Chemistry and Biology of the Zaragozic Acids (Squalestatins)

New natural products seldom arouse much excitement. However, with their unprecedented and heavily oxygenated molecular structure, and potentially lucrative biological activity, the zaragozic acids (squalestatins) provoked a flurry of activity among academic and industrial chemists and biologists in the early 1990s. Since they are powerful inhibitors of squalene synthase, the enzyme catalyzing the first committed step on the biosynthetic pathway to cholesterol, hopes were high that the zaragozic acids would follow the huge commercial success of the mevinic acids by becoming second-generation cholesterol-lowering drugs. The unusual and characteristic 2,8-dioxabicyclo[3.2.1]octane-3,4,5-tricarboxylic acid “core” structure of the zaragozic acids stimulated a large number of diverse synthetic studies, ranging from the traditional to the avant garde. In this review we attempt to bring together for the first time the chemistry and biology of this fascinating class of molecules.     

Photooxygenation of pyrazin-2(1h)-ones

1-Alkyl-5,6-diphenylpyra2in-2(1H)-ones (1a-b) reacted with singlet oxygen in dichloromethane to afford the stable endoperoxide (1a-b), while in methanol to afford the 1:1-adduct (3a-b) of the endoperoxide (2a-b) and methanol.     

N-m-Tolyl-o-Methoxybenzohydroxamic Acid (m-T-o-MBHA) as a Specific Reagent for Vanadium

Abstract

A high selective and sensitive spectrophotometric method is described for the determination of traces of vanadium(V) using N-m-tolyl-o-methoxybenzohydroxamic acid. The violet complex extracted into chloroform (λ_max = 545 nm) is stable for several days. As little as 0. 05 μg of vanadium is detectable.     

On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H₂-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.     

烟草烘丝尾气收集液分级装置构建与评价

本文构建了一种基于FLASH色谱技术的烟草烘丝尾气收集液的分级装置。该装置采用阳离子交换柱、阴离子交换柱和大孔吸附树脂柱串联的方法分级烟草烘丝尾气收集液,优化分离条件,结合气相色谱/质谱(GC/MS)分析对烟草烘丝尾气收集液分级装置进行评价。结果显示,烟碱吸附于732型的阳离子交换树脂中,而717型阴离子交换树脂和AB-8型大孔吸附树脂富集了乙酰基吡咯、二氢猕猴桃内酯、β-二氢大马酮等烟草中的多种致香成分。     

Furan derivatives of group V elements (review)

Methods of synthesis, physical properties, chemical transformations, and biological activity data for the furan derivatives of phosphorus, arsenic, and antimony are reviewed.Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–632. May, 1996. Original article submitted February 21, 1996.     

Furan derivatives of group VIII elements (review)

Methods for the synthesis of the furan derivatives of iron, cobalt, nickel, rhodium, palladium, osmium, iridium, and platinum and their physicochemical and chemical properties are reviewed.Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 154–179, February, 1997.     

Furan derivatives of group VI elements (review)

Methods of synthesis and the physical and chemical properties of the furan derivatives of selenium, tellurium, chromium, molybdenum, and tungsten are reviewed.Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 867–895, July, 1996. Original article submitted March 6, 1996.     

Furan derivatives of group VII elements (review)

Methods for the synthesis of the furan derivatives of manganese and their chemical properties are reviewed.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 151–153, February, 1997.     

Furan derivatives of group IV elements (review)

Published data and the results of personal investigations on the methods of synthesis, chemical and physical properties, and biological activity of the furan derivatives of silicon, germanium, tin, lead, titanium, and zirconium are summarized.Latvian Institute of Organic Synthesis, Riga, Latvia, Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1587–1690, December, 1995 Original article submitted June 3, 1995.     

Furan derivatives of group I elements (review)

Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsikiicheskikh Soedinenii, No. 4, pp. 435–473, April, 1995. Original article submitted February 22, 1995.     

Core Halogenation as a Construction Principle in Tuning the Material Properties of Tetraazaperopyrenes

A detailed study on the effects of core halogenation of tetraazaperopyrene (TAPP) derivatives is presented. Its impact on the solid structure, as well as the photophysical and electrochemical properties, has been probed by the means of X‐ray crystallography, UV/Vis and fluorescence spectroscopy, high‐resolution electron energy loss spectroscopy (HREELS), cyclic voltammetry (CV), and DFT modeling. The aim was to assess the potential of this approach as a construction principle for organic electron‐conducting materials of the type studied in this work. Although halogenation leads to a stabilization of the LUMOs compared to the unsubstituted parent compound, the nature of the halide barely affects the LUMO energy while strongly influencing the HOMO energies. In terms of band‐gap engineering, it was demonstrated that the HOMO–LUMO gap is decreased by substitution of the TAPP core with halides, the effect being found to be most pronounced for the iodinated derivative. The performance of the recently reported core‐fluorinated and core‐iodinated TAPP derivatives in organic thin‐film transistors (TFTs) was investigated on both a glass substrate, as well as on a flexible plastic substrate (PEN). Field‐effect mobilities of up to 0.17 cm² Vs^?1 and on/off current ratio of >10⁶ were established.     

Malonylation/Decarbalkoxylation of Furan Derivatives as Key Steps for the Preparation of Nonactic Acid Derivatives. Part II [1]

A malonylation/decarbalkoxylation sequence from 2-substituted furans was investigated in view of developing a scalable synthesis of hydrophobic nonactic acid analogues.     

Malonylation/Decarbalkoxylation of Furan Derivatives as Key Steps for the Preparation of Nonactic Acid Derivatives. Part II [1]

Summary. A malonylation/decarbalkoxylation sequence from 2-substituted furans was investigated in view of developing a scalable synthesis of hydrophobic nonactic acid analogues.