Rauvomines A and B, Two Monoterpenoid Indole Alkaloids from Rauvolfia vomitoria

Formation of Trideuteromethylated Artifacts of Pyrrole-Containing Natural Products

Pyrrole-containing natural products form a large group of structurally diverse compounds that occur in both terrestrial and marine organisms. In the present study the formation of trideuteromethylated artifacts of pyrrole-containing natural products was investigated, focusing on the discorhabdins. Three deuterated discorhabdins, 1, 3, and 5, were identified to be isolation procedure artifacts caused by the presence of DMSO-d6 during NMR sample preparation and handling. Three additional semisynthetic derivatives, 7-9, were made during the investigation of the mechanism of formation, which was shown to be driven by trideuteromethyl radicals in the presence of water, methanol, TFA, and traces of iron in the deuterated solvent. Generation of trideuteromethylated artifacts was also confirmed for other classes of pyrrole-containing metabolites, namely, makaluvamines, tambjamines, and dibromotryptamines, which had also been dissolved in DMSO-d6 during the structure elucidation process. Semisynthetic discorhabdins were assessed for antiproliferative activity against a panel of human tumor cell lines, and 14-trideuteromethyldiscorhabdin L (3) averaged low micromolar potency.

Discovery of Unusual Ajmaline-Macroline Type Bisindole Alkaloids from Alstonia macrophylla by Building Blocks-Based Molecular Networking

Three unusual ajmaline-macroline type bisindole alkaloids, alsmaphylines A-C, together with their postulated biogenetic precursors, were isolated from the stem barks and leaves of Alstonia macrophylla via the building blocks-based molecular network (BBMN) strategy. Alsmaphyline A represents a rare ajmaline-macroline type bisindole alkaloid with an S-shape polycyclic ring system. Alsmaphylines B and C are two novel ajmaline-macroline type bisindole alkaloids with N-1-C-21' linkages, and the former possesses an unconventional stacked conformation due to the presence of intramolecular noncovalent interactions. The chemical structures including absolute configurations of alsmaphylines A-C were established by comprehensive spectroscopic analyses, electronic circular dichroism (ECD) calculations, and single-crystal X-ray crystallography. In addition, a plausible biosynthetic pathway of these bisindole alkaloids as well as their ability to promote the protein synthesis on HT22 cells were discussed.

Mukaiyama aldol reaction: an effective asymmetric approach to access chiral natural products and their derivatives/analogues

The Mukaiyama aldol reaction is generally a Lewis-acid catalyzed cross-aldol reaction between an aldehyde or ketone and silyl enol ether. It was first described by Mukaiyama in 1973, almost 5 decades ago, to achieve the enantioselective synthesis of β-hydroxy carbonyl compounds in high percentage yields. Mukaiyama aldol adducts play a pivotal role in the synthesis of various naturally occurring and medicinally important organic compounds such as polyketides, alkaloids, macrolides, etc. This review highlights the significance of the Mukaiyama aldol reaction towards the asymmetric synthesis of a wide range of biologically active natural products reported recently (since 2020).

Discovery of 3-Formyl-N-(un)Substituted Benzylindole Pyrimidines as an Acaricidal Agent and Their Mechanism of Action

To discover the pronounced acaricide candidate, herein, a series of 3-formyl-N-(un)substituted benzylindole pyrimidines were prepared by structural modification of indoles at the N-1 and C-3 positions via the successive Vilsmeier-Haack-Arnold (VHA), aldol condensation, and cyclization reactions. The steric structures of nine compounds were undoubtedly confirmed by X-ray single-crystallography. Against Tetranychus cinnabarinus Boisduval, compounds V-15, V-31, V-34, V-42, V-44, and V-60 exhibited promising acaricidal activity with LC50 values of 0.299-0.481 mg/mL. In particular, compound V-34 displayed 4.2 times the acaricidal activity of its precursor 6-methylindole. Scanning electron microscopy (SEM) imaging revealed that the construction of the cuticle layer of V-34-treated T. cinnabarinus was seriously destroyed. Furthermore, RNA-Seq analysis indicated that compound V-34 could regulate the homeostasis metabolism of T. cinnabarinus through arachidonic acid and linoleic acid metabolism and lysosome pathways. These results suggested that compound V-34 can be further studied as a lead acaricidal agent.

