Structure of scillicyanoside. 57. Section on cardiac glycosides

Based on chemical and NMR. evidence structure 1 is assigned to the cardioactive scillicyanoside isolated from white squill.     

A Note on Intramolecular Photochemical Cycloaddition of N-substituted Dimethacrylimides

The intramolecular photochemical [2+ 2]-cycloaddition of N-substituted dimethacrylimides 1a and 1c , respectively, proceeds under conditions of direct irradiation (λ = 254 nm) as well as triplet photosensitization highly regioselectively yielding predominantly the «cross» bonding (head-to-tail) cycloadducts 3a and 3c , respectively, with a 3-azabicyclo [3.1.1]heptane ring system.     

Effective transmission of light for media culture, plates and tubes

The results of many investigations on low‐level laser therapy are contradictory and this is due to the large number of illumination parameters as well as the inability to measure the possible effects after irradiation with the necessary objectivity and the fact that the light needs to pass thorough barriers (usually the plastic of the culture dish/plate and culture medium) to reach the cells. In this manner, the objective of this study was to determine the absorption coefficient, penetration depth and effective transmission in materials commonly used in cell cultures. Among the most commonly used wavelengths in low‐level laser therapy, the lowest absorption coefficients were reached by DMEM and RPMI (α = 0.03 cm^?1), from 633 to 690 nm, which reach an effective transmission of 93% of incident radiation and penetration depth of 33 cm. Among the solid materials in the same range of the electromagnetic spectrum, the lowest absorption coefficient was obtained for the polystyrene (Petri dish and well plate), with α = 1.31 cm^?1, 78% of effective transmission and 0.76 cm of penetration depth. This article also presents a simple equation for estimating the amount of energy that will actually reach the sample.     

A Computationally Efficient Oracle Estimator for Additive Nonparametric Regression with Bootstrap Confidence Intervals

Abstract

This article makes three contributions. First, we introduce a computationally efficient estimator for the component functions in additive nonparametric regression exploiting a different motivation from the marginal integration estimator of Linton and Nielsen. Our method provides a reduction in computation of order n which is highly significant in practice. Second, we define an efficient estimator of the additive components, by inserting the preliminary estimator into a backfitting˙ algorithm but taking one step only, and establish that it is equivalent, in various senses, to the oracle estimator based on knowing the other components. Our two-step estimator is minimax superior to that considered in Opsomer and Ruppert, due to its better bias. Third, we define a bootstrap algorithm for computing pointwise confidence intervals and show that it achieves the correct coverage.     

Influence of the alignment of load and oscillation on the frictional shakedown of an elastic rolling contact with Coulomb friction

We examine frictional shakedown of a three dimensional elastic rolling contact. Slight oscillatory rolling of one contacting body varies the normal pressure distribution. In turn this causes incremental sliding processes and a macroscopic rigid body motion. We consider two settings: tangential force and rolling direction aligned parallel and perpendicular to each other. In both cases, the slip ceases after the first few periods and a safe shakedown occurs if the oscillation is sufficiently small. Otherwise ratcheting occurs and the accumulated slip leads to a continuing rigid body motion.Numerical simulations with Kalker’s and Vollebregt’s software CONTACT show that the rolling direction leads to differences in the contact region and the traction distribution. Using the method of dimensionality reduction we derive the analytical shakedown limits for the tangential load and the oscillation amplitude. The results show strong agreement with experimental data and allow the accurate prediction of the shakedown displacement and the maximum tangential load capacity in the shakedown state. It shows that a perpendicular alignment of force and rolling direction increases the final displacement in case of shakedown as well as the incremental shift in case of ratcheting.     

Cyclopropylphenylcarbene - thermal control of intermolecular addition

At 25°, photolytically generated cyclopropylphenylcarbene affords phenylcyclobutene (63%, by ring expansion), phenylacetylene (16%, by fragmentation), and only traces (<3%) of the adduct to isobutene; at lower temperatures, however, the latter compound becomes the major product.     

Optimal control of photoisomerization

We report on optimal control of the photoisomerization of 3,3-diethyl-2,2-thiacyanine iodide dissolved in methanol. Enhancement and reduction of the relative yield of cis to trans isomers are achieved; i.e., the quantum efficiency of the photoisomerization is controlled with optimally phase and amplitude shaped 400 nm femtosecond laser pulses. Single-parameter control schemes, like chirp or intensity variation, fail to change the ratio of the photoproducts. The successful modification of the molecular structure can be regarded as a first step towards controlled stereoselectivity in photochemistry.     

Indolo[3,3a,4-gh]chinoline und 10a, 6a-Iminopropanoindolo[3,3a,4-gh] chinoline. Stereospezifische Synthesen und Umlagerungen. Teil I. 8. Mitteilung über synthetische Indolverbindungen

The stereospecific cyclization of derivatives of 1-benzyl-5-oxo-1,3,4,5-tetrahydrobenzo[cd]indole to trans-octahydroindolo[3,3a,4-gh]quinolines 3 and 4 is described. The trans methyl esters ( 4b and 4c ) were converted with BF₃/CH₃OH to the thermodynamically more stable cis-epimers 5 . The structures and stereochemistry of the products, deduced from chemical evidence and analysis of models, are compatible with the NMR. data.     

Derivate des 5, 9-Methano-6, 7,8, 9-tetrahydro-5 H-benzocycloheptens und Umlagerungen zum 1, 4-Äthano-1,2,3,4-tetrahydronaphtalin-System

Derivatives of 5,9-Methano,7,8,9-tetrahydro-5H-benzocycloheptene and Rearrangements to the 1,4-Ethano-I,2,3,4-tetrahydronaphthalene System Reduction of the oxime 2 with Raney alloy gives the amine 3a , with AlH₃ a mixture of the isomeric amines 3a and 3b , whilst LiAlH₄ yields the aziridines 4a and 4b . The bicyclo[3.2.1]octane 4b rearranges under acidic conditions to the bicyclo[2.2.2]octane 5 . The olefin 7 can be converted to the aminoalcohol 9 via the epoxide 8 and to the amine 13 using iodine isocyanate: the carbon skeleto. remains intact. However, treatment of the olefin 17 with iodine isocyanate leads to the bicyclo[2.2.2]octanes 21 and 24 in which a skeletal rearrangement has taken place. The configuration was determined by NMR. and X-ray analysis.     

Boscialin and Boscialin 4′-O-Glucoside,Two New Compounds Isolated from the Leaves of Boscia salicifolia OLIV

Boscialin ( 1 ), a new compound structurally related to the ionones and abscisic acid, and its 4′-O-glucoside 2 were isolated from the MeOH extract of the leaves of the African medicinal plant Boscia salicifolia. The structures of the two compounds were determined mainly by NMR spectroscopy and by acid hydrolysis of the glycoside.