Biosynthesis of the tigloyl esters in Datura: The role of 2-methylbutyric acid

Datura innoxia plants were wick fed with (±)-2-methylbutyric acid-[1-¹⁴C] and harvested after 7 days. The root alkaloids 3α,6β-ditigloyloxytropane and 3α,6β-ditigloyloxytropan-7β-ol were isolated and degraded. In each case the radioactivity was located in the ester carbonyl group indicating that this acid is an intermediate in the biosynthesis of tiglic acid from l-isoleucine. On the other hand, (±)-2-hydroxy-2-methylbutyric acid-[1-¹⁴C], which was fed to hydroponic cultures of Datura innoxia alongside isoleucine[U-¹⁴C] positive control plants, is not an intermediate.     

6β-Hydroxyipolamiide,an iridoid glucoside from Stachytarpheta mutabilis

A new iridoid glucoside has been isolated from Stachytarpheta mutabilis and assigned the structure and configuration of 6β-hydroxyipolamiide on the basis of ¹H NMR and ¹³C NMR evidence. The conversion of this compound into penta- acetyllamiol proved the above assignment.     

Biosynthesis of the tigloyl esters of Datura: Cis-trans isomerism

Datura innoxia plants were wick fed with angelic acid-[1-¹⁴C] and l-isoleucine-[U-¹⁴C] to act as a positive control. After 7 days the root alkaloids 3α-tigloyloxytropane, 3α,6β-ditigloyloxytropane, and 3α,6β-ditigloyloxytropan-7β-ol were isolated and it was determined that angelic acid is not a precursor for the tigloyl moiety of these alkaloids. Tiglic acid-[1-¹⁴C] which was fed via the roots to hydroponic cultures of Datura innoxia, was incorporated to a considerable degree after 8 days.     

Biosynthesis of ditigloyl esters of DI- and tri-hydroxytropanes in Datura

3α-Tigloyloxytropane-[¹⁴CO] [N-¹⁴Me], ratio 1·6:1 and valtropine-[¹⁴CO] [N-¹⁴Me], ratio 1·75:1 were separately fed via cotton wicks to 4-month-old Datura innoxia plants. After 8 days the root alkaloids 3α-tigloyloxytropane, 3α,6β-ditigloyloxytropane and 3α,6β-ditigloyloxytropan-7β-ol were isolated and the distribution of radioactivity in the acid and alkamine moieties was determined by hydrolysis. The precursor ratios were not maintained in the isolated ditigloyl esters, a result which does not support our hypothesis that the ditigloyl esters are formed by the progressive hydroxylation of 3α-tigloyloxytropane.     

Structure and configuration of unedide,an iridoid glucoside from Arbutus unedo

Unedide, a novel iridoid glucoside isolated from Arbutus unedo (Ericaceae), has been established to be 6,7-dihydro-6β-hydroxymonotropein by detailed analysis of ¹H and ¹³ C NMR spectral data.     

Microbiological oxidation of sterols by Coriolus hirstus

Fermentation of cholesterol with a culture of Coriolus hirstus yielded a mixture containing 7-oxo-cholesterol and hydroxylated-cholesterol derivatives. Preparation of a possible precursor of antheridiol, 7-oxofucosterol, by this fungus was also examined.     

Five 3β, 6α-dihydroxysterols in organ-pipe cactus

The sterol diol fraction from the lipids of organ-pipe cactus, Stenocereus thurberi, was separated into five compounds: macdougallin, peniocerol, cyclostenol, stenocereol and thurberol. The last three compounds have not been described before. All compounds were characterized by physical and spectroscopic properties.     

Triterpenoids from enkianthus campanulatus

From the leaves of Enkianthus campanulatus were isolated three new triterpenes, 3-oxo-19,23,24-trihydroxyurs-12-en-28-oic acid, 3β,6β, 19,23-tetrahydroxyurs-12-en-28-oic acid and 3β,6β,23-trihydroxyurs-12-en-28-oic acid.     

Non-reversibility of the isoleucine-acetate pathway in Datura

Five-month-old Datura meteloides plants were fed via the roots with 3-hydroxy-2-methylbutanoic acid-[1-¹⁴C] and isoleucine-[U-¹⁴C] as a positive control. After 5 days the plants were collected and in each case the root alkaloids 3α,6β-ditigloyloxytropane, 3α,6β-ditigloyloxytropan-7β-ol, meteloidine, hyoscine and hyoscyamine were isolated. Whereas isoleucine served as a precursor for the tiglic acid moieties 3-hydroxy-2-methylbutanoic acid did not.     

