Copper-catalyzed allylations of o-vinylbenzylzirconocene intermediate

Benzylzirconocene intermediate, which was readily prepared by the reaction of o-alkoxymethylstyrene with `Cp₂Zr' under mild conditions, reacted with allylic halides or phosphates in the presence of catalytic amount of CuCl to give allylated products in good yields.     

Synthetic studies toward swinhoeisterol A,a novel steroid with an unusual carbon skeleton

Swinhoeisterol A is a novel steroid with unusual 6/6/5/7 tetracyclic skeleton. The model compound with BCD rings is constructed by Friedel–Crafts acylation and an oxidative dearomatization as key steps.     

A convenient synthesis of quinolines by reactions of o-isocyano-β-methoxystyrenes with nucleophiles

2,4-Disubstituted quinolines have been synthesized by reactions of o-isocyano-β-methoxystyrenes, which can be easily prepared from commercially available o-aminophenyl ketones in three steps, with alkyl(or aryl)lithiums in generally good yields. Subsequently, o-isocyano-β-methoxystyrenes have also proved to react efficiently with lithium dialkylamides to afford the corresponding 4-substituted N,N-dialkylquinolin-2-amines in satisfactory yields.     

Synthetic studies related to diketopyrrolopyrrole (DPP) pigments. Part 2: The use of esters in place of nitriles in standard DPP syntheses: Claisen-type acylations and furopyrrole intermediates

Ethyl 2-aryl-4,5-dihydro-5-oxopyrrole-3-carboxylates react with esters or acyl halides in the presence of a strong base to give 4-acyl derivatives, which exist predominantly as either E- or Z-enols. These are cyclised, either in solution at temperatures >200 °C or by microwave irradiation, to 3,6-disubstituted 1H-furo[3,4-c]pyrrolediones which, after N-protection, are convertible by reaction with primary amines into novel N,N′-disubstituted DPP derivatives.     

Structure and properties of polyimide aerogels with different skeleton flexibilities

ABSTRACT

In order to better understand the influences of polyimide (PI) skeleton structure and freeze-drying process on the properties of PI aerogel materials, PI molecular chains (ODPA-ODA, BPDA-ODA, BPDA-PPDA) with different stiffnesses and flexibilities were designed and a series of PI aerogels were accordingly fabricated by freeze-drying technique. The aerogels produced featured light weight (density of 0.01–0.16 g/cm³) and high flexibility, and their density, pore structure, and compress recovery performance could be well controlled by delicately tuning the molecular chain structure and solid contents of the poly (amic acid) salt solution. In addition, a hard PI aerogel with enhanced compressive strength was obtained by quick-freezing in liquid nitrogen.     

Synthesis of polycyclic pyrazoles through formation of the first fused heterocyclic o-quinodimethane intermediate

1-Benzoyl-4,6-dibromo-3-methyl-1,4,5,6-tetrahydrocyclopenta[c]pyrazole (2) was used as a precursor for o-quinodimethane 3, which was trapped by in situ reactions with dienophiles to give bridged pyrazole derivatives.     

Efficient synthesis of o-alkynyl-N-pivaloylanilines from o-acyl-N-pivaloylanilines and lithium trimethylsilyldiazomethane

Reaction of o-acyl-N-pivaloylanilines with lithium trimethylsilyldiazomethane efficiently gave the corresponding o-alkynyl-N-pivaloylanilines via alkylidenecarbene intermediates.     

Photoconversion of o-hydroxycinnamates to coumarins and its application to fluorescence imaging

(E)-o-Hydroxycinnamates were synthesized and their photochemical behavior was investigated in liquid and solid states. It was confirmed by ¹H NMR spectroscopy that the (E)-o-hydroxycinnamates converted into the corresponding coumarins via (Z)-o-hydroxycinnamate intermediates. The photoconversion was greatly accelerated in the presence of p-toluenesulfonic acid. The optical properties of the cinnamates were compared with those of the corresponding coumarins. Fluorescence imaging was successfully accomplished by photoirradiation of PMMA films containing the cinnamates.     

