Activation and inactivation of thyroxine by cultured rat hepatoma cells

The metabolism of thyroxine, 3,3′,5-triiodothyronine and 3,3′,5′-triiodothyronine was investigated in rat hepatoma cell cultures (R117-21B). These iodothyronines were labeled with ¹²⁵I in the phenolic ring and the metabolites were analyzed by ion-exchange column chromatography.When thyroxine was incubated with the cells at 37°C, its glucuronide was the major product and a little increase in ¹²⁵I^? was detected. Although 3,3′,5-triiodothyronine was not observed in the incubation medium, this metabolite was clearly identified in the ethanol extract obtained from the cell homogenates after 24 h incubation.This cell line also metabolized labeled 3,3′,5-triiodothyronine added to culture medium. After 24 h incubation, 3,3′,5-triiodothyronine glucuronide was the major metabolite and iodothyronine sulfates were also formed. The sulfates contained, 3,3′,5-triiodothyronine and 3,3′-diiodothyronine sulfates and an unknown component.In the metabolism of 3,3′,5′-triiodothyronine, the cells were very active in carrying out glucuronidation and phenolic ring deiodination, and this metabolism yielded 3,3′,5′-triiodothyronine and 3,3′-diiodothyronine glucuronides. The iodide fraction contained a small amount of 3,3′-diiodothyronine sulfate.These results show that the R117-21B rat hepatoma cells metabolize the thyroid hormones and their analogs by phenolic and nonphenolic ring deiodinations, by glucuronidation and by sulfation.     

Study on the enzymatic 5′-deiodination of 3′,5′-diiodothyronine using a radioimmunoassay for 3′-iodothyronine

A radioimmunoassay for 3′-iodothyronine has been developed. All iodothyronine analogues (except 3,3′-diiodothyronine) showed very little (0.02% at most) cross-reactivity, and the assay was sensitive to 1 pg 3′-iodothyronine/ tube. We have studied the 5′-deiodination of 3′,5′-diiodothyronine by rat liver microsomal fraction in the presence of dithiothreitol. Production of 3′-iodothyronine at 37°C was found to be linear with time of incubation up to 30 min and with concentration of microsomal protein up to 100 μg/ml. The reaction rate reached a limit on increasing 3′,5′-diiodothyronine concentration to 10 μM. The effect of pH on 3′-iodothyronine production was found to depend on 3′,5′-diiodothyronine concentration. Increasing 3′,5′-diiodothyronine concentration from 0.1 to 10 μM resulted in a shift of the pH optimum from 6–6.5 to 7.5. Similar effects on the 5′-deiodination of 3,3′,5′-triiodothyronine were observed, supporting the hypothesis that these reactions are catalysed by a single enzyme (iodothyronine 5′-deiodinase).     

Iodothyronine 5′-deiodinase activity in rat brown adipose tissue during development

Iosothyronine 5′-deiodinase activity in rat brown adipose tissue has a characteristic pattern of developmental changes that is completely different from that of the liver. Fetal brown fat exhibits an extremely high iodothyronine 5′-deiodinase activity that is approx. 10-fold that in adult rats. Even though brown fat iodothyronine 5′-deiodinase activity falls suddenly at birth, there is a new peak in the activity around days 5–7 of life, whereas it remaines very low afterwards. Just after birth, brown adipose tissue iodothyronine 5′-deiodinase activity is already capable of stimulation by noradrenaline. The postnatal peak in brown fat iodothyronine 5′-deiodinase correlates with the known increase in the thermogenic activity of the tissue in the neonatal rat, thus reinforcing the suggestion that local 3′,3,5-triiodothyronine generation could be an important event related to thermogeneis in brown adispose tissue. However, the high fetal activity was only slightly related to the thermogenic activity of brown fat. Moreover, the increased iodothyronine 5′-deiodinase activity of brown adipose tissue during fetal and neonatal life suggests a substantial contribution by brown fat in the overall extrahydroidal 3′,3,5-triiodothyronine production in these physiological periods.     

Improved chromatographic methods for the separation of thyroid hormones and their metabolites.

