Total synthesis of AI-77-B

A new stereoselective approach for the synthesis of AI-77-B has been described. Dihydroisocoumarin fragment was made in two routes using Heck reaction followed by oxidation of the olefin and LDA mediated reaction. The chiral amino acid moiety has been obtained from d-ribose involving Grignard reaction on ribosylimine. Finally, condensation of dihydroisocoumarin with acid fragment furnished the title target AI-77-B.     

Licamichauxiioic-A and -B acids--two ent-kaurene diterpenoids from Licania michauxii

Bioassay-guided fractionation allowed the isolation of two new cytotoxic ent-kaurene diterpenoids, licamichauxiioic-A and -B acids (1 and 2) from the root extract of Licania michauxii Prance (Chrysobalanaceae). They were characterized as ent-15-oxo-9(11),16-kauradien-19-oic acid (1) and ent-15-oxo-13(14),16-kauradien-19-oic acid (2) by various spectroscopic methods, in particular, 1D and 2D NMR spectra, and chemical evidence.     

Nanotubes with the TiO2-B structure

Here we report the first synthesis of TiO2-B nanotubes by a simple hydrothermal route; lithium may be intercalated up to a composition of Li(0.98)TiO2 compared with Li(0.91)TiO2 for the corresponding nanowires.     

掺Eu的SiO2-B2O3体系和SiO2-B2O3-Na2O体系的结构及Eu3+的发光性质

采用溶胶-凝胶技术制备了掺Eu3+的以SiO2-B2O3和SiO2-B2O3-Na2O为基质的玻璃态发光材料. 通过激发光谱、发射光谱研究了Eu3+的发光性质, 通过红外光谱、 TEM 、 XRT进一步研究了基质结构变化对发光性能的影响. 结果显示 材料经 600 ℃退火处理后, 结构已十分稳定. 在588 nm和613 nm处显示弱的Eu3+的特征发射光谱, 对应于Eu3+的5D0-7Fj(j=1,2)跃迁. 以SiO2-B2O3为基质的玻璃材料的红外光谱显示形成了Si-O-B键. 该结构对Eu3+的发光有严重的淬灭作用, 使Eu3+的发光强度大大减弱. 以SiO2-B2O3-Na2O为基质的玻璃材料显示Eu3+的发光增强, 红外光谱显示不存在Si-O-B键的振动吸收. 可能是Na取代B的位置, 形成了Si-O-Na键. 此结构对Eu3+的发光有一定增加作用.     

Stereoselective synthesis of pseudopeptide microbial agent AI-77-B

[structure: see text]. An efficient and highly stereoselective synthesis of the gastroprotective natural product AI-77-B is described. The stereocenters of the hydroxy amino acid moiety were generated by an ester-derived titanium-enolate-mediated syn-aldol reaction, a Curtius rearrangement, and application of Dondoni's aldehyde homologation. Condensation with the dihydroisocoumarin fragment and subsequent deprotecting transformations furnished optically active AI-77-B.     

Two novel aromatic glycosides,pueroside-A and -B,from puerariae radix

Two novel aromatic glycosides were obtained from Puerariae Radix and their chemical structures were characterized.     

Paeonilactone-A, -B,and -C,new monoterpenoids from paeony root

Three new monoterpenoids named paeonilactone-A, -B, and -C were isolated from Paeony root (roots of Paeonia albiflora PALLAS var. trichocarpa BUNGE) and their structures were determined to be $\text{2}$, $\text{3}$, and $\text{4}$, respectively, by means of chemical and spectroscopic studies.     

Synthesis of Some New Imidazo[4,5-B]Pyridine Derivatives Using 2-Cyanomethyl-1-Methyl-1H-Imidazo[4,5-B]Pyridine

Abstract

The reactions of 2-cyanomethyl-1-methyl-1H-imidazo[4,5-b]pyridine with isothiocyanates, nitroso compounds, acid chlorides, and thioglycolic acid were investigated. New imidazo[4,5-b]pyridine derivatives with various substituents in 2-position and derivatives of the new pyrrolo[2′,1′:2,3]imidazo[4,5-b]pyridine ring system were synthesized. The compounds obtained were tested in vitro for their tuberculostatic activity.     

