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.

Five New Phenylpropanoyl Phloroglucinol Derivatives from Leptospermum scoparium.

Leptosperols C-G (1-5), five new phenylpropanoyl phloroglucinol derivatives were isolated from the leaves of Leptospermum scoparium. Compounds 1-3 are phenylpropanoyl phloroglucinol-sesquiterpene adducts with new carbon skeletons. Their structures with absolute configurations were elucidated by detailed spectroscopic analyses, single-crystal X-ray diffraction, and electronic circular dichroism (ECD) calculation. Compounds 2 and 3 exhibited moderate anti-inflammatory activity in zebrafish acute inflammatory models.

Angiogenesis-Inhibitory Piperidine Alkaloids from the Leaves of Microcos paniculata.

Eight new 2,6-disubstituted piperidin-3-ol alkaloids (1-8), featuring a C10 unsaturated alkyl side chain, together with three previously reported analogues (9-11) were isolated from the leaves of medicinal plant Microcos paniculata. Their structures and absolute configurations were elucidated unambiguously by means of 1D and 2D NMR spectroscopic data analysis, modified Mosher's method, Snatzke's method, and quantum chemical electronic circular dichroism (ECD) calculations, as well as single-crystal X-ray crystallography. The isolates were evaluated for their antiangiogenic effects on human umbilical vein endothelial cells (HUVECs). Compound 2 displayed an inhibitory effect on tube formation of HUVECs in a concentration-dependent manner.

Cajanusoids A-D, Unusual Atropisomeric Stilbene Dimers with PTP1B Inhibitory Activities from the Leaves of Cajanus cajan.

Four novel stilbene dimers (1-4), together with their biosynthetically related stilbene monomers (5 and 6), were isolated from the leaves of Cajanus cajan. Their structures with absolute configurations were determined by comprehensive analysis of spectroscopic data and electronic circular dichroism calculations. Compounds 1 and 2 are two novel dimeric stilbenes with an unusual coupling pattern that resulted in a rare configurationally stable Csp2-Csp3 chiral axis with both point and axial chirality in their molecules. Due to their unique inherent structural features, both of them naturally occur as equilibrating mixtures of unequally populated atropo-diastereomers and their respective enantiomers. Compounds 3 and 4 are two pairs of novel dimeric stilbene atropisomers featuring a rotationally hindered central biaryl axis. Notably, 3 contains a rare arylbenzoquinone core and 4 is a symmetric dimer with a C2 symmetry axis. The hypothetical biosynthetic pathway of 1-4 was also proposed herein. All the new compounds exhibited significant protein tyrosine phosphatase-1B (PTP1B) inhibition effects. In addition, the preliminary mode of action for the most potent compound 3 was investigated by molecular docking and binding free energy calculation.

Quassinoids from the Roots of Eurycoma longifolia and Their Anti-Proliferation Activities.

A phytochemical investigation on the roots of medicinal plant Eurycoma longifolia resulted in the isolation of 10 new highly oxygenated C20 quassinoids longifolactones G‒P (1-10), along with four known ones (11-14). Their chemical structures and absolute configurations were unambiguously elucidated on the basis of comprehensive spectroscopic analysis and X-ray crystallographic data. Notably, compound 1 is a rare pentacyclic C20 quassinoid featuring a densely functionalized 2,5-dioxatricyclo[5.2.2.04,8]undecane core. Compound 4 represents the first example of quassinoids containing a 14,15-epoxy functionality, and 7 features an unusual α-oriented hydroxyl group at C-14. All isolated compounds were evaluated for their anti-proliferation activities on human leukemia cells. Among the isolates, compounds 5, 12, 13, and 14 potently inhibited the in vitro proliferation of K562 and HL-60 cells with IC50 values ranging from 2.90 to 8.20 µM.

[Two new pyranonaphthoquinones from Mansoa alliacea].

