Synthesis of Tricyclic beta-Methylene Spiro Lactones Related to Bakkenolides by Successive Radical Cyclization-High Pressure Diels-Alder Reactions

The synthesis of some novel bakkenolides and their epi-spiro analogues was achieved by a new approach. Photolysis of allyl 1-(phenylseleno)-2-oxocyclopentanecarboxylates 7-9 afforded the corresponding spiro lactones 10-12 by radical cyclization via group transfer of the phenylseleno group. Selenoxide elimination of 11 and 12 produced the corresponding beta-methylene lactones 14 and 15. Diels-Alder cycloaddition of lactone11 with piperylene failed at ambient pressure, but proceeded in generally good yield in the presence of various Lewis acids at pressures of ca. 16 kbar, to give mixtures of beta-exo, alpha-endo, and beta-endo cycloadducts 19, 21, and 23, respectively. The preponderance of endo products 21 and 23, formed via highly hindered, but more compact, transition states was attributed to the high pressure and resulted in trans-dimethyl configurations of the products. The facial selectivity was dependent upon the Lewis acids, and the greatest alpha:beta ratio was observed with catalysts of the type TiCl(2)(OR)(2). Epimerization of the C-4 methyl group in 21 and 23 to furnish the corresponding cis-dimethyl analogues was achieved via exo-epoxidation, regioselective reduction, oxidation to the corresponding 3-keto derivatives, and base-catalyzed equilibration, thereby affording (+/-)-3,6-dioxobakkenolide-A (39) and its epi-spiro derivative 28, respectively. When the radical cyclization step was performed subsequent to the Diels-Alder cycloaddition by photolysis of perhydrindane 43, only the epi-spiro product 44 was obtained.     

Displacement affinity chromatography of protein phosphatase one (PP1) complexes

Background  

Protein phosphatase one (PP1) is a ubiquitously expressed, highly conserved protein phosphatase that dephosphorylates target protein serine and threonine residues. PP1 is localized to its site of action by interacting with targeting or regulatory proteins, a majority of which contains a primary docking site referred to as the RVXF/W motif.     

Rearrangement in the mass spectrometer via a 3,3,1-bicyclic reaction path

The fragmentation of some azoacylals showed a 3,3,1 bicyclic rearrangement which could be demonstrated by a deuterium labelling study.     

Characterizing STEM Teacher Education: Affordances and Constraints of Explicit STEM Preparation for Elementary Teachers

Although science, technology, engineering, and mathematics (STEM) education sits at the center of a national conversation, comparatively little attention has been given to growing need for STEM teacher preparation, particularly at the elementary level. This study analyzes the outcomes of a novel, preservice STEM teacher education model. Building on both general and STEM‐specific teacher preparation principles, this program combined two traditional mathematics and science methods courses into one STEM block. Analysis compared preservice teachers in the traditional courses with those enrolled in the STEM block, investigating STEM teaching efficacy, reported and exhibited pedagogical practices, and STEM literacies using a pre‐post survey as well as analysis of lesson planning products. Linear regression models indicated that substantial growth was seen in both approaches but STEM block preservice teachers reported significantly greater gains in STEM teaching efficacy as compared with traditional‐route teachers. Lesson planning artifacts also demonstrated increased facilitation of STEM literacies, with specific attention to content integration, engineering and design, and arts inclusion. Technology and computational thinking emerged as areas for further growth and clarification in STEM teacher education models. Findings contribute to a growing research base on developing the STEM teacher workforce.     

