Trihydroxy-C18-acids and a labdane from rudbeckia fulgida

Extraction of Rudbeckia fulgida furnished 13αH-labd-8(17)-en-15-al-19-oic acid, two new C₁₈-acids tentatively formulated as 9 (S*),12 (S*),13 (S*)-trihydroxyoctadeca-10(E),15 (Z)-dienoic acid and 9 (S*),12 (S*),13 (S*)-trihydroxyoctadec-10 (E)-enoic acid, several known C₁₄-polyacetylenes and several flavone glycosides.     

Preparation, properties and crystal structure of two isomers of R,R,S,S- and R,S,R,S-[chloro(1,3,10,12,16,19-hexaazatetracyclo[17,3,1,1,0]tetracosane)copper(II)]

Two isomers (R,S,R,S- and R,R,S,S-) of five coordinate complex [Cu(L)Cl]⁺ have been separated and characterised. These two isomers have significantly different spectrochemical and electrochemical properties. Absorption maximum of R,S,R,S-[Cu(L)Cl]⁺ shifts to longer wavelength and its reduction potential shifts to more positive direction comparing those of R,R,S,S-[Cu(L)Cl]⁺. R,S,R,S-[Cu(L)Cl]⁺ is significantly distorted to trigonal-bipyramidal structure, whereas R,R,S,S-[Cu(L)Cl]⁺ retains almost square-planar geometry. The average bond distance of Cu-N in basal plane of R,S,R,S-[Cu(L)Cl]⁺ is longer by 0.024 Å than that of R,R,S,S-[Cu(L)Cl]⁺, whereas the bond distance of Cu-Cl in former is shorter by 0.200 Å than that in latter. The isolated square-planar complexes of R,R,S,S- and R,S,R,S-[Cu(L)](ClO₄)₂ are converted to the R,R,S,S- and R,S,R,S-[Cu(L)Cl]⁺ by the addition of Cl⁻ in nitromethane solution with the rate constants, k=1.70 (±0.02) and 8.31 (±0.07) M⁻¹ s⁻¹, respectively.     

Dihydrofurocoumarin glucosides from Angelica archangelica and Angelica silvestris

A water-soluble root extract of Angelica archangelica subsp. litoralis afforded, in addition to adenosine, coniferin and the two known dihydrofurocoumarin glycosides, apterin and 1′-O-β-d-glycopyranosyl-(S)-marmesin (marmesinin), two new dihydrofuranocoumarin glycosides, 1′-O-β-d-glucopyranosyl-(2S, 3R)-3-hydroxymarmesin, and 2′-β-d-glucopyranosyloxymarmesin. For the latter a 2S-configuration was demonstrated, the stereochemistry at position 1′ remaining undefined. Roots of A. silvestris similarly afforded 1′-O-β-d-glucopyranosyl-(2S, 3R)-3-hydroxymarmesin. By correlation with the aglycone 2S,3R)-3-hydroxymarmesin obtained in this work, the absolute configurations (2S,3R) were established for the known dihydrofurocoumarin diesters smirniorin and smirnioridin.     

Cycloartanes from Lindheimera texana

The following new cycloartanes were isolated from the aerial parts of Lindheimera texana: (16S,23S)- and (16S,23R)-16,23-epoxycycloart-24-en-3-one, (3S,16S,23S)- and (3S,16S,23R)-16,23-epoxycycloart-24-en-3ol, (16S,23R)-16,23-epoxy-23,25-epidioxycycloartan-3-one, (16S)-23,24,25,26,27-pentanorcycloartan-3-one-16,22-olide, (16S,23S,24R)- or (16S,23R,24S)-23,24-epoxycycloartan-3-one-16,25-diol and (16S,23ζ,24ζ)-cycloartan-3-one-16,23,24,25-tetrol. Structures were established by chemical transformations and spectroscopic methods and, in the case of (16S,23R)-16,23-epoxy-23,25-epidioxycycloartan-3-one, by X-ray crystallography. Norambreinolide, several known labdanes and oleanolic acid were also isolated.     

