Synthesis of a dibenzylchitin-type polysaccharide by acid-catalyzed polymerization

This paper describes the polymerization of 2-methyl-(3,6-di-O-benzyl- 1,2-dideoxy-α-D -glucopyrano)-[2,1-d]-2-oxazoline ( 1 ) with an acid catalyst. The polymerization proceeds involving stereoregular glycosylation to give polysaccharide 2 . The polymer structure, 2-acetamido-3,6-di-O-benzyl-2-deoxy-(l→4)-β-D -glucopyranan was determined by means of ¹H NMR, ¹³C NMR, and IR spectra as well as elemental analysis. The molecular weight was at most 4900 (degree of polymerization ≈ 13).     

Powder-to-powder polycondensation of natural saccharides. Facile preparation of highly branched polysaccharides

Solid-state polycondensation of a natural saccharide was found to take place in the presence of H3PO4(5 mol%) at 110 degrees C under a N2 flow, giving a highly branched polysaccharide (conv. 11-84%, Mw = 1400-19000, Mn = 1200-3700); the reaction mixture was powdery throughout the polymerization. Interestingly, alpha- and beta-anomers showed different polymerization behaviour; the former was polymerized more slowly, however, they gave comparable molecular weight polymers. The polysaccharide product was per-O-methylated and subjected to structure analyses. The acid-hydrolysis products, the partially O-methylated monosaccharides, suggested that the polysaccharide products have highly branched structures. MALDI-TOF mass analysis revealed that intramolecular glycosylation and acetal exchange reactions are involved in the polymerization mechanism.     

Group‐transfer polymerization of cyclic trimethylsilyl dienolate as a new monomer

This communication reports the group‐transfer polymerization of a cyclic trimethylsilyl dienolate, 2‐(trimethylsilyloxy)furan ( 1 ), initiated with benzaldehyde. The polymerization proceeded in the presence of a tetrabutylammonium salt as the catalyst in THF solvent at 0–50°C. The product was isolated as an ethyl acetate insoluble fraction after acidic work‐up. The structure of the product polymer was determined by means of ¹H NMR, ¹³C NMR, and IR spectroscopy to be polylactone 3 . The mechanism of the polymerization can be explained by a Michael‐type addition of 1 onto the propagating end.     

NMR analysis of the O‐antigen polysaccharide from Escherichia coli strain F171

The structure of the O‐antigen polysaccharide from Escherichia coli strain F171 has been determined. NMR analysis of the polysaccharide showed that it was composed of pentasaccharide repeating units. The ¹H and ¹³C signals were assigned by 2D NMR techniques which revealed severe spectral overlap for key resonances at substitution positions. The structure of the repeating unit was deduced from ¹H,¹³C HMBC and, in particular, by ¹H,¹H NOESY experiments as follows: The structure is identical with that of the O‐antigen from Escherichia coli O25 previously determined by chemical degradation methods and the strain F171 should therefore belong to this serogroup. Copyright © 2003 John Wiley & Sons, Ltd.     

3,3,7,7,9-五甲基-1,5-二氧螺[5.5]十一烷-8-酮的核磁共振研究

以1,3-环己二酮为起始原料,经过3步合成,得到了适用于多种天然产物合成中的关键中间体3,3,7,7,9-五甲基-1,5-二氧螺[5.5]十一烷-8-酮。利用红外光谱、元素分析以及1H与13CNMR确定了目标化合物的准确结构;利用二维核磁共振技术1H-1HCOSY、NOESY、HMBC以及HSQC,对其1H和13CNMR进行了全归属,并得到了目标化合物的空间结构相关信息。     

Asymmetric synthesis of novel thioiso dideoxynucleosides with exocyclic methylene as potential antiviral agents

Novel thioiso pyrimidine and purine nucleosides substituted with exocyclic methylene have been synthesized, starting from D-xylose. The glycosyl donor 14 was synthesized from D-xylose, using cyclization of dimesylate 10 with sodium sulfide as a key step. Cyclization proceeded in pure S(N)2 reaction without going through S(N)1 reaction in the presence of an allylic functional group at low reaction temperature (0 degrees C) in polar solvent (DMF), affording compound 12 as a major product. At higher temperatures, S(N)2' product 11 was almost exclusively obtained as a major product. On the other hand, glycosylation of 14 with 6-chloropurine under Mitsunobu conditions afforded the desired S(N)2 product 26, while palladium-catalyzed glycosylation resulted in the sole formation of S(N)2' product 34.     

