated with BACE1-, NCSTN-, GSK3β-, and CDK5-mediated pathways, suggesting these alkaloids' potential against AD.

Genus Rauvolfia: A review of its ethnopharmacology, phytochemistry, quality control/quality assurance, pharmacological activities and clinical evidence

ETHNOPHARMACOLOGICAL RELEVANCE

The plants are from the genus Rauvolfia Plum. ex L. (Apocynaceae), which is represented by 74 species with many synonyms, and distributed worldwide, especially in the Asian, and African continents. Traditionally, some of them are used for the treatment of various disorders related to the central nervous system (CNS), cardiovascular diseases (CVD), and as an antidote due to the presence of monoterpene indole alkaloids (MIAs) such as ajmaline (144), ajmalicine (164) serpentine (182), yohimbine (190) and reserpine (214).

AIM

The present review provides comprehensive summarization and critical analysis of the traditional to modern applications of Rauvolfia species, and the major focus was to include traditional uses, phytochemistry, quality control, pharmacological properties, as well as clinical evidence that may be useful in the drug discovery process.

MATERIALS AND METHODS

Information related to traditional uses, chemical constituents, separation techniques/analytical methods, and pharmacological properties of the genus Rauvolfia were obtained using electronic databases such as Web of Science, Scopus, SciFinder, PubMed, PubChem, ChemSpider, and Google Scholar between the years 1949-2021. The scientific name of the species and its synonyms were checked with the information of The Plant List.

RESULTS

A total of seventeen Rauvolfia species have been traditionally explored for various therapeutic applications, out of which the roots of R. serpentina and R. vomitoria are used most commonly for the treatment of many diseases. About 287 alkaloids, seven terpenoids, nine flavonoids, and four phenolic acids have been reported in different parts of the forty-three species. Quality control (QC)/quality assurance (QA) of extracts/herbal formulations of Rauvolfia species was analyzed by qualitative and quantitative methods based on the major MIAs such as compounds 144, 164, 182, 190, and 214 using HPTLC, HPLC, and HPLC-MS. The various extracts of different plant parts of thirteen Rauvolfia species are explored for their pharmacological properties such as antimicrobial, antioxidant, antiprotozoal, antitrypanosomal, antipsychotic, cardioprotective, cholinesterase inhibitory, and hepatoprotective. Of which, clinical trials of herbal formulations/extracts of R. serpentina and MIAs have been reported for CVD, CNS, antihypertensive therapy, antidiabetic effects, and psoriasis therapy, while the extracts and phytoconstituents of remaining Rauvolfia species are predominantly significant, owning them to be additional attention for further investigation under clinical trials and QC/QA.

CONCLUSION

The present communication has provided a comprehensive, systematic, and critically analyzed vision into the traditional uses, phytochemistry, and modern therapeutic applications of the genus Rauvolfia are validated by scientific evidence. In addition, different plant parts from this genus, especially raw and finished herbal products of the roots of R. serpentina have been demonstrated for the QC/QA.

Bioinspired Transformations Using Strictosidine Aglycones: Divergent Total Syntheses of Monoterpenoid Indole Alkaloids in the Early Stage of Biosynthesis

A series of bioinspired transformations that are applied to convert strictosidine aglycones into monoterpenoid indole alkaloids is reported. The highly reactive key intermediates, strictosidine aglycones, were prepared in situ by simple removal of a silyl protecting group from the silyl ether derivatives, and converted selectively via bioinspired transformations under substrate control into heteroyohimbine- and corynantheine-type, and akagerine and naucleaoral related alkaloids. Thus, concise, divergent total syntheses of 13 monoterpenoid indole alkaloids, (-)-cathenamine, (-)-tetrahydroalstonine, (+)-dihydrocorynantheine, (-)-corynantheidine, (-)-akagerine, (-)-dihydrocycloakagerine, (-)-naucleaoral B, (+)-naucleidinal, (-)-naucleofficines D and III, (-)-nauclefiline, and (-)-naucleamides A and E, were accomplished in fewer than 13 steps.