In order to analyze iodoamino acids, two elution systems were established for cation-exchange column chromatography on AG50W-X4. A rapid method suitable for the separation of iodide, monoiodotyrosine, diiodotyrosine, 3,3′,5-triiodothyronine, and thyroxine, permits those compounds to be analyzed within 1.5 h. In this system, the volume of the starting solution (0.04 m ammonium acetate, pH 4.7) is kept constant throughout chromatography by adding 0.04 m Tris(hydroxymethyl)aminomethane, whereby a convex gradient of Tris is obtained. Both solutions contain 30% ethanol. Another system is suitable for the analysis of metabolites of thyroxine as well as for iodotyrosines and is based on the use of simultaneous NH₄OH (0 → 0.7 m) and ethanol (30 → 0%) linear gradients. Furthermore, 1-butanol saturated with 0.2 m NH₄OH was found useful for the separation of iodothyronine sulfates by thin-layer chromatography. The R_f values of various iodothyronines, iodotyrosines, and sulfates in thin-layer chromatography on silica gel were measured in several solvent systems and certain correlations between iodothyronine structure and R_f values were found.     

Hydrolysis of iodothyronine sulfates by sulfatase activity of anaerobic bacteria from the rat intestinal flora

Abstract 2 Obligately anaerobic bacteria isolated from rat cecal flora have previously been shown to possess sulfatase activity towards 3,3'-diiodothyronine sulfate [5]. These strains have now been tested for their ability to hydrolyze the sulfate conjugates of other iodothyronines, including the thyroid hormones thyroxine and 3,3',5-triiodothyronine. In anaerobic incubations at 37°C with approximately 10⁷ bacteria per ml, variable amounts of the conjugated substrates, ranging from 15–90%, were hydrolysed in 24 h. These results showed a potent iodothyronine sulfate hydrolysing capacity of rat intestinal microflora. The strains were characterized by carbohydrate fermentation tests. One strain belonged to the genus Lactobacillus , the other strain probably to Eubacterium or Lachnospira .     

Hydrolysis of iodothyronine glucuronides by obligately anaerobic bacteria isolated from human faecal flora

Abstract 35 bacterial strains isolated from the human faecal flora were screened for hydrolysis of the glucuronides of 3,3',5-triiodothyronine and 3,3'-diiodothyronine. Two Gram-positive obligately anaerobic strains possessed glucuronidase activity. These strains probably belong to the genus Eubacterium , but ethanol was produced in high concentrations during glucose fermentation, which makes final classification difficult. Considering the number of bacteria in the intestinal flora (> 10⁸/ml) and the biliary excretion of iodothyronine conjugates, the strains must be able to hydrolyse a major part of the total daily intestinal supply of these iodothyronine metabolites. The study extends previous observations with faecal suspensions of human and rat origin [24]. The relevance of bacterial β-glucuronidase activity for a possible enterohepatic circulation of iodothyronines is discussed.     

Uptake and metabolism of thyroid hormones by cultured monkey hepatocarconoma cells Effects of potassium cyanide and dinitrophenol

Cultured monkey hepatocarcinoma cells (NCLP-6E) were used to investigate the uptake and metabolism of thyroid hormones. Intracellular accumulation was shown by the failure to acutely release hormone from cells subsequently exposed to serum proteins, and by the metabolic transformation of the hormones to deiodinated products and their sulfates. When hepatocarconoma cell monolayers were studied at hormone concentrations below 10^?10 M, neither KCN nor dinitrophenol inhibited uptake. Taken together with previous findings that uptake was neither saturable nor reduced at low temperature, these results indicate that this process was not active transport. Deiodination of both the phenolic and non-phenolic rings, however, was partially inhibited by KCN but not by dinitrophenol. Sulfation of 3,3′-diiodothyronine and 3′-monoiodothyronine was strongly inhibited by both KCN and dinitrophenol.Uptake of the hormones and their metabolites was also measured in suspended hepatocarcinoma cells and compared with the uptake by normal rat hepatocytes, human fibroblasts and human lymphocytes. In these experiments 1 μM triiodothyronine and 0.47 mM dinitrophenol were used to inhibit deiodination and sulfation, respectively. Uptake was similar in all cell types. Accumulation was highest with 3,5,3′-triiodothyronine, intermediate with other compounds having iodines in both rings, lowest with compounds iodinated in only one ring, and absent with iodothronine sulfates. These findings help to explain the relative rates of metabolism of the iodothyronines and their release from the cells.     

