CINQ alcaloides nouveaux de Strychnos henningsii

Five new alkaloids have been isolated from the leaves and stems of Strychnos henningsii: tsilanimbine, N_a-desacetyl-17-O-acetyl-18-hydroxyisoretuline, 18-hydroxyisoretuline, N_a-desacetylisoretuline and N_a-desacetyl-18-hydroxyisoretuline. The two latter, unknown as natural products, have already been obtained by degradation of strychnine.     

Alkaloids from the leaves of Strychnos wallichiana

The leaves of Strychnos wallichiana Steud. ex. DC. from Bangladesh contain icajine and novacine as their major alkaloids. Smaller amounts of strychnine, brucine, pseudostrychnine, pseudobrucine, N-methyl-sec.-pseudo-β-colubrine, 14-hydroxyicajine, strychnine N-oxide, and brucine N-oxide are also present. The new bases 14 hydroxynovacine and icajine N-oxide have been isolated.     

Versatile coordination behavior of N,N-di(alkyl/aryl)-N′-benzoylthiourea ligands: Synthesis, crystal structure and cytotoxicity of palladium(II) complexes

The synthesis and characterization of Pd(II) complexes with the general formula cis-[Pd(L-O,S)₂] (HL = N,N-diethyl-N′-benzoylthiourea, N,N-diisobutyl-N′-benzoylthiourea or N,N-dibenzyl-N′-benzoylthiourea) and trans-[PdCl₂(HL-S)₂] (HL = N,N-diphenyl-N′-benzoylthiourea, N,N-di-n-butyl-N′-benzoylthiourea or N,N-diisopropyl-N′-benzoylthiourea) are reported. These complexes were formed from the reaction between PdCl₂ and N,N-di(alky/aryl)-N′-benzoylthiourea in acetonitrile with the formulation dependent on the nature of HL. The new Pd(II) complexes have been characterized by analytical and spectral (FT-IR, UV-Vis, ¹H NMR and ¹³C NMR, Mass) techniques. The molecular structures of two of the complexes (1 and 5) have been conformed by X-ray crystallography. Complex 1 shows cytotoxicity against human breast cancer cells.     

Nicotine N-oxides

Nicotine-1-N-oxide, trans and cis isomers of nicotine-1′-N-oxide and of nicotine-1,1′-di-N-oxide have been prepared and characterised by NMR, MS and reduction to nicotine. The trans and cis isomers of nicotine-1′-N-oxide have been identified in leaves, stems and roots of Nicotiana tabacum, N. affinis and N. sylvestris.     

Magnetic, spectroscopic, structural and biological properties of mixed-ligand complexes of copper(II) with N,N,N,N″,N″-pentamethyldiethylenetriamine and polypyridine ligands

Two new mixed ligand complexes of copper(II) with N,N,N^′,N″,N″-pentamethyldiethylenetriamine and polypyridine ligands have been prepared and characterized by means of spectroscopic, magnetic and single-crystal X-ray diffraction methods. These two complexes are isomorph and isostructure in which the coordination polyhedron about the copper(II) ion is distorted square pyramidal. [Cu(PMDT)(bipy)]²⁺ and [Cu(PMDT)(phen)]²⁺ show an absorption wavelength maximum at 625 and 678 nm, respectively, assigned to the d-d transition. Antibacterial, antifungal and superoxide dismutase activities of these complexes have also been measured. It was observed that [Cu(PMDT)(bipy)](ClO₄)₂ was more effective against P. Pyocyanea and Klebsiella sp. than S. aureus. Similarly, Fusarium sp. was highly susceptible against [Cu(PMDT)(bipy)](ClO₄)₂ but less susceptible against [Cu(PMDT)(phen)](ClO₄)₂.     

Cytochrome cs from Rhodymenia palmata and Porphyra umbilicalis and the amino acid sequences of their N-terminal regions

Basic c-type cytochromes homologous with plant and animal mitochondrial cytochrome c have been isolated and purified from Rhodymenia palmata and Porphyra umbilicalis. The N-terminal regions have been analysed using a Beckman 890C automatic sequencer. When compared to animal cytochrome c, the Rhodymenia cytochrome c has an unblocked N-terminal tail of 10 amino acids, whereas Porphyra has an unblocked N-terminal tail of only a single amino acid.     

Preparation of NG-monoethyl-l-arginine

N^G-Monoethyl-l-arginine, a putative in vivo product after administration of the potent hepatocarcinogen l-ethionine to rats, has been chemically synthesized by coupling N-ethyl, S-methylthiopseudouronium iodide with α-amino-blocked l-ornithine. The structure of the compound as N^G-monoethyl-l-arginine was confirmed by ¹³C NMR. Its elution time on an automatic amino acid analyzer, R_f values using thin-layer chromatography, and isoelectric point have been compared with those of N^G-monomethyl-l-arginine.     