Indole Alkaloids of Rauvolfia ligustrina and Their Anxiolytic Effects in Adult Zebrafish

Rauvolfia species are well known as producers of bioactive monoterpene indole alkaloids, which exhibit a broad spectrum of biological activities. A new vobasine-sarpagan-type bisindole alkaloid (1: ) along with six known monomeric indoles (2, 3/4, 5: , and 6/7: ) were isolated from the ethanol extract of the roots of Rauvolfia ligustrina. The structure of the new compound was elucidated by interpretation of their spectroscopic data (1D and 2D NMR and HRESIMS) and comparison with published data for analog compounds. The cytotoxicity of the isolated compounds was screened in a zebrafish (Danio rerio) model. The possible GABAergic (diazepam as the positive control) and serotoninergic (fluoxetine as the positive control) mechanisms of action in adult zebrafish were also evaluated. No compounds were cytotoxic. Compound 2: and the epimers 3: /4: and 6: /7: showed a mechanism action by GABAA, while compound 1: showed a mechanism action by a serotonin receptor (anxiolytic activity). Molecular docking studies showed that compounds 2: and 5: have a greater affinity by the GABAA receptor when compared with diazepam, whereas 1: showed the best affinity for the 5HT2AR channel when compared to risperidone.

Aconicumines A-D, an advanced class of norditerpenoid alkaloids with an unprecedented N,O-diacetal motif from Aconitum taipeicum Hand.-Mazz., exhibit anti-inflammatory properties in vitro

Aconicumines A-D, an advanced class of norditerpenoid alkaloids, and seven known alkaloids, were isolated from Aconitum taipaicum Hand.-Mazz. (Ranunculaceae). The structures of the previously undescribed compounds, including their absolute configurations, were fully elucidated based on spectroscopic and single-crystal X-ray diffraction data analysis. Aconicumines A-D exhibit interesting cage-like structure, characterised by an unprecedented N,O-diacetal moiety (C6-O-C19-N-C17-O-C7) that has not been previously observed in diterpenoid alkaloids. Possible biosynthetic pathways for aconicumines A-D were proposed. Aconitine, hypaconitine, and aconicumine A showed significant inhibition of nitric oxide production in RAW 264.7 macrophages induced by lipopolysaccharide with IC₅₀ values ranging from 4.1 to 19.7 μM compared to positive control (dexamethasone, IC₅₀ = 12.5 μM). Furthermore, the primary structure-activity relationships for aconicumines A-D were also represented.

Total Synthesis of Vinorine

The asymmetric total synthesis of vinorine, a polycyclic and cage-like alkaloid, has been realized in a flexible approach. Key features of the current synthesis include an aza-Achmatowicz rearrangement/Mannich-type cyclization to install the highly functional 9-azabicyclo-[3.3.1]nonane scaffold, a high yield Fischer indole annulation to synthesize the common intermediate for sarpagine-ajamaline type alkaloids, and an Ireland-Claisen rearrangement to construct the C15-C20 bond.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

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.

Rauwolfia vomitoria extract suppresses benign prostatic hyperplasia by inducing autophagic apoptosis through endoplasmic reticulum stress

Background

The current drug treatments for benign prostatic hyperplasia (BPH) have negative side effects. Therefore, it is important to find effective alternative therapies with significantly fewer side effects. Our previous study revealed that Rauwolfia vomitoria (RWF) root bark extract reversed BPH development in a rat model. However, the molecular mechanism of its inhibitory effects on BPH remains largely unknown.

