Disila‐Galaxolide and Derivatives: Synthesis and Olfactory Characterization of Silicon‐Containing Derivatives of the Musk Odorant Galaxolide

A series of silicon‐containing derivatives of the polycyclic musk odorant galaxolide ( 4 a ) was synthesized, that is, disila‐galaxolide ((4RS,7SR)‐ 4 b /(4RS,7RS)‐ 4 b ), its methylene derivative rac‐ 9 , and its nor analogue rac‐ 10 . The tricyclic title compounds with their 7,8‐dihydro‐6,8‐disila‐6 H‐cyclopenta[g]isochromane skeleton were prepared in multistep syntheses by using a cobalt‐catalyzed [2+2+2] cycloaddition of the mono‐ yne H₂C?CHCH₂OCH₂C?CB(pin) (B(pin)=4,4,5,5‐tetramethyl‐1,3,2‐di‐ oxaborolan‐2‐yl) with the diynes H₂C?C[Si(CH₃)₂C?CH]₂ or H₂C‐ [Si(CH₃)₂C?CH]₂ as the key step. Employing [Cr(CO)₃(MeCN)₃] as an auxiliary, the disila‐galaxolide diastereomers (4RS,7SR)‐ 4 b and (4RS,7RS)‐ 4 b could be chromatographically separated through their tricarbonylchromium(0) complexes, followed by oxidative decomplexation. The identity of the title compounds and their precursors was established by elemental analyses and multinuclear NMR spectroscopic studies and in some cases additionally by crystal structure analyses. Compounds (4RS,7SR)‐ 4 b , (4RS,7RS)‐ 4 b , rac‐ 9 , and rac‐ 10 were characterized for their olfactory properties, including GC‐olfactory studies of the racemic compounds on a chiral stationary phase. As for the parent galaxolide stereoisomers 4 a , only one enantiomer of the silicon compounds (4RS,7SR)‐ 4 b , (4RS,7RS)‐ 4 b , rac‐ 9 , and rac‐ 10 , smelt upon enantioselective GC‐olfactometry, which according to the elution sequence is assumed to be also (4S)‐configured as in the case of the galaxolide stereoisomers. The disila‐analogues (4S,7R)‐ 4 b and (4S,7S)‐ 4 b were, however, about one order of magnitude less intense in terms of their odor threshold than their parent carbon compounds (4S,7R)‐ 4 a and (4S,7S)‐ 4 a . The introduction of a 7‐methylene group in disila‐galaxolide ( 4 b →rac‐ 9 ) improved the odor threshold by a factor of two. With the novel silicon‐containing galaxolide derivatives, the presumed hydrophobic bulk binding pocket of the corresponding musk receptor(s) could be characterized in more detail, which could be useful for the design of novel musk odorants with an improved environmental profile.     

From an α‐Functionalized Silicon‐Stereogenic N,O‐Silane to a Monomeric and Tetracoordinate tBuLi Adduct with Lithium‐Centered Chirality

Donor‐functionalized silanes with stereogenic silicon centers are extremely rare. A convenient stereocontrolled route to a nitrogen‐oxygen‐functionalized silicon‐chiral compound with an additional aminomethyl function is presented. This silane was directly achieved in stereochemically pure form by a simple nucleophilic substitution reaction. Owing to the unique asymmetry of this silane and the presence of three donor functions, the first monomeric butyllithium compound with lithium‐centered chirality could be isolated; the configuration was assigned by X‐ray crystallography. This [silane? tBuLi] complex undergoes an unexpected deprotonation/stereospecific substitution sequence in toluene, leading to the development of a convenient one‐pot synthesis of a functionalized silicon‐chiral benzylsilane, which proceeds with inversion of configuration and complete preservation of the stereochemical integrity at silicon.     

Silicon Nanocrystals and Silicon‐Polymer Hybrids: Synthesis,Surface Engineering,and Applications

Silicon nanocrystals (Si‐NCs) are emerging as an attractive class of quantum dots owing to the natural abundance of silicon in the Earth's crust, their low toxicity compared to many Group II–VI and III–V based quantum dots, compatibility with the existing semiconductor industry infrastructure, and their unique optoelectronic properties. Despite these favorable qualities, Si‐NCs have not received the same attention as Group II–VI and III–V quantum dots, because of their lower emission quantum yields, difficulties associated with synthesizing monodisperse particles, and oxidative instability. Recent advancements indicate the surface chemistry of Si‐NCs plays a key role in determining many of their properties. This Review summarizes new reports related to engineering Si‐NC surfaces, synthesis of Si‐NC/polymer hybrids, and their applications in sensing, diodes, catalysis, and batteries.     

