Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

Efficient, mild, parallel and purification-free synthesis of aryl ethers via the Mitsunobu reaction

A wide range of commercial diazodicarboxylates and phosphines were screened in an attempt to find purification-free conditions for application in parallel synthesis. The combination of immobilized triphenylphosphine and TMAD proved to be suitable for the synthesis of aryl ethers via the Mitsunobu reaction. Nine ethers were synthesized in good yield and excellent purity, the purification being limited to a filtration step.     

Chemical and electrochemical oxidative coupling of N,N-dialkyl-p-phenylenediamines and arylsulfinic acids. Synthesis of sulfonamide derivatives

Electrochemical and chemical oxidation of N,N-dialkyl-p-phenylenediamines have been studied in the presence of arylsulfinic acids as nucleophiles in aqueous solutions for the synthesis of sulfonamide derivatives. The results indicate that the electrochemically or chemically generated quinone-diimines participate in Michael-type addition reactions with arylsulfinic acids and are converted into the corresponding sulfonamide derivatives.     

Truncated diastereoselective Passerini reaction, a rapid construction of polysubstituted oxazole and peptides having an α-hydroxy-β-amino acid component

The reaction of aldehydes and ketones, including aliphatic and aromatic ones, with amides of α-isocyano-β-phenylpropionic acid in toluene in the presence of lithium bromide gives 2,4,5-trisubstituted oxazoles in good to excellent yield. Protected chiral α-amino aldehydes participate in this reaction to give, after hydrolysis of the oxazoles, norstatine-containing peptides in good overall yield. The nucleophilic addition of isonitriles to N,N-dibenzylphenylalanal is investigated for the first time and is found to be stereoselective leading predominantly to the anti-adduct (dr=9/1). On the other hand, the reaction between the N-Boc phenylalanal and isonitrile is non-stereoselective.     

Synthesis and characterization of a tetraruthenium butterfly cluster containing a quadruply-bridging ligand derived from an N,N′-dipyrid-2-ylurea

The tetraruthenium cluster complex [Ru₄(μ₄-κ⁴-dmpu)(CO)₁₀], H₂dmpu = N,N′-bis(6-methylpyrid-2-yl)urea, has been prepared by treating [Ru₃(CO)₁₂] with H₂dmpu in toluene at reflux temperature. An X-ray diffraction study has determined that this cluster has a butterfly metallic skeleton hold up by a doubly-deprotonated N,N′-bis(6-methylpyrid-2-yl)urea ligand (dmpu). This ligand has the pyridine N atoms attached to the wing-tip Ru atoms and the amido N atoms spanning Ru-Ru wing-edges, in such a way that the cluster has C₂ symmetry. The donor atoms of doubly-deprotonated N,N′-dipyrid-2-ylureas seem to be appropriately arranged to hold butterfly tetranuclear clusters.     

Synthesis of new heteroaromatic systems: Naphth[2,1-e]imidazo[5,1-c]-1,2,4-triazines and benz[e]imidazo-[5,1-c]-1,2,4-triazines

Cyclization of azo compounds, synthesized from 5-diazoimidazoles and 2-naphthol or p-substituted phenols, into naphth[2,1-e]imidazo[5,1-c]-1,2,4-triazines and benz[e]imidazo[5,1-c]-1,2,4-triazines occurs only in the presence of p-toluenesulfonic acid. Imidazo[4,5-d]-1,2,3-triazines are also formed in this reaction when an amide substituent is present in the imidazole ring.Ural State Technical University, Ekaterinburg 620002, Russia: e-mail: mokr@htf.ustu.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 540–546, April, 2000.     

Segment Coupling to a Highly Hindered N-Terminal, Alamethicin-Related alpha-Aminoisobutyric Acid (Aib) Residue

A model [6+5] segment coupling process involving a C-terminal valine hexapeptide acid and a resin-attached pentapeptide amide, which N-terminated in a hindered Aib unit, was examined using a variety of HOAt-derived coupling reagents. Best results were observed with N-HAPyU in DCM solvent in which loss of configuration amounted to 5.8%.     

Synthesis of a useful anomeric thioacetate of an N-acetyllactosamine derivative and its application

A novel anomeric β-thioacetate of an N-acetyllactosamine derivative was efficiently synthesized in high yield from the known 2-azido glycosyl chloride using thioacetic acid as a convenient reagent. The synthesis involved not only an S_N2 replacement of the chloride by a carbothiolate anion but also a reductive acetamidation of the azide group. Applications of the thioacetate for glycosidation were demonstrated to provide both O- and S-glycosides in high yields. Furthermore, both intermediates gave a new class of glycoclusters that included thioglycosidic linkages.     