Methods

BPH-1 and WPMY-1 cell lines derived from BPH epithelial and prostatic stromal compartments were selected to investigate how RWF extract inhibits BPH in vitro by MTT and flow cytometry assays. Microarray, quantitative real-time PCR, immunoblotting, and GFP-LC3 immunofluorescence assays were performed to evaluate the effects of RWF extract on endoplasmic reticulum stress (ER stress) and autophagic apoptosis pathways in two cell lines. A human BPH ex vivo explant assay was also employed for validation.

Results

RWF extract treatment decreased cell viability and induced apoptotic cell death in both BPH-1 and WPMY-1 cells in a concentration-dependent manner with the increase of pro-apoptotic PCDC4 protein. RWF extract induced autophagy by enhancing the levels of autophagic genes (ULK2 and SQSTM1/p62) and the LC3II:LC3I ratio, with the increase of GFP-LC3 puncta. Moreover, RWF extract activated PERK- and ATF6-associated ER stress pathways by inducing the transcriptional levels of EIF2AK3/PERK, DDIT3/CHOP and ATF6, accompanied by the reduction of BiP protein level, but not its mRNA level. Another ER stress pathway was not induced by RWF extract, as manifested by the lack of XBP1 splicing. Pharmacological inhibition of autophagy by 3-methyladenine abrogated apoptosis but not ER stress; while inhibition of ER stress by 4-phenylbutyrate alleviated the induction of autophagy and apoptosis. In addition, pretreatments with either 3-methyladenine or 4-phenylbutyrate suppressed RWF extract-induced cytotoxicity. Notably, the inductions of PERK- and ATF6-related stress pathways and autophagic apoptosis were confirmed in a human BPH ex vivo explant.

Conclusions

Our data have demonstrated that RWF extract significantly suppressed the viabilities of BPH epithelial cells and BPH myofibroblasts by inducing apoptosis via upregulating ER stress and autophagy. These data indicate that RWF extract is a potential novel alternative therapeutic approach for BPH.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03610-4.

Structure units oriented approach towards collective synthesis of sarpagine-ajmaline-koumine type alkaloids

Sarpagine-Ajmaline-Koumine type monoterpenoid indole alkaloids represent a fascinating class of natural products with polycyclic and cage-like structures, interesting biological activities, and related biosynthetic origins. Herein we report a unified approach towards the asymmetric synthesis of these three types of alkaloids, leading to a collective synthesis of 14 natural alkaloids. Among them, akuammidine, 19-Z-akuammidine, vincamedine, vincarine, quebrachidine, vincamajine, alstiphylianine J, and dihydrokoumine are accomplished for the first time. Features of our synthesis are a new Mannich-type cyclization to construct the key indole-fused azabicyclo[3.3.1]nonane common intermediate, a SmI₂ mediated coupling to fuse the aza-bridged E-ring, stereoselective olefinations to install either the 19-E or 19-Z terminal alkenes presented in the natural alkaloids, and an efficient iodo-induced cyclization to establish the two vicinal all-carbon quaternary centers in the Koumine-type alkaloids.

Do Double-Hybrid Exchange-Correlation Functionals Provide Accurate Chemical Shifts? A Benchmark Assessment for Proton NMR

A benchmark density functional theory (DFT) study of ¹H NMR chemical shifts for data sets comprising 200 chemical shifts, including complex natural products, has been carried out to assess the performance of DFT methods. Two new benchmark data sets, NMRH33 and NMRH148, have been established. The meta-GGA revTPSS performs remarkably well against the NMRH33 benchmark set (mean absolute deviation (MAD), 0.10 ppm; maximum deviation (max), 0.26 ppm) with the smallest MAD of all evaluated functionals. The best-performing double-hybrid density functional (DHDF), revDSD-BLYP (MAD, 0.16 ppm; max, 0.35 ppm), performs similarly to hybrid-GGA methods (e.g., mPW1PW91/6-311G(d) (MAD, 0.15 ppm; max, 0.36 ppm)), but at a considerably higher computational cost. The results indicate that currently available double-hybrid DFT methods offer no benefit over GGA (including hybrid and meta) functionals in the calculation of ¹H NMR chemical shifts.