2-甲基-4-甲氧基苯基苯胺的合成

邻硝基甲苯在甲醇、乙酸和硫酸混合溶液中, 在Pt/C的催化下发生氢化和Bamberger重排生成2-甲基-4-甲氧基苯胺. 后者在Pd/C的存在下以苯酚为反应介质与环已酮缩合生成2-甲基-4-甲氧基苯基苯胺, 反应总产率63.0%. 文中给出了产物与中间产物的核磁共振氢谱和质谱, 同时讨论了影响反应的因素.     

二胸苷二氨合铂的合成及其平衡常数的测定

用逐步中和法,在pH=9.0的条件下合成了二胸苷二氨合铂,用Sephadex G-10分离得到纯配合物,并用元素分析、TG、DTA和~(13)CNMR对此进行了表征。用~1H NMR法测定和计算了配位反应的平衡常数,其值为1gK_1=9.95,1gK_2=6.92。     

Toward the development of a structurally novel class of chiral auxiliaries. Conformational properties of the aldol adducts of oxadiazinones: observation of unusual shielding effects

Asymmetric aldol reactions were conducted with the titanium enolate of N(3)-hydrocinnamoyl-3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one to afford aldol adducts 5a-j. The dominant product of the asymmetric aldol reaction was the non-Evans syn adduct as determined by (1)H NMR spectroscopy and X-ray crystallography. When evaluating the (1)H NMR spectra of adducts 5a-j, a highly shielded signal with an average chemical shift of 0.05 ppm was observed. This signal was readily determined to be the C(5)-methyl group of the oxadiazinone. It is presumed that the overall conformation adopted by the aldol adducts in solution places an aromatic ring of the N(3)-substituent in close proximity to the C(5)-methyl group. An investigation of this conformational preference is conducted employing (1)H NMR spectroscopy, X-ray crystallography, and computational methods.     

Structure of an Extracellular Polysaccharide from a Strain of Lactic Acid Bacteria

A new extracellular polysaccharide (EPS-I) isolated and purified from Z222, a strain of Lactic acid bacteria has been investigated. Sugar composition analysis, methylation analysis and ^1H NMR and ^13C NMR spectroscopy reveal that the EPS-I is composed of a pentasaccharide repeating unit. The sequence of sugar residue was determined by using two-dlmensional NMR spectroscopy, including heteronudear multiple-bond correlation(HMBC) and nuclear overhauser effect spectroscopy (NOESY).     

糖基化青蒿素衍生物的合成

以糖[D-葡萄糖(1a),D-木糖(1b),D-甘露糖(1c),乳糖(1d)和D-半乳糖(1e)]为原料,经溴化、乙酰化一锅法使糖基乙酰化制得相应的溴代乙酰化糖(2a～2e);2在相转移催化剂四丁基硫酸氢铵催化下分别与二氢青蒿素经醚化反应合成了五个糖基化青蒿素衍生物,其结构进行1H NMR,13C NMR,IR和LC-MS表征。     

Synthesis of branched aminopolysaccharides by acid-catalyzed polymerization of sugar oxazoline monomer

Acid-catalyzed polymerization of a sugar oxazoline monomer 1b having two free hydroxy groups was carried out to produce a branched aminopolysaccharide 2b. The reaction proceeded via the stereoregular glycosylation through oxazoline ring-opening process, giving rise to 2b consisting of β-glycosidic linkages. The structure of 2b was determined by the ¹H NMR, ¹³C NMR, and IR spectra. The molecular weights determined by GPC measurements were 4200-6100. The degrees of branching were estimated by the ¹H NMR spectra of the products by the reaction of 2b with 3,5-dinitrobenzoyl chloride. Deprotection of 2b was carried out by the catalytic hydrogenation in the presence of 10% Pd-C to produce a free branched aminopolysaccharide.     