6α-Hydroxylation of taurochenodeoxycholic acid and lithocholic acid by CYP3A4 in human liver microsomes

The aim of the present study was to identify the enzymes in human liver catalyzing hydroxylations of bile acids. Fourteen recombinant expressed cytochrome P450 (CYP) enzymes, human liver microsomes from different donors, and selective cytochrome P450 inhibitors were used to study the hydroxylation of taurochenodeoxycholic acid and lithocholic acid. Recombinant expressed CYP3A4 was the only enzyme that was active towards these bile acids and the enzyme catalyzed an efficient 6α-hydroxylation of both taurochenodeoxycholic acid and lithocholic acid. The V_max for 6α-hydroxylation of taurochenodeoxycholic acid by CYP3A4 was 18.2 nmol/nmol P450/min and the apparent K_m was 90 μM. Cytochrome b₅ was required for maximal activity. Human liver microsomes from 10 different donors, in which different P450 marker activities had been determined, were separately incubated with taurochenodeoxycholic acid and lithocholic acid. A strong correlation was found between 6α-hydroxylation of taurochenodeoxycholic acid, CYP3A levels (r²=0.97) and testosterone 6β-hydroxylation (r²=0.9). There was also a strong correlation between 6α-hydroxylation of lithocholic acid, CYP3A levels and testosterone 6β-hydroxylation (r²=0.7). Troleandomycin, a selective inhibitor of CYP3A enzymes, inhibited 6α-hydroxylation of taurochenodeoxycholic acid almost completely at a 10 μM concentration. Other inhibitors, such as α-naphthoflavone, sulfaphenazole and tranylcypromine had very little or no effect on the activity. The apparent K_m for 6α-hydroxylation of taurochenodeoxycholic by human liver microsomes was high (716 μM). This might give an explanation for the limited formation of 6α-hydroxylated bile acids in healthy humans. From the present results, it can be concluded that CYP3A4 is active in the 6α-hydroxylation of both taurochenodeoxycholic acid and lithocholic acid in human liver.     

Terpenes and steroids from leaves of Oxandra sessiliflora R. E. Fries

The EtOH extract from the leaves of Oxandra sessiliflora R. E. Fries (Annonaceae) was partitioned using hexane and CH₂Cl₂. After several chromatographic steps, caryophyllene oxide and spathulenol were isolated from hexane phase while, from CH₂Cl₂ phase, we isolated (E)-phytol, spathulenol, 4β,10α-dihydroxyaromadendrane, 1β,6α-dihydroxyeudesm-4(15)-ene, and 4α,7β,10α-trihydroxyguai-5-ene, the latter being a new sesquiterpene derivative. Additionally, a mixture of steroids (campesterol, sitosterol, and stigmasterol) was obtained from the CH₂Cl₂ phase. The isolated compounds were characterized by mass spectrometry and analysis of their ¹H and ¹³C NMR spectroscopic data, including bidimensional analysis.     

Synthesis of novel anticancer iridoid derivatives and their cell cycle arrest and caspase dependent apoptosis

Nyctanthes arbortristis Linn (Oleaceae) is widely distributed in sub-Himalayan regions and southwards to Godavari, India commonly known as Harsingar and Night Jasmine. In continuation of our drug discovery programme on Indian medicinal plants, we isolated arbortristoside-A (1) and 7-O-trans-cinnamoyl 6β-hydroxyloganin (2) from the seeds of N. Arbortristis, which exhibited moderate in vitro anticancer activity. Chemical transformation of 2 led to significant improvement in the activity in derivative 8 and 15 against HepG2 (human hepatocellular carcinoma), MCF-7 (breast adenocarcinoma) cell lines. The compounds 8 and 15 were also capable of cell cycle arrest and caspase dependent apoptosis in HepG2 cell lines. These iridoid derivatives hold promise for developing safer alternatives to the marketed drugs.     

Structure of maritimin,a sesquiterpene lactone from artemisia maritima gallica

1-Keto-6β,7α,11β-H-selin-4(5)-en-6,12-olide, vulgarin and a new eudesmanolide, maritimin, were isolated from Artemisia maritima gallica. The structure and stereochemistry of this lactone have been determined by spectral studies and chemical transformations.     

Implications of cholesterol autoxidation products in the pathogenesis of inflammatory diseases

There is rising interest in non-enzymatic cholesterol oxidation because the resulting oxysterols have biological activity and can be used as non-invasive markers of oxidative stress in vivo. The preferential site of oxidation of cholesterol by highly reactive species is at C₇ having a relatively weak carbon–hydrogen bond. Cholesterol autoxidation is known to proceed via two distinct pathways, a free radical pathway driven by a chain reaction mechanism (type I autoxidation) and a non-free radical pathway (type II autoxidation). Oxysterols arising from type II autoxidation of cholesterol have no enzymatic correlates, and singlet oxygen (¹ΔgO₂) and ozone (O₃) are the non-radical molecules involved in the mechanism. Four primary derivatives are possible in the reaction of cholesterol with singlet oxygen via ene addition and the formation of 5α-, 5β-, 6α- and 6β-hydroxycholesterol preceded by their respective hydroperoxyde intermediates. The reaction of ozone with cholesterol is very fast and gives rise to a complex array of oxysterols. The site of the initial ozone reaction is at the Δ_5,6 –double bond and yields 1,2,3-trioxolane, a compound that rapidly decomposes into a series of unstable intermediates and end products. The downstream product 3β-hydroxy-5-oxo-5,6-secocholestan-6-al (sec-A, also called 5,6-secosterol), resulting from cleavage of the B ring, and its aldolization product (sec-B) have been proposed as a specific marker of ozone-associated tissue damage and ozone production in vivo. The relevance of specific ozone-modified cholesterol products is, however, hampered by the fact sec-A and sec-B can also arise from singlet oxygen via Hock cleavage of 5α-hydroperoxycholesterol or via a dioxietane intermediate. Whatever the mechanism may be, sec-A and sec-B have no enzymatic route of production in vivo and are reportedly bioactive, rendering them attractive biomarkers to elucidate oxidative stress-associated pathophysiological pathways and to develop pharmacological agents.     