Mansoa alliacea,commonly known as garlic vine,is native to the tropical rain forests of South America and widely cultivated in South China. As a popular folk medicine with various biological activities,however,this plant remains to be fully elucidated in terms of its phytochemical constituents. In this study,two new pyranonaphthoquinones were isolated from the 95% ethanol extract of the leaves and twigs of M. alliacea by various chromatographic approaches including silica gel,octadecyl silica( ODS),Sephadex LH-20,and preparative high-performance liquid chromatography( PHPLC). Their structures were determined to be 8,9-dimethoxy-α-lapachone( 1) and 7-hydroxy-8,9-dimethoxy-α-lapachone( 2) by comprehensive spectroscopic analyses and therefore respectively named as mansonin A( 1) and mansonin B( 2).

Discovery of Neuritogenic Securinega Alkaloids from Flueggea suffruticosa by a Building Blocks-Based Molecular Network Strategy.

A combined strategy of building blocks recognition and molecular network construction, termed the building blocks-based molecular network (BBMN), was first presented to facilitate the efficient discovery of novel natural products. By mapping the BBMN of the total alkaloid fraction of Flueggea suffruticosa, three Securinega alkaloids (SEAs) with unusual chemical architectures, suffranidines A-C (1-3), were discovered and isolated. Compound 1 characterizes an unprecedented 8/5/6/5/6/6/6/6-fused octacyclic scaffold with a unique cage-shaped 3-azatricyclo[6.4.0.03,11 ]dodecane core. Compounds 2 and 3 are highly modified SEA dimers that incorporate additional C6 motifs. A hypothetical biosynthetic pathway for 1-3 was proposed. In addition, 1 significantly induced neuronal differentiation and neurite extension by upregulating eukaryotic elongation factor 2 (eEF2)-mediated protein synthesis.

[A new flavonostilbene glycoside from roots of Polygonum multiflorum].

Polygonflavanol B(1), a new flavonostilbene glycoside, was isolated from the roots of Polygonum multiforum(Polygonaceae) by various column chromatography methods including macroporous resin HP-20, silica gel, Sephadex LH-20, and preparative HPLC. The structure with absolute configuration of the new compound was identified by its physicochemical properties, spectroscopic data, ECD calculation, and chemical method.

Eleven New Triterpenoid Glycosides from the Roots of Ilex asprella.

Asprellosides A-K, nine new ursane-type triterpenoid glycosides (1-9), and two new oleanane-type triterpenoid glycosides (10 and 11), including six rare sulfated triterpenoid glycosides, were isolated from the roots of Ilex asprella. Their structures were determined on the basis of comprehensive spectroscopic analysis and chemical methods. Among these compounds, asprelloside B (2) and asprelloside C (3) are the first examples of triterpenoid glycosides bearing a rare 3,4-O-disulfo-xylopyranosyl residue. All the saponins isolated showed no significant effects against respiratory syncytial virus (RSV) and lipopolysaccharide-induced nitric oxide production in Raw264.7 macrophages.

Evaluation of Diarylheptanoid-Terpene Adduct Enantiomers from Alpinia officinarum for Neuroprotective Activities.

Two pairs of new diarylheptanoid-monoterpene adduct enantiomers, (±)-alpininoids A and B [(±)-1 and (±)-2], as well as three pairs of new diarylheptanoid-sesquiterpene adduct enantiomers, (±)-alpininoids C-E [(±)-3-(±)-5], together with four known diarylheptanoids (6-9) were isolated from the rhizomes of Alpinia officinarum. Their structures with absolute configurations were elucidated on the basis of comprehensive spectroscopic analyses and computational calculation methods. The skeletons of these cyclohexene-containing hybrid natural products were hypothesized to be generated via a crucial Diels-Alder cycloaddition between the diarylheptanoids (7 and 8) and terpenes, of which 1 represents a new carbon skeleton. All isolated compounds were evaluated for their neuroprotective effects against MPP+ (1-methyl-4-phenylpyridinium)-induced cortical neuron injury. At a concentration of 16 µM, (+)-1 significantly increased cell viability when compared with MPP+ treatment alone.

Securinega alkaloids from the fruits of Flueggea suffruticosa.

Phytochemical investigation on the fruits of Flueggea suffruticosa resulted in the isolation of three new Securinega alkaloids, secu'amamine H (1), 15ß-methoxy-14,15-dihydrosecurinine (3), and securinol E (7), as well as eight known ones (2, 4-6, and 8-11). Their structures were elucidated by means of spectroscopic techniques (1D and 2D NMR, MS, UV, and IR). The absolute configurations of the new compounds were established by single-crystal X-ray diffraction and CD analyses.