Phenolic ring deiodination in cultured rat hepatoma cells, and subcellular localization of deiodinases in cultured rat hepatoma, monkey hepatocarcinoma cells and normal rat liver homogenates

The cultured rat hepatoma cell (R117-21B) homogenates metabolized 3,[3′,5′-¹²⁵I]triiodothyronine by phenolic ring deiodination and produced radioactive iodide and 3,3′-diiodothyronine. Thyroxine (T₄) was converted to 3,3′,5-triidothyronine (T₃). The production of ¹²⁵I⁻ presented the deiodinase activity. The optimal pH for phenolic ring deiodination was observed to be pH 6.0–7.0. This enzyme reaction was accelerated by dithiothreitol. Propylthiouracil strongly inhibited the phenolic ring deiodination at 0.1 mM, whereas an effect of 20 mM methylmercaptoimidazol on the deiodination was very weak or absent.Excess unlabeled iodothyronines (T₄, T₃ and 3,5-diiodo-l-thyronine inhibited the phenolic ring deiodination of labeled 3,3′,5′-triiodothyronine, althought their inhibitory effect was slightly different. Triiodothyroacetic acid was a better inhibitor than T₃. Diiodotyrosine did not affect phenolic ring deiodination in cultured rat hepatoma cell homogenates.Phenolic and nonphenolic ring deiodinase activities of cultured monkey hepatocarcinoma cell and rat liver homogenates were also studied by the use of 3,[3′,5′-¹²⁵I]triiodothyronine and [3,5-¹²⁵I]thyroxine, respectively. Both deiodinase activities were observed in particulate fractions (mitochondrial and microsomal) of cultured cell and rat liver homogenates.     

Effect of thyroid hormone analogues on the displacement of 125I-L-triiodothyronine from hepatic and heart nuclei in vivo: possible relationship to hormonal activity

The capacity of iodotyrosines and iodothyronine analogues to displace tracer[¹²⁵I] L-3,5,3′ triiodothyronine from specific nuclear binding sites in rat liver and heart was related to the displacement capacity of nonradioactive triiodothyronine. Iodotyrosines and L-3,3′,5′ triiodothyronine (“reverse T₃”) were devoid of displacement activity. Analogues with 3,5 substitution in the “inner” ring and single “bulk” substitution in the 3′ position in the phenolic ring exhibited the strongest displacement activity. When the distribution, fractional removal rates and metabolic conversion of the analogues were taken into account, displacement activity appeared to correlate well with the reported thyromimetic activity. These results support the biologic relevance of the nuclear sites.     

Different pathways of iodothyronine 5′-deiodination in rat cerebral cortex

Microsomal fractions of rat cerebral cortex catalyze the 5′-deiodination of 3,3′,5′-triiodothyronine (rT₃) in the presence of thiols such as dithiothreitol. Evidence is presented that two different enzymatic pathways are involved. One of these has a low apparent K_m (2.7 nM) for rT₃, is inhibited by nanomolar concentrations of thyroxine (T₄), but not by up to 1 mM 6-propyl-2-thiouracil (PTU). The other pathway has a high apparent K_m (31 nM) for rT₃, is inhibited by PTU, but not by <1 μM T₄. The relative proportion of rT₃ 5′-deiodination via either pathway depends on thyroid status, with increased contributions from the low-K_m system especially in short-term hypothyroidism.     