Monoterpene Indole Alkaloids with Cav3.1 T-Type Calcium Channel Inhibitory Activity from Catharanthus roseus

Catharanthus roseus is a well-known traditional herbal medicine for the treatment of cancer, hypertension, scald, and sore in China. Phytochemical investigation on the twigs and leaves of this species led to the isolation of two new monoterpene indole alkaloids, catharanosines A (1) and B (2), and six known analogues (3–8). Structures of 1 and 2 were established by ¹H-, ¹³C- and 2D-NMR, and HREIMS data. The absolute configuration of 1 was confirmed by single-crystal X-ray diffraction analysis. Compound 2 represented an unprecedented aspidosperma-type alkaloid with a 2-piperidinyl moiety at C-10. Compounds 6–8 exhibited remarkable Ca_v3.1 low voltage-gated calcium channel (LVGCC) inhibitory activity with IC₅₀ values of 11.83 ± 1.02, 14.3 ± 1.20, and 14.54 ± 0.99 μM, respectively.

Bisindole Alkaloids from the Alstonia Species: Recent Isolation, Bioactivity, Biosynthesis, and Synthesis

Bisindoles are structurally complex dimers and are intriguing targets for partial and total synthesis. They exhibit stronger biological activity than their corresponding monomeric units. Alkaloids, including those containing C-19 methyl-substitution in their monomeric units, their synthetic derivatives, and their mismatched pairs can be attractive targets for synthesis and may unlock better drug targets. We herein discuss the isolation of bisindoles from various Alstonia species, their bioactivity, putative biosynthesis, and synthesis. The total synthesis of macralstonidine, macralstonine, O-acetylmacralstonine, and dispegatrine, as well as the partial synthesis of alstonisidine, villalstonine, and macrocarpamine are also discussed in this review. The completion of the total synthesis of pleiocarpamine by Sato et al. completes the formal synthesis of the latter two bisindoles.

Chemical Diversity and Bioactivities of Monoterpene Indole Alkaloids (MIAs) from Six Apocynaceae Genera

By the end of the twentieth century, the interest in natural compounds as probable sources of drugs has declined and was replaced by other strategies such as molecular target-based drug discovery. However, in the recent times, natural compounds regained their position as extremely important source drug leads. Indole-containing compounds are under clinical use which includes vinblastine and vincristine (anticancer), atevirdine (anti-HIV), yohimbine (erectile dysfunction), reserpine (antihypertension), ajmalicine (vascular disorders), ajmaline (anti-arrhythmic), vincamine (vasodilator), etc. Monoterpene Indole Alkaloids (MIAs) deserve the curiosity and attention of researchers due to their chemical diversity and biological activities. These compounds were considered as an impending source of drug-lead. In this review 444 compounds, were identified from six genera belonging to the family Apocynaceae, will be discussed. These genera (Alstonia, Rauvolfia, Kopsia, Ervatamia, and Tabernaemontana, and Rhazya) consist of 400 members and represent 20% of Apocynaceae species. Only 30 (7.5%) species were investigated, whereas the rest are promising to be investigated. Eleven bioactivities, including antibacterial, antifungal, anti-inflammatory and immunosuppressant activities, were reported. Whereas cytotoxic effect represents 47% of the reported activities. Convincingly, the genera selected in this review are a wealthy source for future anticancer drug lead.

Voacafrines A-N, aspidosperma-type monoterpenoid indole alkaloids from Voacanga africana with AChE inhibitory activity

Fourteen undescribed monoterpenoid indole alkaloids, voacafrines A-N, along with 7 known monoterpenoid indole alkaloids were isolated from the seeds of Voacanga africana Stapf. Among them, voacafrines A-G were aspidosperma-aspidosperma type bisindole alkaloids, while voacafrines H-N were aspidosperma-type monomers. Their structures and absolute configurations were elucidated by a combination of NMR, MS, and ECD analyses. Voacafrines A-C were characterized by an acetonyl moiety at C-5', while voacafrine H possessed a methoxymethyl moiety at C-14 within aspidosperma-type alkaloids. The acetylcholinesterase (AChE) inhibitory activity and cytotoxicity of voacafrines A-N were evaluated. Voacafrines A-C and E-G were bisindole alkaloids that exhibited AChE inhibitory activity with IC₅₀ values of 4.97-33.28 μM, while voacafrines I and J were monomers that showed cytotoxicity against several human cancer cell lines with IC₅₀ values of 4.45-7.49 μM.