Suffrutines A and B: a pair of Z/E isomeric indolizidine alkaloids from the roots of Flueggea suffruticosa.

Suffrutines A (1) and B (2), a pair of novel photochemical Z/E isomeric indolizidine alkaloids, with a unique and highly conjugated C20 skeleton, were isolated from the roots of Flueggea suffruticosa. The structures were elucidated by extensive analysis of NMR spectra and single-crystal X-ray diffraction. The light-induced isomerization and hypothetical biogenetic pathway to 1 and 2, as well as their activity for regulating the morphology of Neuro-2a cells are also discussed.

Chemical constituents from the roots and stems of Erycibe obtusifolia and their in vitro antiviral activity.

Three new quinic acid derivatives, 4-O-caffeoyl-3-O-sinapoylquinic acid methyl ester (1), 5-O-caffeoyl-4-O-syringoylquinic acid methyl ester (2), and 4-O-caffeoyl-3-O-syringoylquinic acid methyl ester (3), as well as four new coumarin glycosides, 7-O-(3-O-sinapoyl-ß-D-glucopyranosyl)-6-methoxycoumarin (12), 7-O-(6-O-sinapoyl-ß-D-glucopyranosyl)-6-methoxycoumarin (13), 7-O-(2-O-sinapoyl-ß-D-glucopyranosyl)-6-methoxycoumarin (14), and 7-O-(6-O-syringoyl-ß-D-glucopyranosyl)-6-methoxycoumarin (15), together with eight known compounds (4-11) were isolated from the roots and stems of Erycibe obtusifolia. Their structures were elucidated on the basis of spectroscopic analysis and chemical evidence. All the compounds were screened for their in vitro antiviral activity against respiratory syncytial virus with a cytopathic effect reduction assay. Among them, the di-O-caffeoyl quinates 8-11 displayed a potent in vitro anti-respiratory syncytial virus effect.

Stilbenes from the leaves of Cajanus cajan and their in vitro anti-inflammatory activities.

Eighteen stilbenes (1-18), including six previously undescribed ones (1-6), with diverse modification patterns were isolated from the leaves of edible and medicinal plant Cajanus cajan. Among the new isolates, compounds 1-3 were initially obtained as three racemic mixtures, which were further resolved into three pairs of optically pure enantiomers, respectively, by chiral HPLC. Besides, compounds 8, 10, 11, and 18 were obtained from C. cajan for the first time. The chemical structures and absolute configurations of the new stilbenes were elucidated unambiguously on the basis of extensive spectroscopic analyses, single crystal X-ray crystallographic study, and quantum chemical electronic circular dichroism (ECD) calculations. In addition, the in vitro anti-inflammatory activities of all isolated stilbenes were evaluated. Compounds 2, 9, 10, 11, and 14 exerted moderate suppression of nitric oxide (NO) secretion in lipopolysaccharide (LPS)-induced RAW264.7 cells without exhibiting substantial cytotoxicity.

Securinine Promotes Neuronal Development and Exhibits Antidepressant-like Effects via mTOR Activation.

Impaired differentiation of newborn neurons or abnormalities at the synapses resulted from stress maladaptation could be the key etiology of depression. Recent studies have shown that mTOR, a crucial factor for neuronal differentiation and synapse development, acts as a common factor that mediates the rapid antidepression effects of several new-class antidepressants. In this study, the antidepressant-like activity of securinine, an alkaloid that has central nervous system stimulation ability, was investigated. Both securinine and its enantiomer virosecurinine exhibited potent in vitro activity on neuronal differentiation and synapse development in Neuro-2a cells and cultured hippocampal neurons, and this activity was dependent on the activation of the AKT-mTOR-S6K pathway. Interestingly, only securinine but not virosecurinine showed mTOR stimulation and antidepressant-like activity in mice. Importantly, a single dose of securinine was capable of alleviating the behavioral deficits induced by both acute and chronic stress models within 30 min of administration, suggesting that securinine has rapid onset of action. Moreover, neither a single dose nor a 3 week treatment of securinine had adverse effects on exploratory locomotion of mice. Together, this study identifies that securinine is a potent agent in promoting neuronal differentiation and synapse formation and shows rapid antidepressant-like activity, without inducing abnormal locomotion, via mTOR activation.

