Synthesis of 1-substituted 2,3-dihydro-7H-oxepin-4-one from an amino acid

3,4-Dihydro-7H-oxepin-4-one system is potentially convenient starting material for the synthesis of diverse oxepane-based compounds such as peptidomimetics. We have developed a simple, five-step synthesis of 1-substituted-3,4-dihydro-7H-oxepin-4-one 11 from Boc-d-phenylalanine using a combination of statine synthesis methodology and olefin ring closing metathesis reaction.     

A new mode of cyclic carbamate formation via tert-butyldimethylsilyl carbamate. Stereoselective syntheses of statine and its analogue

Stereoselective construction of 1,2- and 1,3-amino hydroxyl systems was carried out using S_N2′ (initiated by AgF or AgF-Pd(II)) cyclic carbamate formations from tert-butyldimethyl silyl carbamates. This method was applied to the syntheses of statine and AHPPA, efficiently.     

Synthesis of macrocyclic cage compounds by diamine-dihalide one-step coupling reaction

Macropolycyclic cage compounds were synthesized by a direct reaction between diamines and bis(bromomethyl) compounds. The procedure for constructing the polycyclic cage structure is simple and straightforward. The macropolycyclic compounds obtainable from this cyclization procedure are three-dimensional cage compounds, and any other isomers were not obtained except for two examples. Benzene, pyridine, and aliphatic units could be introduced into the cage structure. The macrocycles that have strong cation affinity were obtained as their potassium complexes.     

[N]-Isotopic labeling: a suitable tool to study the reactivity of bis lactams

The unexpected reactivity of 2,5-diketopiperazines under basic conditions, thanks to N-Boc activation, allows access to valuable pharmacological scaffolds, such as original statine derivatives. Toward this transannular rearrangement of activated lactams (TRAL), we report here the study of bis lactam reactivity using [¹⁵N]-isotopic labeling.     

Simple linear asymmetrical complexes of silver(I): NC-Ag-NH3 and Br-Ag-NH3

The compounds Ag(CN)(NH(3)) and Ag(Br)(NH(3)) are remarkable in that they form solids containing the simple molecular units NC-Ag-NH(3) and Br-Ag-NH(3), rather than extended solids, and are the first examples of simple linear asymmetric complexes of silver(I).     

Rapid assay of cyclic AMP phosphodiesterase and 5'-nucleotidase by means of chromatography on cellulose-nitrate membrane strips

A simple chromatographic procedure with the use of modified cellulose-nitrate membrane strips, 80 x 40 mm, has been worked out for the rapid isotopic assay of cyclic AMP (cAMP) phosphodiesterase (EC 3.1.4.17) and 5'-AMP nucleotidase (EC 3.1.3.5) in crude extracts of various tissues from animals and plants. The assay is based on enzymatic conversion of the product to adenine, a relatively inert compound which, in contrast to cAMP and 5'-AMP, is strongly adsorbed by the cellulose-nitrate membrane. Due to this property rapid separation of adenine from the unconverted substrate (cAMP or 5'-AMP) is possible. Commercial 5'-nucleotidase and easily obtainable crude extract of adenosine nucleosidase from barley leaves are used as coupling enzymes for the phosphodiesterase assay. The assay of phosphodiesterase in 0.5-2 microliter of blood (10(-5) to 4.10(-5) units) has been demonstrated on several examples.     

meso-meso-Linked corrole dimers with modified cores: synthesis, characterization, and properties

The synthesis and characterization of the first examples of core-modified corrole dimers linked through the meso positions are described. The dimers are obtained by a simple Ag(I)- or Fe(III)-catalyzed coupling reaction in near-quantitative yields. The corroles obtained are metalated with metal ions, such as Cu(II) and Ni(II). The electronic-absorption spectral studies reveal weak electronic interaction between the two subunits and the exciton coupling observed for the free-base corrole dimer (1717 cm(-1)) is lower than that for the corresponding protonated derivative (4081 cm(-1)). The solution-state structure derived from (1)H and two-dimensional NMR spectral studies reveals a noncoplanar arrangement of two corrole units. Geometry optimization at the B3LYP-631G level also confirms the noncoplanar arrangement of corroles with a dihedral angle of 64.8 degrees between two corrole planes. The electron paramagnetic resonance (EPR) and magnetic characterization studies on the paramagnetic copper-metalated dimer indicate that both copper ions behave as independent spins without any noticeable interaction. Results of fluorescence studies reveal a bathochromic shift of about 60 nm upon dimerization. The first hyperpolarizability (beta) measured by using the hyper Rayleigh scattering (HRS) method reveals doubling of the beta values on progressing from monomer to dimer, attributed to enhanced pi conjugation. The use of copper dimers in the photocleavage of DNA is also explored. It is shown that the bimetallic copper dimer selectively cleaves the nucleic acids without affecting the proteins, suggesting a possible application of the copper complex in the removal of nucleic acid contaminants from protein extracts through a simple photolytic pathway.     

