Stereospecific thermal isomerization of 2, 2-dimethylbenzocyclobutenols to 2-isopropenylphenyl alcohols

Thermolysis of the 1-alkyl-2,2-dimethylbenzocyclobutenol 3 at 160 degrees C gave the 2-isopropenylphenyl alcohol 8 through an (E)-dienol intermediate by a 1,5-sigmatropic hydrogen shift from the isopropylidene methyl group to the carbon bearing hydroxy group. In the thermolysis of each of the diastereomeric 2, 2-dimethylbenzocyclobutenols 6 and 7 which have a hydroxy group on the beta-carbon of the quaternary C(1)-alkyl substituent, the isomerization to the 2-isopropenylphenyl alcohols 10 and 11 took place stereospecifically through a twisted (E)-dienol intermediate. The configuration of the newly formed chiral center in 10 and 11 was the same as that of the ring carbon bearing hydroxy group in the starting 6 and 7.     

Synthesis and Evaluation of 2-Deoxy-2-amino-β-cellobiosides as Cellulase Inhibitors

The cellulase mixture of Hypocrea jecorina (formerly Trichoderma reesei) contains a variety of exo- and endoglucanases that belong to different structural families. As such, these enzymes form an interesting model system to study the enzyme-ligand interactions in glycoside hydrolases. The nucleophilic carboxylate of retaining β-glycosidases is believed to form a hydrogen bond with the 2-hydroxyl group of their substrate. Consequently, replacing this hydroxyl group with an amino group should result in a stronger electrostatic interaction and thus an increased affinity for the ligand. In this study, several modified cellobiosides were synthesized and evaluated as cellulase inhibitors. The introduction of an amino group was found to have an unpredictable effect on the inhibitory power of the ligands. However, the enzymes display a very high affinity for the corresponding 2-azido compounds, precursors in the synthetic route. The new ligand m-iodobenzyl 2-deoxy-2-azido-β-cellobioside even is the strongest inhibitor of cellobiohydrolase I known to date (K_I = 1 μM).     

Synthesis of 2'-N-methylamino-2'-deoxyguanosine and 2'-N,N-dimethylamino-2'-deoxyguanosine and their incorporation into RNA by phosphoramidite chemistry

The 2'-hydroxyl groups within RNA contribute in essential ways to RNA structure and function. Previously, we designed an atomic mutation cycle (AMC) that uses ribonucleoside analogues bearing different C-2'-substituents, including -OCH(3), -NH(2), -NHMe, and -NMe(2), to identify hydroxyl groups within RNA that donate functionally significant hydrogen bonds. To enable AMC analysis of the nucleophilic guanosine cofactor in the Tetrahymena ribozyme reaction and at other guanosines whose 2'-hydroxyl groups impart critical functional contributions, we describe here the syntheses of 2'-methylamino-2'-deoxyguanosine (G(NHMe)) and 2'-N,N-dimethylamino-2'-deoxyguanosine (G(NMe(2))) and their corresponding phosphoramidites. The key step in obtaining the nucleosides involved S(N)2 displacement of 2'-β-triflate from an appropriate guanosine derivative by methylamine or dimethylamine. We readily obtained the G(NMe(2)) phosphoramidite and incorporated it into RNA. However, the G(NHMe) phosphoramidite posed a significantly greater challenge due to lack of a suitable -2'-NHMe protecting group. After testing several strategies, we established that allyloxycarbonyl (Alloc) provided suitable protection for 2'-N-methylamino group during the phosphoramidite synthesis and the subsequent RNA synthesis. This work enables AMC analysis of guanosine's 2'-hydroxyl group within RNA.     