Neutral Penta‐ and Hexacoordinate Silicon(IV) Complexes Containing Two Bidentate Ligands Derived from the α‐Amino Acids (S)‐Alanine, (S)‐Phenylalanine,and (S)‐tert‐Leucine

The neutral hexacoordinate silicon(IV) complex 6 (SiO₂N₄ skeleton) and the neutral pentacoordinate silicon(IV) complexes 7 – 11 (SiO₂N₂C skeletons) were synthesized from Si(NCO)₄ and RSi(NCO)₃ (R=Me, Ph), respectively. The compounds were structurally characterized by solid‐state NMR spectroscopy ( 6 – 11 ), solution NMR spectroscopy ( 6 and 10 ), and single‐crystal X‐ray diffraction ( 8 and 11 were studied as the solvates 8? CH₃CN and 11? C₅H₁₂ ? 0.5 CH₃CN, respectively). The silicon(IV) complexes 6 (octahedral Si‐coordination polyhedron) and 7 – 11 (trigonal‐bipyramidal Si‐coordination polyhedra) each contain two bidentate ligands derived from an α‐amino acid: (S)‐alanine, (S)‐phenylalanine, or (S)‐tert‐leucine. The deprotonated amino acids act as monoanionic ( 6 ) or as mono‐ and dianionic ligands ( 7 – 11 ). The experimental investigations were complemented by computational studies of the stereoisomers of 6 and 7 .     

Synthesis,Structure, and Properties of α,β‐Linked Oligothiazoles with Controlled Sequence

α,β‐Linked oligothiazoles with head‐to‐tail connectivity are presented as a new family of helical scaffolds. Combinations of palladium‐catalyzed cross‐coupling reactions at the 5‐ and 4‐positions of 2‐phenylthiazole led to the synthesis of oligo(2‐phenylthiazoles) with ortho linkages with a variety of defined sequences. The secondary structures of the α,β‐linked oligo(2‐phenylthiazoles) showed a clear dependence on their sequences. X‐ray crystallography of the trimer, tetramer, and hexamer with head‐to‐tail connection revealed the formation of a helical structure, which was stabilized by a combination of intramolecular forces, including interheteroatom (S???N), CH–π, and π–π interactions. The introduction of a chiral end‐group successfully led to the induction of chirality into the helical conformations. Programmable sequences for controlled geometries and photofunctions have been demonstrated through the manifold connection pathways in α,β‐linked oligothiazoles.     

Mixed‐Ligand Complexes of Zinc(II) with α‐Hydroxycarboxylates and Aromatic N‐N Donor Ligands: Synthesis,Crystal Structures and Effect of Weak Interactions on their Crystal Packing

Several new two‐ligand complexes of zinc(II) with the aromatic N, N‐donor ligands 2, 2′‐bipyridine or 1, 10‐phenanthroline and one of three different α‐hydroxycarboxylates (HL′) derived of the α‐hydroxycarboxylic acids (H₂L′) (2‐methyllactic, H₂mL; mandelic, H₂M or benzilic, H₂B) were prepared. The compounds of formula [Zn(HL′)₂(NN)]·nH₂O (HL′ = HM, HB) were isolated as white powders and characterized by elemental analysis, IR spectroscopy and thermogravimetric analysis. The complexes of general formula [Zn(HL′)(NN)₂](HL′)·nH₂O (HL′ = HmL, HM) and [Zn(HB)₂(NN)₂], were obtained as single crystals and were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and X‐ray diffractometry. In all cases, the zinc atom is in a distorted octahedral environment. In [Zn(HL′)(NN)₂](HL′)·nH₂O the α‐hydroxycarboxylato ligands behave as bidentate chelating monoanion and an α‐hydroxycarboxylate as counterion is also present. In [Zn(HB)₂(NN)₂], the monoanionic benzilato ligand behaves as monodentate through one oxygen atom of the carboxylate function. The effect of the classical and no‐classical hydrogen bonding and of the π‐π and C‐H…π interactions in the 3D supramolecular arrangement of these molecular complexes is analyzed.     

Synthesis,Characterization, and Reactivity of Cobalt(III)–Oxygen Complexes Bearing a Macrocyclic N‐Tetramethylated Cyclam Ligand

Mononuclear metal–dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metalloenzymes and their biomimetic compounds. In this work, a side‐on cobalt(III)–peroxo complex bearing a macrocyclic N‐tetramethylated cyclam (TMC) ligand, [Co^III(15‐TMC)(O₂)]⁺, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)–peroxo complex was cleanly converted into an end‐on cobalt(III)–hydroperoxo complex, [Co^III(15‐TMC)(OOH)]²⁺. The cobalt(III)–hydroperoxo complex was further converted to [Co^III(15‐TMC‐CH₂‐O)]²⁺ by hydroxylation of a methyl group of the 15‐TMC ligand. Kinetic studies and ¹⁸O‐labeling experiments proposed that the aliphatic hydroxylation occurred via a Co^IV–oxo (or Co^III–oxyl) species, which was formed by O? O bond homolysis of the cobalt(III)–hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mononuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands.     