Heterologous Biosynthesis of Type II Polyketide Products Using E. coli.

The heterologous biosynthesis of complex natural products has enabled access to polyketide, nonribosomal peptide, isoprenoid, and other compounds with wide-spanning societal value. Though several surrogate host systems exist, Escherichia coli is often a preferred choice due to its rapid growth kinetics and extensive molecular biology protocols. However, a persistent challenge to the utilization of E. coli has been the successful in vivo reconstitution of type II polyketide synthase (PKS) systems. In particular, gene expression of the ketosynthase (KS) components of the minimal PKS has consistently yielded insoluble protein products. In the following report, two type II PKS systems were functionally reconstituted in E. coli. The approach to do so relied upon the utilization of the native transcriptional coupling between the dimeric KS subunits, leading to soluble recombinant protein products and successful polyketide biosynthesis. Resulting strains produced 10 mg/L TW95c and 25 mg/L dehydrorabelomycin. Hence, the strategy offers a new option in the biosynthetic engineering efforts for the heterologous production of type II polyketide products using E. coli.

Absolute Configurations and Stereochemical Inversion Mechanism of Epimeric Securinega Alkaloids from Flueggea suffruticosa.

Three pairs of Securinega alkaloid epimers with a piperidin-2-yl moiety (1-6) were isolated from Flueggea suffruticosa, and their structures including absolute configurations were definitely characterized. An interconvertible C-2' epimerization process within each pair of epimers was observed. The following comprehensive experimental and theoretical investigations demonstrated an unusual stereochemical inversion mechanism of an N-substituted carbon stereogenic center, which was evidenced to be a protic solvent mediated process involving a tandem 1,4-elimination/1,4-addition as the key step.

Dimeric Diarylheptanoids with Neuroprotective Activities from Rhizomes of Alpinia officinarum.

Two novel dimeric diarylheptanoids, alpinidinoids A [(±)-1] and B (2), with two unusual coupling patterns, together with a new naturally occurring diarylheptanoid dimer possessing a rare pyridine ring linkage (alpinidinoid C, 3), were isolated from the rhizomes of Alpinia officinarum. Their structures including absolute configurations were determined by extensive spectroscopic methods and theoretical calculations. All isolates were examined for their neuroprotective activities against oxygen-glucose deprivation and reoxygenation (OGD/R) damage in primary cortical neurons. Remarkably, the dextrorotatory enantiomer of alpinidinoid A [(+)-1] significantly ameliorated OGD/R-induced neuronal apoptosis, which was dependent on the activation of the AKT/mTOR signaling pathway.

Alkaloid constituents from the fruits of Flueggea virosa.

Three new indole alkaloids, flueindolines A-C (1-3), along with nine known alkaloids (4-12), were isolated from the fruits of Flueggea virosa (Roxb. ex Willd.) Voigt. Compounds 1 and 2 are two new fused tricyclic indole alkaloids possessing an unusual pyrido[1, 2-a]indole framework, and 3 presents a rare spiro (pyrrolizidinyl-oxindole) backbone. Their structures with absolute configurations were elucidated by means of comprehensive spectroscopic analysis, chemical calculation, as well as X-ray crystallography. Chiral resolution and absolute configuration determination of the known compounds 4, 10, and 11 were reported for the first time. The hypothetical biogenetical pathways of 1-3 were herein also proposed.

Flueggeacosines A-C, Dimeric Securinine-Type Alkaloid Analogues with Neuronal Differentiation Activity from Flueggea suffruticosa.

Flueggeacosines A-C (1-3), three dimeric securinine-type alkaloid analogues with unprecedented skeletons, were isolated from Flueggea suffruticosa. Compounds 1 and 2 are the first examples of C-3-C-15' connected dimeric securinine-type alkaloids. Compound 3 is an unprecedented heterodimer of securinine-type and benzoquinolizidine alkaloids. Biosynthetic pathways for 1-3 were proposed on the basis of the coexisting alkaloid monomers as the precursors. Compound 2 exhibited significant activity in promoting neuronal differentiation of Neuro-2a cells.