Two new ent-kaurene diterpene glucosides from the roots of Mikania micrantha

Two new ent-kaurene diterpene glucosides, β-d-glucopyranosyl-15α-(3-hydroxyl-3-methylbutanoyloxy)-ent-16-kauren-19-oate (1) and β-d-glucopyranosyl-15α-hydroxy-ent-16-kauren-19-oate (2), were isolated from the roots of Mikania micrantha. Their structures were elucidated on the basis of spectroscopic evidence. Both compounds were evaluated for allelopathic effects on the seed germination and seedling growth of Arabidopsis thaliana. Compound 1 inhibited the seedling growth by 68.3% at the concentration of 0.5 mM.     

New diterpenes from Sideritis sicula

Two new diterpenes have been isolated from Sideritis sicula: sideripol, ent-18-acetoxy-7α-hydroxykaur-15-ene and epoxysideritriol, ent-15β,16β-epoxykauran-7α,17,18-triol. The previously known diterpene eubol, ent-7α-acetoxykaur-16-en-15β,18 diol has also been obtained from the same source.     

Diterpenoids and a sesquiterpene lactone from viguiera ladibractate

Eight known diterpene acids, ent-12-oxokaur-9(11),16-dien-19-oic acid, ent-12β-hydroxykaur-9(11),16-dien-19-oic acid, ent-isokaur-15(16)-en-17,19-dioic acid, ent-15α,16-epoxy-17-hydroxykaura-19-oic acid, ent-kaura-17,19-dioic acid, ent-kaur-16-en-19-oic acid, grandifloric acid, angeloyloxygrandifloric acid, as well as a new sesquiterpene lactone, ladibranolide, were isolated from Viguiera ladibractate. The stereochemistry of the sesquiterpene lactone was established by NOE experiments.     

Two diterpene alcohols from Croton sublyratus

The isolation and structural elucidation of two diterpene alcohols from Croton sublyratus are described. These compounds are ent-3α-hydroxy-13-epimanool and ent-16β,17-dihydroxykaurane.     

Biotransformation of the diterpene 15β-hydroxy-18(4→3)-abeo-ent-kaur-4(19),16-diene by the fungus Fusarium fujikuroi

15β-Hydroxy-18(4→3)-abeo-ent-kaur-4(19),16-diene (4) was biotransformed by the fungus Fusarium fujikuroi into 3α,11β,15β-trihydroxy-18(4→3)-abeo-ent-kaur-4(19),16-diene (5). The hydroxylation at C-3(α) in this diterpene reminds a similar reaction that occurs at C-13 in the biosynthesis of gibberellic acid in this fungus. The presence of the 15β-alcohol in the substrate directs the second hydroxylation at C-11(β), which had been observed in the incubation of ent-kaur-16-ene derivatives with this fungus when the C-19 hydroxylation was inhibited by the existence in the molecule of a 3α-OH or 3-oxo group. We also show that the angelate of the substrate is an undescribed natural product now identified as a component of the plant Distichoselinum tenuifolium.     

Comparison of ent-kaurene and ent-isokaurene synthesis in cell-free systems from etiolated shoots of normal and dwarf-5 maize seedlings

An active cell-free system, prepared from young etiolated shoots of normal Zea mays seedlings, was shown to biosynthesize the terpenoid hydrocarbons ent-kaur-16-ene, squalene and phytoene from mevalonic acid. The biosynthesis of ent-kaur-16-ene from mevalonic acid was compared using cell-free systems obtained from normal and dwarf-5 seedlings. ent-Kaur-16-ene was the predominant diterpene hydrocarbon synthesized by extracts from the normals; however, ent-kaur-15-ene was the major diterpene hydrocarbon synthesized by the dwarf-5 mutants. ent-Kaur-15-ene and ent-kaur-16-ene were also produced as minor products in the normal and dwarf-5 systems, respectively. The possible significance of the synthesis of the ‘wrong isomer’ (ent-kaur-15-ene) by the mutant is discussed.     

