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991.
A mixture of the red calcareous algae Lithothamnion corallioides CROUAN and Lithothamnion calcareum (PALLAS ) ARESCHOUGH , from Brittany waters, gives, on ethanolic extraction, the novel icosanoids ethyl 13-hydroxy-arachidonate (=(+)-all-Z-ethyl 13-hydroxyicosa-5,8, 11,14,-tetraenoate; (+)- 1 )), ethyl 13-hydroxytimnodonate (=(+)-(all-Z)-ethyl 13-hydroxyicosa-5,8,11,14,17-pentaenoate ((+)- 2 ), and (5Z,9E,11E,14E)-ethyl 8-hydroxy-13-oxoicosa-5,9,11,14-tetraenoate ( 3 ). Moreover, the ethyl esters of four known icosatetraenoic acids are contained in the above algae. Structural elucidations of these metabolites are based mainly on NMR data. 相似文献
992.
Electrospray ionization mass spectrometry for identification and structural characterization of pregnane glycosides 总被引:1,自引:0,他引:1
Dal Piaz F De Leo M Braca A De Simone F Morelli I De Tommasi N 《Rapid communications in mass spectrometry : RCM》2005,19(8):1041-1052
Pregnane glycosides are a class of naturally occurring substances characterized by some interesting biological activities and widely distributed in the plant kingdom and in some marine organisms. Their toxicity and use in herbal drugs and folk medicines has generated great interest in the chemical characterization of these molecules. In the study reported here the potential of electrospray ionization mass spectrometry (ESI-MS) in the identification and structural characterization of pregnane glycosides was examined. ESI-MS/MS and ESI-MS(n) analyses were performed on 27 different compounds employing two mass spectrometers equipped with a triple-quadrupole or an ion-trap analyzer. The data illustrate the ability of the ESI techniques in the identification of pregnane glycosides, including the nature of the pregnane core, the kind of ester substituents, the types of sugar residues (hexose, deoxyhexose, dideoxyhexose, O-methyldeoxyhexose and O-methyldideoxyhexose), and the primary structure of the saccharide chain. From these data, a generalized fragmentation pathway was proposed by comparing the spectra acquired for all the compounds. Interestingly, similar results were obtained from the two instruments, thus demonstrating that detailed analyses of product ion spectra obtained using a triple-quadrupole mass spectrometer led to structural information comparable to those obtainable in MSn experiments using an ion trap. Different and complementary information was deduced by fragmenting the [M+H]+ or the [M+Na]+ ions, or the protonated aglycone [Agl+H]+ generated by in-source fragmentation. The present evidence clearly suggests that, in order to obtain a complete characterization of pregnane glycosides by MS, all three of these species should be accurately analyzed. 相似文献
993.
A complete screening and confirmation analytical method for the direct determination of six endogenous (cortisol, cortisone, deoxycorticosterone, tetrahydrocortisol, tetrahydrocortisone, tetrahydro-S) and 17 synthetic (amcinonide, betamethasone, desoximethasone, dexamethasone, fludrocortisone, flumethasone, flunisolide, flucinolone acetonide, flucinonide, fluprednisolone, flurandrenolide, fluorometholone, 6-methylprednisolone, prednisolone, prednisone, triamcinolone, triamcinolone acetonide) glucocorticoids in human urine by gas chromatography with mass spectrometric detection (GC-MS) is presented.The analytical technique comprises a pre-treatment procedure and the instrumental analysis of the trimethylsilyl (TMS) derivatives, performed by GC-MS (quadrupole) with electron impact (EI) ionization. The derivatization yields obtained by two different derivatizing mixtures, namely N-methyl-N(trimethylsilyl)trifluoroacetamide (MTSFA):NH4I:dithioerythritol (DTE) 1000:2:4 (usually indicated as TMSiodine); and N-trimethylsilylimidazole (TMSim):N,O-bis(trimethylsilyl)acetamide (BSA):trimethylchlorosilane (TMCS) 3:3:2, both under direct thermal heating and with microwave (MW) irradiation, were evaluated, also as a function of the temperature, of the MW power and of the incubation time.The highest yields of the derivatization process were obtained, for most of the compounds here considered, by a two-step procedure: a microwave-assisted derivatization stage (40 min in a microwave oven at 900 W emitted power), followed by a traditional heat transfer derivatization (1.5 h in a thermostated bath at 70 °C) with the derivatization mixture TMSim:BSA:TMCS 3:3:2. In these operating conditions, diagnostic EI-MS spectra of all considered glucocorticoids were obtained. Limits of detection (LOD) of synthetic glucocorticoids in urine ranged from 3 to 25 μg/l. The effectiveness of the method for the determination of glucocorticoids in urine was evaluated on spiked urine samples and on real samples obtained from patients under pharmacological treatment with synthetic glucocorticoids.Apart from the clinical monitoring of glucocorticoids in urine, the method can be applied as a complete screening + confirmation analytical protocol in antidoping tests for the detection of illicit administration of glucocorticoids by the athletes. 相似文献
994.
