122 research outputs found
Diastereoselective synthesis of [alpha]-tocopherol
Vitamin E exists in eight different forms, four tocopherols and four tocotrienols. All
possess a hydrophobic side chain, which allows them to penetrate into biological
membranes. Their second common feature is a chromanol moiety with a hydroxyl
group that can donate a hydrogen atom. These properties make vitamin E a very
important radical chain-breaking antioxidant in living organisms, and therefore also
an industrial product.
α-Tocopherol is the member of the vitamin E family that is preferentially absorbed
and accumulated in humans. There are three stereocenters in α-tocopherol, whereas
RRR-α-tocopherol (1) is the natural and biologically most active form. The
R-configuration at C(2) is essential in order to be recognised by the α-tocopherol
transport protein and thus maintained in the plasma. The biological activity rendered
RRR-α-tocopherol (1) a synthetic target.
In this work two novel syntheses of RRR-α-tocopherol (1) are presented. Both
syntheses involve a highly diastereoselective epoxidation of the bis-protected phytyl
hydroquinone 132 as the key step followed by a cyclisation to form the chromanol
ring (figure 70).
In order to find suitable stereoselective epoxidation catalysts, cyclodextrin-based
catalysts were prepared and tested (figure 71). However, none of these catalysts were reactive or selective enough to be applicable to the epoxidation of bis-protected
phytyl hydroquinones.
However, the asymmetric Shi epoxidation proved to be a suitable epoxidation
method for this purpose. A number of bis-protected phytyl hydroquinones were
synthesised and subsequently epoxidised under Shi epoxidation conditions. The
highest diastereoslectivity could be obtained for substrate 132. By applying Shi
ketone 114, which is derived from D-fructose, epoxide 148 could be obtained with
96% de, whereas if the enantiomer ent-114 (synthesised in 5 steps from L-sorbose)
was used, 147 was formed with 97% de (figure 71).
The epoxide function in 148 could be selectively opened with hydride. Further
transformations led to the hydroquinone 155, which could be cyclised under acidic
conditions to form the chromanol ring of 1 with the desired R-configuration at C(2)
(figure 72). α-Tocopherol could be synthesised in 8 steps with 93% de via this route.
To the best of my knowledge, this highly diasteroselective synthesis of α-tocopherol (1) is one of the shortest in terms of numbers of steps, employing a commercially
available organocatalyst.
In a different approach an acid supported, “anti-Baldwin” epoxide ring opening of
desilylated 147 under inversion of configuration led to the 6-membered chromanol
ring. α-Tocopherol could be synthesised in 10 steps and with 93% de. This synthesis
was carried out in collaboration with Julien Chapelat.
To the best of our knowledge this is the second application of an organocatalyst to
the construction of chromanols, having a tetrasubstituted chiral carbon centre, in high
diastereoselectivity.7
First Study of Combined Blazar Light Curves with FACT and HAWC
For studying variable sources like blazars, it is crucial to achieve unbiased
monitoring, either with dedicated telescopes in pointing mode or survey
instruments. At TeV energies, the High Altitude Water Cherenkov (HAWC)
observatory monitors approximately two thirds of the sky every day. It uses the
water Cherenkov technique, which provides an excellent duty cycle independent
of weather and season. The First G-APD Cherenkov Telescope (FACT) monitors a
small sample of sources with better sensitivity, using the imaging air
Cherenkov technique. Thanks to its camera with silicon-based photosensors, FACT
features an excellent detector performance and stability and extends its
observations to times with strong moonlight, increasing the duty cycle compared
to other imaging air Cherenkov telescopes. As FACT and HAWC have overlapping
energy ranges, a joint study can exploit the longer daily coverage given that
the observatories' locations are offset by 5.3 hours. Furthermore, the better
sensitivity of FACT adds a finer resolution of features on hour-long time
scales, while the continuous duty cycle of HAWC ensures evenly sampled
long-term coverage. Thus, the two instruments complement each other to provide
a more complete picture of blazar variability. In this presentation, the first
joint study of light curves from the two instruments will be shown, correlating
long-term measurements with daily sampling between air and water Cherenkov
telescopes. The presented results focus on the study of the variability of the
bright blazars Mrk 421 and Mrk 501 during the last two years featuring various
flaring activities.Comment: 6 pages, 2 figures. Contribution to the 6th International Symposium
on High Energy Gamma-Ray Astronomy (Gamma2016), Heidelberg, Germany. To be
published in the AIP Conference Proceeding
Hazenella coriacea gen. nov., sp nov., isolated from clinical specimens
A Gram-staining-positive, endospore-forming rod was isolated independently from clinical specimens in New York State, USA, once in 2009 and twice in 2011. The three isolates had identical 16S rRNA gene sequences and, based on their 16S rRNA gene sequence, are most closely related to the type strains of Laceyella sediminis and L. sacchari (94.6% similarity). The partial 23S rRNA gene sequences of the three strains were also 100% identical. Maximumlikelihood phylogenetic analysis suggests that the new isolates belong to the family Thermoactinomycetaceae. Additional biochemical and phenotypic characteristics of the strains support the family designation and suggest that the three isolates represent a single species. In each of the strains, the predominant menaquinone is MK-7, the diagnostic diamino acid is mesodiaminopimelic acid and the major cellular fatty acids are iso-C15 : 0, anteiso-C15 : 0 and iso-C13 : 0.