2(S),3(S)-3-hydroxy-4-methyleneglutamic Acid from Gleditsia caspica

A new natural product, 2(S),3(S)-3-hydroxy-4-methyleneglutamic acid (G3) has been isolated from seeds of Gleditsia caspica. The structure has been established by chemical and spectroscopic methods. Catalytic reduction of G3 yields 2(S),4(S)-4-methylglutamic acid and a new amino acid, 2(S),3(S),4(S)-3-hydroxy-4-methylglutamic acid. Ozonolysis of G3 followed by oxidation gives 2(S),3(R)-3-hydroxyaspartic acid. The S- (or l-) configurations at C₂ in G3 and in 2(S),3(S),4(S)-3-hydroxy-4-methyglutamic acid and the S-configurations at C₃ for G3 and 2(S),3(S),4(S)-3-hydroxy-4-methylglutamic acid and at C₄ for 2(S),3(S),4(S)-3-hydroxy-4-methylglutamic acid are inferred from the configurations at C₂ in 2(_S),4(_S)-4-methylglutamic acid and at C₂ and C₃ in 2(S),3(R)-3-hydroxyaspartic acid. The seeds also contain appreciable quantities of 2(S),3(S),4(R)-3-hydroxy-4-methylglutami c acid (G1) and 2(S),4(R)-4-methylglutamic acid.     

Two sesquiterpene lactones from Trichogonia gardneri

The structures and stereochemistries of two sesquiterpene lactones from Trichogonia gardneri were established as (6R,7S,8S,9S,IOR)-4E-9,10-dihydroxy-8-tigloxygermacr-4-en-6,12-olide) and (5R*,6R*,7S*,8S*,9R*)-14-acetoxy-3-chloro-9-hydroxy-2-oxo-8-tigloxyguia-1(10),3-dien-6,12-of olide by a combination of NMR spectrometry and X-ray diffraction. The results show that the structures of several sesquiterpene lactones which were isolated previously from related species require revision.     

Flavonoids from Millettia pulchra

Chemical examination of Millettia pulchra yielded (?)-maackiain, (?)-pterocarpin, (?)-sophoranone and the new compounds (6S, 6aS, 11aR)-6α-methoxypterocarpin, (6S, 6aS,11aR)-6α-methoxyhomopterocarpin, (2S)5,7,4′-trihydroxy-8,3′,5′-triprenylflavanone, (2R,3R)7,4′-dihydroxy-8,3′,5′-triprenyldihydroflavanol, 5,7,2′,4′-tetrahydroxy-6,3′-diprenylisoflavone and 5,7,4′-trihydroxy-2′-methoxy-6,3′-diprenylisoflavone.     

Antimalarial sesquiterpene lactones from Distephanus angulifolius

Combined use of bioassay-guided fractionation based on in vitro antiplasmodial assay and dereplication based on HPLC-PDA-MS-SPE-NMR led to isolation of (6S,7R,8S)-14-acetoxy-8-[2-hydroxymethylacrylat]-15-helianga-1(10),4,11(13)-trien-15-al-6,12-olid and (5R,6R,7R,8S,10S)-14-acetoxy-8-[2-hydroxymethylacrylat]-elema-1,3,11(13)-trien-15-al-6,12-olid, along with vernodalol, vernodalin, and 11,13β-dihydroxyvernodalin from extract of Distephanus angulifolius. All compounds were identified by spectroscopic methods, including 1D and 2D homo- and heteronuclear NMR experiments. The isolated compounds showed IC₅₀ values in the range 1.6-3.8 μM and 2.1-4.9 μM against chloroquine sensitive D10 and chloroquine resistant W2 Plasmodium falciparum strains, respectively.     

Two novel phytotoxic substances from Leucas aspera

Leucas aspera (Lamiaceae), an aromatic herbaceous plant, is well known for many medicinal properties and a number of bioactive compounds against animal cells have been isolated. However, phytotoxic substances from L. aspera have not yet been documented in the literature. Therefore, current research was conducted to explore the phytotoxic properties and substances in L. aspera. Aqueous methanol extracts of L. aspera inhibited the germination and growth of garden cress (Lepidum sativum) and barnyard grass (Echinochloa crus-galli), and the inhibitory activities were concentration dependent. These results suggest that the plant may have phytotoxic substances. The extracts were then purified by several chromatographic runs. The final purification was achieved by reversed-phase HPLC to give an equilibrium (or inseparable) 3:2 mixture of two labdane type diterpenes (compounds 1 and 2). These compounds were characterized as (rel 5S,6R,8R,9R,10S,13S,15S,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (1) and (rel 5S,6R,8R,9R,10S,13S,15R,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (2) by spectroscopic analyses. A mixture of the two compounds inhibits the germination and seedling growth of garden cress and barnyard grass at concentrations greater than 30 and 3 μM, respectively. The concentration required for 50% growth inhibition (I₅₀) of the test species ranges from 31 to 80 μM, which suggests that the mixture of these compounds, are responsible for the phytotoxic activity of L. aspera plant extract.     