Synthetic studies of didemnins. III : Syntheses of statine and isostatine stereoisomers

The stereoselectivity of the reduction of β-keto ester precursors leading to several stereoisomers of statine and isostatine was investigated. As a result, a short and highly stereoselective route to the isomar of isostatine found in the didemnins, (3S,4R,5S)-isostaline, was devised.     

Photoswitchable mixed valence

For a molecular electronics technology to be fully serviceable, switching functions will be indispensable. Specifically, it will be desirable to control the conductivity of a given molecule using an external stimulus. This tutorial review discusses photoswitchable mixed valence systems that are comprised of a reversibly photoisomerizable bridging unit connecting two redox-active moieties, and as such represent some of the most simple chemical systems in which switching of charge delocalization can be explored. As photoisomerizable units, dithienylethenes have received much attention in the context of photoswitchable mixed valence, but there are also more exotic examples such as norbornadiene- and dimethyldihydropyrene-based switchable systems. As redox-active units responsible for the mixed valence phenomenon, both metal-containing as well as purely organic moieties have been employed. Typical investigations in this area involve the comparison of cyclic voltammograms and (near-infrared) optical absorption spectra of the two isomeric forms of a given system. The magnitude of the comproportionation constant and evaluation of intervalence absorption bands using appropriate theoretical models yield information regarding the extent of charge delocalization in the two isomeric forms. In several of the compounds investigated so far, the light stimulus induces a substantial increase of charge delocalization, or in the terminology commonly used in mixed valence chemistry, a changeover from class I to class II or even class III behavior.     

Stereoselective reduction of N-phthaloyl α-amino ketones: an expeditious synthesis of statine

A highly diastereoselective synthesis of a protected statine derivative via syn-selective LiAlH(OBu-t)₃ reduction of a leucine derived N-phthaloyl α-amino ketone is described.     

Raman spectroscopic study of pascoite Ca3V10O(28)·17H2O

Raman spectroscopy has been used to study the molecular structure of the vanadate mineral pascoite. Pascoite, rauvite and huemulite are examples of simple salts involving the decavanadate anion (V10O28)6-. Decavanadate consists of four distinct VO6 units which are reflected in Raman bands occurring at higher wavenumbers. The Raman spectrum of pascoite is characterised by two intense bands at 991 and 965 cm(-1). Raman bands are observed at 991, 965, 958 and 905 cm(-1) and originate from four distinct VO6 sites in the mineral structure. In the infrared spectra of pascoite, two wavenumber regions are observed between: (1) 837 and 860, and (2) between 803 and 833 cm(-1). These bands are assigned to ν3 antisymmetric stretching modes of (V10O28)6- or (V5O14)3- units. The spectrum is highly complex in the lower wavenumber region, and therefore the assignment of bands is difficult. Bands observed in the 404 to 458 cm(-1) region are assigned to the ν2 bending modes of (V10O28)6- or (V5O14)3- units. Raman bands observed in the 530-620 cm(-1) region are assigned to the ν4 bending modes of (V10O28)6- or (V5O14)3- units. The Raman spectra of the vanadates in the low wavenumber region are complex with multiple overlapping bands which are probably due to VO subunits and MO bonds.     

Mannich-Type Reactions of Alkylzinc Reagents

Mannich-type reactions involving alkylzinc reagents have been developed using different strategies. We show that the addition of these organometallic species to sulfonyl imines occurs upon simple heating and affords Mannich products in moderate to excellent yields (14 examples, 30–99 %). Interestingly, N-alkyl imines were also found to be suitable partners after activation as an acyliminium by acetyl chloride (12 examples, 49–86 %) or, more originally, by TMSCl (14 examples, 26–87 %). These methods proved complementary, leading to the preparation of both N-protected secondary or tertiary amines and N-unprotected secondary amines in good yields, with an increased eco-compatibility, and under simple conditions.     

Structural paradigms in macropolyhedral boranes

Macropolyhedral borane clusters are concave polyhedra constituting fused convex simple polyhedra. They are formally obtained by condensation of simple polyhedral boranes under elimination of between one and four BH(3) or isoelectronic units. The number of eliminated vertexes from simple polyhedra equals the number of shared vertexes in macropolyhedral boranes. For each of the eight classes with general formulae ranging from B(n)H(n-4) to B(n)H(n+10), more than one structure type is possible, differing in the number of shared vertexes and in the types of the two combined cluster fragments. However, only one type of "potential structures" is represented by experimentally known examples and is found to be favored by theoretical calculations. A sophisticated system exists among the favored macropolyhedral borane structures. For each class of macropolyhedral boranes, the number of skeletal electron pairs is directly related to the general formula, the number of shared vertexes and the type of fused cluster fragments. In order to predict the distribution of vertexes among the fused fragments, we propose the concept of preferred fragments. Preferred fragments are those usually present in the thermodynamically most stable structure of a given class of macropolyhedral boranes and are also frequently observed in the experimentally known structures. This allows us to completely predict the cluster framework of the thermodynamically most stable macropolyhedral borane isomers.     