Dissociable and non-dissociable cytoplasmic protein-thyroid hormone interactions

Dog kidney cytosol contains a high molecular weight (50 000–70 000) and a low molecular weight (approx. 6000) thyronine-binding protein. Low molecular weight cytosol thyronine-binding protein has not been previously recognized in cytoplasm. Binding of thyroxine (tetraiodothyronine, T₄) by the low molecular weight protein has a half-time of association of more than 24 h and accounts for 32% of bound cytoplasmic tetraiodothyronine after 48 h of incubation. Binding of labeled tetraiodothyronine and triiodothyronine by this moiety is non-dissociable in the presence of 1 · 10^?5 M unlabeled tetra- or triiodothyronine. The low molecular weight protein exists in a dispersed and apparently aggregated form; the latter elutes in the void volume on Sephadex G-100 and its generation is minimized by 2 mM Ca²⁺. This binding protein elutes in a fraction which has a high A_260nm : A_280nm ratio, is pentose enriched (orcinol method) and which, because of these characteristics and low susceptibility to digestion by nuclease, is postulated to be a ribosylated cytoplasmic protein or polypeptide.Binding of tetra- and triiodothyronine by the high molecular weight protein has a half-time of association of 2 h and is saturable. Displacement of labeled triiodothyronine from this cytosol thyronine-binding protein is more readily effected with excess unlabeled tetra- than with triiodothyronine, indicating the absence of a triiodothyronine-specific cytosol thyronine-binding protein site. 3,3′,5′-Triiodothyronine (reverse triiodothyronine) is bound with low avidity. Uptake of high molecular weight protein by isolated kidney cell nuclei cannot be demonstrated.Binding of tetraiodothyronine by cytosol proteins is independent of pH in the pH range 6.8–8.9, but binding of triiodothyronine is minimized at pH 7.4 and enhanced at alkaline pH to the point of equivalency of tetra- and triiodothyronine binding at pH 8.9.At concentrations of tetraiodothyronine calculated to exist intracellularly, essentially all soluble fraction tetraiodothyronine is bound to cytosol thyronine-binding protein, restricting access of this iodothyronine to binding sites in nucleus and mitochondria. Cytosol removes labeled tetra- and triiodothyronine previously reacted in vitro with isolated cell nuclei; such removal is a linear function of cytosol protein concentration and is blocked by saturation of cytosol thyronine-binding protein with unlabeled iodothyronines. Only the high molecular weight protein accounts for unbinding by cytosol of nuclear hormone.     

Synthesis and biological evaluation of 3′,4′,5′-trimethoxychalcone analogues as inhibitors of nitric oxide production and tumor cell proliferation

A series of 23 3′,4′,5′-trimethoxychalcone analogues was synthesized and their inhibitory effects on nitric oxide (NO) production in LPS/IFN-γ-treated macrophages, and tumor cell proliferation has been investigated. 4-Hydroxy-3,3′,4′,5′-tetramethoxychalcone (7), 3,4-dihydroxy-3′,4′,5′-trimethoxychalcone (11), 3-hydroxy-3′,4,4′,5′-tetramethoxychalcone (14), and 3,3′,4′,5′-tetramethoxychalcone (15) were the most potent growth inhibitory agents on NO production, with an IC₅₀ value of 0.3, 1.5, 1.3 and 0.3 μM, respectively. The tumor cells proliferation assay results revealed that several compounds exhibited potent inhibition activity against different cancer cell lines. The chalcone 15 was the most potent anti-proliferative compound in the series with IC₅₀ values of 1.8 and 2.2 μM toward liver cancer Hep G2 and colon cancer Colon 205 cell lines, respectively. 2,3,3′,4′,5′-Pentamethoxychalcone (1), 3,3′,4,4′,5,5′-hexamethoxychalcone (3), 2,3′,4,4′,5,5′-hexamethoxychalcone (5), 2-hydroxy-3,3′,4′,5′-tetramethoxychalcone (10), 11 and 14 showed significant anti-proliferation actions in Hep G2 and Colon 205 cells with an IC₅₀ values ranging between 10 and 20 μM. Among the tested agents, compound 7 showed selective NO production inhibition (IC₅₀ = 0.3 μM), while has no effect on tumor cell proliferation (IC₅₀ >100 μM). 3,3′,4,4′,5′-Pentamethoxychalcone (2) showed selective anti-proliferation effect in Hep G2 cells, in addition to its potent NO inhibition, however has no such response in Colon 205 cells. In contrast, 3-formyl-3′,4′,5′-trimethoxychalcone (22) showed moderate growth inhibition in Colon 205 cells, while has no such effect on NO production and Hep G2 cells proliferation. These results provide insight into the correlation between some structural properties of 3′,4′,5′-trimethoxychalcones and their in vitro anti-inflammatory and anti-cancer differentiation activity.     