酮-过氧化氢体系对烯烃的环氧化

过氧化酮是优良的烯烃环氧化试剂,可将烯烃氧化成环氧化物。在这些反应中,所用的氧化剂都是过硫酸氢钾或商品Oxone^[1-6]。用其它氧化剂与酮生成过氧化酮使烯烃环氧化的报道很少^[7,8],只有一例是使用过氧化氢作氧化剂的,但其只研究了一种酮与过氧化氢对烯烃的环氧化^[8]。本文使用价格便宜,且没有污染的过氧化氢取代Oxone,与酮反应形成的过氧化酮使烯烃环氧化,并首次研究了一系列酮化合物与过氧化氢组成的催化体系对烯烃的环氧化反应,考察了各种酮的催化活性。     

Three-dimensional structures of phosphorus-containing heterocycles 50. 2-dimethylamino-2-oxo- and -2-thiono-1,3,2-oxathiaphosphorinanes

Conclusions A chair conformation with an axial orientation of the phosphoryl or thiophosphoryl group is preferable for 2-dimethylamino-2-oxo- and-2-thiono-1,3,2-oxathiaphosphorinanes. The cis isomer of 2-dimethylamino-2-oxo-4-methyl-1,3,2-oxathiaphosphorinane has a similar structure with an equatorial orientation of the 4-methyl group, while the corresponding sulfide is characterized by a trans configuration with a reoriented positioning of the substituents attached to the phosphorus atom.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1369–1374, June, 1989.The authors thank I. A. Litvinov and V. A. Naumov for carrying out the x-ray diffraction analysis.     

C-PhosphorylatedN 2-2-thiazolylformamidines

C-Phosphorylation of 2-thiazolylformamidines by phosphorus tribromide was studied. It was shown that the 1,3-diazabut-1-enyl (formamidine) substituent can be used as both an activating and protective group. 5-Phosphorylated thiazoles containing either a formamidine fragment or an amino group were obtained. Some properties of the compounds synthesized were studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1353–1359, July, 1999.     

Syntheses and structures of metallocene methyltrihydroborate derivativies: Cp2ZrCl[(mu-H)2BHCH3], Cp2Zr[(mu-H)2BHCH3]2, and Cp2Ti[(mu-H)2BHCH3

In reactions of zirconocene dichloride, Cp(2)ZrCl(2), with 1 equiv and an excess amount of LiBH(3)CH(3), the methyltrihydroborate complexes, Cp(2)ZrCl[(mu-H)(2)BHCH(3)], 1, and Cp(2)Zr[(mu-H)(2)BHCH(3)](2), 2, were isolated. The reaction of titanocene dichloride, Cp(2)TiCl(2), with an excess amount of LiBH(3)CH(3) produced the monosubstituted methyltrihydroborate complex, Cp(2)Ti[(mu-H)(2)BHCH(3)], 3. The titanium was reduced from Ti(IV) to Ti(III), producing a 17-electron, paramagnetic titanocene complex. Under a dynamic vacuum at room temperature, compound 2 decomposed and produced the zirconium hydride compound Cp(2)ZrH[(mu-H)(2)BHCH(3)]. Single crystal X-ray structures of 1, 2, and 3 were determined. Crystal data for 1: space group P2(1)/c, a = 13.7921(3) A, b = 13.4227(3) A, c = 13.0868(3) A, beta = 91.6448(12) degrees, Z = 8. Crystal data for 2: space group Pna2(1), a = 15.2949(4) A, b = 9.3417(2) A, c = 9.3211(2) A, Z = 4. Crystal data for 3: space group Fmm2, a = 9.1795(3) A, b = 13.0993(5) A, c = 8.8520(3) A, Z = 4.     

2-Pyridylhydrazone als Carbonylderivate zur Steuerung der Fragmentierung in der Massenspektrometrie

2-Pyridylhydrazones as Carbonyl Derivatives to induce Fragmentation in Mass Spectrometry It was found that the 2-pyridylhydrazone is a derivative of the carbonyl group, which is able to induce fragmentation of an alicyclic skeleton with an efficiency comparable to that of the tertiary amino group and the ethylene acetal group.     

