A stereoselective synthesis of the C(3)-C(13) and C(14)-C(24) fragments of macrolactin A

Synthetic studies towards(he C(3)-C(13)and C(14)-C(24)segments(3,4)of the potent antiviral and antitumor compound macrolactin A(1)are presented.Compound 3 was constructed via a convergent and facile approach,exploiting Wittig olefination to generate the sensitive E,Z-diene moiety.Compound 4 was synthesized from the chiral-pod derived sul-fone 39a via an o-alkylation-desulfonation reaction sequence.Cu(Ⅱ)-catalyzed coupling of a Grignard reagent with an al-lylic bromide and Julia olefination were also investigated for the preparation of compound 4.     

A convenient synthesis of (2-styrylchromon-8-yl)acetic acids

(2-Styrylchromon-8-yl)acetic acids, structural analogs of (flavon-8-yl)acetic acid (FAA) have been synthesized with satisfactory yields according to two different methods. The ¹H and ¹³C nmr data fovor the S-trans stereoisomers.     

Effect of synthesis conditions of polyallylamine-beads-glucose (PAA-Glu) on boron adsorption

In this study, we assessed the boron adsorption characteristic of our synthesized adsorbent: polyallylamine-beads-glucose (PAA-Glu) by using the adsorption amount and adsorption site availability (ASA), and determined the optimum conditions for PAA-Glu synthesis. ASA is our proposed indicator and it expresses the percentage of the experimental equilibrium adsorption in relation to the theoretical equilibrium adsorption and indicates the availability of adsorption sites (hydroxyl groups) on adsorbents. We investigated the effects of the degree of cross-linking (20, 40 and 60 %), the introduction amount of α-D-glucose (40, 60 and 80 %), and the introduction temperature (30–150 °C) as regards PAA-Glu on the boron adsorption amount. The boron adsorption amount for PAA-Glu (20 % cross-linked, 30 °C) was superior to that for another degree of cross-linked PAA-Glu. However, the ASA for PAA-Glu (60 % cross-linked, 30 °C) exhibited the best value in this synthesized PAA-Glu. Furthermore, we examined the introduction temperature at which glucose was introduced to PAA-Glu (20 % cross-linked) in the 30–150 °C range, and we confirmed that the optimum temperature range for the synthesis of PAA-Glu was 60–80 °C. We found that controlling the space between the main chains of the polymer by using a spacer such as a cross-linker allowed boron molecules to come and go and led to an improvement in the boron adsorption amount and ASA.     

New approach to the synthesis of tris(perfluoroalkyl)borane adducts with dialkylamines

A convenient synthetic approach to the adducts (C _n F_2n+1)₃BNHR₂ (n = 2–4, 6; R = Me, Et) was developed, based on the reaction of lithium perfluoroalkyls with dichloro(dialkylamino)boranes at temperatures below ?90°C. The target products can be synthesized with preparative yields of 50–90%.     

The synthesis of a precursor of polybenzimidazole (PBI) and blends with polyamic acid (PAA)

The precursor of polybenzimidazole (PBI), poly(3,3′-diamino-4,4′-benzidine isophthalamide) (PDABI), was synthesized from poly(3,3′-dinitro-4,4′-benzidine isophthalamide) (PDNBI) by reduction. With increasing temperature, the NH₂ moiety which was protected by SnCl₅^?1 could cyclize and form PBI. Blends with polyamic acid (LaRC-TPI) were prepared. Clear blend films were prepared at up to 400°C. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of their cured blends. © 1993 John Wiley & Sons, Inc.     

One-pot synthesis of bis (phenylimino dihydro thiazolyl-2H-chromene) derivatives

A novel series of bis (phenylimino dihydro thiazolyl-2H-chromene) derivatives have been synthesized through an efficient one-pot multicomponent approach involving different substituted of 3-(2-bromoacetyl)-2H-chromen-2-ones, phenyl isothiocyanates and para-phenylenediamine in presence of dimethylformamide solvent. The target compounds were obtained in a shorter reaction time through simple reaction work up with good yields. All the synthesized products were characterized by their spectral and analytical data like IR, ¹H NMR, ¹³C NMR, Roesy, and mass spectral data.     

Nano-sized Cu(II) and Zn(II) complexes and their use as a precursor for synthesis of CuO and ZnO nanoparticles: A study on their sonochemical synthesis,characterization, and DNA-binding/cleavage,anticancer, and antimicrobial activities

