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The crude methanol extract of the seeds of Derris trifoliata showed potent and dose dependent larvicidal activity against the 2nd instar larvae of Aedes aegypti. From this extract two unusual rotenoid derivatives, a rotenoloid (named 7a-O-methyl-12a-hydroxydeguelol) and a spirohomooxarotenoid (named spiro-13-homo-13-oxaelliptone), were isolated and characterised. In addition a rare natural chromanone (6,7-dimethoxy-4-chromanone) and the known rotenoids rotenone, tephrosin and dehydrodeguelin were identified. The structures were assigned on the basis of spectroscopic evidence. The larvicidal activity of the crude extract is mainly due to rotenone. (c) 2006 Elsevier Ltd. All rights reserved
From the stem bark of Erythrina burttii, a new isoflavone, 5,2',4'-trihydroxy-7-methoxy-6-(3- methylbut-2-enyl)isoflavone (trivial name, 7-O-methylluteone) and a new flavanone, 5,7-dihydroxy-4'-methoxy- 3'-(3-methylbutadienyl)-5'-(3-methylbut-2-enyl)flavanone (trivial name, burttinonedehydrate) along with three known isoflavonoids (8-prenylluteone, 3-O-methylcalopocarpin and genistein) were isolated. The structures were detd. on the basis of spectroscopic evidence.
From the stem bark of Erythrina sacleuxii two new isoflavanones, (R)-5,7-dihydroxy-2',4',5'- trimethoxyisoflavanone (trivial name, (R)-2,3-dihydro-7-demethylrobustigenin) and (R)-5-hydroxy- 2',4',5'-trimethoxy-2'',2''- dimethylpyrano[5'',6'':6,7]isoflavanone (trivial name, (R)-saclenone) were isolated. In addition the known compounds shinpterocarpin, 2,3-dehydrokievitone, abyssinone V, abyssinone V-4'-methyl ether, erythrinasinate and 4'-O-methylsigmoidin B were isolated. The structures were determined on the basis of spectroscopic evidence.
From the root bark of Erythrina burttii three new isoflav-3-enes, 7,4'-dihydroxy-2'-methoxy-6- (1'',1''-dimethylallyl)isoflav-3-ene (trivial name, burttinol-A), 4'-hydroxy-2'- methoxy-(2'',2''-dimethylpyrano[5'',6'':8,7]isoflav-3-ene (trivial name, burttinol-B), 7,4'-dihydroxy-2'-methoxy-8-(3'',3''-dimethylallyl)isoflav-3-ene (trivial name, burttinol-C), and a new 2-arylbenzofuran, 6,4'-dihydroxy-2'-methoxy-5- (1'',1''-dimethylallyl)-2-arylbenzofuran (trivial name, burttinol-D) were isolated. In addition, the known compounds, abyssinone V-4'-methyl ether, bidwillol A, calopocarpin, erybraedin A, erythrabyssin II, isobavachalcone, phaseollidin and phaseollin were identified. The structures were determined on the basis of spectroscopic evidence.
From the fruits of Bulbine abyssinica three new dimeric anthracene derivatives, (P)-8,9,1',8'- tetrahydroxy-3,3'-dimethyl[10,7'-bianthracene]-1,4,9',10'- tetraone (trivial name abyquinone A), (10R)-1,4,8,1',8-pentahydroxy-3,3'-dimethyl-[10,7'-bianthracene]9,9',10' (10H)-trione (trivial name abyquinone B), and (10R)-3,4'-dihydro-1,4,8,3',8',9'-hexahydroxy-3,3'- dimethyl-[10,7'-biant hracene]9,1'(10H,2'H)-dione (trivial name abyquinone Q were isolated. Despite their structural differences, these three compounds are connected to each other by the apparently biomimetic conversion of abyquinone C (a preanthraquinonylanthrone with two stereogenic centers) into B (an anthraquinonylanthrone with one stereogenic center) and finally into A (an axially chiral bianthraquinone) under mild conditions, involving a highly efficient center-to-axis chirality transfer. In addition, the known anthraquinones islandicin and chrysophanol were identified. The structures were determined on the basis of spectroscopical evidences, chemical transformations, and quantum chemical CD calculations. (C) 2005 Elsevier Ltd. All rights reserved
The stem extract of Tephrosia purpurea showed antiplasmodial activity against the D6 (chloroquine-sensitive) and W2 (chloroquine-resistant) strains of Plasmodium falciparum with IC(50) values of 10.47 +/- 2.22 mu g/ml and 12.06 +/- 2.54 mu g/ml, respectively. A new prenylated flavone, named terpurinflavone, along with the known compounds lanceolatin A, (-)-semiglabrin and lanceolatin B have been isolated from this extract. The new compound, terpurinflavone, showed the highest antiplasmodial activity with IC(50) values of 3.12 +/- 0.28 mu M (D6) and 6.26 +/- 2.66 mu M (W2). The structures were determined on the basis of spectroscopic evidence.