Reflexin A, a new indole alkaloid from Rauvolfia reflexa induces apoptosis against colon cancer cells

One new indole alkaloid, reflexin A (1), and two known indoles, macusine B (2) and vinorine (3), were isolated from the bark of Rauvolfia reflexa. Their structures were elucidated by 1D and 2D NMR, UV, IR, and MS spectroscopic analyses. Compound 1 displayed anticancer activity against HCT-116 colon cancer cells with an IC₅₀ value of 30.24 ± 0.75 µM. The results implied that the newly isolated 1 induced apoptosis in HCT-116 cells, suggesting its possible role as an anticancer agent. In vivo acute toxicity study was performed on compound 1 to evaluate its safety profile.

Expanding the Diversity of Plant Monoterpenoid Indole Alkaloids Employing Human Cytochrome P450 3A4

Human drug‐metabolizing cytochrome P450 monooxygenases (CYPs) have enormous substrate promiscuity; this makes them promising tools for the expansion of natural product diversity. Here, we used CYP3A4 for the targeted diversification of a plant biosynthetic route leading to monoterpenoid indole alkaloids. In silico, in vitro and in planta studies proved that CYP3A4 was able to convert the indole alkaloid vinorine into vomilenine, the former being one of the central intermediates in the ajmaline pathway in the medicinal plant Rauvolfia serpentina (L.) Benth. ex Kurz. However, to a much larger extent, the investigated conversion yielded vinorine (19R,20R)‐epoxide, a new metabolite with an epoxide functional group that is rare for indole alkaloids. The described work represents a successful example of combinatorial biosynthesis towards an increase in biodiversity of natural metabolites. Moreover, characterisation of the products of the in vitro and in planta transformation of potential pharmaceuticals with human CYPs might be indicative of the route of their conversion in the human organism.

Three new compounds from the flower branch of Gastrodia elata Blume and anti-microbial activity

Three new compounds (1–3): gastrodinol (1), 2-(4′-hydroxybenzoyl)-3-hydroxyethyl indole (2) and 2-(4′-hydroxybenzoyl)-3-(4′′-hydroxybenzyl)indole (3) were isolated from the flower branch of G. elata, and anti-microbial activity.

Specific Synthesis of 3H-Indole Derivatives via Rh(III)-Catalyzed Cascade Annulation between N-Phenylbenzimidamides and Pyridotriazoles

An efficient synthetic method to construct 3H-indole derivatives has been successfully developed involving rhodium-catalyzed highly selective C-H bond activation of N-phenylbenzimidamides and subsequent couplings with pyridotriazoles. This cascade approach features excellent chemoselectivity and unique of products containing quaternary carbon center with the pyridyl moiety.

Bioactivity-Guided Isolation and Identification of New and Immunosuppressive Monoterpenoid Indole Alkaloids from Rauvolfia yunnanensis Tsiang

Three new 11-hydroxyburnamine (1) and rauvoyunnanines A-B (2-3), and fourteen known (4-17) monoterpenoid indole alkaloids were isolated from the total alkaloids extract of Rauvolfia yunnanensis, which exhibited promising immunosuppressive activity on T cell proliferation in preliminary screening. Their structures were determined by analysis of high-resolution electrospray ionization mass (HRESIMS), ultraviolet (UV) and nuclear magnetic resonance (NMR) data, and by comparison with the literature. All the alkaloids were evaluated for inhibitory activity on T cell proliferation. Among them, one new compound (1) and reserpine (6) exhibited moderate immunosuppressive activity, with IC50 values of 5.9 μM and 5.0 μM, respectively.

Performances of Alkaloid Extract from Rauvolfia macrophylla Stapf toward Corrosion Inhibition of C38 Steel in Acidic Media

Alkaloid extract from Rauvolfia macrophylla Stapf (AERMS) was studied as the corrosion inhibitor for C38 steel in 1 M HCl and 0.5 M H₂SO₄ using electrochemistry and surface analysis. The corrosion inhibition was efficient and proceeds via adsorption of AERMS on the steel surface due to the active functional groups present in the molecules. AERMS acts as a mixed inhibitor in HCl and as a cathodic inhibitor in H₂SO₄. In H₂SO₄ corrosive medium, the presence of iodides improves the adsorption of the alkaloid molecules by reducing the surface charge of the electrode and thus substantially decreases the corrosion rate. Two pure alkaloids (tetrahydroalastonine (THA) and perakine (PER)) were quantitatively isolated from AERMS, and their anticorrosive properties for C38 steel in 1 M HCl and 0.5 M H₂SO₄ were evaluated. THA showed the highest efficiency while the performance of PER was less important compared to the extract. This confirms that the efficiency of AERMS was the result of the complementary action of the chemical compounds present in the extract.