A diterpenoid from Elaeoselinum foetidum

A new diterpene acid has been isolated from the roots of Elaeoselinum foetidum. Its structure was established as ent-7α-senecioxy-15α-hydroxy-atis-16-en-19-oic acid by ¹H NMR and ¹³C NMR spectroscopic studies of its methyl ester derivative and confirmed by correlation with a margotianin derivative.     

Ent-labdane derivatives from gutierrezia grandis

Two new diterpenes, 3α-angeloyloxy-18-hydroxy-13-furyl-ent-labda-8(17)-ene and 3α-hydroxy-18-angeloyloxy- 13-furyl-ent-labda-8(17)-ene and an only recently reported third diterpene, 3α, 18-dihydroxy-13-furyl-ent-labda-8(17)-ene, were isolated from the leaves of Gutierrezia grandis. Their structures were determined by mass spectral, IR, ¹H NMR and ¹³C NMR data was well as chemical evidence.     

Differential metabolism of diastereoisomeric diterpenes by Preussia minima,found as endophytic fungus in Cupressus lusitanica

The plant diastereoisomeric diterpenes ent-pimara-8(14)-15-dien-19-oic acid, obtained from Viguiera arenaria, and isopimara-8(14)-15-dien-18-oic acid, isolated from Cupressus lusitanica, were distinctly functionalized by the enzymes produced in whole cell cultures of the fungus Preussia minima, isolated from surface sterilized stems of C. lusitanica. The ent-pimaradienoic acid was transformed into the known 7β-hydroxy-ent-pimara-8(14)-15-dien-19-oic acid, and into the novel diterpenes 7-oxo-8 β-hydroxy-ent-pimara-8(14)-15-dien-19-oic and 7-oxo-9β-hydroxy-ent-pimara-8(14)-15-dien-19-oic acids. Isopimara-8(14)-15-dien-18-oic acid was converted into novel diterpenes 11α-hydroxyisopimara-8(14)-15-dien-18-oic acid, 7β,11α-dihydroxyisopimara-8(14)-15-dien-18-oic acid, and 1β,11α-dihydroxyisopimara-8(14)-15-dien-18-oic acid, along with the known 7β-hydroxyisopimara-8(14)-15-dien-18-oic acid. All compounds were isolated and fully characterized by 1D and 2D NMR, especially ¹³C NMR. The diterpene bioproduct 7-oxo-9β-hydroxy-ent-pimara-8(14)-15-dien-19-oic acid is an isomer of sphaeropsidin C, a phytotoxin that affects cypress trees produced by Shaeropsis sapinea, one of the main phytopathogen of Cupressus. The differential metabolism of the diterpene isomers used as substrates for biotransformation was interpreted with the help of computational molecular docking calculations, considering as target enzymes those of cytochrome P450 group.     

Ent-hardwickiic acid from C. pubiflora and its microbial metabolites are more potent than fluconazole in vitro against Candida glabrata

The incidence of Candida glabrata infections has rapidly grown and this species is among those responsible for causing invasive candidiasis with a high mortality rate. The diterpene ent-hardwickiic acid is a major constituent in Copaifera pubiflora oleoresin and the ethnopharmacological uses of this oleoresin by people from Brazilian Amazonian region point to a potential use of this major constituent as an antimicrobial. Therefore, the goal of this study was to evaluate the antifungal activity of ent-hardwickiic acid against Candida species and to produce derivatives of this diterpene by using microbial models for simulating the mammalian metabolism. The microbial transformations of ent-hardwickiic acid were carried out by Aspergillus brasiliensis and Cunninghamella elegans and hydroxylated metabolites were isolated and their chemical structures were determined. The antifungal activity of ent-hardwickiic acid and its metabolites was assessed by using the microdilution broth method in 96-well microplates and compared with that of fluconazole. All the diterpenes showed fungistatic effects (ranging from 19·7 to 75·2 µmol l⁻¹) against C. glabrata at lower concentrations than fluconazole (163·2 µmol l⁻¹) and were more potent fungicides (ranging from 39·5 to 150·4 µmol l⁻¹) than fluconazole, which showed fungicidal effect at the concentration of 326·5 µmol l⁻¹.     

