Reduction of olefinic bond under ammonia chemical ionization

The unsaturated $\text{trans}$dicarboxylates (III and IV) form stable (M+N₂H₇)⁺ adducts in addition to the (M+NH₄)⁺ adduct. At high ammonia pressure in the ion source, bimolecular reactions between (M+NH₄)⁺ (M+N₂H₇) adducts and NH₃ result in the reduction of olefinic bonds in unsaturated $\text{cis}$ and $\text{trans}$ dicarboxylates. Evidence was obtained from MIKE/CAD data on the possible structure of the product ion.     

An aldol approach to the synthesis of the EF fragment of spongistatin 1

A synthesis of the C29-C51 fragment of spongistatin 1, containing the E and F rings, has been completed. The approach relies on four diastereoselective aldol additions and an asymmetric glycolate alkylation to establish eight of the eleven stereogenic centers. The intact chlorodiene side chain was appended by a Lewis acid catalyzed addition of an allylstannane to an epoxy enol ether.     

The 4He(p,d)3He reaction at 770 MeV

The differential cross section of the ⁴He(p, d)³He pick-up reaction has been measured at E_p = 770 MeV. The data are analysed in the framework of the DWBA; both one-nucleon and one-N¹ transfers are considered.     

Elucidation de structure et comportement de produits naturels sous ionisation chimique—II: Aminolyse et substitution nucleophile produites—en phase gazeuse avec l'ammoniac—sur la cinerubine a

The structure of cinerubine A has been studied by chemical ionisation mass spectrometry. In the NH₃/Cl mode, this type of compound with polyfunctional sites undergoes as aminolysis reaction, i.e. hydroxyl and carbonyl groups are substituted by NH₃. The protonated molecular ions formed in the ion source fragment to give intense ions which provide useful structural information. Unimolecular fragmentations in the first field-free region permit determination of the reactive sites. Use of ND₃ as reagent gas provides information on the number of mobile H atoms and permits the assignment of structure for these ionic species.     

Theoretical and gas-phase studies of specific cationized purine base quartet

Guanine tetraplexes are biological non-covalent systems stabilized by alkali cations. Thus, self-clustering of guanine, xanthine and hypoxanthine with alkali cations (Na(+), K(+) and Li(+)) is investigated by electrospray ionization mass spectrometry (ESI-MS) in order to provide new insights into G-quartets, hydrogen-bonded complexes. ESI assays displayed magic numbers of tetramer adducts with Na(+), Li(+) and K(+), not only for guanine, but also for xanthine bases. The optimized structures of guanine and xanthine quartets have been determined by B3LYP hybrid density functional theory calculations. Complexes of metal ions with quartets are classified into different structure types. The optimized structures obtained for each quartet explain the gas-phase results. The gas-phase binding sequence between the monovalent cations and the xanthine quartet follows the order Li(+) > Na(+) > K(+), which is consistent with that obtained for the guanine quartet in the literature. The smallest stabilization energy of K(+) and its position versus the other alkali metal ions in guanine and xanthine quartets is consistent with the fact that the potassium cation can be located between two guanine or xanthine quartets, for providing a [gua(or (xan))(8)+K](+) octamer adduct. Even if an abundant octamer adduct with K(+) for xanthine was detected by ESI-MS, it was not the case for guanine.     

Increased Lewis acidity in hafnium-substituted polyoxotungstates

Monolacunary polyoxotungstates [alpha(1)-P(2)W(17)O(61)](10-) and [alpha-PW(11)O(39)](7-) react with HfCl(4) to yield [alpha(1)-HfP(2)W(17)O(61)](6-) and [alpha-Hf(OH)PW(11)O(39)](4-), isolated as organo-soluble tetrabutylammonium (TBA) salts. Subsequent analyses, including mass spectrometry, show that they are stronger Lewis acids than (TBA)(5)H(2)[alpha(1)-YbP(2)W(17)O(61)]. The new polyoxotungstates catalyze Lewis acid mediated organic reactions, such as Mukaiyama aldol and Mannich-type additions. In particular, reactions with aldehydes, which were impossible with lanthanide polyoxotungstates, are made possible. Thus these modifications of the polyoxometalate composition allowed fine tuning of the Lewis acidity. The catalysts could be easily recovered and reused.     

Mass spectral characterization of ergot alkaloids by electrospray ionization, hydrogen/deuterium exchange, and multiple stage mass spectrometry: Usefulness of precursor ion scan experiments

Six ergot alkaloids belonging to the lysergic acid derivatives (ergonovine (EGN) and methysergide hydrogen maleinate (MHM)) and peptide-type derivatives (ergocristine (EGR), ergotamine (EGT), ergocornine (EGC) and alpha-ergokryptine (EGK)) were studied by positive electrospray tandem mass spectrometry. The fragmentation mechanisms of these compounds were studied by collision-induced dissociation (CID) using triple quadrupole and ion trap mass spectrometers, and the nature of the major product ions further confirmed by hydrogen/deuterium (H/D) exchange experiments. A common abundant product ion at m/z 223 was characteristic of the two classes of ergot alkaloids. Therefore, a precursor ion scan of m/z 223 that triggers information data acquisition (IDA) in combination with CID experiments was used to identify other potential ergot alkaloids. Using this approach, it was possible to confirm the presence of ergosine, another peptide-type ergot alkaloid, in a rye flour extract at trace levels.