New ψ-Santonin Derivatives from Crossostephium chinense and Their Anti-Proliferative Activities against Leishmania major and Human Cancer Cells A549.

Previously, we reported two cytotoxic ψ-santonin-amino acid conjugates isolated from the EtOAc layer of Crossostephium chinense. However, a further phytochemical investigation seems to be required because of the few reports of similar derivatives. In this study, we targeted the 1-BuOH layer, which resulted in the isolation of seven new ψ-santonin derivatives (1-7) together with ten known compounds (8-17). The structures of 1-7 were elucidated based on spectroscopic methods, including 1D and 2D NMR experiments (1H, 13C, DEPT, COSY, HSQC, and HMBC), IR spectrum, and high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS). The stereochemistry of new compounds was confirmed by NOESY and ECD calculations. All isolated compounds were evaluated by in vitro experiments for their anti-proliferative activities against Leishmania major, human lung cancer cell line A549, and Vero cells. As a result, most of the ψ-santonin derivatives, especially 1-5, showed significant cytotoxicity against L. major with a lower IC50 than the positive control we used (miltefosine).

Two New Cytotoxic Sesquiterpene-Amino Acid Conjugates and a Coumarin-Glucoside from Crossostephium chinense.

The Asteraceae family is a promising source of bioactive compounds, such as the famous Asteraceae plants Tanacetum cinerariifolium (pyrethrin) and Artemisia annua (artemisinin). As a result of our series of phytochemical studies of the subtropical plants, two novel sesquiterpenes, named crossoseamines A and B in this study (1 and 2, respectively), one undescribed coumarin-glucoside (3), and eighteen known compounds (4-21) were isolated from the aerial part of Crossostephium chinense (Asteraceae). The structures of isolated compounds were elucidated by spectroscopic methods, including 1D and 2D NMR experiments (1H, 13C, DEPT, COSY, HSQC, HMBC, and NOESY), IR spectrum, circular dichroism spectrum (CD), and high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS). All isolated compounds were evaluated for their cytotoxic activities against Leishmania major, Plasmodium falciparum, Trypanosoma brucei (gambiense and rhodesiense), and human lung cancer cell line A549 because of the high demand for the discovery of new drug leads to overcome the present side effects and emerging drug-resistant strains. As a result, the new compounds (1 and 2) showed significant activities against A549 (IC50, 1: 3.3 ± 0.3; 2: 12.3 ± 1.0 µg/mL), L. major (IC50, 1: 6.9 ± 0.6; 2: 24.9 ± 2.2 µg/mL), and P. falciparum (IC50, 1: 12.1 ± 1.1; 2: 15.6 ± 1.2 µg/mL).

Crotofolanes, rearranged crotofolanes, and a novel diterpene: isocrotofolane from Croton cascarilloides, collected in Okinawa.

To this day, since about 50% of all medicines are derived from natural sources, natural product chemistry, especially the search for biologically active natural components, remains extremely important (Newman and Cragg in J Nat Prod 83:770-803, 2020). In this review, we deal with our continuing research work for promising constituents from plants collected in the Ryukyu Archipelago. The isolation of islands in the archipelago by the sea or by straits gives rise to endemic plant species that are unique to the islands. The structural diversity of the constituents produced by this unique flora is of great scientific interest in various aspects, including chemical structures, biosynthesis, and biological activities. The components from this structural diversity have great potential as new pharmaceutical seeds. In our continuing studies, we have successfully investigated new but extremely unusual diterpenoids: crotofolanes and their rearranged varieties (nor-crotofolane, trinor-crotofolane, neocrotofolane) and a glycoside with a new skeletal diterpenoid (isocrotofolane glucoside) from Croton cascarilloides. This review summarizes our reports on the investigation of crotofolanes as well as those on crotofolanes by other research groups.

Omphalines A-E: ent-Rosane-Type Diterpenoids from the Madagascar Endemic Plant, Omphalea oppositifolia.