1‐hydroxy‐1,1‐bis(H‐phosphinates): Synthesis,stability, and sorption properties

A synthesis of 1‐hydroxy‐1,1‐bis(H‐phosphinates) from acylchlorides is described. Solid‐state structures of two bis(phosphinates) determined by X‐ray diffraction showed variations in the P C distances. The compounds show negligible sorption on hydroxyapatite and an intermediate chemical stability in aqueous solution. The hydrolysis occurs in acidic as well as alkaline media. Hydrolysis rates of four derivatives show the lowest stability for aromatic derivatives as a result of the electron‐withdrawing effect. Main products of hydrolysis are 1‐hydroxy‐(H‐phosphinates) and phosphorous acid. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:195–201, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21003     

Novel arylpyridine‐based 1,3,4‐oxadiazoles: Synthesis,antibacterial, and anti‐inflammatory evaluation

In view of developing novel bioactive compounds, a series of 2‐(5‐[2‐methyl‐6‐arylpyridin‐3‐yl]‐1,3,4‐oxadiazol‐2‐ylthio)‐1‐arylethanones (6a–n) were designed and synthesized in good yield. Novel compounds were evaluated for their antibacterial and anti‐inflammatory activities. All synthesized compounds were screened for their antibacterial activity against Staphylococcus aureus, Bascillus subtilis, Eschericia coli, and Pseudomonas aeruginosa strains. Compounds 6a , 6b , 6c , 6h , and 6i displayed the highest antibacterial activity with minimal inhibitory concentration (MIC) values ranging from 6.25–12.5 μg/mL in comparison with the standard Ciprofloxacin. The results of anti‐inflammatory activity of carrageenan‐induced footpad edema assay indicated that tested compounds exhibited remarkable anti‐inflammatory activity with percentage of inhibition of 63.9–70.1% (potency 96.8–106.20% of indomethacin activity) after 3 hr. Particularly, 6c – e and 6j – l were found to be excellent inhibitors of inflammation, with potential higher than that of the standard, Indomethacin.     

Novel Ladder π‐Conjugated Materials—Sila‐Pentathienoacenes: Synthesis,Structure, and Electronic Properties

A novel series of ladder π‐conjugated materials—sila‐pentathienoacenes ( Si‐PTA ) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on molecular packing. A densely packed structure with an interfacial distance of about 3.66 Å between the adjacent molecules is observed for the compound with shorter alkyl chains. However, a large interfacial distance (7.99 Å) is obtained for another compound because of the insertion of long alkyl chains between two planes. The investigation of the optical and electrochemical properties shows that the silylene bridge incorporated into the pentathienoacene framework exerts a clear effect on the electronic properties by the σ*–π* conjugation. Although only a slight enhancement is observed for the HOMO levels, with respect to that of pentathienoacene, the LUMO levels are significantly lowered. The observed electronic properties are consistent with the theoretical calculations.     

Supramolecular Structures with the 2‐Propyl‐4,5‐dicarboxy‐1H‐imidazole Ligand: Hydrothermal Synthesis,Structures, and Photoluminescence

Self‐assembly of the rigid organic ligand 2‐propyl‐4,5‐dicarboxy‐1H‐imidazole ( L ) with different metal ions (Zn²⁺, Ni²⁺, Cu²⁺, Cd²⁺) led to four new complexes, namely, [M( L )(phen)] [M = Zn ( 1 ); Ni ( 2 ); Cd ( 3 )] and [Cu( L )( 4 )] (phen = 1,10‐phenanthroline). Their structures were determined by single‐crystal X‐ray diffraction analyses, and they were further characterized by elemental analysis, IR spectroscopy, and thermogravimetric analysis. Whereas compounds 1 , 2 , and 3 are discrete units, hydrogen‐bonding interactions play a vital role in these complexes. Compounds 1 and 2 form one‐dimensional (1D) and two‐dimensional (2D) structures through hydrogen‐bondinginteractions with helical character. In 1 , the hydrogen bonds (O–H ··· O) alternately bridge the M^II cations of the discrete units to form a one‐dimensional (1D) infinite helical chain. Complex 2 forms a 2D helical layer through parallel hydrogen bonds (N/O–H ··· O/N) between two adjacent helical chains. In 3 , the hydrogen bonds (N–H ··· O) connect adjacent discrete units into a ten‐membered ring with extension into a one‐dimensional double‐chain supramolecular structure. Complex 4 is a two‐dimensional gridlike (4,4) topological layer which is extended to a 3D network by hydrogen bonding. The solid‐state fluorescence spectrum of complex 3 was determined.     