Solid phase synthesis of 2-aminoquinazoline-based compounds

A versatile method for the solid-phase synthesis of 2-aminoquinazoline-based derivatives, 3-substituted-3,4-dihydroquinazolin-2-amines and imidazoquinazolines, has been developed. They were obtained by treating the amino group of polymer-linked amino acids with 2-nitrobenzaldehyde followed by reduction of the nitro group to an amine. Cyclization of the resulting immobilized intermediates with cyanogen bromide followed by acidic/basic cleavage yielded the desired quinazoline-based compounds in high yields and purities.     

Lewis base mediated autoionization of GeCl2 and SnCl2

Cationic and anionic species of heavier low-valent group 14 elements are intriguing targets in main group chemistry due to their synthetic potential and industrial applications. In the present study, we describe the synthesis of cationic (MCl(+)) and anionic (MCl(3)(-)) species of heavier low-valent group 14 elements of germanium(II) and tin(II) by using the substituted Schiff base 2,6-diacetylpyridinebis(2,6-diisopropylanil) as Lewis base (LB). Treatment of LB with 2 equiv of GeCl(2)·dioxane and SnCl(2) in toluene gives compounds [(LB)Ge(II)Cl](+)[Ge(II)Cl(3)](-) (1) and [(LB)Sn(II)Cl](+)[Sn(II)Cl(3)](-) (2), respectively, which possess each a low-valent cation and an anion. Compounds 1 and 2 are well characterized with various spectroscopic methods and single crystal X-ray structural analysis.     

Synthesis and in vivo distribution of 2-deoxy-2-aminodiglucose-prednisolone conjugate(DPC)

In order to develop a novel kidney-targeted drug delivery system,a small molecular carrier(2-deoxy-2-aminodiglucose) was synthesized,and then the 2-deoxy-2-aminodiglucose-prednisolone conjugate(DPC) was synthesized to verify the kidney targeting capability of the carrier.Both 2-deoxy-2-aminodiglucose and DPC were confirmed by NMR and MS spectrum.The tissue distribution studies showed that DPC presented an excellent kidney targeting property in vivo,compared with prednisolone group, 4.9-fold of drug concentration in kidney was observed in the DPC group.Thus,it indicated that 2-deoxy-2-aminodiglucose could be a potential carrier for kidney-targeted drug delivery.     

Conformational study of N-vinyl-2-isopropyl- and N-vinyl-2-cyclopropylpyrroles by1H and13C NMR

In N-vinyl-2-isopropylpyrrole the isopropyl group is in a conformation with the CH₃ group in an anti position to the vinyl group. On introducing a substituent at the 3 position of the ring the isopropyl group passes into a gauche and (or) a syn conformation, leading to an increase in the dihedral angle between the plane of the vinyl group and the pyrrole ring. In N-vinyl-2-cyclo-propylpyrrole the cyclopropyl group is 80% in the gauche form, which is attributed to the repulsion between the electrons of the -shells of the cyclopropyl and pyrrole fragments.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1031–1038, May, 1991.     

Reaction of [P(2)N(2)]Ta==CH(2)(Me) with ethylene: synthesis of [P(2)N(2)]Ta(C(2)H(4))Et, a neutral species with a beta-agostic ethyl group in equilibrium with an alpha-agostic ethyl group ([P(2)N(2)] = PhP(CH(2)SiMe(2)CH(2))(2)PPh).