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.

Discovery of natural anti-inflammatory alkaloids: Potential leads for the drug discovery for the treatment of inflammation

Inflammation is an adaptive response of the immune system to tissue malfunction or homeostatic imbalance. Corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs) are frequently applied to treat varieties of inflammatory diseases but are associated with gastrointestinal, cardiovascular, and kidney side effects. Developing more effective and less toxic agents remain a challenge for pharmaceutical chemist due to the complexity of the different inflammatory processes. Alkaloids are widely distributed in plants with diverse anti-inflammatory activities, providing various potential lead compounds or candidates for the design and discovery of new anti-inflammatory drug candidates. Therefore, re-examining the anti-inflammatory alkaloid natural products is advisable, bringing more opportunities. In this review, we summarized and described the recent advances of natural alkaloids with anti-inflammatory activities and possible mechanisms in the period from 2009 to 2020. It is hoped that this review of anti-inflammatory alkaloids can provide new ideas for researchers engaged in the related fields and potential lead compounds for the discovery of anti-inflammatory drugs.

Monoterpenoid indole alkaloids from the fruits of Gelsemium elegans and their anti-inflammatory activities

Two novel monoterpenoid indole alkaloids (MIAs), gelsechizines A-B (1-2), along with four known ones (3-6) were isolated from the fruits of Gelsemium elegans. Compound 1 features a new carbon skeleton with two additional carbon atoms forming a 4-methylpyridine unit. Their structures with absolute configurations were elucidated by NMR, MS, X-ray diffraction and electronic circular dichroism (ECD) calculations. Compounds 1-3 showed significant anti-inflammatory effects in vivo and in vitro, which may be related to the inhibition of the trecruitment of neutrophils and macrophages as well as the secretion of TNF-α and IL-6. Preliminary structure-activity relationship analysis revealed that the β-N-acrylate moiety plays an important role in the anti-inflammatory effect.

Cytotoxic Yohimbine-Type Alkaloids from the Leaves of Rauvolfia vomitoria

Two new yohimbine-type monoterpene indole alkaloids, rauvines A and B, and six known derivatives were obtained from the leaves of R. vomitoria. The structures of rauvines A and B were determined by extensive spectroscopic analyses, ¹³ C-NMR, and ECD calculations. This is the first time to determine the absolute configurations of yohimbine-type N-oxides by quantum chemistry calculations (¹³ C-NMR and ECD calculations). All the isolates were tested for their cytotoxicity against five human cancer cell lines. Rauvine B showed moderate cytotoxicity on human MCF-7 breast, SWS80 colon, and A549 lung cancer cell lines with IC₅₀ values of 25.5, 22.6, and 26.0 μM, respectively.

Deploying Microbial Synthesis for Halogenating and Diversifying Medicinal Alkaloid Scaffolds

Plants produce some of the most potent therapeutics and have been used for thousands of years to treat human diseases. Today, many medicinal natural products are still extracted from source plants at scale as their complexity precludes total synthesis from bulk chemicals. However, extraction from plants can be an unreliable and low-yielding source for human therapeutics, making the supply chain for some of these life-saving medicines expensive and unstable. There has therefore been significant interest in refactoring these plant pathways in genetically tractable microbes, which grow more reliably and where the plant pathways can be more easily engineered to improve the titer, rate and yield of medicinal natural products. In addition, refactoring plant biosynthetic pathways in microbes also offers the possibility to explore new-to-nature chemistry more systematically, and thereby help expand the chemical space that can be probed for drugs as well as enable the study of pharmacological properties of such new-to-nature chemistry. This perspective will review the recent progress toward heterologous production of plant medicinal alkaloids in microbial systems. In particular, we focus on the refactoring of halogenated alkaloids in yeast, which has created an unprecedented opportunity for biosynthesis of previously inaccessible new-to-nature variants of the natural alkaloid scaffolds.