Total Synthesis of the Gastroprotective Substance AI-77-B and of Analogues

The Diels-Alder adducts 8 of furan to 1-cyanovinyl acetate were converted into (Methyl 3-chloro)-5-O-(3-chlorobenzoyl)-2, 3-dideoxy-α-dl-arabino-hexofuranosid)uronic acid ((α)- 18a ) and into (methyl 3-azido-5-O-(3-chlorobenzoyl_-2,3-dideoxy-α-dl-ribo-hexofuranosid)uronic acid ((α)- 41a ). These compounds were condensed to (3S)-3-[(1′S)-1′-amino-3′-methylbutyl]-3,4-dihydro-8-hydroxyisocoumarin hydrochloride ((?)- 2 ); the resulting mixtures of diastereoisomeric amides were transformed and separated to give the gastroprotective substance AI-77- B ((?)- 1 ) and analogues.     

Two novel sesquiterpene lactones,cytotoxic vernolide-A and -B,from Vernonia cinerea

Bioassay-directed fractionation of an ethanolic extract of stems of Vernonia cinerea has resulted in the isolation of two novel sesquiterpene lactones, vernolide-A and -B. Their structures were elucidated on the basis of spectroscopic analysis. Biological evaluation showed that vernolide-A demonstrated potent cytotoxicity against human KB, DLD-1, NCI-661, and Hela tumor cell lines (ED(50)=0.02, 0.05, 0.53, 0.04 microg/ml for KB, DLD-1, NCI-661, and Hela, respectively); vernolide-B had marginal cytoxicity (ED(50)=3.78, 5.88, 6.42 microg/ml for KB, NCI-661, and Hela, respectively).     

The state-of-the-art in the analysis of type-A and -B trichothecene mycotoxins in cereals

The aim of this review is to describe the state-of-the-art in the analysis of A- and B-trichothecene mycotoxins in cereals and to support knowledge and experience exchange between laboratories in the field of Fusarium mycotoxin analysis. Current screening tests and quantitative methods for the most prevalent type-A and -B trichothecenes, HT-2 and T-2-toxin, and deoxynivalenol (DON) are reviewed. This includes the extraction and clean-up procedures and chromatographic methods (TLC, HPLC, GC) applied and the immunochemical methods, especially enzyme-linked immunosorbent assay (ELISA), employed for the determination of these mycotoxins. Results from recent intercomparison studies of the determination of DON are also discussed. Experience gained during these intercomparisons clearly shows the need for further improvement in the determination of trichothecenes, to obtain more accurate and comparable results. This also indicates there is a strong need for the development of further certified reference materials (CRM) which would enable comparison of measurement results between different European laboratories for several A- and B-trichothecenes. For both A- and B-trichothecenes there is still a lack of simple and reliable screening methods enabling the rapid detection of these mycotoxins at low cost.     

Selective Interactions of O-Methylated Flavonoid Natural Products with Human Monoamine Oxidase-A and -B

A set of structurally related O-methylated flavonoid natural products isolated from Senecio roseiflorus (1), Polygonum senegalense (2 and 3), Bhaphia macrocalyx (4), Gardenia ternifolia (5), and Psiadia punctulata (6) plant species were characterized for their interaction with human monoamine oxidases (MAO-A and -B) in vitro. Compounds 1, 2, and 5 showed selective inhibition of MAO-A, while 4 and 6 showed selective inhibition of MAO-B. Compound 3 showed ~2-fold selectivity towards inhibition of MAO-A. Binding of compounds 1–3 and 5 with MAO-A, and compounds 3 and 6 with MAO-B was reversible and not time-independent. The analysis of enzyme-inhibition kinetics suggested a reversible-competitive mechanism for inhibition of MAO-A by 1 and 3, while a partially-reversible mixed-type inhibition by 5. Similarly, enzyme inhibition-kinetics analysis with compounds 3, 4, and 6, suggested a competitive reversible inhibition of MAO-B. The molecular docking study suggested that 1 selectively interacts with the active-site of human MAO-A near N5 of FAD. The calculated binding free energies of the O-methylated flavonoids (1 and 4–6) and chalcones (2 and 3) to MAO-A matched closely with the trend in the experimental IC_50′s. Analysis of the binding free-energies suggested better interaction of 4 and 6 with MAO-B than with MAO-A. The natural O-methylated flavonoid (1) with highly potent inhibition (IC₅₀ 33 nM; Ki 37.9 nM) and >292 fold selectivity against human MAO-A (vs. MAO-B) provides a new drug lead for the treatment of neurological disorders.     