Thyroid hormone inhibition of synaptosome amino acid uptake and protein synthesis.

Abstract— 3,3′,5-Triiodothyronine (T₃) inhibited L-[¹⁴C]leucine uptake into synaptosomes. Inhibition was competitive with a K_i of 3.1 × 10^?5m . Hofstee plot revealed an inverted hyperbolic curve suggestive of a two carrier or carrier plus diffusion mediated system for amino acid uptake. Both the carrier mediated and diffusional components were inhibited by thyroid analogues. l -Thyroxine and analogues inhibited the incorporation of l -[¹⁴C] leucine into cerebral synaptosome protein. At 50 μm , the triiodo-compounds were more inhibitory than tetraiodo->3,5-triiodo-l -thyronine >3,3′,5-triiodothyropro-pionic> l -thyroxine >3,5-diiodo-l -tyrosine. Thyroid analogue inhibition was not seen in liver or brain mitochondrial protein synthesis. 3,3′,5-Triiodothyronine had no effect on respiratory control or 2,4-DNP stimulated synaptosome respiration supported by malate plus pyruvate. Ouabain did not inhibit [¹⁴C]leucine uptake into adult synaptosomes. There was synergistic inhibition of synaptosome protein synthesis by thyroid analogues in the presence of 0.2 mm -ouabain. 3,3′,5-Triiodothyronine had no effect on synaptosome fraction ATPase or Na-K ATPase. Addition of T₃ induced further inhibition of synaptosome protein synthesis in the presence of either chloramphenicol (100μm ) or cycloheximide (50μg/ml). [¹⁴C]Glycine uptake and incorporation into synaptosome protein was inhibited by 3,3′,5-triiodothyronine. There was no inhibition of [¹⁴C]proline uptake or incorporation. The above evidence and kinetic data strongly favor a selective competitive block in amino acid transport at the synaptosome membrane leading to a decreased rate of protein synthesis.     

Sulfhydryl groups regulate thyroid hormone binding at nuclear receptor sites: further evidence for a separate binding site for reverse T3

Pig and rat liver nuclei possess specific, high affinity, low capacity binding sites for 3,3′,5′-triiodothyronine (reverse T₃) distinct from known 3,5,3′-triiodothyronine (T₃) binding sites. Sulfhydryl (SH) stabilishing and oxidising agents have profound and opposite, but not equal, effects upon in vitro binding of reverse T₃ and T₃. In the absence of SH stabilising agents T₃ and reverse T₃ bind with similar affinity (Ka 0.83 × 10⁹ v.s. 0.57 × 10⁹ M^?1). SH stabilising agents produce a small increase in the binding affinity of T₃ and a profound decrease in the binding affinity of reverse T₃. Chromatography of nuclear protein preincubated with both radioligands revealed two separate peaks of protein bound radioactivity consistent with two nuclear binding sites. These data suggest that SH groups may regulate binding of T₃ and reverse T₃ to nuclear receptors, and provide a mechanism for biological action of reverse T₃.     

Dibenzocyclooctadiene lignans from Magnolia and Talauma (Magnoliaceae): Their absolute configuration ascertained by circular dichroism and X-ray crystallography and re-evaluation of previously published pyramidatin structures