Ent-kaurene diterpenoids and lignan from Leontopodium leontopodioides and their inhibitory activities against cyclooxygenases-1 and 2

Two new ent-kaurene diterpenoids, 13α,15α-dihydroxy-18-carboxy-19-nor-ent-kaur-16-ene-2β-O-(2′-angelate)-β-d-glucopyranoside (leontocin A, 1), 13α,15α-dihydroxy-18-carboxy-19-nor-ent-kaur-16-ene-2β-O-(2′-angelate-6′-acetyl)-β-d-glucopyranoside (leontocin B, 2), and one new lignan, 2,3-bis[(3,4-di-hydroxyphenyl)methylene]-monoethyl ester-butanedioic acid (leontolignan A, 3), together with three known phenolic acids (4-6) were isolated from the aerial parts of Leontopodium leontopodioides (Asteraceae). Their structures were elucidated by chemical and spectroscopic methods. All isolates were evaluated for their anti-inflammatory activities by measuring their inhibitory effects against cyclooxygenase-1 and 2 in vitro.     

Structures of the Metabolites from Steviol Methyl Ester by Gibberella fujikuroi

Steviol methyl ester (methyl ent-13-hydroxykaur-16-en-19-oate)* was converted into five new metabolites together with a known compound, methyl ent-7α,13-dihydroxykaur-16-en-19-oate, by Gibberella fujikuroi in the presence of a plant growth retardant. The structures of these new metabolites were elucidated to be methyl ent-7β,13-dihydroxykaur-16-en-19-oate, methyl ent-11α,13-dihydroxykaur-16-en-19-oate, methyl ent-7β,11α,13-trihydroxykaur-16-en-19-oate, methyl ent-11α, 13,15β-trihydroxykaur-16-en-19-oate and methyl ent-13,15β-dihydroxy-11-oxokaur-16-en-19-oate mainly by spectroscopic analyses.     

The microbiological transformation of some ent-3β-hydroxykaur-16-enes by Gibberella fujikuroi

The preparation of ent-3β-hydroxykaur-16-ene from linearol and of ent -3β,18-dihydroxykaur-16-ene from foliol is described. The microbiological transformation of these and of foliol by Gibberella fujikuroi has been studied. A 3α-hydroxyl group appears to exert an inhibitory effect on transformations involving oxidation at C-19.     

Three ent-kaurene diterpenes from Vellozia caput-ardeae

Three new ent-kaurene diterpenes have been isolated from the roots and stem of Vellozia caput-ardeae. Their structures were elucidated by spectroscopic methods as ent-9β-hydroxy kaur-16-ene, ent-11α-hydroxy kaur-16-ene and ent-9β,11α-dihydroxy kaur-16-ene.     

Biotransformation of 7α-hydroxy- and 7-oxo-ent-atis-16-ene derivatives by the fungus Gibberella fujikuroi

The microbiological transformation of 7α,19-dihydroxy-ent-atis-16-ene by the fungus Gibberella fujikuroi gave 19-hydroxy-7-oxo-ent-atis-16-ene, 13(R),19-dihydroxy-7-oxo-ent-atis-16-ene, 7α,11β,19-trihydroxy-ent-atis-16-ene and 7α,16β,19-trihydroxy-ent-atis-16-ene, while the incubation of 19-hydroxy-7-oxo-ent-atis-16-ene afforded 13(R),19-dihydroxy-7-oxo-ent-atis-16-ene and 16β,17-dihydroxy-7-oxo-ent-atisan-19-al. The biotransformation of 7-oxo-ent-atis-16-en-19-oic acid gave 6β-hydroxy-7-oxo-ent-atis-16-en-19-oic acid, 6β,16β,17-trihydroxy-7-oxo-19-nor-ent-atis-4(18)-ene and 3β,7α-dihydroxy-6-oxo-ent-atis-16-en-19-oic acid.     

