Improved Synthesis of C2-Symmetrical Pyridinediols and Synthesis of Cs-Symmetrical Pyridinediols

Base-induced reaction of 2,6-dimethylpyridine (2,6-lutidine) (1) with two equivalents of various ketones has been reported to provide C2-symmetrical pyridine diols 3. Closer examination reveals that competitive di-addition to a single methyl group can occur providing Cs-symmetrical pyridine diols 7. By varying the lithiation times, the formation of this side product could be maximized or minimized on the basis of a mechanistic proposal for the competing pathways. The formation of the Cs-diol 7 could be excluded completely by using potassium diisopropylamide as base; high yields of C2-symmetrical pyridine diols 3 are obtained. Regioselective additions of 1 to (R)-fenchone and (-)-menthone were also achieved.

The asparagus genome sheds light on the origin and evolution of a young Y chromosome

Several models have been proposed to explain the emergence of sex chromosomes. Here, through comparative genomics and mutant analysis, Harkess et al. show that linked but separate genes on the Y chromosome are responsible for sex determination in Asparagus, supporting a two-gene model for sex chromosome evolution

The clinico-radiological paradox of cognitive function and MRI burden of white matter lesions in people with multiple sclerosis: a systematic review and meta-analysis.

Moderate correlation exists between the imaging quantification of brain white matter lesions and cognitive performance in people with multiple sclerosis (MS). This may reflect the greater importance of other features, including subvisible pathology, or methodological limitations of the primary literature.To summarise the cognitive clinico-radiological paradox and explore the potential methodological factors that could influence the assessment of this relationship.Systematic review and meta-analysis of primary research relating cognitive function to white matter lesion burden.Fifty papers met eligibility criteria for review, and meta-analysis of overall results was possible in thirty-two (2050 participants). Aggregate correlation between cognition and T2 lesion burden was r = -0.30 (95% confidence interval: -0.34, -0.26). Wide methodological variability was seen, particularly related to key factors in the cognitive data capture and image analysis techniques.Resolving the persistent clinico-radiological paradox will likely require simultaneous evaluation of multiple components of the complex pathology using optimum measurement techniques for both cognitive and MRI feature quantification. We recommend a consensus initiative to support common standards for image analysis in MS, enabling benchmarking while also supporting ongoing innovation

Archeologisch onderzoek in De Schammer

In 2009 is in De Schammer gelegen bij Amersfoort een archeologische opgraving uitgevoerd. In de ondergrond ekenden zich de sporen af van vier boerderijen uit de IJzertijd en een volledig erf met boerderij, hooibergen en erfgreppels uit de Late Middeleeuwen. De resultaten van de opgraving in de Schammer moeten als voorlopig worden beschouwd, omdat veel veldgegevens nog moeten worden uitgewerk

Opgraving in Wieken-Vinkenhoef

Een korte analyse van de opgravingen tijdens het onderzoeksproject Wieken-Vinkenhoef te Amersfoort. Na acht jaar is het graven voorbi

Archeologie van de Tweede Wereldoorlog

Verslag van archeologisch onderzoek in Amersfoort en Leusde

Thiol and Disulfide Derivatives of Ephedra Alkaloids 2: A Mechanistic Study of Their Effect on the Addition of Diethyl Zinc to Benzaldehyde

Thiol and disulfide derivatives of ephedrine have been shown previously to catalyse in high enantiomeric excess (ee) the reaction of diethyl zinc with benzaldehyde. We find that this reaction involves non-linear correlations between the ee of product and catalyst. Osmotic measurements indicate a high degree of aggregation of the zinc thiolates. The behaviour of the thiol derivatives deviates sharply from that of the oxygen analogue, N-methyl ephedrine.

Easy preparation of enantiopure C2 symmetrical hydroxy and amino sulfides derived from ephedrine and their application in a Pd catalyzed coupling reaction

Ephedrine can be readily converted by means of intramolecular SN2 substitution by the hydroxyl or amino substituent into, respectively, the corresponding epoxide or aziridine with high stereocontrol. Subsequent stereoselective ring opening at the benzylic centre using tetrabutylammoniumfluoride (TBAF) and dithiols affords the C2 symmetrical hydroxy or amino sulfides in excellent yield. Application of these ligands in a palladium-catalyzed asymmetric allylic substitution reaction gave moderate to high enantiomeric excesses (up to 79%) and high yields of product.