From the less polar fraction of the MeOH extract of the leaves and twigs of Omphalea oppositifolia, five new ent-rosane-type diterpenoids, named omphalines A-E (1-5), were isolated together with one known compound, 7-keto-ent-kaurane-16ß,17-diol (6), by a combination of various kinds of chromatography. The structure of omphaline A (1) was elucidated to be 19-nor-ent-rosane-4,15-diene-2ß,6α-diol-3-one. Omphalines B (2), C (3), D (4), and E (5) possessed two double bonds at 5- and 15-positions, and hydroxy functional groups at 3ß-, 2α,3α-, 2α,3ß-, and 2α,19-positions, respectively. The absolute configuration of 1 was determined by the comparison of the experimental electronic circular dichroism (ECD) spectrum and calculated ECD spectra.

Four new glucosides from the aerial parts of Equisetum sylvaticum.

Two previously undescribed megastigmane glucosides, (3S)-3-hydroxy-4-oxo-7,8-dihydro-ß-ionone-3-O-ß-D-glucopyranoside (1), (3S)-3-hydroxy-4-oxo-ß-ionone-3-O-ß-D-glucopyranoside (2), an apocarotenoid glucoside named equiseoside A (3) and an unusual aromatic compound with a glucose-fused skeleton named equiseoside B (4), together with 35 known compounds (5-39) were isolated from the aerial parts of Equisetum sylvaticum. The structures of these compounds were elucidated by spectroscopic methods, including 1D and 2D NMR, IR, CD, and HR-MS.

Crotofolane-Type Diterpenoids: Crotocascarins R-V, Rearranged Trinorcrotofolane: Crotocascarin δ and a Phorbol Derivative from the Leaves of Croton cascarilloides.

Five new crotofolanes, named crotocascarins R-V (1-5), one rearranged trinorcrotofolane, crotocascarin δ, and one phorbol derivative were isolated from the EtOAc-soluble fraction of the MeOH extract of the leaves of Croton cascarilloides. Crotocascarins R (1), T (3), and U (4) possessed isobutyric acid as an acyl moiety and crotocascarin B (2) an acetyl group, whereas crotocascarin V (5) was elucidated to be a hydroxylated compound of crotocascarin K at the 9-position. Crotocascarin δ (6) was a trinor rearranged crotofolane with a tertiary hemiketal functional group at the 8-position. The absolute configuration of the 8-position was determined by the comparison of the experimental electronic circular dichroism (ECD) spectrum and calculated ECD spectra. Compound 7 was a phorbol ester derivative with a peroxide functional group. The fatty acid attached at the 12-position was found to be a single species-i.e., lauric acid (C-12)-from the evidence of the mass spectral data.

Detecting and Differentiating Monosaccharide Enantiomers by 1H NMR Spectroscopy.

Monosaccharides play important roles in living organisms. They are present in essential glycoproteins, nucleic acids, and glycolipids as well as cell walls and bioactive natural product glycosides and polysaccharides. Monosaccharides are optically active, and as a routine, scientists make sure that their absolute configurations are determined when new natural glycosides are isolated. Many determination methods for the absolute configuration of monosaccharides have been reported, and thus far, taking advantage of their optical rotation differences is the most used and efficient method to distinguish enantiomers. This method, however, is not very convenient, because it requires a milligram amount of each pure sample and the availability of a polarimeter. Identification methods dealing with comparison of the retention times of the d- and l-diastereomeric monosaccharide derivatives by GC, TLC Rf values, HPLC, or UPLC have been also reported. Although effective, these methods still require sample preparation and a few milligrams of the test compounds. A new method with simple sample preparation to distinguish enantiomers of monosaccharides by analyzing the 1H NMR spectra of their diastereomeric derivatives has been developed. The monosaccharide components of a commercially available saponin-rich Panax ginseng and monoglycosides have been successfully identified using this procedure.

Ardisiatetrons A and B: tetronic acid derivatives and triterpenes from the leaves of Ardisia quinquegona and their biological activity.

From the leaves of Ardisia quinquegona, two alkylated tetronic acid derivatives, named ardisiatetrons A and B (1, 2), and four triterpenoids (3-6) were isolated together with one known compound (7) by a combination of various kinds of chromatography. The structure of new methyl migrated triterpene (3) was confirmed by X-ray crystallographic analysis. Compounds 2, 3, and 7 showed moderate anti-Leishmania activity and cytotoxicity towards A549 cells.