High-performance liquid chromatography separation of the (S,S)- and (R,S)-forms of S-adenosyl-l-methionine

S-adenosyl-l-methionine (AdoMet), an important biological cofactor, exists in two chiral forms, (S,S)- and (R,S)-, only the former of which is biologically active. Here, we have developed a chromatographic method to obtain pure (S,S)-AdoMet using a single C18 column.     

New erythrina alkaloids of Cocculus laurifolia

Four abnormal Erythrina alkaloids have been isolated from the leaves of Cocculus laurifolia. Of these, two new bases, isococculidine and coccoline, have been assigned the structures (3S,5S)-3,15-dimethoxyerythrin-1-ene and (3R,5S)-15-hydroxy-3-methoxyerythrin-1-en-8-one respectively.     

Determination of (R)- and (S)-alprenolol and (R)- and (S)-metoprolol as their diastereomeric derivatives in human plasma by reversed-phase liquid chromatography

A high-performance liquid chromatographic method is described for the determination of (R)- and (S)-alprenolol and (R)- and (S)-metoprolol in human plasma. Separation of the enantiomers was accomplished after preparation of diastereomeric derivatives with symmetrical anhydrides of tert.-butoxycarbonyl-l-leucine followed by treatment with trifluoroacetic acetic acid at 0°C to remove the tert.-butoxycarbonyl group. The separations of the diastereomeric derivatives were performed using a reversed-phase system with μBondapak C₁₅ as support and phosphate buffer pH 3.0 with the addition of acetonitrile as the mobile phase. High stability of the chromatographic system was achieved.The reproducibilities in the determination of (R)- and (S)-alprenolol and (R)- and (S)-metoprolol in human plasma were 9.4 and 9.8% (relative standard deviation) for alprenolol and metoprolol, respectively, at drug levels of 0.5 ng/ml.In two subjects who received single oral doses of alprenolol (100-mg tablet) and metoprolol (50-mg tablet) the plasma levels of the (R)-isomers were lower than for the (S)-isomers.     

Identification of a plausible biosynthetic enzyme for the IM-2-type autoregulator in Streptomyces antibioticus

Virginiae butanolides (VBs) and IM-2 are members of Streptomyces hormones called ‘butyrolactone autoregulators’ which regulate the antibiotic production in Streptomyces species at nanomolar concentrations. Cell-free extract of a VB-A overproducer, Streptomyces antibioticus NF-18, is capable of catalyzing the final step of the autoregulator biosynthesis, namely, the NADPH-dependent reduction of 6-dehydroVB-A. However, physico-chemical analyses of the purified enzymatic products revealed that, in addition to the VB-type isomer [(2R,3R,6S)-enantiomer], IM-2-type isomers [(2R,3R,6R)- and (2S,3S,6S)-enantiomers] were also produced from (±)-6-dehydroVB-A, suggesting the existence of several 6-dehydroVB-A reductases with respective stereoselectivities. The reductase activity of the crude extracts was separated into two activity peaks, peak I (major) and peak II (minor), by DEAE-5PW HPLC. Chiral HPLC analyses demonstrated that peak I enzyme and peak II enzyme catalyzed the production of (2R,3R,6S), (2R,3R,6R) and (2S,3S,6S) isomers at ratios of 46:1:3.2 and 4.9:1:1.5, respectively, indicating clearly that S. antibioticus NF-18 possesses at least two 6-dehydroVB-A reductases: one much favored toward VB-A biosynthesis, the other with relaxed stereoselectivity capable of synthesizing both VB-type and IM-2-type autoregulators.     

(25R)-Isonuatigenin,an unusual steroidal sapogenin from Vestia lycioides

(25R)-Isonuatigenin, a ⁵-spirosten-3β,25-diol, was isolated from aerial parts of Vestia lycioides. Its structure was elucidated mainly by ¹H NMR and ¹³C NMR spectroscopy. A mixture of (25R)-nuatigenin and (25S)-isonuatigenin was also characterized. This is the first report on the natural occurrence of the two (25R)-isomers.     

Application of a Burkholderia cepacia lipase-immobilized silica monolith micro-bioreactor to continuous-flow kinetic resolution for transesterification of (R, S)-1-phenylethanol

Burkholderia cepacia lipase was immobilized in silicates forming from n-butyl-substituted precursors within a silica monolith from methyl-substituted precursors. The resultant preparation gave about 12 times higher rates of transesterification of (R, S)-1-phenylethanol with vinyl acetate and an approximately two-fold increase in the enantioselectivity toward (R)-1-phenylethanol, as compared to a non-immobilized counterpart. The highest enzymatic activity and enantioselectivity (reaching 250) were found at a low water activity of 0.11. The continuous-flow kinetic resolution of (R, S)-1-phenylethanol was successfully conducted using lipase-immobilized silica monolith micro-bioreactors with various inside diameters ranging from 0.25 to 1.6 mm. The reactor performance during continuous operation was consistent with the prediction from the batch reactor. A steady state conversion of 40% and enantiomeric excess more than 98% were maintained over a time period of 15 days.     