Isolation and Characterization of intermediate in the Synthesis of α-Fluorodiesters

The anion [(EtO)₂P(O)CFCO₂Et]^?Li⁺, pregenerated from its precursor diethyl (carboethoxyfluoromethyl)phosphonate (EtO)₂P(O)CFHCO₂Et and n-butyllithium, was added via syringe to a THF solution of ethyl oxaiyl chloride to yield an acylated phosphonate (EtO)₂P(O)CF(COCO₂Et)CO₂Et. In situ reaction with Grignard reagents RMgX produces the α-fluorodiesters (E,Z)-R(CO₂Et)C=CFCO₂Et in good yields. In contrast, addition of ethyl oxalyl chloride to a THF solution of diethyl (carboethoxyfluoromethyl)phosphonate anion gives an isolated intermediate (EtO)₂P(O)CFCO₂Et(CO₂Et)C=CFCO₂Et. Subsequent reaction of this isolated intermediate with Grignard reagents also affords a one-pot synthesis of the α-fluorodiesters with high E-stereoselectivity. The E-stereoselectivity increases when HMPT or DMPU is used as a cosolvent in the preparation of diethyl 2-fluoro-3-phenylfumarate (E,Z)-Ph(CO₂Et)C=CFCO₂Et.     

The Prins reaction using ketones: rationalization and application toward the synthesis of the portentol skeleton

We report a TMSI-promoted Prins cyclization reaction with ketones as carbonyl partners to prepare polysubstituted chiral spirotetrahydropyrans. In the presence of racemic 2-methylcyclohexanone a dynamic kinetic resolution occurred affording one stereoisomer. The observed enantiospecificity has been rationalized by DFT calculation.     

Determination of association constants of inclusion complexes of steroid hormones and cyclodextrins from their electrophoretic mobility

CE estimation of the association constants of several steroid hormones with beta-CD and gamma-CD and their hydroxypropyl derivative is presented. Estriol, 17beta-estradiol, ethynylestradiol, estrone, progesterone, mestranol and norethindrone are among the target analytes. The calculation of the cyclodextrin:analyte association constants were performed from the electrophoretic mobility values of steroids at different concentration of CDs in the run buffer. The reliability of the final data was ensured by employing three different linearisation plots (double reciprocal fit, Y-reciprocal fit and X-reciprocal fit). The highest inclusion affinity of target analytes was observed towards gamma-CD and its hydroxypropyl derivative, which is demonstrated by high association constant values and corresponding good linearity of the plots. The affinity of steroids towards a particular CD type based on physical and structural characteristics is explored.     

New synthetic strategy for o-NBS protected amino acids and their use in synthesis of mono-benzylated peptides

A synthetic strategy to prepare o-NBS protected Fmoc-amino acids under mild conditions, in a rapid and efficient way, characterised by high yields and excellent purity of the final products has been developed. The o-NBS protected Fmoc-amino acids are employed in solid phase peptide synthesis to prepare peptidomimetics carrying mono-benzylated moieties on peptide side chains.     

Synthesis and cytotoxicity screening of derivatives of the simplified ecteinascidin pentacyclic skeleton as anticancer agents

A series of new ecteinascidin pentacyclic-derived compounds bearing aryl carboxylic amide side chains at C-22 have been designed and synthesized. The cytotoxicity evaluation confirmed their potent antitumor activity by use of eight different cell lines. Studies on the structure-activity relationship of them showed that the chemical structure of C-22 pendants have great effects on the tumor-killing activity. Notably, Compounds 6, 7 and 8 with benzo[b]thiophene-2-carboxamide pendants exhibited excellent broad-spectrum antitumor activity with the low IC₅₀ values of 10^?7?M.     

Elucidation of steroid glycosides in Anemarrhena asphodeloides extract by means of comprehensive two-dimensional reversed-phase/polyamine chromatography with mass spectrometric detection

In the work presented here, a novel approach to comprehensive two-dimensional liquid chromatography is evaluated. Reversed-phase liquid chromatography was employed for the first-dimension separation and polyamine chromatography was chosen for the second-dimension separation mode. The two dimensions are highly orthogonal and the separation efficacy of the developed octadecylsilica × polyamine was tested by separating an extract from Anemarrhena asphodeloides. The steroid glycosides identified by comprehensive two-dimensional liquid chromatography in this experiment were compared to those obtained for monodimensional liquid chromatography. The comprehensive two-dimensional liquid chromatography system, thanks to the complementary separation selectivity and enhanced peak capacity provided by the two columns, allowed to distribute five compounds of low amounts otherwise unachievable by monodimensional liquid chromatography. In addition, four steroid isomers with similar fragmentation characteristics in MS/MS spectra, were newly separated based on their different chemical structures.     