Resonance line radiative transfer for hot atom coronae using Kappa distributions

Hot atomic populations are an important component of the planetary exospheres. Usually, radiative transfer models describing the scattering of light by moving atoms assume that these populations have a Maxwellian velocity distribution. However, the velocity distributions of the hot populations could actually have some more extended wings. Popular velocity distributions often used in plasma physics and recently proposed to describe neutral planetary environments are Kappa velocity function distributions. In this paper, following the work of Hummer [Non-coherent scattering: I The redistribution functions with Doppler broadening. R Astron. Soc Month Not 1962;125:21] and Cranmer [Non-Maxwellian redistribution in solar coronal Lyα emission. Astrophys J 1998;508:925–39], we calculate the frequency redistribution functions of radiation scattered by moving atoms with Kappa velocity distribution. We also present a detailed study of a radiative transfer model taking into account Kappa velocity distribution functions, for integer and semi-integer values of κ. We apply this theory to a model of Jupiter hydrogen corona containing 0.1% column density of hot hydrogen to quantify the spectroscopic and imaging differences between Kappa velocity distributions and bi-Maxwellian velocity distributions. When assuming a Kappa velocity distribution with κ=2 for the hot population, intensity increases of 40% occur at the bright limb and 15% on the disk compared with the same calculations done using a Maxwellian velocity distribution. The line profile differs slightly from a Maxwellian distribution on the disk and at the bright limb, but the difference is larger above the limb. Kappa distributions used to study the Jovian atmosphere are speculative and further studies are needed to link the formation of the hot exospheric populations to the Kappa velocity distributions.     

Chemo- and regioselective cyclohydrocarbonylation of alpha-keto alkynes catalyzed by a zwitterionic rhodium complex and triphenyl phosphite

alpha-Keto alkynes react with CO and H(2) in the presence of catalytic quantities of the zwitterionic rhodium complex (eta(6)-C(6)H(5)BPh(3))(-)Rh(+)(1,5-COD) and triphenyl phosphite affording either the 2-, 2(3H)-, or 2(5H)-furanones in 61-93% yields. The cyclohydrocarbonylation is readily accomplished using substrates containing alkyl, aryl, vinyl, and alkoxy groups at the acetylenic terminal, as well as a variety of primary, secondary, and tertiary alkyl, aryl, and heteroaryl groups connected to the ketone functionality. Structural and electronic properties present in the starting materials mediate the chemo- and regioselectivity of the reaction.     

Molecular Understanding of Collagen Stabilization: Interaction of Valeraldehyde with Collagen

The present study explains the molecular level interaction of valeraldehyde with collagen. Valeraldehyde is a monoaldehyde, which involves crosslinking with protein through covalent linkages. The role of valeraldehyde as a crosslinking agent for collagen stabilization was studied. Molecular modeling approaches was used to understand the interaction of collagen like peptide with valeraldehyde, which mimic the aldehyde tanning processes involved in protein stabilization. Crosslinking efficiency of valeraldehyde was found to increase with an increase in concentration due to the higher availability of aldehydic groups involved in crosslinking with collagen. Valeraldehyde interacted collagen membrane showed an increase in thermal stability by 25°C at pH 8. In the presence of valeraldehyde, collagen fibrils nucleation center was shifted from a lower to a higher range. Shift in the nucleation center was observed in the reduction of gelling time. Water accessibility in valeraldehyde interacted collagen membrane was reduced due to a higher crosslinking rate in the collagen. Modified collagen membrane by valeraldehyde at incubation of about 96 h showed higher resistance to collagenolytic activity of 81%. The amino groups reacting appear to be involved in crosslinking with valeraldehyde. Several interaction sites were identified and the docking energy obtained was ?5.539 kcal/mol. The participation of the aldehyde group with amino groups in collagen was observed, which plays a dominant role in the stabilization of peptide by valeraldehyde. It was found that complexes exhibit covalent bonding, hydrogen bonding and electrostatic interaction in the process of stabilization.     

CuCl-mediated intramolecular oxidative coupling of aryl- and alkenyltrimethylstannane functions

[reaction: see text] The syntheses of bis-trimethylstannanes 8, 10, 12-14, 16, 18, 21, and 22 are described. Treatment of these substances with approximately 5 equiv of CuCl in DMF at rt for 30-60 min effects, in each case, oxidative coupling between the two sp2 carbon centers bearing the Me3Sn function to produce good-to-excellent yields of tricyclic products 23-31, respectively.