Hydroxylated glutamic acids in Phlox,lepidium and Rheum species

The two diastereoisomers, (2S,4R)-4-hydroxyglutamic acid and (2S,4S)-4-hydroxyglutamic acid, occur in characteristic concentration ratios in Phlox species. The second of these compounds is the principal free amino acid in the green parts of the plants. The presence of (2S,4R)-4-hydroxyglutamic acid in plants is reported for the first tiine. No other 4-substituted acidic amino acids were detected in the Phlox species analysed, although special attention was paid to the possible presence of 4-hydroxy-4-methylglutamic acids which have previously been reported in plants. It was found, however, that both diastereoisomers of (2S)-4-hydroxy-4-methylglutamic acid co-exist in Ledenbergia roseoaenea and also in Pandanus veitchii. Although the presence of 3,4-dihydroxyglutamic acids in green parts of Lepidium sativum and Rheum rhaponticum has been previously reported, we were not able to detect or isolate any of the possible diastereoisomers from the green parts or seeds of these plants. We did isolate glutathione which was found to have some properties in common with those reported for the dihydroxy compounds.     

Coumarin sulphates of Seseli libanotis

Three new sulphate ester salts derived from known coumarin alcohols–one of them tertiary–have been obtained from roots of Seseli libanotis subsp. eu-libanotis. Their structures were established as (2′S)-rutaretin-1″-sulphate, (3′R)-lomatin-3′-sulphate and (3′R,4′R)-khellactone-3′-sulphate. They were together with their parent alcohols characterized by ¹³C NMR spectroscopy. It is the first report on coumarin sulphates in plants.     

Enantioselectivity and stereoselectivity in the reactions of the enantiomers of the platinum complex [PtCl2(ahaz)] (ahaz = 3(R)- or 3(S)-aminohexahydroazepine) with DNA

The platinum-DNA adduct profile formed by the R- and S-enantiomers of [PtCl₂(ahaz)] (ahaz = 3(R)-aminohexahydroazepine or 3(S)-aminohexahydroazepine) on reaction with salmon sperm DNA were characterised using HPLC and GFAAS (graphite furnace atomic absorption spectrometry) analyses. At a platinum to nucleotide ratio (R_t) equalling 0.05, the R-enantiomer forms a substantially larger amount (approximately 60%) of monofunctional adducts than the S-enantiomer (less than 35%). Fewer intrastrand GpG adducts are formed by the R-enantiomer (approximately 21%) than the S-enantiomer (approximately 37%). For both enantiomers, two isomeric GpG adducts, corresponding to the different orientations of the primary amine of ahaz ligand with respect to the O6 atom of the 5′ guanine, were observed in the ratios of 1:1.3 and 1:4.3 for the R- and S-enantiomers, respectively. The reasons for this enantioselectivity and stereoselectivity are discussed.     

Phenylpropanoids and other derivatives from Thapsia villosa

Five phenylpropanoids related to hemanticine have been obtained from Thapsia villosa roots. We propose for these substances the trivial names isohelmanticine, neohelmanticine, isoneohelmanticine, epoxyhelmanticine and epoxyhelmanticine angelate. All these substances are based on (1S,2R)1-(3-methoxy-4,5-methylenedioxyphenyl)-1,2-propanediol, which is esterified variously by acetic, angelic, epoxyangelic and/or (2R,3S)2,3-dihydroxy-2-methylbutyric acids. We also report three C₆-guaianolides and their hydrolysis products. The name thapsivillosin K is proposed for a new guaianolide.     

4-Hydroxyisoleucine from seed of Trigonella foenum-graecum

The principal free amino acid present in seed of Trigonella foenum-graecum has been isolated and identified as (2S, 3R, 4R)-4-hydroxyisoleucine. This compound has not been reported previously as a constituent of higher plants, but it is a component of the toxic peptide, γ-amanitin, produced by Amanita phalloides. The (2S, 3R, 4R)-isomer lactonizes readily under acidic conditions, whilst strong acid causes partial epimerization. The (2R, 3R, 4R)-isomer forms a minor component of Trigonella seed. The 4-hydroxyisoleucine content of fenugreek increases during the growth of seedlings and plants, and ¹⁴C-isoIeucine was used effectively as a biosynthetic precursor.