Chiral pool based synthesis of pyrrolidinium ionic liquids

Chiral ionic liquids show promising applications in various different fields. A series of pyrrolidinium-based chiral ionic liquids bearing a chiral cation, a chiral anion or both was prepared in good yields using an efficient, economic and simple pathway. The chirality was introduced using (l)-lactate and (l)-menthol derivatives. The resultant chiral compounds were characterized by both spectroscopy and polarimetry. We envision that these new chiral compounds can serve as effective reaction media and chiral catalysts for asymmetric reactions, which are presently being investigated in our lab.     

Separation techniques for biotechnology in the 1990s.

Scientists are constantly looking for better and cheaper separation techniques to replace or complement the current technology. Over the past few decades, and in particular the last 10 years, new separation techniques or modifications of existing techniques have become available for separating compounds from complex sample matrices. There are many areas, however, where the separation technology is not sufficient to achieve high purity and yield while remaining cost effective. In the area of biotechnology, separation techniques are urgently needed to meet demands for ultra-high purity and yield. Thus, a variety of techniques are being developed to address these needs. Generally, biological compounds for the pharmaceutical and biotechnology industries must be obtained at greater than 99.9% purity (sometimes greater than 99.99%) while maintaining high yield. In any area of chemistry this degree of purity would cause problems; in biotechnology it is even more difficult to achieve because of the complex sample matrices. In addition, the compounds of interest may be very similar to impurities or contaminants in the sample matrix, and the compounds could be denatured (or even destroyed) by certain solvents and/or high temperature. In particular, three areas of biotechnology have presented scientists with problems in separations: cell separations, DNA-RNA separations, and protein-peptide separations. The current technology available and possible future trends in these areas are discussed, and also problems to be solved in the future.     

N-Heterocyclic carbene–carbodiimide (NHC–CDI) betaine adducts: synthesis,characterization, properties,and applications

N-Heterocyclic carbenes (NHCs) are an important class of reactive organic molecules used as ligands, organocatalysts, and σ-donors in a variety of electroneutral ylide or betaine adducts with main-group compounds. An emerging class of betaine adducts made from the reaction of NHCs with carbodiimides (CDIs) form zwitterionic amidinate-like structures with tunable properties based on the highly modular NHC and CDI scaffolds. The adduct stability is controlled by the substituents on the CDI nitrogens, while the NHC substituents greatly affect the configuration of the adduct in the solid state. This Perspective is intended as a primer to these adducts, touching on their history, synthesis, characterization, and general properties. Despite the infancy of the field, NHC–CDI adducts have been applied as amidinate-type ligands for transition metals and nanoparticles, as junctions in zwitterionic polymers, and to stabilize distonic radical cations. These applications and potential future directions are discussed.

N-heterocyclic carbene-carbodiimide betaine adducts are zwitterionic amidinate-like structures with tunable properties that have applications as ligands, junctions in supramolecular polymers, and stabilizers for radical cations.     

Ladderane Natural Products: From the Ground Up

The ladderane family of natural products are well known for their linearly concatenated cyclobutane skeletal structure. Owing to their unique carbocyclic framework, several chemical syntheses have been reported since their discovery in 2002. The focus of this review is to showcase the novel tactics that have been used to generate the ladderane core and the challenges that are associated with the synthesis of these unusual and complex natural products.     

A computational study of substituent effects on the stability and geometry of carbazole‐pyridine complexes

Hydrogen bonding between carbazole and pyridine is known to quench fluorescence emission of carbazole. Three carbazolopyridinophanes—compounds composed of carbazole and pyridine subunits such that an intramolecular hydrogen bond may exist between them—have been pursued as reversible fluorescent sensors that detect given analytes through fluorescence restoration. However, these sensors exhibit background fluorescence believed to be related to the proportion of non‐hydrogen‐bonded conformers present. In this computational investigation, the potential energy surfaces of various hydrogen‐bonded carbazole:pyridine complexes are investigated using density functional theory with the intent of explaining the observed background fluorescence for the carbazolopyridinophanes. The results indicate carbazolopyridinophane conformers most resembling the geometry of their corresponding free carbazole:pyridine complexes exhibit the least background fluorescence.     

Liquid chromatography–mass spectrometry applications for quantification of endogenous sex hormones

Liquid chromatography, coupled with tandem mass spectrometry, presents a powerful tool for the quantification of the sex steroid hormones 17‐β estradiol, progesterone and testosterone from biological matrices. The importance of accurate quantification with these hormones, even at endogenous levels, has evolved with our understanding of the role these regulators play in human development, fertility and disease risk and manifestation. Routine monitoring of these analytes can be accomplished by immunoassay techniques, which face limitations on specificity and sensitivity, or using gas chromatography–mass spectrometry. LC–MS/MS is growing in capability and acceptance for clinically relevant quantification of sex steroid hormones in biological matrices and is able to overcome many of the limitations of immunoassays. Analyte specificity has improved through the use of novel derivatizing agents, and sensitivity has been refined through the use of high‐resolution chromatography and mass spectrometric technology. This review highlights these innovations, among others, in LC–MS/MS steroid hormone analysis captured in the literature over the last decade.     

Linkage isomerism in 5-exo thiocyanate and isothiocyanate substituted tricarbonyl(η-cyclohexa-1,3-diene)iron and tricarbonyl(η-cyclohepta-1,3-diene)iron

Nucleophilic addition to the tricarbonyl(η-cyclohexadienyl)iron cation and the tricarbonyl(η-cycloheptadienyl)iron cation by the thiocyanate ion forms initially the 5-exo-isothiocyanate (NCS) isomers, C₆H₇NCSFe(CO)₃ and C₇H₉NCSFe(CO)₃, both of which isomerise to the corresponding 5-exo thiocyanate isomers C₆H₇SCNFe(CO)₃ and C₇H₉SCNFe(CO)₃ on exposure to air.     

Synthesis of 2-amino-6-chloro- and 2,6-diammopunne 3-oxides

N-Oxidation of 2-amino-6-chloropurine to the 3-oxide provided a convenient intermediate for the synthesis of 2-amino-6-substituted purine 3-oxides, including the previously unavailable 2,6-diaminopurine 3-oxide. Thiation of the 6-halogen was accompanied by reduction of the N-oxide. The properties of the 1- and 3-oxides of 2,6-diaminopurine are compared.     

Syntheses totales et etudes de lignanes biologiquement actifs—I : Application de la reaction d'ullmann a la synthese de biaryles precurseurs de lignanes bisbenzocyclooctadienes

Several biaryls bearing various substituents on both rings were synthesized in a preparative fashion, and in yields up to 88% by a technical improvement on the classical Ullmann reaction. All these biaryls bear reactive functional groups (i.e. formyl, methoxycarbonyl, dimethoxycarbonylpropyl and butanolidylmethyl) in both the o and o′ positions. The biaryls 9, 13, 21 and 26–33 are plausible synthons for bisbenzocyclooctadiene lignans such as schizandrin and steganacin.