Synthesis and Spectroscopic Studies of Arylethynylsilanes

A variety of arylethynylsilanes (Ar‐C?C? C₆H₄? C?C)_nSiMe_4?n were prepared successfully by reaction of the corresponding chlorosilanes Me_4?nSiCl_n with Ar? C?C? C₆H₄? C?CM (M=Li, MgBr), which was prepared by treatment of ethynyl(diarylethyne)s Ar? C?C? C₆H₄? C?CH with BuLi or MeMgBr. The ethynyl(diarylethyne)s were readily prepared in good yields by the double‐elimination method: addition of lithium hexamethyldisilazide to a mixture of ArCH₂SO₂Ph, TMS? C?C? C₆H₄? CHO, and ClP(O)(OEt)₂, followed by desilylation. In the tetrakis(arylethynyl)silanes (Ar? C?C? C₆H₄? C?C)₄Si thus prepared, through‐space conjugation of four triple bonds on the silicon atom emerges as a result of participation of the silicon orbitals in the acetylenic π orbitals. This participation enhances the emissive quantum yields of arylethynylsilanes with an increase in the number of arylethynyl moieties on silicon: quantum yields of emission (Φ_F) of 0.72 for (MeOC₆H₄? C?C? C₆H₄? C?C)₄Si, 0.53 for (MeOC₆H₄? C?C? C₆H₄? C?C)₂SiMe₂, and 0.47 for MeO‐C₆H₄? C?C? C₆H₄? C?CSiMe₃ were obtained. Although this enhancement effect was also observed in the phenylethynylarylsilane (MeOC₆H₄? C?C? C₆H₄)₂SiMe₂, the bis(arylethynyl)disilane (MeOC₆H₄? C?C? C₆H₄? C?C‐SiMe₂)₂ exhibited non‐enhanced emission.     

Self‐Alignment of Low‐Valent Octanuclear Palladium Atoms

A linear tetraphosphine, meso‐bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) was used to synthesize linear octapalladium‐extended metal atom chains as discrete molecules of [Pd₈(μ‐dpmppm)₄](BF₄)₄ ( 1 ) and [Pd₈(μ‐dpmppm)₄L₂](BF₄)₄ (L=2,6‐xylyl isocyanide (XylNC; 2 ), acetonitrile ( 3 ), and N,N‐dimethylformamide (dmf; 4 )), which are stable in the solution states and show interesting temperature‐dependent photochemical properties in the near IR region. Variable temperature NMR studies demonstrated that at higher temperature T≈140 °C the Pd₈ chains were dissociated into Pd₄ fragments, which were thermodynamically self‐aligned to restore the Pd₈ chains at lower temperature T<60 °C. The coldspray ionization mass spectra suggested a possibility for further aggregation of the linear tetrapalladium units.     

Photoinduced addition and addition–elimination reactions of perfluoroalkyl iodides to electron-deficient olefins

Photoinduced radical perfluoroalkylation of various simple electron-deficient olefins was achieved in the presence of an aqueous Na₂S₂O₃ solution. The reactions proceeded smoothly to give addition or addition–elimination products. The ability of the products to be used as radical precursors or Michael acceptors was also demonstrated.     

(E)‐,(Z)‐Parallel Preparative Methods for Stereodefined β,β‐Diaryl‐ and α,β‐Diaryl‐α,β‐unsaturated Esters: Application to the Stereocomplementary Concise Synthesis of Zimelidine

Parallel and practical methods for the preparation of both (E)‐ and (Z)‐β‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 1 and (E)‐ and (Z)‐α‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 2 are described. These methods involve accessible, robust, stereocomplementary N‐methylimidazole (NMI)‐mediated enol tosylations (14 examples, 70–99 % yield), as well as stereoretentive Suzuki–Miyaura cross‐couplings (36 examples, 64–99 % yield). The highlighted feature of the present protocol is the use of parallel and stereocomplementary approaches to obtain highly (E)‐ and (Z)‐pure products 1 and 2 by utilizing sequential enol tosylations and cross‐coupling reactions. An expeditious and parallel synthesis of (E)‐ and (Z)‐zimelidine ( 3 ), which is a highly representative selective serotonin reuptake inhibitor (SSRI), was performed by utilizing the present methods.     

