Abietane diterpenoids from the bark of Cryptomeria fortunei

Integrated Transcriptomic, Metabolomic, and Physiological Analyses Reveal New Insights into Fragrance Formation in the Heartwood of Phoebe hui

Phoebe hui is an extremely valuable tree that is the main source of the fragrant golden-thread nanmu wood. Although the fragrance of wood has been investigated in several trees, the potential substances and gene regulation mechanisms that are involved in fragrance formation are poorly understood. Here, three radial tissues, sapwood (SW), heartwood (HW), and the transition zone (TZ) in between them, were compared via integrative physiological, volatile-metabolomic, and transcriptomic analyses to identify the key metabolites and regulatory mechanisms involved in fragrance formation. During heartwood formation, gradual starch grain loss was accompanied by the deposition of lipids and extractives in the cell lumen. Extracts of terpenoids were synthesized and accumulated in the heartwood, including monoterpenoids (limonene and p-cymene) and sesquiterpenes (cubebene and guaiadiene); these were identified as being closely related to the special fragrance of the wood. Additionally, the expression of transcripts showed that the genes related to primary metabolism were specifically upregulated in the SW, whereas genes annotated in terpenoid biosynthesis were specifically upregulated in the HW. Therefore, we speculated that terpenoid biosynthesis occurs in situ in the HW via the HW formation model of Type-III (Santalum) using the precursors that were produced by primary metabolism in the SW. The expression levels of transcription factors (e.g., MYB, WRKY, and C2H2) acted as the major regulatory factors in the synthesis of terpenoids. Our results explain the special fragrance in P. hui and broaden the current knowledge of the regulatory mechanisms of fragrance formation. This work provides a framework for future research that is focused on improving wood quality and value.

Functional Characterization of a 2OGD Involved in Abietane-Type Diterpenoids Biosynthetic Pathway in Salvia miltiorrhiza

Salvia miltiorrhiza is one of the most commonly used Chinese medicinal herbs. Tanshinones, the most abundant lipid-soluble bioactive constituents of S. miltiorrhiza, are a class of structural highly oxidized abietane-type diterpenoids with multiple pharmacological activities. Although several enzymes, including diterpene synthase, cytochrome P450, and Fe(II)/2-oxoglutarate-dependent dioxygenase (2OGD), have been functionally characterized in biosynthesis of abietane-type diterpenoids, the highly oxidized structure and complex secondary metabolic network of tanshinones imply that more oxidases should be characterized. Here, we identified a new 2OGD (Sm2OGD25) from S. miltiorrhiza. Molecular cloning and functional studies in vitro showed that Sm2OGD25 could catalyze the hydroxylation of sugiol at C-15 and C-16 positions to produce hypargenin B and crossogumerin C, respectively. The phylogenetic analysis of the DOXC family demonstrated that Sm2OGD25 belongs to the DOXC54 clade. Furthermore, structural modeling and site-directed mutagenesis characterization revealed the importance of the hydrogen-bonding residue Y339 and the hydrophobic residues (V122, F129, A144, A208, F303, and L344) in substrate binding and enzyme activity. This study will promote further studies on the catalytic characterization of plant 2OGDs and the secondary metabolic biosynthesis network of diterpenoids.

Palladium-Catalyzed Asymmetric [3 + 2] Annulation of Vinylethylene Carbonates with Alkenes Installed on Cyclic N-Sulfonyl Imines: Highly Enantio- and Diastereoselective Construction of Chiral Tetrahydrofuran Scaffolds Bearing Three Vicinal and Quaternary Stereocenters

A multisubstituted tetrahydrofuran building block bearing three vicinal chiral carbon centers widely exists in a broad spectrum of bioactive natural products, and the development of efficient and convenient methods to establish this skeleton remains a challenging task. Herein, we have developed an efficient method for the construction of significant tetrahydrofuran scaffolds bearing three vicinal and α-quaternary chiral carbon stereocenters through Pd-catalyzed asymmetric [3 + 2] annulation of vinylethylene carbonates with alkenes installed on cyclic N-sulfonyl imines. A series of multisubstituted tetrahydrofuran derivatives are obtained in high efficiencies with excellent enantioselectivities and diastereoselectivities. Density functional theory (DFT) studies are accomplished to rationalize the stereocontrol of the annulation process and disclose that methanol could be applied to stabilize the reactive zwitterionic π-allylpalladium via the H-bond interaction.