Vinje J Intini FP Natile G Sletten E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(14):3569-3578
The reactions of the anticancer complex trans-[PtCl(2)[(E)-HN==C(OMe)Me](2)] (trans-EE) with both single-stranded and double-stranded deoxyribonucleotides have been studied by HPLC and 2D [(1)H,(15)N] HMQC NMR spectroscopy and compared with those of cis-[PtCl(2)(NH(3))(2)] (cis-DDP). Reactions of trans-EE with the single-stranded oligonucleotides d(CCTCGCTCTC) and d(CCTGGTCC) proceed rapidly through solvolysis of the starting substrate and subsequent formation of G-N7/monochloro trans-EE adducts. The rate of reaction is comparable to that of formation of an adduct from trans-EE and the dinuclotide d(ApG). Quite unexpectedly, the double-helical duplexes, d(TATGGTACCATA)(2) and d(TATGGCCATA)(2), with no terminal G residues, are practically inert towards trans-EE, and only minor species (< 5 % as estimated from HPLC traces) appear during 24 h reaction time. However, the duplexes d[(CCTCGCTCTC). (GAGAGCGAGG)] and d(GATAGGCCTATC)(2), which contain both terminal and central G residues, undergo platination only at the terminal, solvent-exposed, G residues, thereby confirming that the interior of the duplex is not accessible to trans-EE due to steric hindrance. In contrast, cis-DDP was found to bind exclusively to the central GG pair in d(GATAGGCCTATC)(2). 相似文献
995.
The raspailynes (novel long-chain enol ethers of glycerol having the enol ethers double bond conjugated in sequence, to an acetylenic and an olefinic bond, isolated from the North-East-Atlantic sponges Raspailia pumila and R. ramosa) are stable under normal hydrolytic conditions for enol ethers. In contrast, when their solutions are evaporated, these lipids such as raspailyne Bl (=(?))-3-[(1Z,5Z)-(tetradeca-1,5-dien-3-ynyl)oxy]-1,2-propanediol;(?- 2 ) rapidly react with aerial O2 under normal laboratory-daylight conditions, with rupture of the C=C enol ether bond to give 1-O-formylglycerol ( 3 ) and an aldehyde (such as tridec-4-en-2ynal( 4 ) from (?)- 2 ). This reaction must be caused by triplet O2, since thermally generated singlet O2 has no effect on (?)- 2 in solution. That the mere presence of an enol-ether moiety conjugated to an acetylenic group is responsible for such a behaviour is demonstrated with the model compounds 1-methoxypentadec-1-en-3-yn-5-ol ( 6a ) and its 5-O-acetyl or 5-O-tetra-hydropyranyl derivatives 6b and 6c , respectively. Resistance to both hydroytic conditions and singlet O2 of these compounds is thought to arise from electron depletion at the enol-ether C(beta;) atom by the acetylenic group. Plausible reaction pathways for enol-ether bond rupture in these compounds by aerial O2 are outlined. 相似文献
996.