In this article, the synthesis of analogs of N,N',N''-triacetylchitotriose in which the central sugar residue was replaced by a succinic acid is presented. Mol. modeling calcns. revealed that the pseudotrisaccharides exist in low energy extended conformations which show similar space filling as N,N',N''-triacetylchitotriose. Of the N,N',N''-triacetylchitotriose pseudosugar analogs tested as chitinase inhibitors, none showed any appreciable competition (numerical data not presented). The conformational anal. along with further synthetic efforts will hopefully lead to more efficient pseudosaccharides as chitinase inhibitors.
The synthesis of six analogs of N,N;-diacetylchitobiose is reported, including a novel transglycosylation reaction for the preparation of S-aryl thioglycosides. The conformations of the compounds were studied by a combination of NMR spectroscopy and molecular modeling, using force field calculations. In the case of the S-aryl thioglycosides with exclusively S-glycosidic linkages, dihedral angles of the disaccharidic S-glycosidic bonds, ;; and ;; and of the S-arylglycoside bonds, ; and ;, were found to be similar, whereas they were different in mixed glycosides and in a thiazoline derivative. An adequate correlation between the calculated H,H-distances of the local minima and the measured NOE contacts was achieved by applying population-weighted averages over participating conformers based on weighted relative energies.
Novel substituted pyrimidines were synthesized from methyl 2,4-dioxo-4-phenyl-butanoate (I-A) and urea, followed by Mitsunobu coupling of I-A with benzyl or allyl alcohol to give the corresponding 2-hydroxypyrimidine ethers in good yields. Saponification of I-A, followed by reaction with benzyl or allyl amines in the presence of TBTU yielded 2-hydroxy-6-phenyl-pyrimidine 4-carboxamides. AChE and BuChE assays revealed 2-hydroxy-6-phenyl-pyrimidine-4-carboxyallyamide as the most active compound, IC50=90 mu M, with no inhibition of BuChE.
The recent work on a variety of family 18 chitonolytic enzymes has yielded important data concerning the structure, substrate-binding, catalysis, inhibitor-binding and even dynamics. These data have been useful in helping to better understand the roles of various types of chitinases in chitin hydrolysis, to rationally engineer the properties of these enzymes, thus making them more suitable as biocatalysts, and to study and understand the effectiveness of natural and designed chitinase inhibitors, which may be of medical interest. On the other hand, the recent work on ChiB shows that catalysis in family 18 chitinases is a highly complicated process, involving larger parts of the enzyme and dynamics. Thus, despite recent discoveries, there is still a lot more to discover about how these enzyme work.
Chitinase B (ChiB) from Serratia marcescens is a family 18 exochitinase whose catalytic domain has a TIM-barrel fold with a tunnel-shaped active site. We have solved structures of three ChiB complexes that reveal details of substrate binding, substrateassisted catalysis, and product displacement. The structure of an inactive ChiB mutant (E144Q) complexed with a pentameric substrate (binding in subsites 22 to 13) shows closure of the ''roof'' of the active site tunnel. It also shows that the sugar in the 21 position is distorted to a boat conformation, thus providing structural evidence in support of a previously proposed catalytic mechanism. The structures of the active enzyme complexed to Allosamidin (an analogue of a proposed reaction intermediate) and of the active enzyme soaked with pentameric substrate show events after cleavage of the glycosidic bond. The latter structure shows reopening of the roof of the active site tunnel and enzyme-assisted product displacement in the 11 and 12 sites, allowing a water molecule to approach the reaction center. Catalysis is accompanied by correlated structural changes in the core of the TIM barrel that involve conserved polar residues whose functions were hitherto unknown. These changes simultaneously contribute to stabilization of the reaction intermediate and alternation of the pKa of the catalytic acid during the catalytic cycle.
Structural and physicochem. characteristics of mesquite gum (from Prosopis velutina) were investigated using FT- IR spectroscopic, mass spectrometric and chromatog. methods. Four fractions (F-I, F-IIa, F-IIb and F-III) were isolated by hydrophobic interaction chromatog. The samples were characterized and analyzed for their monosaccharide and oligomers compn. by high performance anion-exchange chromatog. with pulsed amperometric detection (HPAEC-PAD). L-Arabinose (L-Ara) and D-galactose (D-Gal) were found as the main carbohydrate constituent residues in the polysaccharides from mesquite gum and their ratio (L-Ara/D-Gal) varied within the range 2.54 to 3.06 among the various fractions. Small amts. of D- glucose (D-Glc), D-mannose (D-Man) and D-xylose (D-Xyl) were also detected, particularly in Fractions IIa, IIb and III. IR spectroscopy identified polysaccharides and protein in all the samples. Data from mass spectrometry (MALDI-TOF MS) was consistent with the idea that the structure corresponding to the periphereal chains of Fraction I is predominantly a chain of pentoses attached to uronic acid. [on SciFinder (R)].