Zinc (II) and AIEgens: The “Clip Approach” for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of “AIEgens” was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic–inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d¹⁰ zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016–2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.     

A Giant [8+12] Boronic Ester Cage with 48 Terminal Alkene Units in the Periphery for Postsynthetic Alkene Metathesis

Dynamic covalent chemistry (DCC) is a powerful synthetic tool to construct large defined molecules in one step from rather simple precursors. The advantage of the intrinsic dynamics of the applied reversible reaction steps is a self-correction under the chosen conditions, to achieve high yields of the target compound. To date, only a few examples are known, in which DCC was used to build up a molecular defined but larger product that was chemically transferred to a more stable congener in a second (irreversible) step. Here, we present a nanometer-sized [8+12] boronic ester cage containing 48 peripheral terminal alkene units which allows to put a hydrocarbon exoskeleton around the cage via alkene metathesis.     

Raman and infrared spectroscopy of selected vanadates

Raman and infrared spectroscopy has been used to study the structure of selected vanadates including pascoite, huemulite, barnesite, hewettite, metahewettite, hummerite. Pascoite, rauvite and huemulite are examples of simple salts involving the decavanadates anion (V10O28)6-. Decavanadate consists of four distinct VO6 units which are reflected in Raman bands at the higher wavenumbers. The Raman spectra of these minerals are characterised by two intense bands at 991 and 965 cm(-1). Four pascoite Raman bands are observed at 991, 965, 958 and 905 cm(-1) and originate from four distinct VO6 sites. The other minerals namely barnesite, hewettite, metahewettite and hummerite have similar layered structures to the decavanadates but are based upon (V5O14)3- units. Barnesite is characterised by a single Raman band at 1010 cm(-1), whilst hummerite has Raman bands at 999 and 962 cm(-1). The absence of four distinct bands indicates the overlap of the vibrational modes from two of the VO6 sites. Metarossite is characterised by a strong band at 953 cm(-1). These bands are assigned to nu1 symmetric stretching modes of (V6O16)2- units and terminal VO3 units. In the infrared spectra of these minerals, bands are observed in the 837-860 cm(-1) and in the 803-833 cm(-1) region. In some of the Raman spectra bands are observed for pascoite, hummerite and metahewettite in similar positions. These bands are assigned to nu3 antisymmetric stretching of (V10O28)6- units or (V5O14)3- units. Because of the complexity of the spectra in the low wavenumber region assignment of bands is difficult. Bands are observed in the 404-458 cm(-1) region and are assigned to the nu2 bending modes of (V10O28)6- units or (V5O14)3- units. Raman bands are observed in the 530-620 cm(-1) region and are assigned to the nu4 bending modes of (V10O28)6- units or (V5O14)3- units. The Raman spectra of the vanadates in the low wavenumber region are complex with multiple overlapping bands which are probably due to VO subunits and MO bonds.     

Unusual regioselection in the Mitsunobu reactions of syn-2,3-dihydroxy esters: synthesis of statine and its diastereomer

Mitsunobu reactions of syn-2,3-dihydroxy esters exhibit a complete regioselection for the beta-hydroxyl group. Benzoylation, azidation, and tosylation have been performed under these conditions. Beta-functionalizations of syn-2,3-dihydroxy esters are uncommon, and the Mitsunobu reactions are complementary to other diol chemistries in the regioselection. In addition, the configurational inversion accompanying the Mitsunobu protocol offers a means for diastereochemical diversity, as exemplified by a synthesis of statine and its anti diastereomer. These findings will further expand the synthetic utilities of the Sharpless AD process.     

Stereocontrolled approaches to (+)- and (−)-γ-trifluoromethyl-GABOB,a new hydroxymethylene (statine) dipeptide isostere

Two efficient approaches to both enantiomers of syn-γ-trifluoromethyl γ-amino β-hydroxy butyric acid (γ-Tfm-GABOB) (10), a new hydroxymethylene (statine) dipeptide isostere, are described. One exploits the recently disclosed `non-oxidative' Pummerer reaction, by means of which α-lithium alkyl sulfoxides are used as chiral α-hydroxyalkyl anion equivalents in the synthesis of β-amino alcohols. Trifluoropyruvaldehyde-N,S-ketal (R)-11, a novel stereochemically stable synthetic equivalent of α-amino trifluoropropanal, is used in the second approach.     

基于苹果酰亚胺的不对称合成方法学研究进展

综述了以苹果酰亚胺为手性吡咯烷(酮)合成子等效体的合成方法学研究进展。通过新建立的高度区域和立体选择性的灵活多用的不对称还原烷基化方法,可方便地合成反式-5-烷基-4-羟基-2-吡咯烷酮,进而转化为反式-2-烷基-3-羟基(胺基)吡咯烷和反侧-Υ-烷基-Υ-氨基-β-羟基酸。由此打开了通向依莫必利,茴香霉素,pyrrolamA,hapalosin的Υ-氨基酸片断和statine类似物(3S,4R)-ACHPA活化形式的多用途合成路线。