Advantages of using a modified orthogonal sampling configuration originally designed for LC-ESI-MS to couple CE and MS for the determination of antioxidant phenolic compounds found in virgin olive oil

A ThermoFinnigan sheath liquid flow capillary electrophoresis-mass spectrometry system designed for coupling via a co-axial interface was coupled through an adapted via an alternative, commercially available interface for orthogonal sampling. The affordable, reversible structural alterations made in the commercial LC-MS interface resulted in improved analytical performance.The results of a conventional capillary electrophoresis (CE) method using a commercial co-axial source to determine antioxidant phenolic acids present in virgin olive oil, were compared with those obtained by using a modified orthogonal sampling position. In both cases, separations were done using a 10 mM ammonium acetate/ammonium hydroxide buffer solution at pH 10.0 and a constant applied voltage of 25 kV. The operating variables for the mass spectrometry interface were re-optimized for the modified orthogonal orientation. This allowed the sheath liquid, sheath gas flow rates and capillary voltage to be lowered with respect to the co-axial coupling configuration. In addition, the orthogonal sampling position provided a higher selectivity by effect of ion sampling excluding larger droplets—with an increased momentum along the axis—which were drained through the sink at the bottom of the ion source. Also, the new configuration facilitated sample ionization, improved electrospray stability and led to stronger signals as a result.The new system was validated in terms of precision (repeatability), linearity, and limits of detection and quantification. A comparison of the validation data with the results previously obtained by using a commercial co-axial configuration revealed the adapted orthogonal sampling position to provide better repeatability in both migration times and relative peak areas (<1% and 7% respectively with n = 15 replicates), a good linear range (with levels in the microgram-per-litre region) and lower limits of detection—especially for the compounds detected with the lowest sensitivity when co-axial ESI was used, as HFA, GEN, FER and VAN finding LOD among 24-3.0 μg L⁻¹ respectively.     

Synthesis of poly(p-phenylene)s having alternating sugar and alkyl substituents by Suzuki coupling polymerization and evaluation of their main-chain conformations

This paper reports synthesis of poly(p-phenylene)s (PPPs) having alternating sugar and alkyl substituents by Suzuki coupling polymerization of a 1,4-dibromobenzene monomer having peracetylated glucose residues with a 1,4-benzene bis(boronic acid) having alkyl chains using Pd(PPh₃)₄ in a mixed solvent of THF and NaHCO₃ aq. at reflux temperature. The polymerization proceeded with the progress of frequent deacetylation, and thus, the crude product was acetylated, followed by the isolation procedures, giving the PPP having alternating peracetylated glucose and alkyl substituents. The structure of the isolated product was confirmed by the ¹H and ¹³C NMR measurements to be the desired PPP derivative. The M_n values were estimated by GPC analysis with DMF as the eluent to be 5400-12,700. The deacetylation of the polymer completely took place using sodium methoxide in methanol/THF. The conformation of the main-chain was evaluated by the CD spectrum in comparison with that of PPP only with the glucose substituents, indicating that the present PPP derivative had the flexible nature of the main-chain by introduction of the alkyl-substituted units between glucose-substituted units. The Suzuki coupling of a 1,4-dibromobenzne monomer having disaccharide substituents with the benzene bis(boronic acid) monomer was also performed under the similar conditions. The product was precipitated from the reaction mixture, which was simply isolated by filtration. The isolated polymer was purified further by reprecipitation into diethyl ether and its structure was a PPP having free disaccharide or monosaccharide residues. This indicated occurrence of complete deacetylation as well as partial degradation of the glycosidic linkages in the disaccharides during the polymerization. The main-chain of the obtained polymer had also the flexible nature. The fluorescence spectra of the obtained PPP derivatives in this study were also measured.     

Synthesis of a cholesterol-appended Tb-DTPA complex by combined removal of tert-Butyl protecting groups and complexation of terbium(III)

The Tb(III)-complex of a cholesterol-DTPA conjugate was prepared in a one-step procedure from the tert-Butyl-protected form of the ligand through reaction with TbCl₃^.6H₂O and NaI in refluxing acetonitrile. The acid-labile carbamate linker that connects the chelating DTPA moiety with the cholesterol unit of the ligand stays intact under these conditions. The combination of deprotection of the ligand with terbium complexation reduces the overall number of synthetic steps required and thus increases the efficiency and overall yield of the reaction sequence.