Stereoselective direct glycosylation with anomeric hydroxy sugars by activation with phthalic anhydride and trifluoromethanesulfonic anhydride involving glycosyl phthalate intermediates

An efficient direct one-pot glycosylation method with anomeric hydroxy sugars as glycosyl donors employing phthalic anhydride and triflic anhydride as activating agents has been developed. Thus, highly stereoselective beta-mannopyranosylations were achieved by the reaction of 2,3-di-O-benzyl-4,6-O-benzylidene-D-mannopyranose (2) with phthalic anhydride in the presence of DBU at room temperature followed by sequential addition of DTBMP and Tf2O and glycosyl acceptors to the reaction mixture at -78 degrees C in one-pot. Stereoselective alpha-glucopyranosylations with 2,3-di-O-benzyl-4,6-O-benzylidene-D-glucopyranose (25) and other glycosylations with glucopyranoses and mannopyranoses having tetra-O-benzyl- and tetra-O-benzoyl protecting groups were also possible by utilizing the present one-pot glycosylation protocol. The possible mechanism for the beta-mannosylation with 2 was proposed based on the NMR study, in which alpha-mannosyl phthalate 55alpha and alpha-mannosyl triflate 59 were detected as intermediates. The versatility and efficiency of the present glycosylation methodology, especially those of the beta-mannopyranosylation protocol, were readily demonstrated by the efficient synthesis of protected beta-(1-->4)-D-mannotriose 62 and beta-(1-->4)-D-mannotetraose 67 with perfect beta-stereoselectivity.     

Isolation and structural elucidation of a novel homogenous polysaccharide from Tricholoma matsutake

A crude polysaccharide possessing antitumour, radiation-resistant and anti-ageing attributes was extracted from Tricholoma matsutake by water extraction and alcohol precipitation. From this crude polysaccharide, a homogeneous polysaccharide, TMP-5II, was successfully purified by Sephacryl S-300 column chromatography. The average molecular weight (M_w) of TMP-5II was 15.76 kDa. Monosaccharide analysis indicated that the homogeneous polysaccharide contained four different residues: d-glucose, d-galactose, d-mannose and d-fucose. Attenuated total reflectance infrared spectroscopy revealed characteristics typical of carbohydrate polymers and a peak typical of a β-type glycosidic bond. TMP-5II was selected for structural characterisation by nuclear magnetic resonance (NMR) analysis. According to ¹H NMR, ¹³C NMR and two-dimensional-NMR analysis, TMP-5II contains two kinds of linkages, β and α, at a ratio of 4:1. Preliminary results indicated that the polysaccharide had (1-4)-beta-pyran glucose as the main chain, and a branched chain in the O-6 location with fucose (1-2) mannose (1-3)-alpha-pyran galactose.     

富勒烯衍生物引发的富勒烯末端封端聚己内酯的合成

利用带活性羟基的N-取代3,4-富勒烯吡咯烷作为引发剂,引发ε-己内酯开环聚合,制备了一种具有新型结构的富勒烯末端封端聚己内酯,通过核磁共振(1H NMR,13C NMR)、红外光谱(FTIR)和基质辅助激光解吸电离飞行时间质谱(MALDI-TOF-MS)等手段对产物进行了结构表征,并用热重(TG)分析和差示扫描量热(DSC)分析的方法进行了热学性能分析.结果表明,与聚己内酯相比产物热稳定性增加.     

Synthesis of the Rhodiola rosea glycoside rosavin

A synthetic scheme was proposed for the glycoside rosavin that includes a one-step glycosylation of cinnamyl alcohol with a disaccharide. The structure of the product was confirmed by PMR and ¹³C NMR spectroscopy. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 323–324, July–August, 2006.     