Six New Phenylpropanoid Derivatives from Chemically Converted Extract of Alpinia galanga (L.) and Their Antiparasitic Activities.

Chemical conversion of the extract of natural resources is a very attractive way to expand the chemical space to discover bioactive compounds. In order to search for new medicines to treat parasitic diseases that cause high morbidity and mortality in affected countries in the world, the ethyl acetate extract from the rhizome of Alpinia galanga (L.) has been chemically converted by epoxidation using dioxirane generated in situ. The biological activity of chemically converted extract (CCE) of A. galanga (L.) significantly increased the activity against Leishmania major up to 82.6 ± 6.2 % at 25 µg/mL (whereas 2.7 ± 0.8% for the original extract). By bioassay-guided fractionation, new phenylpropanoids (1-6) and four known compounds, hydroquinone (7), 4-hydroxy(4-hydroxyphenyl)methoxy)benzaldehyde (8), isocoumarin cis 4-hydroxymelein (9), and (2S,3S,6R,7R,9S,10S)-humulene triepoxide (10) were isolated from CCE. The structures of isolated compounds were determined by spectroscopic analyses of 1D and 2D NMR, IR, and MS spectra. The most active compound was hydroquinone (7) with IC50 = 0.37 ± 1.37 µg/mL as a substantial active principle of CCE. In addition, the new phenylpropanoid 2 (IC50 = 27.8 ± 0.34 µg/mL) also showed significant activity against L. major compared to the positive control miltefosine (IC50 = 7.47 ± 0.3 µg/mL). The activities of the isolated compounds were also evaluated against Plasmodium falciparum, Trypanosoma brucei gambisense and Trypanosoma brucei rhodeisense. Interestingly, compound 2 was selectively active against trypanosomes with potent activity. To the best of our knowledge, this is the first report on the bioactive "unnatural" natural products from the crude extract of A. galanga (L.) by chemical conversion and on its activities against causal pathogens of leishmaniasis, trypanosomiasis, and malaria.

A cell model in the ventral visual pathway for the detection of circles of curvature constituting figures.

The contour of an arbitrary figure can be represented as a group of circles of curvature in contact with it, with each curvature circle represented by its center OC and radius r. We propose a series of cell models for detecting this circle, which is composed of a lateral geniculate nucleus (LGN) cell, nondirectionally selective (NDS) simple cell, and curvature-circle detection cell (CDC). The LGN and NDS simple cells were previously modeled. The CDC has been modeled as follows. Each tangent in contact with this circle is detected by an NDS simple cell that performs the Hough transformation of LGN cell responses, and then this tangent is transformed to a three-dimensional (3D) normal line in a CDC column. This transformation has been named a 3D normal-line transform. Performing this transformation for all tangents causes a CDC at the intersection of these normal lines to fire most intensively, and thus the OC and r of the circle is detected as the coordinates of this intersection. Therefore, the CDC has been modeled as this 3D normal-line transform. Based on this CDC, we model two types of constancy CDC: a position-invariant CDC and a curvature-invariant CDC. These three types of CDC reflect the response to various stimuli in actual area V4 cells. In order to validate these CDC types neurophysiologically, we propose an experimental method using microelectrodes. Cell models previously reported correspond to this hierarchy: the S1, S2, and C2 cells correspond to the NDS simple cell, CDC, and position-invariant CDC, respectively.

Symplocosins C-P: Fourteen Triterpene Saponins from the Leaves of Symplocos cochinchinensis var. philippinensis.

Extensive phytochemical work on the 1-BuOH-soluble fraction of a MeOH extract of the leaves of Symplocos cochinchinensis var. philippinensis resulted in the isolation of 14 new triterpenene saponins, along with four known ones. Their structures were elucidated by comparison of NMR spectroscopic data with related compounds reported in the literature. Three oleanane-type saponins, symplocosins K, M, and P, possessed glucuronic acid as a sugar component, and their carboxyl groups appeared as methyl esters. These are probably formed during extraction and isolation procedures. Symplocosin K (9) showed moderate cytotoxicity toward A549 cells. In addition, all isolated compounds did not show α-glucosidase inhibitory activity.