Monoterpene indole alkaloids with diverse skeletons from the stems of Rauvolfia vomitoria and their acetylcholinesterase inhibitory activities

Nine undescribed monoterpene indole alkaloids, rauvomitorine A-I, including an unprecedented C-9-methoxymethylene-sarpagine framework alkaloid, two rare suaveoline framework type alkaloids, and six yohimbine framework type alkaloids, as well as eleven known alkaloids, were isolated from the stems of Rauvolfia vomitoria Afzel. (Apocynaceae). The structures of the unreported alkaloids were elucidated by extensive spectroscopic analysis and single-crystal X-ray diffraction analysis with Cu Kα radiation. Rauvomitorine A with an unreported framework type represents the first example of C-9-methoxymethylene-sarpagine alkaloids and its plausible biosynthetic pathway was proposed. All the isolated alkaloids were evaluated their acetylcholinesterase inhibitory (AChE) activities and cytotoxicity against five cancer cell lines and some of them exhibited potential anti-AChE activities with IC₅₀ values ranging from 49.76 to 186.62 μM. Importantly, this is the first report of the AChE inhibitory activities on suaveoline framework type alkaloids, suggesting this type of alkaloids may be valuable sources for the discovery of AChE inhibitory agents. A preliminary structure-activity relationship for AChE inhibitory activities of the isolated alkaloids is also discussed, providing some clues to designing lead compounds for AChE inhibitors.

Monoterpene indole alkaloids with acetylcholinesterase inhibitory activity from the leaves of Rauvolfia vomitoria

Seventeen monoterpene indole alkaloids, including seven new alkaloids (1-7) and ten known analogues (8-17), were isolated and identified from the leaves of R. vomitoria. The structures of new alkaloids were elucidated by extensive spectroscopic analysis and single-crystal X-ray diffraction analysis. Rauvomitorine I (1) represents the first example of an unprecedented C₂₂ yohimbine-type monoterpene indole alkaloid featuring a carboxymethyl at C-14. The exceedingly rare vobasenal (2-3) and affinisine oxindole (5-6) framework type alkaloids are first reported from the Rauvolfia genus. Most notably, the structure of vobasenal-type alkaloids (2-3) were first determined by single-crystal X-ray diffraction analyses. Alkaloids 1-17 were tested their cytotoxicity against five cancer cell lines, however, none of them showed significant cytotoxicity at a concentration of 40 μM. All the isolated alkaloids were evaluated their acetylcholinesterase (AChE) inhibitory activities. Alkaloid 3 exhibited significant anti-AChE activity with an IC₅₀ value of 16.39 ± 1.41 μM and alkaloids 8 and 10 showed moderate anti-AChE activities whereas the others (2, 9, 13, and 17) were weak inhibitors. This is the first report of vobasenal-type alkaloids as AChE inhibitors, indicating this type of alkaloids may be important sources for the discovery of new AChE inhibitors. A preliminary structure-activity relationship for AChE inhibitory activities showed the presence of the N-methyl group in vobasenal-type alkaloids may be essential for anti-AChE activity. Further molecular docking studies of vobasenal-type alkaloids revealed that interaction with Trp133 and Trp86 residues at hydrophobic subsite are necessary for the AChE inhibitory activities. This study not only enriches the chemical diversity of alkaloids in Apocynaceae plants but also provides new potential leading compounds and versatile scaffolds for the design and development of new AChE inhibitors to treat AD.

