N-[1-(Benzotriazol-1-yl)alkyl]amides from N-acyl-α-amino acids or N-alkylamides

A variety of N-(1-methoxyalkyl)amides react with benzotriazole in the presence of PPh₃·HBF₄ and organic bases (Hünig's base, DBU or DABCO) or solid-state-supported bases (SiO₂-Pip or IRA-67) in CHCl₃ to give N-[1-(benzotriazol-1-yl)alkyl]amides in good yields. The most convenient and efficient procedure for obtaining N-[1-(benzotriazol-1-yl)alkyl]amides consists, however, of the addition of benzotriazole sodium salt to a solution of crude 1-(N-acylamino)alkyltriphenylphosphonium salt, obtained in situ from N-(1-methoxyalkyl)amides and PPh₃·HBF₄. A combination of these reactions with the recently described electrochemical decarboxylative α-methoxylation of N-acyl-α-amino acids in the presence of SiO₂-Pip enables an effective two-pot transformation of N-acyl-α-amino acids to N-[1-(benzotriazol-1-yl)alkyl]amides.     

Synthesis,cytotoxicity and antiviral activity studies of the conjugates of cobalt bis(1,2-dicarbollide)(-I) with 5-ethynyl-2′-deoxyuridine and its cyclic derivatives

A series of novel conjugates of cobalt bis(1,2-dicarbollide)(-I) with 5-ethynyl-2′-deoxyuridine and its cyclic derivatives were synthesized. Conjugates with 5-ethynyl-2-deoxyuridine were prepared by the direct Sonogashira coupling of a series of cobalt bis(1,2-dicarbollide)(-I) terminal alkynes and 5-iodo-2′-deoxyuridine. Their furo[2,3-d]pyrimidin-2(3H)-one isomers were obtained either by intermolecular cyclization of the above conjugates or by Sonogashira coupling using Pd/C as a catalyst. Action of ammonia on these furo[2,3-d]pyrimidin-2(3H)-one conjugates resulted in pyrrolo[2,3-d]pyrimidin-2(3H)-one conjugates. Most of the designed compounds have shown low cytotoxicity in several cell lines. Some 5-ethynyl-2-deoxyuridine and furo[2,3-d]pyrimidin-2(3H)-one conjugates have also presented antiviral activity.     

Structure and phase composition of nanocrystalline Ce1−xLuxO2−y

The microstructure and phase stability of nanocrystalline mixed oxide Lu_xCe_1−xO_2−y (x=0-1) are described. Nano-sized (3-4 nm) oxide particles were prepared by the reverse microemulsion method. Morphological and structural changes upon heat treatment in an oxidizing atmosphere were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and Yb³⁺ emission spectroscopy, the latter ion being present as an impurity in the Lu₂O₃ starting material. Up to 950 °C, the samples were single phase, with structure changing smoothly with Lu content from fluorite type (F) to bixbyite type (C). For the samples heated at 1100 °C phase separation into coexisting F- and C-type structures was observed for 0.35<x<0.7. It was also found that addition of Lu strongly hinders the crystallite growth of ceria during heat treatment at 800 and 950 °C.     

4-Azatricyclo[5.2.2.02,6]undecane-3,5,8-triones as potential pharmacological agents

A series of twenty six arylpiperazine and aminoalkanol derivatives of 4-azatricyclo[5.2.2.0(2,6)]undecane-3,5,8-trione have been prepared. The synthesized compounds were evaluated for their cytotoxicity and anti-HIV-1 activity in MT-4 cells.     

4-Methylpseudoproline derived from α-methylserine - synthesis and conformational studies

This paper presents the synthesis and solution conformational studies of the tripeptides Fmoc-Ala-(R)-(αMe)Ser(Ψ(H,H)Pro)-Ala-OBu(t) (6a) and Fmoc-Ala-(S)-(αMe)Ser(Ψ(H,H)Pro)-Ala-OBu(t) (6b). Additionally, the X-ray structure of 6a is given. NMR analysis corroborated by theoretical calculations (XPLOR) shows that in both peptides the amide bond between pseudoproline and the preceding amino acid is in the trans conformation. The same amide bond geometry was observed in the crystal state of 6a. The latter is additionally influenced by the presence of two symmetrically independent molecules in an asymmetric unit. Both molecules adopt a conformation which resembles β-turn type II, stabilized by hydrogen bonding. The conformational preferences and prolyl cis-trans isomerization of Ac-(αMe)Ser(Ψ(H,H)Pro)-NHMe (7) were explored at the IEFPCM/B3LYP/6-31+G(d) level of theory in vacuum, water and chloroform. It has been shown that the trans isomer predominates in water solutions and the cis isomer is preferred in chloroform. The conformation of 7 is down-puckered independently of the geometry of the amide bonds, with lower puckering in the transition state of the cis-trans isomerization.     

Nature of a hydride-halogen bond. A SAPT-, QTAIM-, and NBO-based study

The nature of a hydride-halogen bond is investigated by means of high-level quantum mechanical calculations expended with symmetry-adapted perturbation theory (SAPT), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) methods. As model hydride-halogen bonded systems complexes between either LiH or HBeH and either XCF(3) or XCCH (X = F, Cl, Br, I) are used. It is shown that the formation of a hydride-halogen bond leads to the elongation of the R(δ+)-H(δ-) hydride bond, which is accompanied by the blue shift of the ν(R-H) stretching vibration frequency and the increase of the IR intensity of this mode. All these effects, although untypical in the case of, e.g., hydrogen bonds, can be considered as rather typical for hydride-halogen bonded systems. The decomposition of the interaction energy based on the SAPT method clearly indicates the dominant role of the induction term, thus the inductive nature of a hydride-halogen bond in opposition to previous findings. NBO-based analysis indicates the charge transfer from the hydride molecule to the more remote parts of the halogen donor and that the elongation of the R-H bond is caused by the charge outflow from the σ(RH) bonding orbital.     

Photoisomerization of disperse red 1 studied with transient absorption spectroscopy and quantum chemical calculations

The photoisomerization of the push-pull substituted azo dye Disperse Red 1 is studied using femtosecond time-resolved absorption spectroscopy and other spectroscopic and computational techniques. In comparison with azobenzene, the pipi* state is more stabilized by the effects of push-pull substitution than the npi* state, but the latter is probably still the lowest in energy. This conclusion is based on the kinetics, anisotropy of the excited state absorption spectrum, the spectra of the ground states, and quantum chemical calculations. The S(1)(npi*) state is formed from the initially excited pipi* state in <0.2 ps, and decays to the ground state with time constants of 0.9 ps in toluene, 0.5 ps in acetonitrile, and 1.4 ps in ethylene glycol. Thermal isomerization transforms the Z isomer produced to the more stable E isomer with time constants of 29 s (toluene), 28 ms (acetonitrile), and 2.7 ms (ethylene glycol). The pathway of photoisomerization is likely to be rotation about the N=N bond. Quantum chemical calculations indicate that along the inversion pathway ground and excited state energy surfaces remain well separated, whereas rotation leads to a region where conical intersections can occur. For the ground-state Z to E isomerization, conclusive evidence is lacking, but inversion is more probably the favored pathway in the push-pull substituted systems than in the parent azobenzene.