新型齐墩果酸糖苷化衍生物的合成及体外抗HCT8活性

为提高齐墩果酸的水溶性和稳定性,以齐墩果酸苷元为起始原料,对其28-COOH进行甲基化修饰后制得齐墩果酸-28-羧甲酯(1)。分别以D-半乳糖、D-葡萄糖、D-氨基葡萄糖为起始原料,通过对糖羟基的保护与去保护,得到一系列的二糖、四糖片段。通过三氯乙酰亚胺酸酯途径和对甲苯硫基途径,利用合成的糖片段对1的3-位羟基进行糖化学结构修饰,合成了4种新型的齐墩果酸糖苷化衍生物(2~5),其结构经1H NMR,13C NMR和MS(ESI)表征。采用MTT法测试了2~5对高表达人结肠癌细胞(HCT8)的体外抑制活性。结果表明:2~5对HCT8有一定的抑制作用,化合物5浓度为1×10^-3 mmol/L时,抑制率达到(98.96±0.10)%。     

柘树根多糖的分离纯化及结构表征

以柘树[Cudrania tricuspidata(Carr.) Bur.]的根为材料, 经热水抽提、木瓜蛋白酶-Sevag法除蛋白、乙醇沉淀和DEAE-Sephadex A-50凝胶柱层析分离纯化, 得到一种水溶性的柘树根多糖(CPS-0). 采用HPLC、糖基组成分析、甲基化分析、GC、GC-MS、NMR(1H NMR, 13C NMR及HMQC)、元素分析、UV和IR等技术对CPS-0的纯度、性质、组成和结构进行表征. 结果表明, CPS-0仅含葡萄糖, 分子量为4.6×103, 主链由1,4-连接的α-D-葡萄糖残基组成, 其侧链由末端及1,4-连接的葡萄糖残基构成, 取代于主链分支点葡萄糖的6位, 平均每10个葡萄糖残基组成的重复单元中含有1个分支.     

由三氟异丙烯基溴化镁制备羧酸

以三氟丙烯和溴为原料加成制得1,2-二溴三氟丙烷,脱溴化氢得到2-溴三氟丙烯,再在一定条件下合成2-溴三氟丙烯的格氏试剂（三氟异丙烯基溴化镁）,与CO2反应最终生成1-溴-2-三氟甲基丙酸。 用碳酸钠溶液萃取的方法得到0.8 g产品,纯度为99.6%,收率为3.6%。 对产物进行了MS、IR、1H NMR和13C NMR等表征,并分析了主要副产物1,2-二氟丙二烯和2,3-二三氟甲基-1,3-丁二烯及其与未反应的2-溴三氟丙烯间的[2+2]或[2+4]环加成反应产物。 确定以2-溴三氟丙烯为原料经格氏反应制羧酸较好的反应条件为：以THF为溶剂,1,2-二溴乙烷作引发剂,制备格氏试剂温度为30 ℃,CO2与格氏试剂反应温度为0 ℃。     

Structural Elucidation and Antitumor Activity of Polysaccharide AMP-1 from Atractyloids macrocephalae K.

A polysaccharide named as AMP‐1 was isolated from the root of Atractylodis macrocephalae Koidz, and purified by ethanol fractionation and gel filtration. The homogeneity of AMP‐1 was determined by HPLC and capillary electrophoresis that gave a single peak. AMP‐1 is composed of galactose and mannose in a molar ratio of 1.0:1.9. Its molecular weight is 3.8 × 10³. The structure of ghycan was elucidated by IR, ¹H NMR, ¹³C NMR and methylation analysis, and on the basis of the results was suggested that AMP‐1 contain a backbone of β. (1–2)‐D‐galactose residues with branches of single β‐D‐mannose residue being substituted at the O‐6. Bioactivity assay of AMP‐1 showed that it could inhibit growth of Sarcoma 180 and Lewis pulmonary carcinoma implanted in mice.