The metabolism of steviol to 13-hydroxylated ent-Gibberellanes and ent-kauranes

Steviol(ent-13-hydroxykaur-16-en-19-oic acid) is rapidly metabolised by the mutant B1-41a of Gibberellafujikuroi. The initial product is the ent- 7-α-hydroxy derivative which is then further metabolised to gibberellins A₁, A₁₈, A₁₉, A₂₀, 13-hydroxy GA₁₂, the ent-6α, 7α, 13- and ent-6β, 7α, 13 (19,6-lactone)-trihydroxykaurenoic acids, and a seco-ring B diacid. This apparently low substrate specificity of the enzymes operative beyond the block in the mutant B1-41a provides a useful model for the biosynthetic pathways to 13-hydroxylated gibberellins of higher plants and a preparative route to these plant gibberellins.     

Diterpenoids from Sideritis arborescens subsp. Paulii

Several ent-labda-13(16),14-dienes, ent-13-epi-manoyl oxides and the new natural products ent-6α,8α-dihydroxylabda-13(16),14-diene, ent-18-hydroxy-15(16)peroxylabd-13-ene,ent-16,18-dihydroxymanoyl oxide, ent-13-epi-16,18-dihydroxymanoyl oxide and ent-6α16,18-trihydroxymanoyl oxide have been isolated from Sideritis arborescens subsp. paulii. The structures of these compounds have been established by spectroscopic means and chemical correlations.     

ent-Kaurane diterpenes from the stem bark of Annona vepretorum (Annonaceae) and cytotoxic evaluation

This work describes a novel ent-kaurane diterpene, ent-3β-hydroxy-kaur-16-en-19-al along with five known ent-kaurane diterpenes, ent-3β,19-dihydroxy-kaur-16-eno, ent-3β-hydroxy-kaur-16-eno, ent-3β-acetoxy-kaur-16-eno, ent-3β-hydroxy-kaurenoic acid and kaurenoic acid, as well as caryophyllene oxide, humulene epoxide II, β-sitosterol, stigmasterol and campesterol from the stem bark of Annona vepretorum Mart. (Annonaceae). Cytotoxic activities towards tumor B16-F10, HepG2, K562 and HL60 and non-tumor PBMC cell lines were evaluated for ent-kaurane diterpenes. Among them, ent-3β-hydroxy-kaur-16-en-19-al was the most active compound with higher cytotoxic effect over K562 cell line (IC₅₀ of 2.49 μg/mL) and lower over B16-F10 cell line (IC₅₀ of 21.02 μg/mL).     

Chemical composition of Xylopia nitida: Diterpenes and alkaloids

From the roots of Xylopia nitida, were obtained a new natural diterpene, the ent-kaur-16-en-18,19-diol and a new aporphine alkaloid, the 5,6,6a,7-tetrahydro-1-methoxy-(6aS)-4H-benzo[de][1,3]benzodioxolo [5,6-g]quinoline. Some known compounds were also isolated, ent-trachylobane, ent-trachyloban-18,19-diol, ent-trachyloban-18-oic acid, ent-trachyloban-19-oic acid, (−)-xylopine, 1-O-ethyl-β-D-glucopyranose and a mixture of β-sitosterol and stigmasterol. This is the first phytochemical study about X. nitida. In this paper chemotaxonomic significance of these compounds is discussed.     

Gibberellin biosynthesis in bacteria: Separate ent-copalyl diphosphate and ent-kaurene synthases in Bradyrhizobium japonicum

Gibberellins are ent-kaurene-derived diterpenoid phytohormones produced by plants, fungi, and bacteria. The distinct gibberellin biosynthetic pathways in plants and fungi are known, but not that in bacteria. Plants typically use two diterpene synthases to form ent-kaurene, while fungi use only a single bifunctional diterpene synthase. We demonstrate here that Bradyrhizobium japonicum encodes separate ent-copalyl diphosphate and ent-kaurene synthases. These are found in an operon whose enzymatic composition indicates that gibberellin biosynthesis in bacteria represents a third independently assembled pathway relative to plants and fungi. Nevertheless, sequence comparisons also suggest potential homology between diterpene synthases from bacteria, plants, and fungi.