Longifoside-A and -B: two new cerebrosides from Mentha longifolia (Lamiaceae)

Two new N-acyl-glycosphingosines (cerebrosides) named longifoside-A {6'-tetracosenamide, N-[3,4-dihydroxy-1-(hydroxymethyl)-2-(beta-D-glucopyranosyl) heptadecyl]-(6'E)} and B {6'-tetracosenamide, N-[3-hydroxy-1-(hydroxymethyl)-2-(beta-D-glucopyranosyl)-4Z-heptadecenyl]-(6'E)} have been obtained from the methanolic extract of Mentha longifolia belonging to the family Lamiaceae. Both the cerebrosides were purified as their acetate-derivatives: 6'-tetracosenamide, N-[3,4-diacetoxy-1-(acetoxymethyl)-2-(tetraacetoxy-beta-D-glucopyranosyl) heptadecyl]-(6'E) and 6'-tetracosenamide, N-[3-acetoxy-1-(acetoxymethyl)-2-(tetraacetoxy-beta-D-glucopyranosyl)-4Z-heptadecenyl]-(6'E). They were characterized with the aid of 1D and sophisticated 2D-NMR spectroscopic techniques.     

Novel Synthesis of Pyrido[2,1-B]Benzothiazoles and 1,3-Benzothiazole Derivatives

Abstract

A variety of new pyrido[2,1-b]benzothiazole and benzothiazoles, have been prepared via the reaction of 2-substituted methylthiazole with α,β-unsaturated nitriles and activated methylene compounds. The structures of the reaction products were established based on the elemental analyses and spectral data (IR, ¹H-, ¹³C-NMR, MS).     

Reticuloendothelial system-activating polysaccharides from rhizomes of Panax japonicus. I. Tochibanan-A and -B

From rhizomes of Panax japonicus (Araliaceae), two polysaccharides named tochibanan-A and -B, which show reticuloendothelial-potentiating activity in the carbon clearance test in mice, were isolated. The structure of tochibanan-A (molecular mass: 23,000) was elucidated as a linear beta-1,4-D-galactan. Tochibanan-B (molecular mass: 40,000) consists of D-galactose (87.1%), L-arabinose, D-glucose and D-galacturonic acid and has a beta-D-(1----4)-linked galactopyranosyl backbone possessing GalA-(1----6)-Gal, Ara-(1----5)-Ara, Gal, and Glc side chains. The structure around the branching points and the repeating unit were investigated and a possible structure of tochibanan-B is proposed.     

The Paternò-Büchi reaction—Mechanisms and application to organic synthesis

The [2 + 2] photocycloaddition between an electronically excited carbonyl compound and an alkene leading to oxetanes (Paternò-Büchi reaction) is one of the most investigated organic photochemical reaction. Regio-, stereo- and site selectivities are discussed as a consequence of the reaction mechanism. Spin multiplicity and electron transfer have a significant impact on the outcome of the reaction. Typical carbonyl and alkene reaction partners are presented indicating scope and limitation of the reaction. The Paternò-Büchi reaction possesses particular interest for being applied to organic synthesis, considering the difficulty for non-photochemical reactions to obtain oxetanes, with or without stereoselectivity. Mechanistic details are particularly focused. It has been applied as key step in various multi-step syntheses.     

Synthesis of 2-Aroylimjnopyrimido[3,2-B]-1,2,4-Thiadiazolines

N-Aroyl-N′-(pyrimid-2-yl)-thioureas (2) have been synthesised by the reaction of 2-amino pyrimidines (1) with aroyl chlorides and ammonium thiocyanate in acetone- Cyclisation of 2 with PCl₅ in POCl₃ and as well as by oxidising agents gave 2-aroyHrninopyrimido[3,2-b]-1,2,4-thiadiazolines (3).