The soln.-state conformations of the hevamine inhibitor allosamidin and six potential inhibitor analogs were studied by various NMR spectroscopic techniques and mol. modeling using force field calcns. Detn. solely of the global energy min. conformation was found to be insufficient for consensus with the NMR results, and agreement between the NMR exptl. data and the theor. calcns. was only reached by assessing the structures as population-weighted av. conformers on the basis of Boltzmann distributions derived from the calcd. relative energies. The conformations of the glycosidic linkages in the compds. were found to be similar when the sugar residues were the same, but differences were markedly evident otherwise and also for the various heterocyclic group linkages. The binding of the compds. to hevamine, which may also complex to chitinases in general, was assessed using HMQC, transfer-NOESY, and both 1-D and 2-D satn. transfer difference NMR expts. Under the conditions employed, only allosamidin was implicated to be bound to hevamine, and then only by HMQC with the dipolar coupling-based expts. failing to substantiate the formation of the complex. However, the results are consistent with the biochem. activities of the compds. whereby only allosamidin has been shown to act as a competitive inhibitor.
The soln.-state conformations of N,N',N''-triacetyl chitotriose (1) and other potential chitinase inhibitors 2-4 were studied using a combination of NMR spectroscopy (NOESY) and mol. mechanics calcns. Detn. solely of the global energy min. conformation was found to be insufficient for an agreement with the NMR results. An appropriate consistency between the NMR exptl. data and theor. calcns. was only reached by assessing the structures as population-weighted av. conformers based on Boltzmann distributions derived from the calcd. relative energies. Analogies, but also particular differences, between the synthetic compds. 2-4 and the naturally-occurring N,N',N''-triacetyl chitotriose were found. Furthermore, the conformation of compds. 1 and 2 when bound to hevamine was also studied using transferred NOESY expts. and the binding process was found to impart a level of conformational restriction on the ligands. The preferred conformation as detd. for 1 in the bound state to hevamine belonged to one of the conformational families found for the compd. when free in soln., although full characterization of the bound-state conformations was impeded due to severe signal overlap. Satn. transfer difference NMR expts. were also employed to analyze the binding epitopes of the bound compds. We thus detd. that it is mainly the acetyl amido groups of the trisaccharide and the heterocyclic moiety which are in close contact with hevamine.
This paper presents some results concerning the size-controlled hydroxyapatite nanoparticles obtained in aqueous media in a biopolymer matrix from soluble precursors salts. Taking the inspiration from nature, where composite materials made of a polymer matrix and inorganic fillers are often found, e.g. bone, shell of crustaceans, shell of eggs, etc., the feasibility on making composite materials containing chitosan and nanosized hydroxyapatite was investigated. A stepwise co-precipitation approach was used to obtain different types of composites by means of different ratio between components. The synthesis of hydroxyapatite was carried out in the chitosan matrix from calcium chloride and sodium dihydrogenphosphate in alkaline solutions at moderate pH of 10-11 for 24 h. Our research is focused on studying and understanding the structure of this class of composites, aiming at the development of novel materials, controlled at the nanolevel scale. The X-ray diffraction technique was employed in order to study the kinetic of hydroxyapatite formation in the chitosan matrix as well as to determine the HAp crystallite sizes in the composite samples. The hydroxyapatite synthesized using this route was found to be nano-sized (15-50nm). Moreover, applying an original approach to analyze the (002) XRD diffraction peak profile of hydroxyapatite by using a sum of two Gauss functions, the bimodal distribution of nanosized hydroxyapatite within the chitosan matrix was revealed. Two types of size distribution domains such as cluster-like (between 200 and 400 nm), which are the habitat of "small" hydroxyapatite nanocrystallites and scattered-like, which are the habitat of "large" hydroxyapatite nanocrystallites was probed by TEM and CSLM. The structural features of composites suggest that self-assembly processes might be involved. The composites contain nanosized hydroxyapatite with structural features close to those of biological apatites that make them attractive for bone tissue engineering applications. (c) 2005 Elsevier Ltd. All rights reserved
Oligosaccharides composed of 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) and/or 2-amino-2-deoxy-D- glucopyranose (GlcN) were prepd. by chem. degrdn. of chitin or chitosan and sepd. by gel permeation chromatog. Oligosaccharides obtained after enzymic hydrolysis of chitosan [FA 0.19] with a fungal chitinase were derivatized by reductive amination with 2-aminoacridone and sequenced by matrix-assisted laser desorption ionization time-of-flight postsource decay (PSD) mass spectrometry (MS). The sequence of a trimer, D1A2, was established as D-A-A. The compn. of a hexamer D3A3 was .apprx.65% D-A-D-D-A-A and 35% D-D-A-D-A-A. The PSD MS of a nonamer D5A4-amac revealed four isobaric species D-X-Y-D-X-Y-D-A-A, where A is GlcNAc, D is GlcN, and X and Y (X ¹ Y) are mutually either D or A. This structure motif was also obsd. in a dodecamer D7A5 which was composed of eight isobaric sequences of the general formula (D-X-Y)3- D-A-A.