The photolysis of [P(2)N(2)]TaMe(3) ([P(2)N(2)] = PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh) produces [P(2)N(2)]Ta=CH(2)(Me) as the major product. The thermally unstable methylidene complex decomposes in solution in the absence of trapping agents to unidentified products. However, in the presence of ethylene [P(2)N(2)]Ta=CH(2)(Me) is slowly converted to [P(2)N(2)]Ta(C(2)H(4))Et, with [P(2)N(2)]Ta(C(2)H(4))Me observed as a minor product. A mechanistic study suggests that the formation of [P(2)N(2)]Ta(C(2)H(4))Et results from the trapping of [P(2)N(2)]TaEt, formed by the migratory insertion of the methylene moiety into the tantalum-methyl bond. The minor product, [P(2)N(2)]Ta(C(2)H(4))Me, forms from the decomposition of a tantalacyclobutane resulting from the addition of ethylene to [P(2)N(2)]Ta=CH(2)(Me) and is accompanied by the production of an equivalent of propylene. Pure [P(2)N(2)]Ta(C(2)H(4))Et can be synthesized by hydrogenation of [P(2)N(2)]TaMe(3) in the presence of PMe(3), followed by the reaction of ethylene with the resulting trihydride. Crystallographic and NMR data indicate the presence of a beta-agostic interaction between the ethyl group and tantalum center in [P(2)N(2)]Ta(C(2)H(4))Et. Partially deuterated analogues of [P(2)N(2)]Ta(C(2)H(4))Et show a large isotopic perturbation of resonance for both the beta-protons and the alpha-protons of the ethyl group, indicative of an equilibrium between a beta-agostic and an alpha-agostic interaction for the ethyl group in solution. An EXSY spectrum demonstrates that an additional fluxional process occurs that exchanges all of the (1)H environments of the ethyl and ethylene ligands. The mechanism of this exchange is believed to involve the direct transfer of the beta-agostic hydrogen atom from the ethyl group to the ethylene ligand, via the so-called beta-hydrogen transfer process.     

Dialkylaluminum hydrazides derived from free hydrazine N2H4. Molecular Structures of [(MeC)2AlN2H3]2 and [(MeC)2Al]4(N2H2)2

The reaction of di(tert-butyl)aluminum hydride with hydrazine N2H4 afforded the hydrazide (Me3C)2AlN2H3, 1, by the release of elemental hydrogen. Compound 1 is a dimer in solution and in the solid state and possesses a six-membered Al2N4 heterocycle in a twist conformation with two intact N-N bonds. Further reaction of 1 with an excess of HAl(CMe3)2 yielded the tricyclic aluminum and nitrogen rich Al4N4 compound [(Me3C)2AlN2H2]2[Al(CMe3)2]2, 2, in which each N-N bond of a central six-membered Al2N4 ring similar to that of 1 is side-on-coordinated to an Al(CMe3)2 group. The structure of 2 may be interpreted as a dimer of the dialuminum hydrazide (Me3C)2Al-NH-NH-Al(CMe3)2.     

Templated synthesis of the novel layered silver-antimony sulfides [H3NCH2CH2NH2][Ag2SbS3 and [H3NCH2CH2NH2]2[Ag5Sb3S8

Two new silver-antimony sulfides, [C(2)H(9)N(2)][Ag(2)SbS(3)] (1) and [C(2)H(9)N(2)](2)[Ag(5)Sb(3)S(8)] (2), have been prepared solvothermally in the presence of ethylenediamine and characterized by single-crystal X-ray diffraction, thermogravimetry, and elemental analysis. Compound 1 crystallizes in the space group Pn (a = 6.1781(1) A, b =11.9491(3) A, c = 6.9239(2) A, beta =111.164(1) degrees ) and 2 in the space group Pm (a = 6.2215(2) A, b = 15.7707(7) A, c = 11.6478(5) A, beta = 92.645(2) degrees ). The structure of 1 consists of chains of fused five-membered Ag(2)SbS(2) rings linked to form layers, between which the template molecules reside. Compound 2 contains honeycomb-like sheets of fused silver-antimony-sulfide six-membered rings linked to form double layers. The idealized structure can be considered to be an ordered defect derivative of that of lithium bismuthide, Li(3)Bi, and represents a new solid-state structure type.     

