首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 559 毫秒
1.
ABSTRACT

The stepwise synthesis of methyl α-D-glucopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (EBC-OMe, 1), methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (A(E)BC-OMe, 2), and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranosyl-(1→3)-α-L-rhamnopyranoside (DA(E)BC-OMe, 3) is described. Compounds 1, 2 and 3 constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Methyl 2,4-di-O-benzoyl-α-L-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-L-rhamnopyranoside was an appropriate BC precursor for the synthesis of 1. For the synthesis of the branched targets 2 and 3, a benzyl group was best suited at position 2 of rhamnose C. Thus, methyl 4-O-benzyl-α-L-rhamnopyranosyl-(1→3)-2,4-di-O-benzyl-α-L-rhamnopyranoside was the key intermediate to the BC portion. In all cases, 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride was a convenient E precursor, when used in combination with titanium tetrafluoride. All along, attention was paid to steric hindrance as a factor of major impact on the condensation steps outcome. Therefore, based on previous experience, 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate and 3,4,6-tri-O-acetyl-2-deoxy-2-trichloroacetamido-α-D-glucopyranosyl trichloroacetimidate were used as donors. Both suited all requirements when used as key precursors for residues A and D in the synthesis of 3, respectively.  相似文献   

2.
Abstract

4-Nitrophenyl 2,3-O-isopropylidine-α-D-mannopyranoside 2 was condensed with O-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-(1→2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl bromide 1 and 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl bromide 11 in the presence of mercuric cyanide. Products were deprotected to yield, respectively, 4-nitrophenyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 6 and 4-nitrophenyl O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 14. The 4-nitrophenyl group of 6 was reduced to give title trisaccharide. Bromide 1 was also condensed with methyl 2,3,4-tri-O-benzyl-α-D-manopyranoside 3 in the presence of silver trifluoromethanesulfonate and tetramethylurea to give protected trisaccharide derivative which was deprotected to furnish, methyl O-α-D-mannopyranosyl-(1→2)-O-α-D-mannopyranosyl-(1→6)-α-D-mannopyranoside 10. The identities of all protected and deprotected compounds were supported by 1H and 13C NMR spectral data.  相似文献   

3.
Abstract

A continuous development technique using silica gel linear high performance TLC plates is described for the separation of prostaglandins 6-keto-F, F, E2, 13,14-dihydro-15-keto-F, 13–14-dihydro-15-keto-E2, and thromboxane B2. Complete separation of all six prostaglandins was achieved with a solvent system of ethyl acetate/acetone/acetic acid (90:5:1). The method is simple, rapid and provides excellent resolution of plasma prostaglandins prior to quantitation by gas chromatography-mass spectrometry.  相似文献   

4.
ABSTRACT

The stereocontrolled synthesis of methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (EC, 1), methyl α-L-rhamnopyranosyl-(1→3)-[α-D-glucopyranosyl-(1→4)]-α-L-rhamnopyranoside (B(E)C, 3) and methyl α-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→3)-2-acetamido-2-deoxy-β-D-glucopyranoside (ECD, 4) is described; these constitute the methyl glycosides of branched and linear fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a. Emphasis was put on the construction of the 1,2-cis EC glycosidic linkage resulting in the selection of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (8) as the donor. Condensation of methyl 2,3-O-isopropylidene-4-O-trimethylsilyl-α-L-rhamnopyranoside (11) and 8 afforded the fully protected αE-disaccharide 20, as a common intermediate in the synthesis of 1 and 3, together with the corresponding βE-anomer 21. Deacetalation and regioselective benzoylation of 20, followed by glycosylation with 2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (15) afforded the branched trisaccharide 25. Full deprotection of 20 and 25 afforded the targets 1 and 3, respectively. The corresponding βE-disaccharide, namely, methyl β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranoside (βEC, 2) was prepared analogously from 21. Two routes to trisaccharide 4 were considered. Route 1 involved the coupling of a precursor to residue E and a disaccharide CD. Route 2 was based on the condensation of an appropriate EC donor and a precursor to residue D. The former route afforded a 1:2 mixture of the αE and βE condensation products which could not be separated, neither at this stage, nor after deacetalation. In route 2, the required αE-anomer was isolated at the disaccharide stage and transformed into 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-(1→4)-2,3-di-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (48) as the EC donor. Methyl 2-acetamido-2-deoxy-4,6-O-isopropylidene-β-D-glucopyran-oside (19) was preferred to its benzylidene analogue as the precursor to residue D. Condensation of 19 and 48 and stepwise deprotection of the glycosylation product afforded the target 4.  相似文献   