The involvement of cytochrome b5 in 5β-cholestane-3α,7α,12α-triol 25-hydroxylation and taurodeoxycholate 7α-hydroxylation of rat liver

Role of cytochrome b₅ in NADPH-supported 5β-cholestane-3α,7α,12α-triol 25-hydroxylation and taurodeoxycholate 7α-hydroxylation of rat liver microsomes was investigated using highly purified antibodies against cytochrome b₅. Anti-b₅ antibody strongly inhibited both hydroxylation reactions indicating that cytochrome b₅ is a functional component in these steroid hydroxylation systems. It was shown that the involvement of cytochrome b₅ in these systems could be altered by the conditions of the reaction systems.     

Iridoid glucosides of Linaria clementei

From an acetone extract of the whole plant of Linaria clementei, besides antirride and antirrinoside, the new iridoid glucosides 6-senecioyl- and 6-angeloylantirrinoside were isolated.     

Xanthones from Lawsonia inermis

Two new xanthones isolated from Lawsonia inermis have been characterised as 1, 3-dihydroxy-6, 7-dimethoxyxanthone and 1-hydroxy-3, 6-diacetoxy-7-methoxyxanthone and named laxanthone-I and II, respectively.     

Nanoencapsulation of triterpene 3β,6β,16β-trihydroxylup-20(29)-ene from Combretum leprosum as strategy to improve its cytotoxicity against cancer cell lines

The pentacyclic triterpene 3β,6β,16β-tri-hydroxilup-20(29)-ene is a natural product produced by the Brazilian medicinal plant Combretum leprosum. Its cytotoxicity has been previously reported against breast cancer cell lines. The low water solubility of this natural product, that hampers its bioavailability, motivated the investigation of a new nanoparticle formulation containing the triterpene in order to improve its bioactivity. The triterpene was encapsulated in polycaprolactone (PCL) polymer by nanoprecipitation, producing homogenic nanoparticles with nanometer sizes (122.7 ± 2.06 nm), which were characterized by FT-IR, SEM imaging and DSC. The cytotoxicity (MTT method) of the nanoparticle containing the triterpene 1, besides the free natural product and the nanoparticle control (without 1), was assayed against three human tumor cell lines [human colon carcinoma line (HCT116), prostate (PC3) and glioblastoma (SNB19)] and the normal epithelial embryo kidney human cell line (Hek293T). The nanocarrier produced a significative effect in the cytotoxicity of the natural product in the nanoformulation (IC₅₀ 0.11–0.26 µg mL⁻¹) when compared with its free form (IC₅₀ 1.07–1.44 µg mL⁻¹). Additionally, higher selectivity of the triterpene to the tumor cells was found when it was encapsulated (SI 1.92–4.54) than in its free form (SI 0.42–0.56). In this case, the nanoencapsulated triterpene was more selective to PC3 (SI 3.33) and SNB19 (SI 4.54) tumor cells.     

Tetranortriterpenoids from the seeds of Azadirachta indica

Six new tetranortriterpenoids have been isolated from the extract of neem seeds. The C-7 benzoates of tetranortriterpenoids occurring in Azadirachta indica are described for the first time. The structures of all new compounds were determined by spectroscopical methods.     

Crystal Structures of CusC Review Conformational Changes Accompanying Folding and Transmembrane Channel Formation

Gram-negative bacteria, such as Escherichia coli, frequently utilize tripartite efflux complexes in the RND (resistance–nodulation–cell division) family to expel diverse toxic compounds from the cell. These complexes span both the inner and outer membranes of the bacterium via an α-helical, inner membrane transporter; a periplasmic membrane fusion protein; and a β-barrel, outer membrane channel. One such efflux system, CusCBA, is responsible for extruding biocidal Cu(I) and Ag(I) ions. To remove these toxic ions, the CusC outer membrane channel must form a β-barrel structural domain, which creates a pore and spans the entire outer membrane. We here report the crystal structures of wild-type CusC, as well as two CusC mutants, suggesting that the first N-terminal cysteine residue plays an important role in protein–membrane interactions and is critical for the insertion of this channel protein into the outer membrane. These structures provide insight into the mechanisms on CusC folding and transmembrane channel formation. It is found that the interactions between CusC and membrane may be crucial for controlling the opening and closing of this β-barrel, outer membrane channel.