Incipient Nucleophilic Attack on a Carbonyl Group Adjacent to a Stereogenic Centre in Peri Naphthalene Derivatives

The crystal structures of four peri-naphthalene derivatives model the Felkin–Anh approach of a nucleophilic centre (OH or NMe₂) to a carbonyl group attached to a stereogenic centre bearing a large (phenyl), medium (methyl) and a small (hydrogen) group. Thus, the conformation about the (O=)C−C* bond directs the phenyl group approximately perpendicular to the carbonyl group and away from the nucleophile, whose line of approach lies close to the hydrogen atom attached to the stereogenic centre. The nucleophile approaches the carbonyl group at 102.99(11)-112.34(9)° (for NMe₂) and at 118.56(14)° (for OH). The small pyramidalization of the carbonyl carbon towards the nucleophile increases as the nucleophilic centre approaches closer.     

A novel and highly stereoselective route for the synthesis of non-racemic 3-substituted isoindolin-1-one targets

A new, versatile and highly stereoselective approach for the synthesis of non-racemic 3-substituted isoindolin-1-ones is described from a readily available chiral template. The potential of this new protocol is demonstrated through the synthesis of an enantiomerically enriched 3-alkyl N-H isoindolin-1-one target with an e.e. of 98%.     

Determination of loads applied perpendicularly to the outer boundary of a ring using coefficients of influence

A procedure is explained to determined the amount of several pairs of diametrical loads applied to the outside boundary of a ring when stresses at selected points of the inside or outside boundaries are known. Coefficients of influence are used, following an approach similar to the one presented in a previous paper. Examples of application are given and the possible increase in precision is shown when the number of points of measurements is larger than the number of loads to be determined.     

Preparation and X-ray crystal structure of hexakis(1-methylimidazoline-2(3H)-thione)tetrakis(nitrato)dilead(II)

The title complex, prepared by reacting lead(II) nitrate with a stoichiometric amount of 1-methylimidazoline-2(3H)-thione (mimt) in water, crystallizes in the triclinic space group P with a = 9.334(2), b = 11.340(4), c = 11.398(3) Å, = 108.24(2), β = 95.69(2), γ = 100.27(2)° and Z = 1. In the solid state, the molecules show an unusual dimeric structure, with the formula [(mimt)₂(NO₃)₂Pb(μ-mimt)₂Pb(NO₃)₂(mimt)₂].     

Mildbraedin, a novel kaempferol tetraglycoside from the tropical forest legume Mildbraediodendron excelsum

Aqueous methanol extracts of the leaves of Mildbraediodendron excelsum yielded a novel flavonol glycoside characterized by an O-linked branched tetrasaccharide. The structure of the compound was determined by spectroscopic methods to be kaempferol 3-O-α-l-rhamnopyranosyl(1→3)-α-l-rhamnopyranosyl(1→2)[α-l-rhamnopyranosyl(1→6)]-β-d-galactopyranoside. This previously unrecorded natural product was the major phenolic component of leaf material obtained both from a living specimen of the plant and a historic collection made in the field in 1928.     

Intercomparison study on accurate mass measurement of small molecules in mass spectrometry

The results from an intercomparison of accurate mass measurement of a small molecule (molecular weight 475 Da) across a broad range of mass spectrometers are reported. The intercomparison was designed to evaluate the relative capabilities and the optimum methodology of the diverse range of mass spectrometers currently used to record accurate mass measurements. The data will be used as a basis for developing guidance on accurate mass measurement. The need for guidance has resulted from the continued growth in the use of accurate mass measurements for assignment of elemental formula in the chemical and biochemical industries. This has been fuelled by a number of factors and includes the rapid pace of instrument development, which has enabled accurate mass measurements to be made in a less costly, yet robust fashion. The data from the intercomparison will allow us to compare those protocols that produced excellent accuracy and precision with those that produced poorer accuracy and/or precision for each type of mass spectrometer. The key points for best practice will then be established from this comparison for each type of mass spectrometer and accurate mass measurement technique. A compound was sent to the participating laboratories (in the UK, Europe, and USA), the identity of which was not revealed. Each laboratory was asked to record a minimum of five repeat mass measurements of the molecular species using their local protocols and their preferred ionization technique or techniques. To the best of our knowledge there were no interfering (unresolved) ions that originated from the sample. A questionnaire was also completed with the experimental work. The information from the questionnaires was used to evaluate the protocols used to record the measurements. Forty-five laboratories have reported their results. To summarize the performance of mass spectrometers in the intercomparison, magnetic sector field mass spectrometers used in peak matching mode and FTMS reported the highest mean mass measurement accuracy (88 and 83%, respectively, achieved < or =1 ppm). Magnetic sector field mass spectrometers used in voltage scanning produced 60% of the mean mass measurements with accuracy < or =1 ppm. Magnetic sector field mass spectrometers used in magnet scanning modes, quadrupole-TOF and TOF instruments generally achieved mean mass measurement accuracy between 5 and 10 ppm. The two low resolution triple quadrupoles used in the inter-comparison produced mean mass measurement accuracy of <2 ppm. The precision of the data from each instrument and experiment type is an important consideration when evaluating their relative capabilities. Using both the precision and accuracy, it will be possible to define the uncertainty associated with the elemental formulae derived from accurate mass measurements. Therefore, a thorough statistical evaluation of the data is underway and will be presented in a subsequent publication.