Antibacterial Indole Alkaloids with Complex Heterocycles from Voacanga africana

Voacafricines A and B, two unique monoterpenoid indole alkaloids each bearing five fused heterocycles, were obtained from the fruits of Voacanga africana. Their structures were elucidated by extensive spectroscopic methods and computational studies. A plausible biogenetic pathway was proposed from a common precursor, 19- epi-voacristine. Both compounds exhibited potent activity against Staphylococcus aureus and Salmonella typhi, and their activities were superior to those of the well-known antibacterial drugs berberine and fibrauretine.

Ethnopharmacology, phytochemistry, and biotechnological advances of family Apocynaceae: A review

The family Apocynaceae is one of the largest and important families in angiosperm. Several members of this family have medicinal properties and have been in the treatment of various ailments. Most of them are consumed as food by tribal people whereas a few plants are used as source of poison. Members of family Apocynaceae are rich in alkaloids, terpenoids, steroids, flavonoids, glycosides, simple phenols, lactones, and hydrocarbons. Other compounds such as sterols, lignans, sugars, lignans, and lactones have been isolated and systematically studied. Few studies have reported antioxidant, anti-inflammatory, antimicrobial, and cytotoxic activities of crude extracts as well as single compound(s) isolated from various members of the family Apocynaceae. Holarrhena antidysenterica, Rauvolfia serpentina, Carissa carandas, and Tabernaemontana divaricata are the extensively studied plants in this family. The present review provides a detailed outlook on ethnopharmacology, phytochemistry, and biological activities of selected members of this family. Moreover, it also covers the biotechnological advances used for large-scale production of bioactive compounds of therapeutic interest along with plant tissue culture-based approaches for conservation of this medicinally valuable family.

Taburnaemines A-I, Cytotoxic Vobasinyl-Iboga-Type Bisindole Alkaloids from Tabernaemontana corymbosa

Nineteen vobasinyl-ibogan-type bisindole alkaloids, including nine new compounds, taburnaemines A-I (1-9), were isolated from the twigs and leaves of Tabernaemontana corymbosa. The structures and absolute configurations of the new alkaloids were determined by a combination of MS, NMR, and ECD analyses. Alkaloids 1-5 contain a rare 1,3-oxazinane moiety in the vobasinyl unit, while 6 has an uncommon 1,3-oxazolidine moiety in the iboga unit. The absolute configurations of alkaloid 1 and the known alkaloid tabernaecorymbosine A (10) were confirmed by single-crystal X-ray diffraction analysis. All of the bisindole alkaloids, except 2 and 16'-decarbomethoxytabernaecorymbosine A (14), showed antiproliferative activity (IC₅₀ 2.6-9.8 μM) against several human cancer cell lines, including A-549, MDA-MB-231, MCF-7, KB, and P-glycoprotein-overexpressing multidrug-resistant KB cells. The preliminary structure-activity relationship correlations are also discussed.

Tabercorymines A and B, Two Vobasinyl-Ibogan-Type Bisindole Alkaloids from Tabernaemontana corymbosa

Tabercorymines A (1) and B (2), two new vobasinyl-ibogan-type bisindole alkaloids with an unprecedented skeleton, were isolated from Tabernaemontana corymbosa. Their structures were established by a combination of spectroscopic data, chemical transformation, single-crystal X-ray diffraction, and ECD calculation. Compound 1 represents a novel bisindole alkaloid, characterized by a caged heteropentacyclic ring system incorporating an unprecedented C-7/C-20 bond in the vobasinyl unit. Alkaloids 1 and 2 showed potent antiproliferative activity against several human cancer cell lines, including vincristine-resistant KB.

Elicitation Based Enhancement of Secondary Metabolites in Rauwolfia serpentina and Solanum khasianum Hairy Root Cultures

BACKGROUND

Rauwolfia serpentina and Solanum khasianum are well-known medicinally important plants contained important alkaloids in their different parts. Elicitation of these alkaloids is important because of associated pharmaceutical properties. Targeted metabolites were ajmaline and ajmalicine in R. serpentina; solasodine and α-solanine in S. khasianum.

