Efficient synthesis of phosphonodepsipeptides derived from norleucine

In the present work, we describe in detail an efficient solution synthesis of norleucine-derived phosphonopeptides mimicking the peptide sequences Nle-Gly(Ala) and Nle-Gly(Ala)-Val. The most efficient strategy involved use of the benzyl group. The synthesis was achieved through BOP-catalysed coupling of the monobenzyl ester of the N-Cbz-protected phosphonate derivative of norleucine with the hydroxyl moieties of derivatised l-lactic or glycolic acid. Subsequently, complete deprotection of the products was achieved in good yields by one-step Pd-catalysed hydrogenolysis. We also prepared the Fmoc-Nle-Ψ[PO(OH)O]-CH₂-COOH synthon and demonstrated that this precursor is a suitable building block for the solid-phase synthesis of cysteine-containing phosphonopeptides.     

Synthesis of the end-capped 5-(N,N-dimethylamino)naphthyl-1-ethynyl derivatives and their 1,4-di[5-(N,N-dimethylamino)naphthyl]-1,3-butadiynes: anti rotamer structure

A new family of the end-capped 5-(N,N-dimethylamino)naphthylethynyl chains were synthesized, as terminal acetylenes or poly(yne) structures, by heterocoupling between 5-iodo-N,N-dimethylnaphthalen-1-amine and 2-methyl-3-butyn-2-ol or 4-(5-iodo-1-naphthyl)-2-methyl-3-butyn-2-ol, catalyzed by the palladium-copper system. Catalytic homocoupling of the terminal acetylenes, affords to 1,4-dinaphthyl-1,3-butadiyne nanostructures. X-ray diffraction analysis of 1,4-di(α-naphthyl)-1,3-butadiyne shows that the naphthalene rings are in the anti configuration along the acetylene axis. All the conjugated compounds show an important fluorescent emission radiation.     

Novel 1,3-dipolar cycloaddition reactions of calix[4]bis(spirodienones): synthesis of isoxazolidine derived macrocycles

Calix[4]bis(spirodienones) can perform as either 4π or 2π components in cycloaddition reactions with various carbo- and hetero-dienophiles and with 1,2-benzoquinones leading to the formation of highly functionalized macrocycles. In this Letter we report, highly regio- and stereoselective 1,3-dipolar cycloaddition reactions of a bis(spirodienone) derivative of calix[4]arene with nitrones that provide easy access to isoxazolidine derived macrocycles in excellent yields. These isoxazolidine derivatives can be considered as direct precursors of 1,3-amino alcohols.     

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%.     

Characterisation and determination of fullerenes: A critical review

A prominent sector of nanotechnology is occupied by a class of carbon-based nanoparticles known as fullerenes. Fullerene particle size and shape impact in how easily these particles are transported into and throughout the environment and living tissues. Currently, there is a lack of adequate methodology for their size and shape characterisation, identification and quantitative detection in environmental and biological samples. The most commonly used methods for their size measurements (aggregation, size distribution, shape, etc.), the effect of sampling and sample treatment on these characteristics and the analytical methods proposed for their determination in complex matrices are discussed in this review. For the characterisation and analysis of fullerenes in real samples, different analytical techniques including microscopy, spectroscopy, flow field-flow fractionation, electrophoresis, light scattering, liquid chromatography and mass spectrometry have been reported. The existing limitations and knowledge gaps in the use of these techniques are discussed and the necessity to hyphenate complementary ones for the accurate characterisation, identification and quantitation of these nanoparticles is highlighted.     

Quaternized amino functionalized cross-linked polyacrylamide as a new solid-liquid phase transfer catalyst in reduction of carbonyl compounds with NaBH4

Poly[N-(2-aminoethyl)acrylamido]trimethyl ammonium chloride resin was developed as a new polymeric phase transfer catalyst. This quaternized polyacrylamide catalyzed the chemoselective reduction of aldehydes and ketones by NaBH₄ to give corresponding alcohols in high yields under mild conditions.     

Fluorinated peptidomimetics: synthesis, conformational and biological features

Peptides modified with fluoroalkyl functions in key backbone positions have been scarcely studied so far. Thus, little is known about their synthesis, their structural and physico-chemical properties, and their biological features. Our interest in this field of research led to the development of stereocontrolled synthetic protocols, both in solution and in solid phase, for many different fluoroalkyl peptidomimetics, some of which are overviewed in this paper: (a) ψ[CH(CF₃)NH]-peptide mimics holding a great potential as hybrids between natural peptides and hydrolytic transition state analogs; (b) trifluoromethyl (Tfm) malic peptidomimetics as micromolar inhibitors of some matrix metalloproteinases; (c) bis-Tfm analogs of Pepstatin A, that are nanomolar and selective inhibitors of the protozoal aspartyl protease Plasmepsin II.     