Twelve pyramidatins, i.e., dibenzocyclooctadiene-type lignans, together with Machilin G, were isolated from the dichloromethane extracts of aerial material of Talauma gloriensis, Magnolia fraseri, and Magnolia pyramidata (Magnoliaceae). These lignans contain a highly oxidized 7,9′-epoxy-2,2′-cyclolignane skeleton. Their structures were established using NMR spectroscopy (1D and 2D experiments) and mass spectrometry. The absolute configurations of five pairs of atropisomers (S_a/R_a-pyramidatins) and two single atropisomers (S_a-pyramidatins) were determined by experimental and calculated circular dichroism (CD). In addition, the absolute configuration of (S_a)-3,3′,4,4′,5,5′-hexamethoxypyramidatin was confirmed using X-ray crystallography.Five pyramidatins, (R_a)-3,3′,4,4′,5,5′-hexamethoxypyramidatin, (R_a)-3,3′-dimethoxy-4,5:4′,5′-bis(methylenedioxy)pyramidatin, (S_a)-3,3′,4,5′-tetramethoxy-4,5-methylenedioxypyramidatin, (R_a)-3,3′,4,5′-tetramethoxy-4,5-methylenedioxypyramidatin, and (R_a)-3,3′,4,5-tetramethoxy-4′,5′-methylenedioxypyramidatin are reported herein for the first time. In the current dataset, NMR values are in accordance with the observed and calculated CD values. These values are herein reported with particular reference to previously described data of pyramidatins, which have to be revised.     

Subcellular distribution of iodothyronine 5′-deiodinase in cerebral cortex from hypothyroid rats

We have examined iodothyronine deiodination in subcellular fractions of cerebral cortex obtained from hypothyroid rats. Enzymatic activities were measured at 37°C in the presence of 20 mM dithiothreitol with ¹²⁵I-labeled T₄ and ¹²⁵I-labeled rT₃ as substrate for 5′-deiodination and ¹³¹I-labeled T₃ as the substrate for the 5-deiodinase. Reaction products were separated by descending paper and/or ion-exchange chromatography. Cerebral cortex subcellular fractions were also characterized by marker enzyme analysis and electron microscopy. Under optimal reaction conditions more than 80% of the 5′-deiodinase was recovered after fractionation. Both 5′-deiodinase and (Na⁺ +K⁺-ATPase showed similar subcellular distributions and were enriched approx. 3-fold in the easily sedimenting membrane fraction and nerve terminal plasma membranes. Crude microsomal membranes (6·10⁶g·min pellet) also showed 2-fold enrichment of these enzymes. Nuclei and isolated mitochondria were devoid of deiodinating activity. T₄ and T₃ 5-deiodinating activity was absent in the easily sedimenting membranes and present but not enriched in particulate fractions containing microsomal membranes. These data suggest that iodothyronine 5′-deiodinase is associated with plasma membrane fractions in the cerebral cortex.     

Thyroid hormone analogues potentiate the antiviral action of interferon-γ by two mechanisms

L-thyroxine (L-T₄) potentiates the antiviral activity of human interferon-γ (IFN-γ) in HeLa cells. We have added thyroid hormone and analogues to cells either 1) for 24 h pretreatment prior to 24 h of IFN-γ (1.0 IU/ml), 2) for 24 h cotreatment with IFN-γ, 3) for 4 h, after 20 h cell incubation with IFN-γ, alone, or 4) for 24 h pretreatment and 24 h cotreatment with IFN-γ. The antiviral effect of IFN-γ was then assayed. L-T₄ potentiated the antiviral action of IFN-γ by a reduction in virus yield of more than two logs, the equivalent of a more than 100-fold potentiation of the IFN's antiviral effect. 3,3′,5-L-triiodothyronine (L-T₃) was as effective as L-T₄ when coincubated for 24 h with IFN-γ but was less effective than L-T₄ when coincubated for only 4 h. D-T₄, D-T₃, 3,3′,5-triiodothyroacetic acid (triac), tetraiodothyroacetic acid (tetrac), and 3,5-diiodothyronine (T₂) were inactive. When preincubated with L-T₄ for 24 h prior to IFN-γ treatment, tetrac blocked L-T₄ potentiation, but, when coincubated with L-T₄ for 4 h after 20 h IFN-γ, tetrac did not inhibit the L-T₄ effect. 3,3′,5′-L-triiodothyronine (rT₃) also potentiated the antiviral action of IFN-γ, but only in the preincubation model. Furthermore, the effects of rT₃ preincubation and L-T₃ coincubation were additive, resulting in 100-fold potentiation of the IFN-γ effect. When L-T₄, L-T₃, or rT₃, plus cycloheximide (5 μg/ml), was added to cells for 24 h and then removed prior to 24 h IFN-γ exposure, the potentiating effect of the three iodothyronines was completely inhibited. In contrast, IFN-γ potentiation by 4 h of L-T₄ or L-T₃ coincubation was not inhibited by cycloheximide (25 μg/ml). These studies demonstrate two mechanisms by which thyroid hormone can potentiate IFN-γ's effect: 1) a protein synthesis-dependent mechanism evidenced by enhancement of IFN-γ's antiviral action by L-T₄, L-T₃, or rT₃ preincubation, and inhibition of enhancement by tetrac and cycloheximide, and 2) a protein synthesis-independent (posttranslational) mechanism, not inhibited by tetrac or cycloheximide, demonstrated by 4 h coincubation of L-T₄ or L-T₃, but not rT₃, with IFN-γ. The protein synthesis-dependent pathway is responsive to rT₃, a thyroid hormone analogue generally thought to have little effect on protein synthesis. A posttranslational mechanism by which the antiviral action of IFN-γ can be regulated has not previously been described. © 1996 Wiley-Liss, Inc.     