Anti-inflammatory sesquiterpenoids from the heartwood of Juniperus formosana Hayata

Juniperus formosana Hayata (J. formosana) is a commom needlebush cultivar growing in China. Six new compounds (1-6), including four cadinene sesquiterpenoids (1-4), one abietane diterpenoid (5), and one β-naphthol derivative (6), along with 18 known compounds (7-24) were isolated and identified through phytochemical investigation on the heartwood of J. formosana. The structures of these compounds were fully elucidated by their 1D and 2D NMR, HR-ESI-MS, UV, and IR spectral data analyses. The absolute configurations of compounds 1, 3, and 5 were confirmed by experimental and calculated electronic circular dichroism (ECD) data. Moreover, X-ray crystallographic analysis was carried out to characterize the structure of compound 4. The inhibitory effects on the nitric oxide (NO) production of all the isolated compounds were initially examined in RAW264.7 macrophages induced by lipopolysaccharide (LPS). The results showed that compounds 3 and 12 possessed significant inhibitory potency on NO generation with IC₅₀ values of 3.41 μM and 6.15 μM among the new and known compounds, respectively. The expressions of IL-1β, IL-6, and TNF-α were measured in LPS-stimulated RAW264.7 cells to evaluate the anti-inflammatory effects of compounds 1-24. Compounds 1-6 and 9-12 exhibited potent anti-inflammatory effects. Additionally, the expressions of p38, Erk, and IκBα proteins were further determined to explore the anti-inflammatory mechanism of the most potent compounds 3 and 12. Overall, our findings indicate the potential of J. formosana for developing medicine candidates as the treatments of inflammation.

Integrated Four Comparative-Omics Reveals the Mechanism of the Terpenoid Biosynthesis in Two Different Overwintering Cryptomeria fortunei Phenotypes

Chinese cedar (Cryptomeria fortunei) is a tree species with important ornamental, medicinal, and economic value. Terpenoids extracted from the essential oil of C. fortunei needles have been considered valuable ingredients in the pharmaceutical and cosmetic industries. However, the possible gene regulation mechanisms that limit terpenoid biosynthesis in this genus are poorly understood. Here, we adopted integrated metabolome analysis, transcriptome, small-RNA (sRNA), and degradome sequencing to analyze the differences in terpenoid regulatory mechanisms in two different overwintering C. fortunei phenotypes (wild-type and an evergreen mutant). A total of 1447/6219 differentially synthesized metabolites (DSMs)/unigenes (DEGs) were detected through metabolome/transcriptome analyses, and these DSMs/DEGs were significantly enriched in flavonoid and diterpenoid biosynthesis pathways. In C. fortunei needles, 587 microRNAs (miRNAs), including 67 differentially expressed miRNAs (DERs), were detected. Among them, 8346 targets of 571 miRNAs were predicted using degradome data, and a 72-miRNA-target regulatory network involved in the metabolism of terpenoids and polyketides was constructed. Forty-one targets were further confirmed to be involved in terpenoid backbone and diterpenoid biosynthesis, and target analyses revealed that two miRNAs (i.e., aly-miR168a-5p and aof-miR396a) may be related to the different phenotypes and to differential regulation of diterpenoid biosynthesis. Overall, these results reveal that C. fortunei plants with the evergreen mutation maintain high terpenoid levels in winter through miRNA-target regulation, which provides a valuable resource for essential oil-related bioengineering research.

Construction of novel bridged aromatic ring-fused oxazocine frameworks via an N-heterocyclic carbene-catalyzed azabenzoin reaction and radical-initiated cascade cyclization

A novel method for the construction of 1,5-methanobenzo[f][1,3]oxazocin-6-ones and 6,10-methanopyrido[3,2-f][1,3]oxazocin-5-ones from o-vinyl aromatic aldehydes and N-acylarylimines was developed via NHC-catalyzed and radical-initiated reactions.

Rh(iii)-Catalyzed Csp2–Csp3 bond alkoxylation of α-indolyl alcohols via C–C σ bond cleavage

A Rh(iii)-catalyzed direct Csp²–Csp³ bond alkoxylation of α-(2-indolyl)alcohols with alcohols has been achieved via C–C sigma bond/C–O single bond switch.

Asymmetric Total Syntheses of Di- and Sesquiterpenoids by Catalytic C-C Activation of Cyclopentanones

To show the synthetic utility of the catalytic C-C activation of less strained substrates, described here are the collective and concise syntheses of the natural products (-)-microthecaline A, (-)-leubehanol, (+)-pseudopteroxazole, (+)-seco-pseudopteroxazole, pseudopterosin A-F and G-J aglycones, and (+)-heritonin. The key step in these syntheses involve a Rh-catalyzed C-C/C-H activation cascade of 3-arylcyclopentanones, which provides a rapid and enantioselective route to access the polysubstituted tetrahydronaphthalene cores presented in these natural products. Other important features include 1) the direct C-H amination of the tetralone substrate in the synthesis of (-)-microthecaline A, 2) the use of phosphoric acid to enhance efficiency and regioselectivity for problematic cyclopentanone substrates in the C-C activation reactions, and 3) the direct conversion of serrulatane into amphilectane diterpenes by an allylic cyclodehydrogenation coupling.