Two new divalent copper (C1) and zinc (C2) chelates having the formulae [M(PIMC)₂] (where M = Cu(II), Zn(II) and PIMC = Ligand [(E)-3-(((3-hydroxypyridin-2-yl)imino)methyl)-4H-chromen-4-one] were obtained and characterized by several techniques. Structures and geometries of the synthesized complexes were judged based on the results of alternative analytical and spectral tools supporting the proposed formulae. IR spectral data confirmed the coordination of the ligands to the copper and zinc centers as monobasic tridentate in the enol form. Thermal analysis, UV-Vis spectra and magnetic moment confirmed the geometry around the copper center to be tetrahedral, square pyramidal and octahedral. Study of the binding ability of the synthesized compounds with Circulating tumor DNA (CT-DNA) bas been evaluated applying UV-Vis spectral titration and viscosity measurements. The copper and zinc oxides were achieved from the copper and zinc nano-particles structures Schiff base complexes as the raw material after calcination for 5 hr at 600°C. On the other hand, synthesized of C1 and C2 NPs were used as suitable precursors to the preparation of CuO and ZnO NPs. Finally, the synthesized of the two complexes exhibited enhanced activity against the tested bacterial (Staphylococcus aureus and Escherichia Coli) and fungal strains (Candida albicans and Aspergillus fumigatus) as compared to HPIMC. Among all these synthesized compounds, C1 exhibits good cleaving ability compared to other newly synthesized C2.     

Determination of the optimum conditions for the synthesis of praseodymium(III) chloride

In the present work, we have synthesized praseodymium(III) chloride, PrCl₃, from the praseodymium oxide, Pr₆O₁₁, by dry method in the presence of ammonium chloride, NH₄Cl. This study includes the establishment of an assembly synthesis under inert gas. The thermal decomposing process of pure NH₄Cl was investigated by TG–DTG. The results showed that NH₄Cl begins to lose weight at 188 °C, large loss of weight ending at 302 °C when NH₄Cl is heated at the rate of 10 °C/min under N₂ atmosphere. For chlorination, NH₄Cl participates directly in the reaction, and HCl decomposed from NH₄Cl also contributes to the chlorination reaction. The influence of various synthesis parameters (temperature, contact time and chemical composition) on the reaction yield was studied, and the optimum conditions for synthesis were, thus, determined and discussed.     

Studies on the synthesis of (-)-gymnodimine. Subunit synthesis and coupling

Two principal subunits of the marine algal toxin (-)-gymnodimine were synthesized. A trisubstituted tetrahydrofuran representing C10-C18 of the toxin was prepared via a highly stereoselective iodine-mediated cyclization of an acyclic alkene bearing a bis-2,6-dichlorobenzyl (DCB) ether. The formation of a cis-2,5-disubstituted tetrahydrofuran in this process conforms to a stereodirecting effect by the DCB group proposed by Bartlett and Rychnovsky. A cyclohexene subunit corresponding to the C1-C8, C19-C24 portion of gymnodimine was synthesized via Diels-Alder cycloaddition of a 1,2,3-trisubstituted diene to a symmetrical dienophile obtained from Meldrum's acid. Differentiation of carbonyl groups in the cycloadduct was made by an intramolecular reaction with a neighboring alcohol to form a gamma-lactone. Linkage of the two subunits at C18-C19 was accomplished by using a B-alkyl Suzuki coupling in which a borane prepared from the pendent alkenyl chain of the cyclohexene domain was reacted with the (E)-iodoalkene attached at C16 of the tetrahydrofuran sector. Subsequent transformations positioned functional groups in the coupled product for a future macrocyclization event that would close the 15-membered ring of gymnodimine.     

Block/segmented polymers. A new method of synthesis of copoly(amide-ester)-ester polymer

A new method of preparation of segmented copolymer amide-ester type is described here starting from two oligomers, one hard crystallizable (A) having a glass transition temperature (T_g) above room temperature and the other soft, amorphous (B) having T_g well below room temperature. A, an oligo amide-ester terminated with hydroxyl groups has been synthesized from bis(hydroxy acylo amide) alkane, a reaction product of a lactone and diamine and dicarboxylic acid. B, an oligoester hydroxyl terminated was synthesized by the conventional method. The two oligomers A and B were transesterified removing diol as by-product to obtain segmented (amide-ester)-ester copolymer. The polymer showed mostly two T_gs one at ?40 to ?50°C and other at +40 to +50°C; and one melting temperature 200°C. Max^m inherent viscosity was recorded at 1.75 dL/gm. © 1993 John Wiley & Sons, Inc.     

A practical enantioselective total synthesis of (−)-(S)-stepholidine

A convergent enantioselective total synthesis of (−)-(S)-stepholidine, a drug candidate for the treatment of schizophrenia and/or drug abuse, was described, which represented the first example of successful auxiliary-assisted Bischler–Napieralski cyclization of amide bearing bromine atom at 2-position of the C ring, followed by an introduction of the aryl methyl ester via Br–Li exchange. (−)-(S)-Stepholidine was synthesized in 6 steps, with 52% overall yield and >99% ee. The reported synthesis is practically free from chromatographic separation.     

The synthesis of poly(styrenechromiumtricarbonyl) in the presence of triisobutylboron

Poly(styrenechromiumtricarbonyl) was synthesized by radical homopolymerization of styrenechromiumtricarbonyl in AcOEt at 50 °C in the presence of AIBN and triisobutylboron. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1319–1320, July, 2000.     