Novel Synthesis of 4′C-Aryl-Branched Acyclic Nucleoside Using [3,3]-Sigmatropic Rearrangement

Abstract

A very efficient synthetic route for preparing a novel 4′-C-aryl branched-1′,2′-seco-2′,3′-dideoxy-2′,3′-didehydro-nucleoside is described. Mesylate 7 was successfully synthesized via a Horner-Wadsworth-Emmons reaction and a [3,3]-sigmatropic rearrangement, with which an adenine base was coupled by nucleophilic substitution conditions (K₂CO₃, 18-Crown-6, DMF) to give the target nucleoside 9.     

A new dimeric carbazole alkaloid from Murraya koenigii (L.) leaves with α-amylase and α-glucosidase inhibitory activities

A new dimeric carbazole alkaloid, 3,3′,5,5′,8-pentamethyl-3,3′-bis(4-methylpent-3-en-1-yl)-3,3′,11,11′-tetrahydro-10,10′-bipyrano[3,2-a]carbazole, was isolated from the hexane extract of leaves of Murraya koenigii (L.) Sprengel. (Family: Rutaceae). The structure was elucidated based on ¹³C and ¹H NMR, High-Resolution Mass Spectrometry (HRMS), and 2D NMR data. The in vitro antidiabetic activity of the new dimer was investigated in terms of α-amylase and α-glucosidase enzyme inhibition assays. The dimer exhibited significant α-amylase inhibitory activity (IC₅₀ = 30.32 ± 0.34 ppm) and α-glucosidase inhibitory activity (IC₅₀ = 30.91 ± 0.36 ppm).     

Eusiderins and other neolignans from an Aniba species

A previous report disclosed the presence of benzodioxan and bicyclo[3.2.1]octanoid neolignans in the benzene extract of the trunk wood of an Amazonian Aniba (Lauraceae) species. The chloroform extract of the same material contains additionally two new benzodioxan neolignans [rel-(7S,8R)-Δ^8′-7-hydroxy-3,4,5,5′-tetramethoxy-7.0.3′,8.0.4′-neolignan; rel-(7R,8R)-Δ^7′-3,4,5,5′-tetramethoxy-9′-oxo-7.0.3′,8.0.4′-neolignan], two new bicyclo[3.2.1]-octanoid neolignans [(7R,8S,1′S,2′S,3′S,4′R)-Δ^8′-2′,4′-dihydroxy-3,3′-dimethoxy-4,5-methylenedioxy-1′,2′,3′,4′,5′,6′-hexahydro-5′-oxo-7.3′,8.1′-neolignan; (7R,8S,1′R,2′S,3′S)-Δ^8′-2′-hydroxy-3,3′,5′-trimethoxy-4,5-methylenedioxy-1′,2′,3′,4′-tetrahydro-4′-oxo-7.3′,8.1′-neolignan] and a hydrobenzofuranoid neolignan [(7S,8R,1′S,5′S)-Δ^8′-3,3′,5′-tri-methoxy-4,5-methylenedioxy-1′,4′,5′,6′-tetrahydro-4′-oxo-7.0.2′,8.1-neolignan].