OBJECTIVE

Enhancement of secondary metabolites through biotic and abiotic elicitors in hairy root cultures of R. serpentina and S. khasianum.

MATERIALS AND METHODS

In this report, hairy root cultures of these two plants were established through Agrobacterium rhizogenes mediated transformation by optimizing various parameters as age of explants, duration of preculture, and co-cultivation period. NaCl was used as abiotic elicitors in these two plants. Cellulase from Aspergillus niger was used as biotic elicitor in S. khasianum and mannan from Saccharomyces cerevisiae was used in R. serpentina.

RESULTS

First time we have reported the effect of biotic and abiotic elicitors on the production of important metabolites in hairy root cultures of these two plants. Ajmalicine production was stimulated up to 14.8-fold at 100 mM concentration of NaCl after 1 week of treatment. Ajmaline concentration was also increased 2.9-fold at 100 mg/l dose of mannan after 1 week. Solasodine content was enhanced up to 4.0-fold and 3.6-fold at 100 mM and 200 mM NaCl, respectively, after 6 days of treatments.

CONCLUSION

This study explored the potential of the elicitation strategy in A. rhizogenes transformed cell cultures and this potential further used for commercial production of these pharmaceutically important secondary metabolites.

SUMMARY

Hairy roots of Rauwolfia serpentina were subjected to salt (abiotic stress) and mannan (biotic stress) treatment for 1 week. Ajmaline and ajmalicine secondary metabolites were quantified before and after stress treatmentAjmalicine yield was enhanced up to 14.8-fold at 100 mM concentration of NaCl. Ajmaline content was also stimulated 2.9-fold at 100 mg/l dose of mannan after 1 weekHairy roots of Solanum khasianum were treated with cellulase (biotic elicitor) and salt (abiotic stress)Solasodine content was improved up to 4.0-fold and 3.6-fold at 100 mM and 200 mM NaCl, respectively, after 6.days of treatmentsThe α-solanine content increased to 1.6-fold after 24 h of treatment at 100 μg/mL cellulase concentration. Abbreviations used: MS medium: Murashige and Skoog medium, B5 medium: Gamborg B5 medium, OD: Optical Density, NaCl: Sodium Chloride.

Sarpagan-Ajmalan-Type Indoles: Biosynthesis, Structural Biology, and Chemo-Enzymatic Significance

The biosynthetic pathway of the monoterpenoid indole alkaloid ajmaline in the genus Rauvolfia, in particular Rauvolfia serpentina Benth. ex Kurz, is one of the few pathways that have been comprehensively uncovered. Every step in the progress of plant alkaloid biosynthesis research is due to the endeavors of several generations of scientists and the advancement of technologies. The tissue and cell suspension cultures developed in the 1970s by M.H. Zenk enabled the extraction of alkaloids and crude enzymes for use as experimental materials, thus establishing the foundation for further research on enzymatic reaction networks. In vivo NMR technology was first used in biosynthetic investigations in the 1990s following the invention of high-field cryo-NMR, which allowed the rapid and reliable detection of bioconversion processes within living plant cells. Shortly before, in 1988, a milestone was reached with the heterologous expression of the strictosidine synthase cDNA, which paved the way for the application of "reverse genetics" and "macromolecular crystallography." Both methods allowed the structural analysis of several Rauvolfia enzymes involved in ajmaline biosynthesis and expanded our knowledge of the enzyme mechanisms, substrate specificities, and structure-activity relationships. It also opened the door for rational enzyme engineering and metabolic steering. Today, the research focus of ajmaline biosynthesis is shifting from "delineation" to "utilization." The Pictet-Spenglerase strictosidine synthase, strictosidine glucosidase, together with raucaffricine glucosidase, as pioneers in this area, have become useful tools to generate "privileged structures" and "diversity oriented" syntheses, which may help to construct novel scaffolds and to set up libraries of sarpagan-ajmalan-type alkaloids in chemo-enzymatic approaches.