Firmosides A and B: two new sucrose ferulates from the aerial parts of Silene firma and evaluation of radical scavenging activities.

Two new tri-ferulates of sucrose, firmosides A and B (1 and 2, respectively), together with 18 known compounds (3-20), were isolated from the aerial parts of Silene firma. The structures of the isolated compounds were elucidated by various spectroscopic methods, including 1D, 2D NMR, and high-resolution electro-spray ionization-mass spectrometry (HR-ESI-MS). All the isolated compounds were evaluated for their free radical scavenging activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. As a result, two new compounds (1, 2) and 11 demonstrated significant radical scavenging activity, implying the usefulness as antioxidant agents.

[Structural Diversity of Chemical Constituents from Okinawan Plants].

In our continuing search for secondary metabolites from plants, we investigated the chemical constituents of various Okinawan plants. From the stems and leaves of Croton cascarilloides (Euphorbiaceae), a great number of rare diterpenoids: crotofolanes; crotocascarins A-Q, and new diterpenoids; rearranged nor-crotofolanes: crotocascarins α-γ; a rearranged crotofolane: neocrotocascarin; and a new skeletal diterpenoid: isocrotofolane glucoside were isolated. Their structures were mainly elucidated from NMR spectroscopic evidence. In addition, absolute configurations of crotocascarins A, B, K and O, crotocascarin α and neocrotocascarin were determined by X-ray crystallographic analyses, chiral HPLC analyses of 2-methylbutyric acid in their molecules, application of the circular dichroism rule for the α,ß-unsaturated γ-lactone ring, and the modified Mosher's method. The absolute structures of crotofolanes were reported for the first time, and a biosynthetic mechanism for the formation of crotocascarin α and neocrotocascarin from crotocascarin B was proposed. Other interesting compounds, namely diosmarioside H: a dimeric ent-kaurane glycoside from the leaves of Diospyros maritima, and melionosides A-C: megastigmane glucosides with a spiro-ring structure from the leaves of Meliosma lepidota ssp. squamulata were also isolated.

Ebenamariosides A-D: Triterpene Glucosides and Megastigmanes from the Leaves of Diospyros maritima.

The 1-BuOH-soluble fraction of the methanol (MeOH) extract of Diospyros maritima was separated by chromatographic techniques to give three new oleanane-type and one new ursane-type triterpene glucoside, named ebenamariosides A-D (1-4); two megastigmanes were also isolated. The structures of triterpene glucosides was elucidated with extensive investigation by one and two dimensional NMR spectroscopy and the structures were confirmed by partial enzymatic hydrolyses to give the corresponding mono-glucosides and aglycones. The structures of the megastigmanes, including their absolute stereochemistries, were elucidated by spectroscopic evidence and by the modified Mosher's method. Two megastigmanes were chemically correlated and their absolute structures were unambiguously determined. The cytotoxicity of the triterpene glucosides and their degradation products were assayed. They did not show any significant activity.

Draft Genome Sequence of Streptomyces sp. Strain NL15-2K, a Degrader of Lignin-Derived Aromatic Compounds, Isolated from Forest Soil.

Streptomyces sp. strain NL15-2K is a degrader of lignin-derived aromatic compounds and was isolated from a forest soil sample. Here, we report the draft genome sequence of this strain and its annotation. This genome of 12,072,023 bp exhibits a GC content of 70.32% and encodes 10,874 predicted proteins and 75 RNAs.

Eight ent-Kaurane Diterpenoid Glycosides Named Diosmariosides A-H from the Leaves of Diospyros maritima and Their Cytotoxic Activity.

From the leaves of Diospyros maritima, collected from Okinawa Island, eight new glycosides based on ent-kaurane-type diterpenoids, entitled diosmariosides A-H, were isolated. The absolute structure of diosmarioside E (5) was determined by X-ray crystallographic analysis. The structure of diosmarioside H was elucidated to be a dimeric compound between diosmarioside A and a sugeroside through a ketal bond. An assay of cytotoxicity towards the lung adenocarcinoma (A549) cell line was performed. Among the compounds isolated, only diosmarioside D (4) and sugeroside 9 showed strong activity. The anti-microbial activity toward multi-drug resistant strains was also determined, but no activity was observed.