A new synthesis of homoisoflavanones (3-benzyl-4-chromanones)

Two 7-hydroxyhomoisoflavanones ( / ) have been synthesized from corresponding 2'-hydroxydihydrochalcones ( / ) in about 33% overall yields. The stages are : (1) selective protection of C₄'-hydroxyl in ( / ) with EtO.CH₂Cl (1 molar equiv.) In the presence of dry K₂C0₃ and acetone at r.t.; (ii) reaction with one more molar equiv. of EtO.CH₂Cl at 60–70° without Isolating products ( / ) (iii) cyclizatlon of resulting α-hydroxymethyl derivatives ( / ) with 4% aq. aIc. Na₂C0₃ and (iv) deprotection of resulting 7-ethoxymethoxy homoisoflavanones ( / ) with 10% CH₃0H-HC1. The explanations for the formation of ( / ) and ( / ) are given.     

Highly enantiocontrolled total synthesis of (-)-protoemetinol

Enantiomerically pure (-)-protoemetinol (1) was selectively synthesized from ethylmalonic acid via radical cyclization of the (Z)-α,β-unsaturated ester (12).     

Novel synthesis of biodegradable poly(lactide-co-ethylene glycol) block copolymers

Biodegradable and amphiphilic diblock copolymers [polylactide-block-poly(ethylene glycol)] and triblock copolymers [polylactide-block-poly(ethylene glycol)-block-polylactide] were synthesized by the anionic ring-opening polymerization of lactides in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. The polymerization in toluene at room temperature was very fast, yielding copolymers of controlled molecular weights and tailored molecular architectures. The chemical structure of the copolymers was investigated with ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and differential scanning calorimetry investigations. The monomodal profile of the molecular weight distribution by gel permeation chromatography provided further evidence of block copolymer formation as well as the absence of cyclic species. Additional confirmation of the block copolymers was obtained by the substitution of 2-butanol for poly(ethylene glycol); butyl groups were clearly identified by ¹H NMR as polymer chain end groups. The effects of the copolymer composition and lactide stereochemistry on the copolymer properties were examined. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2235–2245, 2007     

Poly(p-xylene disulfide) and poly(p-xylene tetrasulfide): synthesis,cure and investigation of mechanical and thermophysical properties

Abstract

In this work, two polysulfide polymers were synthesized using aromatic organic monomer (α,α′-dichloro-p-xylene) and sodium disulfide (Na₂S₂) and sodium tetrasulfide (Na₂S₄) aqueous monomers. Then, the curing process of the polymers was carried out at 170° C using a rheometer. The structural characteristics of synthesized and cured samples were identified by Raman and Fourier transform infrared (FT-IR) spectroscopies. Also, morphological and thermophysical properties of samples were studied by using the X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. Moreover, the molecular weight of the synthesized samples was determined by proton nuclear magnetic resonance (¹H NMR). Furthermore, the mechanical properties and hardness of the samples were investigated by tensile test and Shore A. The results showed that in the noncured samples during the increase of sulfur in the polymer structure, solubility was increased whereas it decreased the hardness, melting point (T_m ) and glass transition temperature (T_g ) of polymers. But in cured samples, hardness and T_g increase by increasing sulfur and the mechanical properties also improved. This is due to the increase in crosslinks. Also, Tm and solubility are not observed due to the formation of crosslinks.     

A stereoselective synthesis of (±)-homochelidonine

(±)-Homochelidonine (1) was stereoselectively synthesized from berberine (3) through C₆-N bond cleavage, followed by recyclization between C-6 and C-13 position of the latter according to a biogenetic route.     

An efficient copper(II)-catalyzed synthesis of benzothiazoles through intramolecular coupling-cyclization of N-(2-chlorophenyl)benzothioamides

A wide range of 2-aryl or 2-alkyl-substituted benzothiazoles are synthesized through intramolecular C_(aryl)-S bond forming-cyclization using copper(II)-BINAM-catalyzed coupling of less reactive N-(2-chlorophenyl)benzo or alkylthioamide under mild reaction conditions (82 °C).     

High yield synthesis and characterization of isotopically enriched monoethylmercury chloride (C2H5201HgCl)

An important but commercially unavailable compound isotopically enriched monoethylmercury chloride (C₂H₅²⁰¹HgCl), has been synthesized from commercially available ²⁰¹HgO (98.11% enriched isotopic purity) and tetraethyltin. The required synthesis time is 1 h at 90 °C, and the product is the single product of monoethylmercury chloride, yielding more than 95% as ²⁰¹Hg in C₂H₅²⁰¹Hg⁺ (98.19 ± 0.22% enriched isotopic purity). The synthesized product was analyzed with high‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC‐ICP‐MS) to determine its concentration, isotopic composition and purity. The synthetic isotopically enriched monoethylmercury synthesized can be used in speciated isotope dilution mass spectrometry (SIDMS) and isotope dilution mass spectrometry (IDMS) analyses as a standard. Copyright © 2005 John Wiley & Sons, Ltd.     

The synthesis of (±)-cycloprodigiosin

The cycloprodigiosin isolated from the marine bacteria, $\text{Beneckea gazogenes}$ and $\text{Alteromonas rubra}$ has been synthesized from the fused ring pyrrole (9) and the methoxy formyl bipyrrole (10).