Catalytic asymmetric desymmetrization of meso-diamide derivatives through enantioselective N-allylation with a chiral pi-allyl Pd catalyst: improvement and reversal of the enantioselectivity

In the presence of the Trost ligands-Pd catalysts, N-monoallylation of bis(2,4,6-triisopropylbenzne)sulfonylamides derived from meso-1,2-diamines proceeds with good to excellent enantioselectivity (85-96% ee) to give asymmetric desymmetrization products. Under the same conditions, in the reaction with meso-bistolunesulfonylamide derivatives, reversal of the enantioselectivity is observed.     

Thiocyanate hydrolase is a cobalt-containing metalloenzyme with a cysteine-sulfinic acid ligand

Thiocyanate hydrolase (SCNase) purified from Thiobacillus thioparus THI115 hydrolyzes thiocyanate to carbonyl sulfide and ammonia. DNA sequences of the cloned genes revealed the close relation of SCNase to nitrile hydratase (NHase). The consensus sequences for coordination of the metal ion found in NHases were also conserved in the gamma subunit of SCNase. Here, we showed that the SCNase contained one cobalt atom per alphabetagamma heterotrimer. UV-vis absorption spectrum suggested that the cobalt exists as a non-corrin ion. Reduced SCNase showed an ESR signal characteristic of low-spin Co2+, which closely resembled that of the Co-type NHases. Mass spectrometry for the peptide fragment containing the metal-binding motif of the SCNase gamma subunit indicated that the cysteine residue at position 131 was post-translationally oxidized to a cysteine-sulfinic acid. From these results, we concluded that SCNases and NHases form a novel non-corrin and/or non-heme protein family having post-translationally modified cysteine ligands.     

New efficient organic activators for highly enantioselective reduction of aromatic ketones by trichlorosilane

[reaction: see text] Aryl ketones were reduced to the corresponding alcohols with excellent enantioselectivity (up to 99.7% ee) by Cl3SiH in the presence of a catalytic amount of N-formyl-alpha'-(2,4,6-triethylphenyl)-L-proline as an activator. Both carboxyl group at the alpha-position of the activator and 2,4,6-triethylphenyl group at the alpha'-position were critical for the high enantioselectivity.     

Synthesis of Glycocinnasperimicin D

The first total synthesis of amino sugar antibiotic glycocinnasperimicin D ( 1 ) has been achieved by a convergent, three‐component coupling strategy. The key steps involve the Heck–Mizoroki reaction by using the iodophenyl glycoside 50 and acryl amide 32 to furnish the right core structure of 1 , and the construction of the urea glycoside employing the reaction of glycosyl isocyanate 8 with amino sugar 9 . Glycosyl isocyanate 8 was prepared by the oxidation of isonitrile 10 , which displayed excellent reactivity in the coupling event. Synthetic roadblocks, encountered during this synthetic effort, have led to the development of the α‐selective, Lewis acid catalyzed phenyl glycosylation process with 2‐amino‐hexopyranose and a procedure for acetonide deprotection without affecting the silyl ethers.     

MALDI-Q-TOF mass spectrometric determination of gold and platinum in tissues using their diethyldithiocarbamate chelate complexes

A rapid determination method is presented for gold (Au³⁺) and platinum (Pt⁴⁺) in tissues using matrix-assisted laser desorption ionization quadrupole time-of-flight mass spectrometry (MALDI-Q-TOF-MS). Au and Pt ions in wet-ashed tissue solution were reacted with diethyldithiocarbamate (DDC), and the resulting chelate complex ions Au(DDC)₂ ⁺ and Pt(DDC)₃ ⁺ were detected by MALDI-Q-TOF-MS using α-cyano-4-hydroxycinnamic acid as a matrix. The limit of detection (LOD) was 0.8 ng/g tissue and the quantification range was 2–400 ng/g for Au, and the LOD was 6 ng/g tissue and the quantification range was 20–4,000 ng/g for Pt. The Pt levels detected by MALDI-Q-TOF-MS in several tissues of a patient overdosed with cisplatin were nearly the same as those detected by flow-injection electrospray ionization mass spectrometry. The LODs of Au and Pt were 0.04 pg per well (sample spot) and 0.3 pg per well, respectively. To our knowledge, this is the first attempt to quantify Au³⁺ and Pt⁴⁺ ions in tissues by MALDI-Q-TOF-MS.