Angela M BernardAngelo Frongia Francesco SecciGiovanna Delogu Jean OllivierPier P Piras Jacques Salaün 《Tetrahedron》2003,59(47):9433-9440
Mixtures of (E and Z)-2-cyclobutylidenepropyl sulfonates, readily available from α,α-disubstituted cyclobutanones arising from suitable cyclopropane derivatives ring expansion, underwent regioselective and stereospecific reduction by formate anion to offer, through π-1,1-trimethyleneallylpalladium complexes formed upon treatment with palladium(0), a new and convenient entry to the diastereomeric four-membered ring monoterpenoids (±)-fragranol and (±)-grandisol. 相似文献
997.
A critical comparison of phase-selective fundamental harmonic a.c. anodic stripping voltammetry and differential pulse anodic stripping voltammetry for the determination of Pb, Cd, Cu and Zn in sea-water is reported. Differential pulse anodic stripping voltammetry was found to be slightly more sensitive than the a.c. technique, but the effect of the charging current could be more effectively eliminated by the latter, especially in the determination of zinc(II) and copper(II). The detection limits for both techniques were found to be about 10–10-10–8
M for all four elements. The precision, expressed as relative standard deviation, was of the order of 2–5% for the fundamental harmonic a.c. method and 5–8% for differential pulse voltammetry. The accuracy (expressed as recovery) was 95–105% for the former and 90–110% for the latter. 相似文献
998.
Michele D'Ambrosio Antonio Guerriero Francesco Pietra Ccile Debitus 《Helvetica chimica acta》1996,79(1):51-60
Leucascandrolide A ((+)- 1 ), a doubly O-bridged 18-membered macrolide of a new type, i.e., showing little C1-branching vs. extensive 1,3-dioxygenation and a peculiar side chain, was isolated from a calcareous sponge of a new genus, Leucascandra caveolata BOROJEVIC and KLAUTAU from the Coral Sea. Transesterification of (+)- 1 gave the methyl ester 3 , derived from the side chain, and the 5-hydroxy derivative (+)- 2 , derived from the macrolide portion and with the natural configuration at C(5) (axial). Mosher's MTPA esters 4 and 5 obtained from (+)- 2 showed scattered Δδ = (δ(S) ? δ(R)) data. However, inversion of the configuration at C(5) led, via ketone (+)- 6 , to the less encumbered 5-equatorial hydroxy derivative (+)- 7 , whose MTPA esters 8 and 9 gave consistent Δδ data, allowing the assignment of the absolute configuration of (+)- 7 , and hence of (+)- 1 . The structural novelty of (+)- 1 and its powerful antifungal and cytotoxic activities are likely to renew interest in calcareous sponges, previously limited to scarcely biologically active 2-aminoimidazoles. 相似文献
999.
Peter Belser Alex Von Zelewsky Alberto Juris Francesco Barigelletti Vincenzo Balzani 《Chemical physics letters》1984,104(1):100-104
The luminescence behavior of Ru(bpy)2(pq)2+, Ru(bpy)2(biq)2+, Ru(bpy)2(NO2-bpy)2+, Ru(phen)2(pq)2+, Ru(phen)2 (biq)2+, Ru(phen)2 (DMCH)2+, Ru(bpy)2(i-biq)2+ and Ru(bpy)(i-biq)22+ has been carefully studied. In no case has bona fide dual emission been observed. The reason for the previously reported dual emissions of Ru(bpy)2(NO2-bpy)2+ and Ru(phen)2(pq)2+ are discussed. 相似文献
1000.
Angelo Albert Francesco Paolo Colonna Maurizio Guerra Bianca F. Bonini Germana Mazzanti Zoltàn Dinya Gian Franco Pedulli 《Journal of organometallic chemistry》1981,221(1):47-55
The radical adducts resulting from the reaction between group IVB organometallic radicals MR3 (M = Si, Ge, Sn; R = alkyl or aryl) and a number of thioketones of the chromone and flavone series have been investigated by ESR spectroscopy. The spectral parameters obtained for these species have been compared with those of similar adducts of the corresponding ketones. Both classes of radicals adopt an orthogonal conformation, and the differences between the former and the latter paramagnetic species can be accounted for by the different electronegativity of oxygen and sulphur. the effects of substitution of the heterocyclic oxygen with a sulphur or selenium atom on the spin density distribution are likewise explained. INDO calculations have been carried out on the model systems CH2XSiH3 (X = O, S). 相似文献