Bis(trimethylsilyl)amide und -methanide des Yttriums — Molekülstrukturen von Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl) methyl]yttriat,solvensfreiem Yttrium-tris[bis(trimethylsilyl)amid] sowie dem Bis(benzonitril)-Komplex

Bis(trimethylsilyl)amides and -methanides of Yttrium — Molecular Structures of Tris(diethylether-O)lithium-(μ-chloro)-tris[bis(trimethylsilyl)methyl]yttriate, solvent-free Yttrium Tris[bis(trimethylsilyl)amide] as well as the Bis(benzonitrile) Complex The reaction of yttrium(III) chloride with the three-fold molar amount of LiE(SiMe₃)₂ (E = N, CH) yields the corresponding yttrium derivatives. Yttrium tris-[bis(trimethylsilyl)amide] crystallizes in the space group P3 1c with a = 1 636,3(2), c = 849,3(2) pm, Z = 2. The yttrium atom is surrounded trigonal pyramidal by three nitrogen atoms with Y? N-bond lengths of 222 pm. Benzene molecules are incorporated parallel to the c-axes. The compound with E = CH crystallizes as a (Et₂O)₃LiCl-adduct in the monoclinic space group P2₁/n with a = 1 111,8(2), b = 1 865,2(6), c = 2 598,3(9) pm, β = 97,41(3)° and Z = 4. The reaction of yttrium tris[bis(trimethylsilyl)amide] with benzonitrile yields the bis(benzonitrile) complex, which crystallizes in the triclinic space group P1 with a = 1 173,7(2), b = 1 210,3(2), c = 1 912,4(3) pm, α = 94,37(1), β = 103,39(1), γ = 117,24(1)° and Z = 2. The amido ligands are in equatorial, the benzonitrile molecules in axial positions.     

Complex formation equilibria between Ag(I) and thioureas in n-propanol

Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgL_n (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln β_n on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C.     

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.     

N-Polyfluoro(trimethylsilyl)ethyl azole derivatives

A facile synthetic route to N-polyfluoro(trimethylsilyl)ethyl azole derivatives was developed starting from N-bromo(chloro)polyfluoroethyl-substituted azoles. The silanes thus obtained were reacted with various electrophiles in the presence of the fluoride ion to yield the corresponding fluorinated carbinols, ketones, carboxylic acids, and methyl dithiocarboxylates as well as N-pentafluoroethylbenzimidazole.     

An effective C-C double bond formation via Cu(I)-catalyzed dehydrogenation

A dehydrogenation method using Cu(I) and either N,N-di-tert-butylthiadiaziridine 1,1-dioxide or N,N-di-tert-butyldiaziridinone is reported. The dehydrogenation allows a facile introduction of C-C double bond(s) into various carbocycles and heterocycles such as oxazolines and thiazolines.     

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.     

Synthesis of a novel tetracyclic azaindolo[2,1-c][1,4]benzoxazine ring system

Synthesis of a series of novel fused tetracyclic mono- and diazaindolo[2,1-c][1,4]benzoxazine heterocyclic compounds 3a-o has been achieved in a two-step one-pot reaction set up starting from commercially available or easily accessible inputs. For example, reaction of di-lithiated (N-Boc)-2-amino-3-methylpyridine Li₂-2a with Weinreb amide of 2-(2,4-difluorophenoxy)-2,2-dimethylacetic acid 1a, followed by TFA treatment furnished the tetracyclic compound 3a, which is essentially a fusion of 7-azaindole and 3,4-dihydro[1,4]benzoxazine, in 70% isolated yield. A competitive elimination by-product 4a was also observed (24% isolated yield) in this case. Based on our initial results, a structural basis and molecular mechanism have been suggested to explain these two parallel reactions. Consequently, with appropriate structural tuning of 1, formation of the individual products can be controlled.     

Nucleophilic alkynylation of N-bis(trimethylsilyl)methyl aldimines

N-Bis(trimethylsilyl)methyl aldimines undergo nucleophilic addition reaction with premixed lithium alkynides/BF₃·OEt₂ to give moderate to good yields of N-bis(trimethylsilyl)methyl propargyl amines.