Hexacyclic monoterpenoid indole alkaloids from Rauvolfia verticillata

Five new hexacyclic monoterpenoid indole alkaloids, rauvovertine A (1), 17-epi-rauvovertine A (2), rauvovertine B (3), 17-epi-rauvovertine B (4), and rauvovertine C (5) together with 17 known analogues were isolated from the stems of Rauvolfia verticillata. Compounds 1/2 and 3/4 were obtained as C-17 epimeric mixtures due to rapid hemiacetal tautomerism in solution. The structures of 1-5 were established by spectroscopic analysis and with the aid of molecular modeling. The new alkaloids were evaluated for their cytotoxicity in vitro against human tumor HL-60, SMMC-7721, A-549, MCF-7, and SW-480 cell lines.

Sarpagine and Related Alkaloids

The sarpagine-related macroline and ajmaline alkaloids share a common biosynthetic origin, and bear important structural similarities, as expected. These indole alkaloids are widely dispersed in 25 plant genera, principally in the family Apocynaceae. Very diverse and interesting biological properties have been reported for this group of natural products. Isolation of new sarpagine-related alkaloids and the asymmetric synthesis of these structurally complex molecules are of paramount importance to the synthetic and medicinal chemists. A total of 115 newly isolated sarpagine-related macroline and ajmaline alkaloids, along with their physicochemical properties have been included in this chapter. A general and efficient strategy for the synthesis of these monomeric alkaloids, as well as bisindoles, has been presented, which involves application of the asymmetric Pictet-Spengler reaction (>98% ee) as a key step because of the ease of scale up of the tetracyclic template. Also included in this chapter are the syntheses of the sarpagine-related alkaloids, published since 2000.

Hybrid Monoterpenoid Indole Alkaloids Obtained as Artifacts from Rauvolfia tetraphylla

Five new hybrid monoterpenoid indole alkaloids bearing an unusual 2,2-dimethyl-4-oxopiperidin-6-yl moiety, namely rauvotetraphyllines F-H (1, 3, 4), 17-epi-rauvotetraphylline F (2) and 21-epi-rauvotetraphylline H (5), were isolated from the aerial parts of Rauvolfia tetraphylla. Their structures were established by extensive spectroscopic analysis. The new alkaloids were evaluated for their cytotoxicity in vitro against five human cancer cell lines.

Determination of terpenoid indole alkaloids in hairy roots of Rhazya stricta (Apocynaceae) by GC-MS

INTRODUCTION

Rhazya stricta Decne. (Apocynaceae) is a medicinal plant rich in terpenoid indole alkaloids (TIAs), some of which possess important pharmacological properties. The study material including transgenic hairy root cultures have been developed and their potential for alkaloid production are being investigated.

OBJECTIVE

In this study, a comprehensive GC-MS method for qualitative and quantitative analysis of alkaloids from Rhazya hairy roots was developed.

METHODS

The composition of alkaloids was determined by using GC-MS. In quantification, the ratio between alkaloid and internal standard was based on extracted ion from total ion current (TIC) analyses.

RESULTS

The developed method was validated. An acceptable precision with RSD ≤ 8% over a linear range of 1 to 100 µg/mL was achieved. The accuracy of the method was within 94-107%. Analysis of hairy root extracts indicated the occurrence of a total of 20 TIAs. Six of them, pleiocarpamine, fluorocarpamine, vincamine, ajmalicine and two yohimbine isomers are reported here for the first time in Rhazya. Trimethylsilyl (TMS) derivatisation of the extracts resulted in the separation of two isomers for yohimbine and also for vallesiachotamine. Clearly improved chromatographic profiles of TMS-derivatives were observed for vincanine and for minor compounds vincamine and rhazine.

CONCLUSION

The results show that the present GC-MS method is reliable and well applicable for studying the variation of indole alkaloids in Rhazya samples.

General strategy for synthesis of C-19 methyl-substituted sarpagine/macroline/ajmaline indole alkaloids including total synthesis of 19(S),20(R)-dihydroperaksine, 19(S),20(R)-dihydroperaksine-17-al, and peraksine

A detailed account of the development of a general strategy for synthesis of the C-19 methyl-substituted alkaloids including total synthesis of 19(S),20(R)-dihydroperaksine-17-al (1), 19(S),20(R)-dihydroperaksine (2), and peraksine (6) is presented. Efforts directed toward the total synthesis of macrosalhine chloride (5) are also reported. Important to success is the sequence of chemical reactions which include a critical haloboration reaction, regioselective hydroboration, and controlled oxidation (to provide sensitive enolizable aldehydes at C-20). In addition, the all-important Pd-catalyzed α-vinylation reaction has been extended to a chiral C-19 alkyl-substituted substrate for the first time. Synthesis of the advanced intermediate 64 completes an improved formal total synthesis of talcarpine (26) and provides a starting point for synthesis of macroline-related alkaloids 27-31. Similarly, extension of this synthetic strategy in the ring A oxygenated series should provide easy access to the northern hemisphere 32b of the bisindoles angustricraline, alstocraline, and foliacraline (Figure 4 ).