An Alternative Method for the Preparation of Diphenylboron Chelates. The Crystal and Molecular Structures of (Pyridine‐2‐acetyloximato)diphenylboron and (1‐Phenylazo‐2‐naphtholato)diphenylboron

A convenient method for the preparation of diphenylboron chelates from ammonium tetraphenylborate is described. A variety of five‐ or six‐membered O,O‐, N,O‐ and N,N‐chelates were obtained in yields from 60 to 90 %. The isolated compounds were characterized by elemental analysis, IR spectroscopy and multinuclear magnetic resonance spectroscopy (¹H, ¹³C, and ¹¹B). The crystal and molecular structures of (pyridine‐2‐acetyloximato)diphenylboron and (1‐phenylazo‐2‐naphtholato)diphenylboron were determined by X‐ray diffraction on single crystals.     

Synthesis and Cytotoxic Activity of 1‐{3‐[1‐(5‐Organylsilylfuran‐2‐yl)silinan‐1‐yl]propyl}amines and Some Trimethylgermyl Analogues

New highly cytotoxic 1‐{3‐[1‐(5‐organylsilyl‐furan‐2‐yl)silinan‐1‐yl]propyl}amines and some trimethylgermyl analogues (IC₅₀ 1–7 μg mL^?1) have been synthesized by a hydrosilylation reaction of aliphatic and heterocyclic N‐allylamines in the presence of Speier’s catalyst. The effects of the silacycle, the element‐organic substituent in position 5 of the furan ring, and the structure of the amine on the cytotoxicity of the new compounds have been studied.     

Evidence of Native Metal–S2−–Metallothionein Complexes Confirmed by the Analysis of Cup1 Divalent‐Metal‐Ion Binding Properties

It has previously been shown that recombinant synthesis, under metal‐supplemented conditions, of diverse metallothioneins (MTs) results in the recovery of a subpopulation of S^2?‐containing complexes in addition to the S^2?‐devoid canonical metal–MT species. Further significance of this finding has remained veiled by the possibility of it being a mere consequence of synthesis in a heterologous bacterial system. Herein, we present definitive evidence that S^2? ligands are also constituents of native metal–MT complexes. Because, although practically universal, the highest S^2? content is incorporated by copper‐thioneins when coordinating divalent metal ions, we adapted the Saccharomyces cerevisiae Cup1 protein, which is the most paradigmatic copper‐thionein, as an experimental model. Most significantly, native Cd–Cup1 complexes were purified and fully spectroscopically and spectrometrically characterized from the 301N mutant yeast strain, which allows Cup1 synthesis even in the absence of copper. These results undoubtedly revealed the presence of a Cd–S^2?–Cup1 species in native preparations, which were only recovered when carefully avoiding the use of ion‐exchange chromatography in the purification protocol. Furthermore, complete analysis of recombinant (Escherichia coli) Zn–Cup1, Cd–Cup1, and Cu–Cup1 and those complexes that result from Zn/Cd and Zn/Cu replacements in vitro and acidification/renaturalization processes yielded a comprehensive and comparative overview of the metal‐binding abilities of Cup1. Overall, we consider the main conclusions of this study to go beyond the mere study of the particular Cup1 MT, so that they should be considered to delineate a new point of view on the interaction between copper‐thioneins and divalent metal ions, still an unexplored aspect in MT research.     

Stereoselective Synthesis of α‐3‐Deoxy‐D‐manno‐oct‐2‐ulosonic Acid (α‐Kdo) Glycosides Using 5,7‐O‐Di‐tert‐butylsilylene‐Protected Kdo Ethyl Thioglycoside Donors

An efficient methodology for the synthesis of α‐Kdo glycosidic bonds has been developed with 5,7‐O‐di‐tert‐butylsilylene (DTBS) protected Kdo ethyl thioglycosides as glycosyl donors. The approach permits a wide scope of acceptors to be used, thus affording biologically significant Kdo glycosides in good to excellent chemical yields with complete α‐selectivity. The synthetic utility of an orthogonally protected Kdo donor has been demonstrated by concise preparation of two α‐Kdo‐containing oligosaccharides.     

Photoinduced Reactions of cis,trans,cis‐[PtIV(N3)2(OH)2(NH3)2] with 1‐Methylimidazole

Lighting up new platinum anticancer complexes : Photoactivation of a platinum(IV) diazido anticancer complex in the presence of a derivative of imidazole, an important constituent of biomolecules, gives surprising photoproducts, including a tetrakis imidazole platinum(II) adduct (see figure), together with free azide, dioxygen and ammonia.