Methylpyridylbenz-X-azoles. lH NMR Study

The shielding parameters of benz-X-azolyl substituents in various positions of the pyridine nucleus were determined by means of a regression analysis procedure. Analogously the shielding contributions of pyridyl substituents on homocyclic protons of benz-X-azoles were derived. The results evidence some interactions between the two heterocyclic systems when the benz-X-azolyl substituents are linked at the pyridine α-position.     

High molecular weight polyacetylenes from the nudibranch Peltodoris actromaculata and the sponge Petrosia ficiformis

Two series of high molecular weight straight chain polyacetylenes (C₄₆, C₄₉ and C₄₉, C₅₂, C₅₅) have been isolated from two marine invertebrates and partially characterized.     

Two novel sesterterpene hydroxyquinols from the sponge microcionatoxistyla

The structures of two unique sesterpenes, toxislylide A and B, have been deduced by chemical, spectral, and x-ray crystallographic studies. They are components of the sponge $\text{Microciona}$$\text{toxistyla}$.     

Lepton spectrum in semileptonic b-decay

We present some results from the computation of the charged lepton energy distribution in the decay b → c + $\text{l}$^? + $\text{ν}$ taking into account first order QCD corrections.     

Cholest-4,14-dien-15,20ε-diol-3,16-dione,a novel polyoxygenated marine steroid which easily loses the side chain

The title compound has been isolated from the Mediterranean gorgonian $\text{Leptogorgia sarmentosa}$; upon acetylation it affords a dehydration product and an androstane derivative.     

First evaluation of the thermodynamic properties for spheres to elongated micelles transition of some propanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants in aqueous solution

The apparent and partial molar enthalpies, apparent molar volumes, and adiabatic compressibilities at 298 K of the aqueous solutions of the cationic gemini surfactants propanediyl-alpha,omega-bis(octyldimethylammonium bromide) (8-3-8) and propanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (12-3-12) have been measured as a function of concentration. The trends of the partial molar enthalpies versus concentration are the first well documented thermodynamic evidence of sphere to rod transition in the micellar phase, involving a detectable quantity of heat, and allow the determination of the change in enthalpy associated with this transition. The changes in enthalpies upon micellization and for the sphere to elongated micelles transition, DeltaH(s)(-->)(r), have been obtained from the experimental data by using a pseudo-phase transition approach: -1.5 kJ mol(-1) for 8-3-8 and -3.9 kJ mol(-1) for 12-3-12. No evidence of the above transition is found in the trends of volumetric properties versus m. The apparent adiabatic molar compressibilities for the compounds under investigation are also reported here for the first time: a negative group contribution for the methylene group is evaluated, when the surfactants are present in solution as a single molecule, reflecting its solvation structure. In the micellar phase, the -CH(2)- group contribution becomes positive. A value of 1.17 x 10(-3) cm(3) bar(-1) mol(-1) for the change in adiabatic molar compressibility upon micellization is obtained. The lower values of the methylene group contributions to the volumetric properties for the monomers support the hypothesis of partial association of the chains before the cmc.     

Synthesis of L-carbafuranomycin, an unnatural analogue of the antibiotic amino acid furanomycin

[reaction: see text] L-(+)-carbafuranomycin is a novel analogue of L-(+)-furanomycin, an unusual antibiotic alpha-amino acid that attracted great interest due to its activity as an isoleucine antagonist. We present here a concise and efficient asymmetric synthesis of this carba-analogue starting with the 1,3-dipolar cycloaddition of a chiral nitrile oxide with cyclopentadiene. Notably, the methyl group was introduced by an S(N)2' cuprate substitution with high stereo- and regioselectivity.