New alkaloids from Strychnos icaja

The alkaloids of Strychnos icaja (Loganiaceae) have been studied. An extract from Zaire leaf material yielded nine alkaloids, comprising novacine, the new base 21,22-α-epoxy-4,14-dihydroxy-3-methoxy-N-methyl-sec.-pseudostrychnine, and seven others of known structure previously obtained from the plant. Cameroun leaf material gave five alkaloids, of which one, 21,22-α-epoxy-3,4-dimethoxy-N-methyl-sec.-pseudostrychnine, is new. Fruits from Gabon afforded eight alkaloids; two of them are new and are formulated as 21,22-α-epoxy-4-methoxy-N-methyl-sec.-pseudostrychnine and the corresponding 14-hydroxy derivative.     

N-oxides of hyoscyamine and hyoscine in the solanaceae

The N-oxides of (−)-hyoscyamine and (−)-hyoscine have been prepared and characterized. Two N-oxides of hyoscyamine have been isolated from species of Atropa,Datura,Hyoscyamus,Scopolia andMandragora,andoneN-oxideofhyoscinehasbeenisolatedfromspeciesofthefirstfourgenera.     

Alkaloids of Lycopodium magellanicum

Six alkaloids have been isolated from Lycopodium magellanicum. These include the known alkaloids lycopodine, acetyldihydrolycopodine, lycodine, N-methyllycodine, acetylfawcettine and a new alkaloid, 5-dehydro-magellanine. The chemical correlation of magellanine and paniculatine and the establishment of their absolute configuration are described.     

Nucleophilic displacement reactions of some N-acetyl-N-aryl-β-d-xylopyranosylamines

The 4-O-methanesulphonyl (and toluene-p-sulphonyl), 3,4-di-O-methanesulphonyl (and toluene-p-sulphonyl), and 3,4-di-O-benzoyl-2-O-methanesulphonyl derivatives of N-acetyl-N-p-methoxyphenyl- and N-acetyl-N-p-chlorophenyl-β-d-xylopyranosylamine have been synthesised together with the N-acetyl-N-p-methoxyphenyl and N-acetyl-N-p-chlorophenyl derivatives of 3,4-di-O-benzoyl-2-O-methanesulphonyl-β-d-lyxopyranosylamine. The relative reactivity of the hydroxyl groups of the N-acetyl-N-aryl-β-d-xylopyranosylamines towards sulphonylation has been established. On heating the 2- and 4-mesylates of N-acetyl-N-aryl-β-d-xylopyranosylamines and the 2-mesylate of N-acetyl-N-aryl-β-d-lyxopyranosylamines with sodium azide in N,N-dimethylformamide or acetonitrile, either nucleophilic replacement of the mesyl groups of their solvolysis with participation of the N-acetyl group occurred. In this way, β-d-xylo compounds were converted into α-l-arabino and β-d-lyxo derivatives.     

Occurrence of N-cyano alkaloids in asian Strychnos species

The isolation of N-cyano-sec.-pseudostrychnine and N-cyano-sec.-pseudobrucine from the leaves of Strychnos wallichiana Steud. ex. DC. is reported. N-Cyano-sec.-pseudostrychnine and a N-cyano-sec.-pseudo-colubrine have been found among the alkaloids obtained from the stem bark of S. ignatii Berg.     

Hyoscyamine N-oxide in Atropa belladonna

Separated organs of Atropa belladonna have been examined for their total alkaloid, hyoscyamine and hyoscyamine N-oxide contents during ontogenesis. Marked fluctuations in N-oxide content were observed, the highest being found in the ripe fruit. [G-³H]-atropine was fed to A. belladonna fruits and radioactively labelled hyoscyamine N-oxide isolated.     

Alcaloïdes d'Alstonia quaternata

Eleven alkaloids have been isolated from Alstonia quaternata. Three of them, namely 11-methoxy-epi-3α-yohimbine, 10,11-dimethoxy-picrinine designated quaternine, and 19,20-epoxy-N_(a)-methyl, desacetyl, desformo, 2βH-dihydroakuammiline designated quaternoxine, are new alkaloids.     

Synthesis and characterization of gallium complexes bearing N-arylmethylenethiobenzahydrazone ligands; crystal structure of diethyl[N-(4-N,N-dimethylamino)benzylidene thiobenzahydrazonato]gallium

Five diethylgallium complexes of type Et₂GaL [(L = N-(4-methoxy) benzylidenethiobenzahydrazonato (1), N-(3,4-dimethoxy)benzylidenethio benzahydrazonato (2), N-(4-N,N-dimethylamino)benzylidenethiobenza hydrazonato (3), N-(2-naphthyl)methylenethiobenzahydrazonato (4), N-(9-anthryl)methylenethiobenzahydrazonato (5)] have been synthesized by the reaction of triethylgallium with appropriate N-arylmethylene thiobenzahydrazones. The compounds obtained have been characterized by elemental analysis, ¹H NMR, IR and mass spectroscopies, respectively. The solid structure of 3 has been determined by X-ray single crystal analysis, in which Ga atom is four coordinate. The photoluminescent property of complex 1 was studied. The maximum emission wavelength is 475 nm upon radiation by UV light.     