A new diterpene and other compounds from the unripe female cones of Wollemia nobilis

In this work, the first phytochemical analysis ever performed on the unripe female cones of Wollemia nobilis W. G. Jones, K. D. Hill & J. M. Allen was described. The analysis evidenced the presence of a new derivative of sandaracopimaric acid together with rare diterpenoid derivatives and known compounds of chemosystematic and bioactivity relevance. Some of these were evidenced in the species or in the family for the first time during this study. The further implications of the isolated compounds in the field of chemosystematics, pharmacology and nutraceutics were discussed.

Terpenoids of the Swamp Cypress Subfamily (Taxodioideae), Cupressaceae, an Overview by GC-MS

The resins bled from stems and in seed cones and leaves of Cryptomeria japonica, Glyptostrobus pensilis, Taxodium distichum, and T. mucronatum were characterized to provide an overview of their major natural product compositions. The total solvent extract solutions were analyzed as the free and derivatized products by gas chromatography-mass spectrometry to identify the compounds, which comprised minor mono- and sesquiterpenoids, and dominant di- and triterpenoids, plus aliphatic lipids (e.g., n-nonacosan-10-ol). Ferruginol, 7α-p-cymenylferruginol, and chamaecydin were the major characteristic markers for the Taxodioideae conifer subfamily. The mass spectrometric data can aid polar compound elucidation in environmental, geological, archeological, forensic and pharmaceutical studies.

A Pair of Enantiomeric Bis- seco-abietane Diterpenoids from Cryptomeria fortunei

(±)-Cryptomeriolide, a pair of racemic bis- seco-abietane diterpenoids, were isolated from the bark of Cryptomeria fortunei. The separation of enantiomers was achieved by using chiral stationary phase HPLC. Their structures including the absolute configuration and conformations in solution and solid state were determined by extensive analysis of spectroscopic data, single-crystal X-ray diffraction, and comparison of calculated and experimental electronic circular dichroism data. A bioinspired one-pot enantiomeric synthesis of 1a and 1b was accomplished via a readily made intermediate orthoquinone from sugiol. All compounds including the synthetic intermediates were assayed for their cytotoxic activities on human cancer cell lines HL-60, A549, and SGC7901.

Tandem Oxidative Ring-Opening/Cyclization Reaction in Seconds in Open Atmosphere for the Synthesis of 1-Tetralones in Water-Acetonitrile

A mild and practical tandem oxidative ring-opening/cyclization reaction mediated by Ce⁴⁺ for the synthesis of 1-tetralones is presented. This rapid transformation was completed within 30 s and conducted in an open reactor at 0 °C in a water-acetonitrile mixture. Various cyclobutanol derivatives are transformed into desired products in good to high yields, and this reaction can be easily scaled up to the gram scale.

Abietane diterpenoids from Caryopteris incana (Thunb.) Miq

Twelve new diterpenes, caryopincaolide A-L (1-4, 11-12, 16-19, 27-28), together with twenty-eight known diterpenes, have been isolated from the whole plant of Caryopteris incana (Thunb.) Miq. Their structures were elucidated on the basis of 1D and 2D NMR, IR, X-ray crystal diffraction and mass spectroscopic data, as well as ECD calculations. All compounds were tested for in vitro dipeptidyl peptidase IV (DPP-IV) inhibitory activity, with compounds 3, 4, 28, 29, and 40 exhibiting DPP-IV inhibitory effects with IC50 values ranging from 54.2 to 228.9 μM. Compounds 1, 3 and 4 also showed potent activity toward the inhibition of the growth of human cancer cells and 1 can induce apoptosis in Hey and A-549 cells.