Identification of novel human dipeptidyl peptidase-IV inhibitors of natural origin (Part II): in silico prediction in antidiabetic extracts

BACKGROUND

Natural extracts play an important role in traditional medicines for the treatment of diabetes mellitus and are also an essential resource for new drug discovery. Dipeptidyl peptidase IV (DPP-IV) inhibitors are potential candidates for the treatment of type 2 diabetes mellitus, and the effectiveness of certain antidiabetic extracts of natural origin could be, at least partially, explained by the inhibition of DPP-IV.

METHODOLOGY/PRINCIPAL FINDINGS

Using an initial set of 29,779 natural products that are annotated with their natural source and an experimentally validated virtual screening procedure previously developed in our lab (Guasch et al.; 2012) [1], we have predicted 12 potential DPP-IV inhibitors from 12 different plant extracts that are known to have antidiabetic activity. Seven of these molecules are identical or similar to molecules with described antidiabetic activity (although their role as DPP-IV inhibitors has not been suggested as an explanation for their bioactivity). Therefore, it is plausible that these 12 molecules could be responsible, at least in part, for the antidiabetic activity of these extracts through their inhibitory effect on DPP-IV. In addition, we also identified as potential DPP-IV inhibitors 6 molecules from 6 different plants with no described antidiabetic activity but that share the same genus as plants with known antidiabetic properties. Moreover, none of the 18 molecules that we predicted as DPP-IV inhibitors exhibits chemical similarity with a group of 2,342 known DPP-IV inhibitors.

CONCLUSIONS/SIGNIFICANCE

Our study identified 18 potential DPP-IV inhibitors in 18 different plant extracts (12 of these plants have known antidiabetic properties, whereas, for the remaining 6, antidiabetic activity has been reported for other plant species from the same genus). Moreover, none of the 18 molecules exhibits chemical similarity with a large group of known DPP-IV inhibitors.

Stereoselective, nitro-Mannich/lactamisation cascades for the direct synthesis of heavily decorated 5-nitropiperidin-2-ones and related heterocycles

A versatile nitro-Mannich/lactamisation cascade for the direct stereoselective synthesis of heavily decorated 5-nitropiperidin-2-ones and related heterocycles has been developed. A highly enantioenriched substituted 5-nitropiperidin-2-one was synthesised in a four component one-pot reaction combining an enantioselective organocatalytic Michael addition with the diastereoselective nitro-Mannich/lactamisation cascade. Protodenitration and chemoselective reductive manipulation of the heterocycles was used to install contiguous and fully substituted stereocentres in the synthesis of substituted piperidines.

Rauvotetraphyllines A-E, new indole alkaloids from Rauvolfia tetraphylla

Five new indole alkaloids rauvotetraphyllines A–E (1–5), together with eight known analogues, were isolated from the aerial parts of Rauvolfia tetraphylla. The structures were established by means of spectroscopic methods.

Indole alkaloids from Ervatamia chinensis

Four vobasinyl-ibogan type bisindole alkaloids, ervachinines A-D (1-4), along with 12 known terpenoid indole alkaloids, were isolated from the whole plant of Ervatamia chinensis. Their structures were elucidated by analysis of spectroscopic data, including 1D and 2D NMR, and the absolute configurations of 1-4 were determined by CD exciton chirality method. All of the compounds were evaluated for in vitro cytotoxicity against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480. Bisindole alkaloids 1-6 exhibited inhibitory effects, with IC(50) values comparable to those of cisplatin.