Mo- and W-N2 and -CO complexes with novel mixed P/N ligands: Structural properties and implications to synthetic nitrogen fixation

Four new ligands containing a pyridine or thiazole group and one or more N-(diphenylphosphinomethyl)amine functions have been prepared and employed for the synthesis of Mo(0) and W(0) carbonyl and dinitrogen complexes. For comparison coordination of the literature-known ligand N,N-bis(diphenylphosphinomethyl)-methylamine (PNP, 1) to such systems has been investigated as well. Two new ligands are N,N-bis(diphenylphosphinomethyl)-2-aminopyridine (pyNP₂, 2) and N,N′-bis(diphenylphosphinomethyl)-2,6-diaminopyridine (PpyP, 3). In a third new ligand, N-diphenylphosphinomethyl-2-aminothiazole (thiazNP, 4), the pyridine group is replaced by thiazol. Finally, the pentadentate ligand N,N,N′,N′-tetrakis(diphenylphosphinomethyl)-2,6-diaminopyridine (pyN₂P₄, 5) has been synthesized. Coordination of ligands 2, 3 and 4 to low-valent metal centers is investigated on the basis of the three molybdenum carbonyl complexes [Mo(CO)₃(NCCH₃)(pyNP₂)] (6), [Mo(CO)₄(PpyP)] (7) and [Mo(CO)₄(thiazNP)] (8), respectively, all of which are structurally characterized. Moreover, employing ligands 1 and 2 the two dinitrogen complexes [W(N₂)₂(dppe)(PNP)] (9) and [Mo(N₂)₂(dppe)(pyNP₂) (10), respectively, are prepared. Both systems are investigated by vibrational and NMR spectroscopy; in addition, complex 10 is structurally characterized.     

The characterization of N-acetylglucosaminidases from the limpet Patella vulgata (L.)

The α- and β-N-acetylglucosaminidase activity of the limpet Patella vulgata (L.) is due to two enzymes. One of these enzymes hydrolyses both α- and β-N-acetylglucosaminidases and is referred to α,β-N-acetylglucosaminidase. The other is a β-N-acetylglucosaminidase (EC 3.2.1.30). Both enzymes have been isolated and characterized as glycoproteins containing 12% hexose, mainly galactose. The amino acid, neutral sugar and amino sugar content of the two enzymes is very similar, and the main difference lies in the presence of 9% sialic acid in β-N-acetylglucosaminidase. The molecular weight of α,β-N-acetylglucosaminidase is 217 000 and that of β-N-acetylglucosaminidase is 136 000. Evidence has been obtained for the presence of an additional sub-unit in the α,β-enzyme.     

Quinoline and indolopyridoquinazoline alkaloids from Vepris louisii

The structures of two new 2-quinolone alkaloids from the stem bark of Vepris louisii, N-methylpreskimmianine [7,8 - dimethoxy - 3 - (3 - methylbut - 2 - enyl) - 1 - methyl - 2 - quinolone] and veprisine (7,8 - dimethoxy - N - methylflindersine) have been deduced from their spectral data and confirmed by partial synthesis from known compounds. Two minor indolopyridoquinazoline alkaloids were also isolated and identified as the already known 1-hydroxyrutaecarpine and the hitherto unknown 7,8-dehydro derivative of 1-hydroxyrutaecarpine.     

Conformational changes resulting from the carbazoylation of bovine α-chymotrypsin by p-nitrophenyl N2-acetyl-N1-arylmethylcarbazates

Several (N²-acetyl-N¹-arylmethylcarbazoyl)-α-chymotrypsins with p-substituents in the N¹-arylmethyl group have been prepared. Measurements of (a) accessibility of tryptophyl residues to modification by 2-hydroxy-5-nitrobenzyl bromide, (b) intrinsic fluorescence spectra in the absence and presence of sodium dodecyl sulphate, (c) thermal perturbation spectra indicate that, in general, tryptophyl residues are less accessible to solvent than in the free enzyme and the modified enzymes are more stable than α-chymotrypsin to denaturation by heat or sodium dodecyl sulphate. N²-Acetyl-N¹-p-dimethylaminobenzylcarbazoyl-α-chymotrypsin, however, contains more accessible tryptophyl residues than the other derivatives and is thermally less stable although it is more stable than the free enzyme.     

Conformational basis of N-glycosylation of proteins: conformational analysis of Ac-Asn-Ala-Thr-NH2

The structural requirements of the Asn-X-Thr(Ser) sequence for the N-glycosylation of proteins has been traced to a local conformation acting as a signal for the enzymatic process. The conformational space of the smallest in vivoN-glycosylation substrate, Ac-Asn-Ala-Thr-NH₂, has been thoroughly explored using energy calculations. All the lowest energy conformers have been characterized as bended structures.