5.
ABSTRACT

Stereocontrolled, stepwise synthesis of methyl α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (A(E)B, 1) and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→2)-[α-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside (DA(E)B, 2) is described; these constitute the methyl glycosides of fragments of the O-specific polysaccharide of Shigella flexneri serotype 5a. Two routes to trisaccharide 1 were considered. Route 1 involved the coupling of a precursor to residue A and a disaccharide EB, whereas route 2 was based on the condensation of a precursor to residue E and a disaccharide AB. Rather surprisingly, the latter afforded the β-anomer of 1, namely methyl α-L-rhamnopyranosyl-(1→2)-[β-D-glucopyranosyl-(1→3)]-α-L-rhamnopyranoside as the major product. Route 1 was preferred. Overall, several observations made during this study suggested that, for the construction of higher fragments, a suitable precursor to rhamnose A would require protecting groups of low bulkiness at position 3 and 4. Therefore, the 2-O-acetyl-3,4-di-O-allyl-α-L-rhamnopyranosyl trichloroacetimidate (35) was the precursor of choice to residue A in the synthesis of the tetrasaccharide 2. The condensation product of 35 and methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-4-O-benzyl-α-L-rhamnopyranoside was selectively deacylated and condensed to 2-trichloroacetamido-3,4,6-tri-O-acetyl-2-deoxy-α-D-glucopyranosyl trichloroacetimidate to afford the corresponding fully protected tetrasaccharide 45. Controlled stepwise deprotection of the latter proceeded smoothly to afford the target 2. It should be emphasised that the preparation of 45 was not straightforward, several donors and coupling conditions that were tested resulted only in the complete recovery of the acceptor. Distortion of several signals in the 13C NMR spectra of the fully or partially protected tetrasaccharide intermediates suggested that steric hindrance, added to the known low reactivity of HO-2 of rhamnosyl acceptors, probably played a major role in the outcome of the glycosidation attempts.  相似文献   

6.
Two new ursane-type triterpenoids (1, 2) attached to isopropylidenedioxy group were isolated from the seeds of blackberry (Rubus fructicosus L., Rosaceae) along with two known ursane-type triterpenoids, 2,3-O-isopropylidenyl-2α,3α,19α-trihydroxyurs-12-en-28-oic acid (3) and 1β-hydroxyeuscaphic acid (4). The chemical structures of 1 and 2 were determined to be 2,3-O-isopropylidene-1β,2β,3β,19α-tetrahydroxyurs-12-en-28-oic acid and 1,2-O-isopropylidene-1β,2α,3α,19α-tetrahydroxyurs-12-en-28-oic acid, respectively, based on spectroscopic data. Additionally, their cytotoxic activity towards HL-60 human leukaemia cells was evaluated. Among them, 3 demonstrated a clear cytotoxic activity with 72.8 μM of IC50 value.  相似文献   

7.
The reaction of 3β-acetoxy-5,6α-epoxy-5α-cholestane 1, its 3β-chloro analogue 2, and 5,6α-epoxy-5α-cholestane 3 with carbon dioxide gas in the presence of sodium bromide as catalyst with continuous stirring at 100 °C for 30 min affords selectively the corresponding 1′,3′,-dioxolan-2′-ones (steroidal cyclic cis-carbonates) 4–6 in excellent yields. The structures of these products have been established on the basis of their elemental analysis and spectral data (infrared, 1H NMR, and mass).  相似文献   

