Spectroscopic Discrimination of Diastereomeric Complexes Involving an Axially Chiral Receptor.

The infrared multiphoton dissociation (IRMPD) spectra of electrospray ionization (ESI)-formed proton-bound complexes between the axially chiral multifunctional macrocycle M and d- and l-phenylalanine (P and P ) or d- and l-3,4-dihydroxyphenylalanine (D and D ) are recorded in the ν˜ =2800-3700 cm region. Whereas the diastereomeric [M ⋅H⋅P ] and [M ⋅H⋅P ] complexes do not show any significant spectral differences, the spectrum of [M ⋅H⋅D ] clearly diverges from that of its [M ⋅H⋅D ] diastereomer. A comparison of the experimental spectra with the B3LYP/6-31G**-calculated harmonic vibrational frequencies of a number of stable structures indicates the formation, in the ESI source, of very similar spectroscopically active structures, with the protonated amino acid placed outside the flat cavity of the macrocycle and hydrogen-bonded at its O center.

Boyer's Reaction and Transetherification: Mechanism and New Perspectives.

The progress and stereochemistry of Boyer's reaction were analyzed using several simple, chiral, alcoholic substrates, a variable amount of BiBr3 and different solvents. Basic solvents inhibit the reaction, while cyclohexane works very well; thus, it was our choice for the present study. In contrast to previous works, BiBr3 behaves as a true catalyst, being not consumed during the reaction.

Contact Ion Pairs on a Protonated Azamacrocycle: the Role of the Anion Basicity.

A potassium-containing hexaazamacrocyclic dication, [M•H•K](2+), is able to add in the gas phase mono- and dicarboxylate anions as well as inorganic anions by forming the corresponding monocharged adducts, the structure of which markedly depends on the basicity of the anion. With anions, such as acetate or fluoride, the neutral hexaazamacrocycle M acts as an acceptor of monosolvated K(+) ion. With less basic anions, such as trifluoroacetate or chloride, the protonated hexaazamacrocycle [M•H](+) performs the unusual functions of an acceptor of contact K(+)/anion pairs.

Phytochemical analysis of Achillea ligustica All. from Lipari Island (Aeolian Islands).

A complete chemical investigation of Achillea ligustica All. growing at Lipari (Aeolian Island, Sicily) has been carried out. Seventeen metabolites have been isolated and characterised from dichloromethane and methanol extracts of flowers and aerial parts, and GC/MS analyses of petroleum ether extracts was carried out, revealing a composition in sesquiterpenoids similar to those reported for populations from Greece, Sicily and Algeria, showing the presence of (3RS,6RS)-2,6-dimethyl-1,7-octadiene-3,6-diol (1), 2,6-dimethyl-octa-3(E),7-diene-2,6-diol (2), iso-seco-tanapartholide (3) from DCM fraction.

Structure and conformation of protonated D-(+)-biotin in the unsolvated state.

A combined computational and infrared multiphoton dissociation (IRMPD) spectroscopic investigation shows that protonated d-(+)-biotin, formed in the gas phase by ESI-MS, acquires a folded structure with proton bonding between the ureido and valeryl carbonyls, and that only a single conformer of such a structure predominates. A uniform frequency vs distance correlation function is proposed for the O(+)-H···O and N-H···O bonds involved in the folded conformers of O2'-protonated d-(+)-biotin in the gas phase which, therefore, depends exclusively on the corresponding geometric parameters.

Protonated Hexaazamacrocycles as Selective K(+) Receptors.

Protonated hexaazamacrocycle [M•H](+) is able to detect K(+) ions present at ppb level in methanolic solutions containing 10(-5) M of Na(+) ions. The high sensitivity and selectivity of [M•H](+) for K(+) is ascribed to the favorable energy balance between the K(+) ion desolvation and its coordination to the [M•H](+) macrocycle, which allows the formation of the corresponding adduct before the Coulombic explosion of the ESI-MS nanodroplets.

Pivaloylcodeine, a new codeine derivative, for the inhibition of morphine glucuronidation. An in vitro study in the rat.

We have previously found that phenanthrenic opioids, including codeine, modulate morphine glucuronidation in the rat. Here codeine and five of its derivatives were compared in their effects on the synthesis of morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) from morphine by rat liver microsomal preparations, and by primary cultures of rat hepatocytes previously incubated for 72 h with either codeine or its derivatives. Acetylcodeine and pivaloylcodeine shared the capability of the parent compound of inhibiting the synthesis of M3G by liver microsomes through a noncompetitive mechanism of action.

Hypericum hircinum L. components as new single-molecule inhibitors of both HIV-1 reverse transcriptase-associated DNA polymerase and ribonuclease H activities.

Among HIV-1 reverse transcriptase (RT)-associated functions, DNA polymerase and Ribonuclease H (RNase H) are both essential for HIV replication and excellent targets for drug development. While all RT inhibitors approved for therapy target the DNA polymerase activity, there is the pressing need for new RT inhibitors possibly targeting the RNase H function. In the last 20 years, many natural substances have shown antiviral activity against HIV-1, but only a few against the RNase H function.