Three new indole alkaloids from Rauvolfia yunnanensis

One rare tetracyclic macroline-type indole alkaloid, named rauvoyunine A (1), and two new picraline-type alkaloids rauvoyunines B and C (2 and 3) were isolated from the aerial parts of Rauvolfia yunnanensis. Their structures were elucidated on the basis of extensive spectroscopic analysis. Compounds 2 and 3 were evaluated for their in vitro cytotoxicity against five human tumor cell lines.

Regiospecific, enantiospecific total synthesis of C-19 methyl substituted sarpagine alkaloids dihydroperaksine-17-al and dihydroperaksine

The optically active tetracyclic ketone 8 was converted into the pentacylic core 14 of the C-19 methyl substituted N(a)-H sarpagine and ajmaline alkaloids via a critical haloboration reaction. The ketone 14 was then employed in the total synthesis of 19(S),20(R)-dihydroperaksine-17-al (1) and 19(S),20(R)-dihydroperaksine (2). The key regioselective hydroboration and controlled oxidation-epimerization sequence developed in this approach should provide a general method to functionalize the C(20)-C(21) double bond in the ajmaline-related indole alkaloids.

Cytotoxic indole alkaloids from Melodinus tenuicaudatus

Four new bisindole alkaloids, melodinines H-K (1-4), a new monomer, melodinine L (5), and 11 known alkaloids were isolated from Melodinus tenuicaudatus. The structures of 1-5 were elucidated by extensive spectroscopic methods, and the known compounds were identified by comparison with data in the literature. All of the compounds were evaluated for their cytotoxicity against five human cancer cell lines. Alkaloids 1, 3, and 4 and the known compound 11-methoxytabersonine (8) exhibited inhibitory effects, with IC(50) values comparable to those of cisplatin and vinorelbine.

Melodinines A-G, monoterpenoid indole alkaloids from Melodinus henryi

Nineteen monoterpenoid indole alkaloids including seven new ones, melodinines A-G (1-7), were isolated from Melodinus henryi. The structures of the new compounds were elucidated using spectroscopic methods, and the structure of compound 4 was confirmed by single-crystal X-ray diffraction analysis. The known compounds were identified by comparing their spectroscopic data with those reported in the literature. All of the compounds were evaluated for cytotoxic activity against five human cancer cell lines, and compound 11 exhibited cytotoxicity against HL-60, SMMC-7721, A-549, and SK-BR-3 cells with IC50 values of 2.0, 16.8, 25.9, and 24.7 microM, respectively.

Monoterpenoid indole alkaloids from Alstonia yunnanensis

Eight new monoterpenoid indole alkaloids, alstoyunines A-H (1-8), along with 17 known analogues, were isolated from Alstonia yunnanensis. The structures of the new alkaloids were established by means of extensive spectroscopic methods. Alstoyunines C (3), E (5), and F (6) showed selective inhibition of Cox-2 (>75%). Alstoyunine F (6) showed weak cytotoxicity against the human myeloid leukemia HL-60 (IC50 = 3.89 microM) and hepatocellular carcinoma SMMC-7721 (IC50 = 21.73 microM) cell lines.

Purification, cloning, functional expression and characterization of perakine reductase: the first example from the AKR enzyme family, extending the alkaloidal network of the plant Rauvolfia

Perakine reductase (PR) catalyzes an NADPH-dependent step in a side-branch of the 10-step biosynthetic pathway of the alkaloid ajmaline. The enzyme was cloned by a "reverse-genetic" approach from cell suspension cultures of the plant Rauvolfia serpentina (Apocynaceae) and functionally expressed in Escherichia coli as the N-terminal His(6)-tagged protein. PR displays a broad substrate acceptance, converting 16 out of 28 tested compounds with reducible carbonyl function which belong to three substrate groups: benzaldehyde, cinnamic aldehyde derivatives and monoterpenoid indole alkaloids. The enzyme has an extraordinary selectivity in the group of alkaloids. Sequence alignments define PR as a new member of the aldo-keto reductase (AKR) super family, exhibiting the conserved catalytic tetrad Asp52, Tyr57, Lys84, His126. Site-directed mutagenesis of each of these functional residues to an alanine residue results in >97.8% loss of enzyme activity, in compounds of each substrate group. PR represents the first example of the large AKR-family which is involved in the biosynthesis of plant monoterpenoid indole alkaloids. In addition to a new esterase, PR significantly extends the Rauvolfia alkaloid network to the novel group of peraksine alkaloids.