8.
α,α′,α″,α′″-meso-Tetrahexyltetramethyl-calix[4]pyrrole is easily obtained as a single diastereomer in a one-pot reaction. It exhibits enhanced solubility in organic solvents, including aliphatic solvents, relative to its parent meso-octamethylcalix[4]pyrrole (1). Somewhat surprisingly, the tetrahexyl derivative 2 complexes with tributylmethylammonium chloride in chloroform more strongly than does 1 as shown by NMR titrations. However, 1 and 2 exhibit comparable complexation strength in extraction experiments, the difference between the NMR and extraction results being attributed to the effect of organic-phase water in the extraction systems. Mass-action analysis indicates the formation of the predominant complex TBMA+(1 or 2)Cl? in both NMR and extraction systems, and equilibrium constants are reported. x-Ray crystal structures were obtained for the free ligand 2 and its complex with tetramethylammonium chloride. The free ligand crystallises in the 1,3-alt conformation with equatorial hexyl arms. In the chloride complex with 2 in its cone conformation, the hexyl arms adopt an axial orientation, enveloping the anion. DFT calculations show this binding conformation to be the most stable, mostly owing to destabilising steric interactions involving the pyrrole C–H and alkyl C–H groups positioned equatorially.  相似文献   

9.
以3-硝基邻苯二甲腈为起始原料, 与正戊醇反应合成3-戊氧基邻苯二甲腈(1), 然后在高温溶剂1-氯萘中经缩聚反应合成二氯-轴向取代-四-α-(3-戊氧基)锡酞菁(2), 2进一步与2-羟基吡啶在N,N-二甲基甲酰胺中合成二-吡啶氧基-轴向取代-四-α-(3-戊氧基)锡酞菁配合物3, 同时对相关化合物分别进行了元素分析, IR, 1H NMR, UV/Vis, 荧光和质谱表征.  相似文献   

10.
The fruit body of Lasiosphaera fenzlii was found to show cytotoxicity on cancer cells during a preliminary screening. Repeated column chromatography of the fungal methanol extract resulted in the isolation of six compounds identified as 5α,8α-epidioxy-ergosta-6,22-dien-3β-ol (1), 5α,8α-epidioxy-ergosta-6,9(11),22-trien-3β-ol (2), 5α-ergosta-7,22-dien-3β-ol (3), 5α-ergosta-7,22-dien-3-one (4), ergosta-7,22-dien-3β,5α,6β-triol (5) and 6-dihydroxy-2,3-dihydro-1H-isoindol-1-one (6). The two peroxide compounds, 1 and 2, showed cytotoxic activity and compound 1 was selectively cytotoxic to cancer cells. Furthermore, compound 1 synergised the cytotoxicity of paclitaxel on Hela cells by increasing intracellular accumulation of paclitaxel in cancer cells but not in normal cells.  相似文献   

11.
ABSTRACT

Two fucotriosides with vicinal disubstitution α-L-Fuc-(1→2)[α-L-Fuc-(1→3)]α-L-Fuc-OPr (1) and α-L-Fuc-(1→3)[α-L-Fuc-(1→4)]α-L-Fuc-OPr (2), which are related to fragments of natural polysaccharides fucoidans, have been synthesized together with constituent disaccharides 3-5. Spectral and conformational properties of tri- and disaccharides have been investigated by 1H, 13C and NOE NMR spectroscopy.  相似文献   

12.
Abstract

We have synthesized a single repeat unit of type VIII Group B Streptococcus capsular polysaccharide, the structure of which is {L-Rhap(β1→4)-D-Glcp(β1→4)[Neu5Ac(α2→3)]-D-Galp(β→4)}n. The synthesis presented three significant synthetic challenges namely: the L-Rhap(β→4)-D-Glcp bond, the Neu5Ac(α2→3)-D-Galp bond and 3,4-D-Galp branching. The L-Rhap bond was constructed in 60% yield (α:β 1:1.2) using 4-O-acetyl-2,3-di-O-benzoyl-α-L-rhamnopyranosyl bromide 6 as donor, silver silicate as promotor and 6-O-benzyl-2,3-di-O-benzoyl-1-thio-β-D-glucopyranoside as acceptor to yield disaccharide 18. The Neu5Ac(α2→3) linkage was synthesized in 66% yield using methyl [phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-D-galacto-nonulopyranosid]onate as donor and triol 2-(trimethylsilyl) ethyl 6-O-benzyl-β-D-galactopyranoside as acceptor to give disaccharide 21. The 3,4-D-Galp branching was achieved by regioselective glycosylation of disaccharide diol 21 by disaccharide 18 in 28% yield to give protected tetrasaccharide 22. Tetrasaccharide 22 was deprotected to give as its 2-(trimethylsilyl)ethyl glycoside the title compound 1a. In addition the 2-(trimethylsilyl)ethyl group was cleaved and the tetrasaccharide coupled by glycosylation (via tetrasaccharide trichloroacetimidate) to a linker suitable for conjugation.