Synthesis, structures, and properties of peripheral o-dimethoxy-substituted pentiptycene quinones and their o-quinone derivatives

A series of peripheral o-dimethoxy-substituted pentiptycene quinones and their o-quinone derivatives have been synthesized. Especially, it was found that if two o-dimethoxybenzene moieties were situated at the same side of the pentiptycene quinones, one of them was only oxidized by excess CAN in aqueous acetonitrile. Moreover, the pentiptycene quinones with unique 3D rigid structure could all self-assemble into a 3D microporous structure in the solid state. For the pentiptycene quinones containing the dimethoxybenzene unit(s) and the quinone group(s) simultaneously, interesting intramolecular charge transfer interactions and electrochemical properties were also shown. These peripheral-substituted pentiptycene quinones and their o-quinone derivatives can be used as new useful building blocks and will find wide applications in material science and host-guest chemistry.     

Highly efficient synthesis of capsaicin analogues by condensation of vanillylamine and acyl chlorides in a biphase H2O/CHCl3 system

Highly efficient synthesis of capsaicin analogues was developed using condensation of vanillylamine with acyl chlorides in a biphase H₂O/CHCl₃ system under mild conditions. For C4-C18 aliphatic or aromatic acyl chlorides, the yields were up to 93-96% with high purity after a simple work-up procedure, and only 1-1.16 equiv of acyl chloride was needed in the reaction.     

Stereoselective approach to potential scaffold of A-nor B-aromatic OSW-1 analogues via [4+2] cycloaddition of o-quinodimethane

A-nor B-aromatic steroidal skeleton was efficiently constructed by means of o-quinodimethane chemistry with exclusive stereoselectivity. The benzocyclobutene substrate for generation of the o-quinodimethane intermediate and subsequent [4+2] cycloaddition could be synthesized via (E)-selective Julia–Kocienski olefination and diastereoselective Grignard addition reactions. The synthesized tricyclic steroid-like compound with a trans-diol substructure would be utilized for divergent syntheses of potentially antitumor OSW-1 analogues with the truncated steroidal aglycone.     

Mechanistic and synthetic aspects of hydroboration with a simple atropisomeric ligand prepared from 1-(1′-(isoquinolyl)-2-naphthol

A novel triarylphosphite ligand has been prepared directly from both enantiomers of BINOL and a single enantiomer of 1′-(isoquinolyl)-2-naphthol. In one of the two cases cationic Rh complex proved to be reasonably effective in the asymmetric hydroboration of electron-poor styrenes. It was possible to identify binuclear reactive intermediates when the hydroboration pre-catalyst was examined in the presence of catecholborane at low temperatures.     

HPLC-MS/MS multiclass determination of steroid hormones in environmental waters after preconcentration on the carbonaceous sorbent HA-C@silica

In this study, a sensitive and multiclass method has been developed for analysis of three families of steroid hormones, i.e. progestins, oestrogens, androgens, by SPE-HPLC-ESI-MS/MS. The extraction efficiency of thermally condensed humic acids onto silica sorbent (HA-C@silica), here for the first time studied for multiclass enrichment of these sex hormones, was tested in different environmental waters (tap and river water, urban wastewater treatment plant effluent) spiked at the nanograms per litre levels (5–1000 ng L⁻¹). Quantitative adsorption was achieved using 200 mg sorbent for preconcentration of 250–1000 mL sample, at the native pH (pH = 6.5–7.7). Elution was performed by two sequential fractions (methanol followed by acetonitrile), obtaining in all the matrices investigated satisfactory recoveries (71% to 124% for river waters and 71–113% for urban wastewater treatment plant effluent) and RSDs below 15% (n = 3). The high enrichment factors (up to 4000) coupled with high-performance liquid chromatography tandem mass spectrometry quantification (MRM mode) provided low limits of detection and quantification (a few ng L⁻¹), that are suitable for environmental monitoring. Most of the analytes were detected in river water and in wastewater effluent samples (in the ng L⁻¹ concentration range), attesting their environmental diffusion. The proposed method was extended to a fourth class, Glucocorticoids, achieving good results in river samples, by the same SPE cartridge and chromatographic run.