Abietane-Type Diterpenoid Amides with Highly Potent and Selective Activity against Leishmania donovani and Trypanosoma cruzi

Dehydroabietylamine (1) was used as a starting material to synthesize a small library of dehydroabietyl amides by simple and facile methods, and their activities against two disease-causing trypanosomatids, namely, Leishmania donovani and Trypanosoma cruzi, were assayed. The most potent compound, 10, an amide of dehydroabietylamine and acrylic acid, was found to be highly potent against these parasites, displaying an IC50 value of 0.37 μM against L. donovani axenic amastigotes and an outstanding selectivity index of 63. Moreover, compound 10 fully inhibited the growth of intracellular amastigotes in Leishmania donovani-infected human macrophages with a low IC50 value of 0.06 μM. This compound was also highly effective against T. cruzi amastigotes residing in L6 cells with an IC50 value of 0.6 μM and high selectivity index of 58, being 3.5 times more potent than the reference compound benznidazole. The potent activity of this compound and its relatively low cytotoxicity make it attractive for further development in pursuit of better drugs for patients suffering from leishmaniasis and Chagas disease.

Bioactive Diterpenoids from Clerodendrum kiangsiense

A new abeo-abietane diterpenoid, 12-methoxy-6,11,14,16-tetrahydroxy-17(15→16)-abeo-5,8,11,13-abietatetraen-3,7-dione (8), was isolated from the hydroalcoholic extract of the herb of Clerodendrum kiangsiense along with seven known diterpenoids (1–7). Their structures were identified on the basis of spectroscopic analyses including two-dimensional NMR and comparison with literature data. All of these compounds were evaluated for their cytotoxic activities against the growth of human cancer cells lines HL-60, SMMC-7721, A-549 and MCF-7 by the MTT assay. The results showed that cryptojaponol (4), fortunin E (6) and 8 exhibited significant cytotoxicity against four human cancer cell lines.

Aromatic abietane diterpenoids: their biological activity and synthesis

In this study, the biological properties of abietane-type diterpenoids with an aromatic C ring are reviewed. The review contains about 160 references.

A facile and regioselective synthesis of 1-tetralones via silver-catalyzed ring expansion

A regioselective synthesis of 1-tetralones via silver-catalyzed ring expansion is described.

Prospects of an alternative treatment against Trypanosoma cruzi based on abietic acid derivatives show promising results in Balb/c mouse model

Chagas disease, caused by the protozoa parasite Trypanosoma cruzi, is an example of extended parasitaemia with unmet medical needs. Current treatments based on old-featured benznidazole (Bz) and nifurtimox are expensive and do not fulfil the criteria of effectiveness, and a lack of toxicity devoid to modern drugs. In this work, a group of abietic acid derivatives that are chemically stable and well characterised were introduced as candidates for the treatment of Chagas disease. In vitro and in vivo assays were performed in order to test the effectiveness of these compounds. Finally, those which showed the best activity underwent additional studies in order to elucidate the possible mechanism of action. In vitro results indicated that some compounds have low toxicity (i.e. >150 μM, against Vero cell) combined with high efficacy (i.e. <20 μM) against some forms of T. cruzi. Further in vivo studies on mice models confirmed the expectations of improvements in infected mice. In vivo tests on the acute phase gave parasitaemia inhibition values higher those of Bz, and a remarkable decrease in the reactivation of parasitaemia was found in the chronic phase after immunosuppression of the mice treated with one of the compounds. The morphological alterations found in treated parasites with our derivatives confirmed extensive damage; energetic metabolism disturbances were also registered by (1)H NMR. The demonstrated in vivo activity and low toxicity, together with the use of affordable starting products and the lack of synthetic complexity, put these abietic acid derivatives in a remarkable position toward the development of an anti-Chagasic agent.

Copper-catalyzed intramolecular alkene carboetherification: synthesis of fused-ring and bridged-ring tetrahydrofurans

Fused-ring and bridged-ring tetrahydrofuran scaffolds are found in a number of natural products and biologically active compounds. A new copper-catalyzed intramolecular carboetherification of alkenes for the synthesis of bicyclic tetrahydrofurans is reported herein. The reaction involves Cu-catalyzed intramolecular addition of alcohols to unactivated alkenes and subsequent aryl C-H functionalization provides the C-C bond. Mechanistic studies indicate a primary carbon radical intermediate is involved and radical addition to the aryl ring is the likely C-C bond-forming mechanism. Preliminary catalytic enantioselective reactions are promising (up to 75% ee) and provide evidence that copper is involved in the alkene addition step, likely through a cis-oxycupration mechanism. Catalytic enantioselective alkene carboetherification reactions are rare and future development of this new method into a highly enantioselective process is promising. During the course of the mechanistic studies a protocol for alkene hydroetherification was also developed.

New sesquiterpene and triterpene from the fruits of Cryptomeria fortunei

A new sesquiterpene (1) and a new triterpene (2) along with 25 known compounds were isolated from the fruits of Cryptomeria fortunei (Taxodiaceae). Their structures were elucidated on the basis of spectroscopic analysis.