  相似文献   

13.
The synthetic utility of α,α-difluoro-α-phenylsulfanyl-α-trimethylsilylmethane (PhSCF2SiMe3; 1) as a difluoromethyl building block providing a general strategy to α,α-difluoromethyl aryl ketones was demonstrated. Oxidation, by using m-chloroperoxybenzoic acid, of the readily available 1-aryl-2,2-difluoro-2-phenylsulfanyl-1-trimethylsiloxyethanes obtained from fluoride-catalyzed nucleophilic addition of PhSCF2SiMe3 with aromatic aldehydes followed by flash vacuum pyrolytic elimination provided α,α-difluoromethyl aryl ketones in moderate overall yields.  相似文献   

14.
ABSTRACT

Starting from the known methyl 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl-(1→4)-2-O-benzoyl-α-L-rhamnopyranoside, the stepwise linear syntheses of methyl α-L-rhamnopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→ 3)-[α-D-glucopyranosyl-(1→ 4)]-α-L-rhamnopyranoside (AB(E)C, 4), and methyl 2-acetamido-2-deoxy-β-D-glucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→ 2)-α-L-rhamnopyranosyl-(1→ 3)-[α-D-glucopyranosyl-(1→4)]-α-L-rhamnopyranoside (DAB(E)C, 5) are described; these constitute the methyl glycosides of a branched tetra- and pentasaccharide fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a, respectively. The chemoselective O-deacetylation at position 2B and/or 2A of key tri- and tetrasaccharide intermediates bearing a protecting group at position 2C was a limiting factor. As such a step occurred once in the synthesis of 4 and twice in the synthesis of 5, the regioselective introduction of residue A on a B(E)C diol precursor (12) and that of residue D on an AB(E)C diol precursor (19) was also attempted. In all cases, a trichloroacetimidate donor was involved. The latter pathway was found satisfactory for the construction of the target 4 using the appropriate tri-O-benzoyl rhamnosyl donor. However, attempted chain elongation of 12 using 2-O-acetyl-3,4-di-O-benzyl-α-L-rhamnopyranosyl trichloroacetimidate (8) resulted in an inseparable mixture which needed to be benzoylated to allow the isolation of the target tetrasaccharide. Besides, condensation of the corresponding tetrasaccharide acceptor and the N-acetylglucosaminyl donor was sluggish. As the target pentasaccharide was isolated in a poor yield, this route was abandoned.  相似文献   

15.
Chemical investigations on the fruits of Zanthoxylum armatum Roxb. (Rutaceae) led to the isolation of two new constituents characterised as 2α-methyl-2β-ethylene-3β-isopropyl-cyclohexan-1β, 3α-diol (1) and phenol-O-β-D-arabinopyranosyl-4′-(3″, 7″, 11″, 15″-tetramethyl)-hexadecan-1″-oate (2) along with known compounds m-methoxy palmityloxy benzene (3), acetyl phenyl acetate (4), linoleiyl-O-α-D-xylopyranoside (5), m-hydroxyphenoxy benzene (6) and palmitic acid (7). The chemical structures were established with the help of physical, chemical and spectroscopic methods. The anti-inflammatory potential of isolated compounds 1 and 2 was evaluated using in vitro target-based anti-inflammatory activity in LPS-stimulated primary peritoneal macrophages isolated from mice. Production of pro-inflammatory cytokines (TNF-α and IL-6) was significantly inhibited by the treatment of isolated compounds 1 and 2 in a dose-dependent manner.  相似文献   