Molecular cloning and characterization of vanillin dehydrogenase from Streptomyces sp. NL15-2K.

BACKGROUND: Streptomyces sp. NL15-2K, previously isolated from the forest soil, features an extensive catabolic network for lignin-derived aromatic compounds, including pathways transforming ferulic acid to vanillin, vanillic acid, and protocatechuic acid. To successfully use Streptomyces sp. NL15-2K as a biocatalyst for vanillin production, it is necessary to characterize the vanillin dehydrogenase (VDH) that degrades the produced vanillin to vanillic acid, as well as the gene encoding this enzyme. Here, we cloned the VDH-encoding gene (vdh) from strain NL15-2K and comprehensively characterized its gene product. RESULTS: The vdh open reading frame contains 1488 bp and encodes a 496-amino-acid protein with a calculated molecular mass of 51,705 Da. Whereas the apparent native molecular mass of recombinant VDH was estimated to be 214 kDa by gel filtration analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a subunit molecular mass of ca. 56 kDa, indicating that VDH is a homotetramer. The recombinant enzyme showed optimal activity at 45 °C and pH 9.5. The VDH substrate specificity followed this order: vanillin (100%) > protocatechualdehyde (91%) > benzaldehyde (79%) > p-hydroxybenzaldehyde (56%) > isovanillin (49%) ≈ salicylaldehyde (48%) > anisaldehyde (15%) ≈ veratraldehyde (12%). Although peptide mass fingerprinting and BLAST searches indicated that this enzyme is a salicylaldehyde dehydrogenase (SALDH), the determined kinetic parameters clearly demonstrated that the enzyme is a vanillin dehydrogenase. Lastly, phylogenetic analysis revealed that VDH from Streptomyces sp. NL15-2K forms an independent branch in the phylogenetic tree and, hence, is evolutionarily distinct from other VDHs and SALDHs whose activities have been confirmed experimentally. CONCLUSIONS: Our findings not only enhance the understanding of the enzymatic properties of VDH and the characteristics of its amino acid sequence, but also contribute to the development of Streptomyces sp. NL15-2K into a biocatalyst for the biotransformation of ferulic acid to vanillin.

Alkylated Benzoquinones: Quinquequinones A­H from the Leaves of Ardisia quinquegona and Their Anti-Leishmania Activity [corrected].

Eight alkylated benzoquinone derivatives, named ardisiaquinones A-H, were isolated together with four known compounds from the leaves of Ardisia quinquegona using a combination of different chromatography techniques. Their structures were elucidated by spectroscopy and by the preparation of methyl ethers. Anti-Leishmania activity and cytotoxicity of the isolated compounds were assayed. Some compounds showed moderate anti-Leishmania activity, however, always associated with cytotoxicity.

Microtropins Q-W, ent-Labdane Glucosides: Microtropiosides G-I, Ursane-Type Triterpene Diglucoside and Flavonol Glycoside from the Leaves of Microtropis japonica.

Microtropins Q-W, (2S,3R)-2-ethyl-2,3-dihydroxybutyrate of various glucosides and glucose, as well as three ent-labdane diterpenoid glucosides, named microtropiosides G, H and I, an ursane-type triterpene diglucoside and a flavonoid glycoside were isolated from the MeOH extract of the leaves of Microtropis japonica. The structure of microtropioside A, also isolated from the branches of M. japonica, was elucidated spectroscopically in a previous experiment and was found to possess a rare seven-membered oxyrane ring. Its structure was confirmed by X-ray crystallographic analysis of its pentaacetate.

Aliphatic Glucoside, Zanthoionic Acid and Megastigmane Glucosides: Zanthoionosides A-E from the Leaves of Zanthoxylum ailanthoides.

From the leaves of Zanthoxylum ailanthoides, 4'-O-p-E-coumaric acid esters of 2-propanol ß-D-glucopyranoside, megastigmane and megastigmane glucosides were isolated. Their structures were elucidated by spectroscopic evidence. The absolute configurations of the megastigmane and aglycone of megastigmane glucosides were determined by the octant rule and modified Mosher's method after protection of carboxylic acids by p-bromophenacyl esters and primary alcohols by pivaloyl esters.