The polar lipids are phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, four unknown phospholipids, four unknown aminophospholipids and an unknown lipid. It is proposed that the novel isolates represent a single novel species within a new genus, for which the name Hazenella coriacea gen. nov., sp. nov. is proposed. The type strain of Hazenella coriacea is strain 23436T (5DSM 45707T5LMG 27204T)
Miniature curved artificial compound eyes.
International audienceIn most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories
The relentless variability of Mrk 421 from the TeV to the radio
The origin of the gamma-ray emission of the blazar Mrk 421 is still a matter
of debate. We used 5.5 years of unbiased observing campaign data, obtained
using the FACT telescope and the Fermi LAT detector at TeV and GeV energies,
the longest and densest so far, together with contemporaneous multi-wavelength
observations, to characterise the variability of Mrk 421 and to constrain the
underlying physical mechanisms. We studied and correlated light curves obtained
by ten different instruments and found two significant results. The TeV and
X-ray light curves are very well correlated with a lag of <0.6 days. The GeV
and radio (15 Ghz band) light curves are widely and strongly correlated.
Variations of the GeV light curve lead those in the radio. Lepto-hadronic and
purely hadronic models in the frame of shock acceleration predict proton
acceleration or cooling timescales that are ruled out by the short variability
timescales and delays observed in Mrk 421. Instead the observations match the
predictions of leptonic models.Comment: 10 pages, 8 figures, 1 tabl
ContribuciĂłn al conocimiento de Porosagrotis gypaetina (Guen.) (Lep.:Noctuidae)
p.15-22Este trabajo tiene por finalidad brindar una descripcion detallada de los diferentes estados de desarrollo, asi como de los estadios larvales, de Porosagrotis gypaetina (Guen.) y estimar sus principales parametros biologicos. Se trata de una oruga conocida vulgarmente como gusano pardo que frecuenta cultivos de alfalfa, trebol bianco, maiz y girasol y determinadas malezas. Los caracteres considerados para su identificacion fueron, en el huevo: numero y distribucion de costas; en la larva: pigmentacion, distribucion de manchas y cerdas corporales; en la pupa: tamaño, forma y color y caracteristicas del cremaster; y en el adulto: ubicacion y coloracion de maculas y nervaduras alares. La emergencia de imagos alcanzo su maximo en abril y mayo. El periodo embrionario se completo en 22 a 26 dias. Aproximadamente la mitad de las larvas cumplieron su ciclo en 6 estadios y las restantes en 7; la duracion total del periodo larval fue de 134 a 141 dias, sin considerar la forma prepupal e independientemente del numero de estadios. Las orugas permanecieron como prepupas durante la temporada estival (aproximadamente 161 dias). El estado pupal duro 40 a 57 dias. Las observaciones realizadas permiten expresar que, inediante los caracteres descriptos, es factible reconocer la especie a traves no solo de los adultos, sino de sus estados inmaduros. Posee una sola generacion anual; transcurre el inviemo como larva; el daño tipico de corte lo produce a partir del cuarto estadio larval
An autoactive NB-LRR gene causes Rht13 dwarfism in wheat
Semidwarfing genes have greatly increased wheat yields globally, yet the widely used gibberellin (GA)-insensitive genes Rht-B1b and Rht-D1b have disadvantages for seedling emergence. Use of the GA-sensitive semidwarfing gene Rht13 avoids this pleiotropic effect. Here, we show that Rht13 encodes a nucleotide-binding site/leucine-rich repeat (NB-LRR) gene. A point mutation in the semidwarf Rht-B13b allele autoactivates the NB-LRR gene and causes a height reduction comparable with Rht-B1b and Rht-D1b in diverse genetic backgrounds. The autoactive Rht-B13b allele leads to transcriptional up-regulation of pathogenesis-related genes including class III peroxidases associated with cell wall remodeling. Rht13 represents a new class of reduced height (Rht) gene, unlike other Rht genes, which encode components of the GA signaling or metabolic pathways. This discovery opens avenues to use autoactive NB-LRR genes as semidwarfing genes in a range of crop species, and to apply Rht13 in wheat breeding programs using a perfect genetic marker
Validity of the Modified Child Psychopathy Scale for Juvenile Justice Center Residents
Adult psychopathy has proven to be an important clinical and forensic construct, but much less is known about juvenile psychopathy. In the present study, we examined the construct validity of the self report modified Child Psychopathy Scale mCPS; Lynam (Psychological Bulletin 120:(2), 209–234, 1997) in a sample of 57 adolescents residing in a Dutch juvenile justice center, aged between 13 and 22 years. The mCPS total score was reliably related to high externalizing problems, low empathy, high anger and aggression, high impulsivity, high (violent) delinquency, and high alcohol/drug use. Unique relations were found for the antisocial-impulsive (mCPS Factor 2), but not the callous-unemotional facet of psychopathy (mCPS Factor 1). Our findings support the validity of the mCPS in that it encompasses the antisocial-impulsive facet of psychopathy, but it is less clear whether the mCPS sufficiently captures the affective-interpersonal facet of psychopathy
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