16.
An efficient synthesis of NeuAcα-(2→3)-Galβ-(1→3)-[NeuAcα-(2→6)]-GalNAcα1- O-(Z)-Serine (N-protected MUC II oligosaccharide–serine, 14) by a chemoenzymatic strategy is described. The enzymatic reaction of GalNAcα1- O-(Z)-Ser- OAll 7 with pNP-β-Gal in the presence of recombinant β1,3-galactosidase from Bacillus circulans gave Galβ-(1→3)-GalNAcα1- O-(Z)-Ser- OAll 3 in 68%. The introduction of two sialic acids into 3 was accomplished by a stepwise method. The branched Galβ-(1→3)-[NeuAcα-(2→6)]-GalNAcα1- O-(Z)-Ser- OAll 11 was constructed by a chemical method. Sialylation at the C-3 position of the terminal Gal residue on Galβ-(1→3)-[NeuAcα-(2→6)]-GalNAcα1- O-(Z)-Serine 2 using α2,3-(O)-sialyltransferase from rat liver gave a target compound 14 in a practical yield.  相似文献   

17.
Two new polyhydroxylated triterpenoids were isolated from the acetone extract of the aerial parts of Salvia urmiensis Bunge. Their structures were elucidated by 1D and 2D NMR and HR-ESI-MS analyses as olean-12-ene-1β,3β,11α,22α-tetraol (1) and urs-12-ene-1β,3β,11β,22α-tetraol (2). The effect of these compounds on cell viability of MCF-7 cells was investigated by the MTT assay. Compounds 1 and 2 showed weak cytotoxicity with IC50 values of 110.23 ± 0.12 and 88.35 ± 0.09 μM, respectively.  相似文献   

18.
Abstract

A new triterpene, javablumine A (1) along with six known ones were isolated from the aerial parts of Sambucus javanica Blume. They were identified as 3β,23-dihydroxy-11α,12α-epoxy-urs-20(30)-en-28,13β-olide (1), ursolic acid (2), pomolic acid (3), oleanic acid (4), 2α-hydroxy-oleanolic acid (5), α-amyrin (6), and lupeol palmitate (7), respectively. Compounds 1 and 3 exhibited inhibitory effect against nitric oxide (NO) production in lipopolysaccharide (LPS)-activated RAW264.7 macrophage cell lines with IC50 values of 17.4 and 26.2?μM, respectively.  相似文献   

19.
Two new oleanane-type triterpenoid glycosides, 3-O-β-D-xylopyranosyl-(1→2)-α-L-arabinopyranosyl-(1→3)-[β-D-glucuronopyranosyl-(1→2)]-β-D-glucuronopyranosyl-22α-angeloyloxyolean-12-ene-15α,16α,28-triol(1) and 3-O-β-D-xylopyranosyl-(1→2)-α-L-arabinopyranosyl-(1→3)-[β-D-glucuronopyranosyl-(1→2)]-β-D-glucuronopyranosyl-21β-acetyl-22α-angeloyloxyolean-12-ene-16α,28-diol (2) were isolated from the stems of Camellia oleifera Abel. Their structures were elucidated by means of spectroscopic methods and chemical evidence. The cytotoxic activities of compounds 1–2 were evaluated against five human tumour cell lines (HCT-8, BGC-823, A5049, and A2780). Compounds 1–2 showed cytotoxic activity against five human cancer cell lines, with IC50 values ranging from 3.15 to 7.32 μM.  相似文献   

20.
Nine compounds were isolated from Nocardia sp. YIM 64630, and their structures were elucidated as 5′-O-acetyl-2′-deoxyuridine (1), 22E,24R-5α,6α-epoxyergosta-8(14),22-diene-3β,7α-diol (2), 22E,24R-5α,6α-epoxyergosta-8,22-diene-3β,7α-diol (3), 22E,24R-ergosta-7,22-diene-3β,5α,6β-triol (4), 5α,8α-epidioxyergosta-6,22-dien-3β-ol (5), 4′,5,6-trihydroxy-7-methoxyisoflavone (6), 2,4,4′-trihydroxy-deoxybenzoin (7), methyl [4-hydroxyphenyl]acetate (8) and daidzein by extensive spectroscopic analyses. Compound 1 was isolated from natural resources for the first time. The antimicrobial and antioxidant activities of compounds 18 were investigated.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号