Alkaloid and iridoid glucosides from Palicourea luxurians (Rubiaceae: Palicoureeae) indicate tryptamine- and tryptophan-iridoid alkaloid formation apart the strictosidine pathway

The first phytochemical examination of extracts from leaves and stem bark of Palicourea luxurians (Rusby) Borhidi yielded two undescribed and one known alstrostine derivative together with the oxindole alkaloid javaniside as well as with 5α-carboxystrictosidine. Additionally, five iridoids and four secologanin derived isolation artifacts have been isolated. Lack of strictosidine and its follow-up metabolization products suggested that the Pictet-Spenglerase in P. luxurians does barely or not catalyze the formation of strictosidine. Against this background the biosynthesis of javaniside and 5α-carboxystrictosidine is discussed with regard to possible reaction mechanisms. Similarly, P. luxurians used an independent biosynthetic pathway to produce alstrostine type structures from secologanin and tryptamine in a 2:1 ratio. The structure of isoalstrostine A, which was isolated for the first time, allowed the refinement of a previously reported pathway to the alstrostine type carbon skeleton as well as to some follow-up metabolization products. In spite of various biosynthetic pathways incorporating secologanin to gain different types of tryptophan- and tryptamine-iridoid alkaloids, P. luxurians accumulates this compound as well a couple of further metabolized iridoids deriving from loganin and secologanin.

Total synthesis study of rauvomines A and B: construction of the pentacyclic core structure

The fifth ring of rauvomines can be annulatedviaa Mukaiyama-Aldol reaction as a new strategy for sarpagine scaffold construction.

Alstolarines A and B, two unusual monoterpenoid indole alkaloids with an acetal moiety from Alstonia scholaris

Two novel monoterpenoid indole alkaloids, alstolarines A and B (1 and 2), were isolated from Alstonia scholaris, and exhibited promising vasorelaxant activities.

Bioactive terpenoids from Croton laui

Two new highly-oxygenated neo-clerodane diterpenoids, 3S-acetoxyl-mollotucin D dilactone ester (1) and 6S-crotoeurin C (2), and a new lupane-type triterpene, 16β-hydroxyl-3β-O-trans-coumaroyl-betulin (6), as well as three known analogues (3-5) were obtained from the leaves of Croton laui. The structures of the new compounds were determined by extensive spectroscopic methods, and their absolute configurations were determined by combination of single-crystal X-ray diffraction analysis, electronic circular dichroism (ECD) spectra, and literature data. Compounds 2 and 3 exhibited inhibitory activities of lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophages with IC₅₀ values of 1.2 and 1.6 μM, respectively. Additionally, compound 6 exhibited activity against Col205 and HepG2 cell lines with IC₅₀ values of 12.9 and 17.7 μM, respectively.

Alstonlarsines A-D, Four Rearranged Indole Alkaloids from Alstonia scholaris

Four indole alkaloids, alstonlarsines A-D (1-4), were isolated from Alstonia scholaris and structurally characterized. Compound 1 possesses a new carbon skeleton with a cage-shaped 9-azatricyclo[4.3.1.0^3,8]decane motif, and compounds 2-4 feature a rare carbon skeleton that was found in nature for the first time. Plausible biosynthetic routes for 1-4 are proposed. Compound 1 showed DRAK2 inhibitory activity with an IC₅₀ value of 11.65 ± 0.63 μΜ.

Survey of natural products reported by Asian research groups in 2017

The new natural products reported in 2017 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2017 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Gelsecorydines A-E, Five Gelsedine-Corynanthe-Type Bisindole Alkaloids from the Fruits of Gelsemium elegans

Five monoterpenoid bisindole alkaloids with new carbon skeletons, gelsecorydines A-E (1-5), together with their biogenetic precursors were isolated from the fruits of Gelsemium elegans. Compounds 1-5 represent the first examples of heterodimeric frameworks composed of a gelsedine-type alkaloid and a modified corynanthe-type one. Notably, compound 2 featured an unprecedented caged skeleton with a 6/5/7/6/5/6 heterohexacyclic ring system, which possessed a pyridine ring that linked the two monomers. Their structures and absolute configurations were elucidated by spectroscopic analysis, X-ray diffraction, and electronic circular dichroism (ECD) calculation. A plausible biosynthetic pathway for compounds 1-5 is proposed. Compounds 1, 3, 4, and 5 exhibited a significant inhibitory effect against nitric oxide (NO) production in macrophages.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as caesalpinflavin A from Caesalpinia enneaphylla.