The influence of the purine 2-amino group on DNA conformation and stability-II: Synthesis and physical characterization of d[CGT(2-NH2)ACG], d[CGU(2-NH2)ACG], and d[CGT(2-NH2)AT(2-NH2)ACG]

Synthesis of an N-protected derivative of 2-amino-2'-deoxyadenosine (dA') from 2'-deoxyguanosine is reported. The syntheses of several oligodeoxynucleotides containing this modified nucleoside are described, together with physical characterization via melting studies and CD conformational analysis. As expected, the 2-amino group is seen to add to the duplex stability. Although the sequence d(TA')₃ was found to undergo a salt-induced conformational transition, mixed sequences such as d(CGTA'CG) did not display this behavior. All guanine residues present in these sequences were O⁶ protected, either with the cyanoethyl group or the 4-nitrophenylethyl group, to eliminate guanine degradation during phosphorylation and condensation reactions. Procedures for the introduction and removal of these O⁶ protecting groups are described.     

Perfluoroalkylphosphine coordination chemistry of platinum: synthesis of (C2F5)2PPh and (C2F5)PPh2 complexes of platinum(II)

A 1:1 addition of Ph2PCl to an ethereal solution of C2F5Li (formed from the reaction of BuLi with C2F5Cl) yields Ph2P(C2F5)(abbreviated pfepp) (1). The introduction of a fluoroethyl group results in a phosphine with electronic characteristics that approximate phosphites, bridging the electronic gap between traditional donor phosphine ligands and more electrophilic phosphine ligands like PhP(C2F5)2 (2). The pfepp ligand 1 is isolated as a high boiling liquid, which crystallizes upon standing at room temperature in an inert atmosphere. A series of Pt(II) complexes of the type trans-L2PtCl2 (L = pfepp 3; PhP(C2F5)2 4) have been prepared and structurally characterized by multinuclear NMR, IR and X-ray crystallography. The crystal structure of is the first example of a structurally characterized monodentate phosphine with a pentafluoroethyl pendant group.     

One-pot synthesis of 2-(quinoxalin-2-yl)benzoate through NBS-mediated sequential reaction of 2-alkynylbenozate and aryl-1,2-diamine

A metal-free route involving a sequential reaction of 2-alknylbenzoate and aryl-1,2-diamine is described for the generation of 2-(quinoxalin-2-yl)benzoate. The sequential reaction combines NBS-mediated diketonization of 2-alknylbenzoate and condensation reaction with aryl-1,2-diamine, and proceeds smoothly under mild reaction conditions and an array of 2-(quinoxalin-2-yl)benzoate is achieved with high efficiency and excellent functional group tolerance. Mechanism studies indicate oxygen transfer reaction is observed and water is incorporated into neighboring ester group.     

Reactions of trichloromethyldialkylamines with 2-methylbenzothiazole, 2-methylbenzoxazole,and their salts

Trichloromethyldialkylamines react with nitrogen heterocyclic compounds containing an active methyl group or with their salts to give 2-heteryl-1,1,3,3-tetrachloro-1,3-bis(dialkylamino) propanes, which are hydrolyzed by water to heterylmalonamides. Cyanine dyes containing a dimethylcarbamoyl group in the α position relative to the polymethine chain were obtained.     

Synthesis and characterization of Th2N2(NH) isomorphous to Th2N3

Using a new, low-temperature, fluoride-based process, thorium nitride imide of the chemical formula Th(2)N(2)(NH) was synthesized from thorium dioxide via an ammonium thorium fluoride intermediate. The resulting product phase was characterized by powder X-ray diffraction (XRD) analysis and was found to be crystallographically similar to Th(2)N(3). Its unit cell was hexagonal with a space group of P3m1 and lattice parameters of a = b = 3.886(1) and c = 6.185(2) ?. The presence of -NH in the nitride phase was verified by Fourier transform infrared spectroscopy (FTIR). Total energy calculations performed using all-electron scalar relativistic density functional theory (DFT) showed that the hydrogen atom in the Th(2)N(2)(NH) prefers to bond with nitrogen atoms occupying 1a Wyckoff positions of the unit cell. Lattice fringe disruptions observed in nanoparticle areas of the nitride species by high-resolution transmission electron microscopic (HRTEM) images also displayed some evidence for the presence of -NH group. As ThO(2) was identified as an impurity, possible reaction mechanisms involving its formation are discussed.