The use of CO2 as a massive and polarizable drift gas is shown to greatly improve peak-to-peak resolution (Rp-p), as compared with N2, for the separation of disaccharides in a Synapt G2 traveling wave ion mobility cell. Near or baseline Rp-p was achieved for three pairs of sodiated molecules of disaccharide isomers, that is, cellobiose and sucrose (Rp-p?=?0.76), maltose and sucrose (Rp-p?=?1.04), and maltose and lactose (Rp-p?=?0.74). Ion mobility mass spectrometry using CO2 as the drift gas offers therefore an attractive alternative for fast and efficient separation of isomeric disaccharides.
A new synthesis of 9 alpha-hydroxy-alpha-agarofuran (6 alpha) is described, using a microbiological hydroxylation alpha-agarofuran (5) as the key reaction. The stereochemistry of the biohydroxylation was determined on the basis of a NOESY-experiment and GIAO calculations at the B3LYP/cc-pVDZ level. A strong gamma-effect was observed at C15 of the agarofuran ring which was correctly predicted by the GIAO-B3LYP calculations
Heterochitooligosaccharides possess interesting biol. properties. Isobaric mixts. of such linear heterochitooligosaccharides can be obtained by chem. or enzymic degrdn. of chitosan. However, the sepn. of such mixts. is a challenging anal. problem which is so far unresolved. It is shown that these isobaric mixts. can be sequenced and quantified simultaneously using std. derivatization and multistage tandem mass spectrometric techniques. A linear ion trap mass spectrometer equipped with a vacuum matrix-assisted laser desorption ionization (vMALDI) source is used to perform MS2 as well as MS3 expts. [on SciFinder (R)].
A model system of tanning of a protein matrix within a fibrous structure, such as most commonly found in insect cuticle, was developed, using the cellulose of paper in place of chitin. The paper was impregnated with a tripeptide, DOPA-Gly-Gly, or a protein (BSA) plus catechol and treated with tyrosinase to oxidize the catechol. The resulting material was waterproof and had very high wet strength. If the material was wetted and dried repeatedly its water retention decreased by a factor of at least two.
Based on NMR spectroscopic information about the allosamidin-hevamine complex, ab initio MO calcns. of the ring current effect of the arom. moieties of Trp255, Tyr183 and Tyr6 of hevamine were carried out to investigate the role of these amino acid residues in binding interactions with allosamidin in soln. In addn., the intermol. steric compression effect on the 13C chem. shifts of the allosamizoline carbon atoms and the hydrogen bonding to Glu127 was identified. It can be inferred that the binding forces are strongest in the allosamizoline moiety of allosamidin.
The six possible isomers of di-N-acetylchitotetraoses [AADD, ADDA, ADAD, DADA, DAAD, and DDAA, where D stands for 2-amino-2-deoxy-3-D-glucose (GlcN) and A for 2-acetamido-2-deoxy-beta-D-glucose (GlcNAc)] were analyzed by ESI(+)-MSn. Collision induced dissociation via MSn experiments were performed for the sodiated molecules of m/z 769 [M+Na](+) for each isomer, and fragments were generated mainly by glycosidic bond and cross-ring cleavages. Rules of fragmentation were then established. A reducing end D residue yields the (O.2)A(4) cross-ring [M-59+Na](+) fragment of m/z 710 as the most abundant, whereas isomers containing a reducing end A prefer to lose water to form the [M-18+Na](+) ion of m/z 751, as well as abundant (O.2)A(4) cross-ring [M-101+Na](+) fragments of m/z 668 and B-3 [M-221+Na](+) ions of m/z 548. MS3 of C- and Y-type ions shows analogous fragmentation behaviour that allows identification of the reducing end next-neighbour residue. Due to gas-phase anchimeric assistance, B-type cleavage between the glycosidic oxygen and the anomeric carbon atom is favoured when the glycon is an A residue. Relative ion abundances are generally in the order B >> C > Y, but may vary depending on the next neighbour towards the non-reducing end. These fragmentation rules were used for partial sequence analysis of hetero-chitooligosaccharides of the composition D(2)A(3), D(3)A(3), D(2)A(4), D(4)A(3), and D(3)A(4).