Acid-promoted reaction of the stilbene antioxidant resveratrol with nitrite ions: mild phenolic oxidation at the 4'-hydroxystiryl sector triggering nitration, dimerization, and aldehyde-forming routes

In 0.1 M phosphate buffer, pH 3.0, and at 37 degrees C, resveratrol ((E)-3,4',5-trihydroxystilbene, 1a), an antioxidant and cancer chemopreventive phytoalexin, reacted smoothly at 25 microM or 1 mM concentration with excess nitrite ions (NO2(-)) to give a complex pattern of products, including two novel regioisomeric alpha-nitro (3a) and 3'-nitro (4) derivatives along with some (E)-3,4',5-trihydroxy-2,3'-dinitrostilbene (5), four oxidative breakdown products, 4-hydroxybenzaldehyde, 4-hydroxy-3-nitrobenzaldehyde, 3,5-dihydroxyphenylnitromethane, and 3,5-dihydroxybenzaldehyde, two dimers, the resveratrol (E)-dehydrodimer 6 and restrytisol B (7), and the partially cleaved dimer 2. The same products were formed in the absence of oxygen. 1H,15N HMBC and LC/MS analysis of the crude mixture obtained by reaction of 1a with Na (15)NO2 suggested the presence of 3,4',5,beta-tetrahydroxy-alpha-nitro-alpha,beta-dihydrostilbene (8) as unstable intermediate which escaped isolation. Under similar conditions, the structurally related catecholic stilbene piceatannol ((E)-3,3',4,5'-tetrahydroxystilbene, 1b) gave, besides (E)-3,3',4,5'-tetrahydroxy-beta-nitrostilbene (3b), 3,4-dihydroxybenzaldehyde and small amounts of 3,5-dihydroxybenzaldehyde. Mechanistic experiments were consistent with the initial generation of the phenoxyl radical of 1a at 4'-OH, which may undergo free radical coupling with NO2 at the alpha- or 3'-position, to give eventually nitrated derivatives and/or oxidative double bond fission products, or self-coupling, to give dimers. The oxygen-independent, NO2(-)-mediated oxidative fission of the double bond under mild, physiologically relevant conditions is unprecedented in stilbene chemistry and is proposed to involve breakdown of hydroxynitro(so) intermediates of the type 8.     

Polyamine concentration, transglutaminase activity and changes in protein synthesis during cryopreservation of shoot tips of apple variety Annurca

Changes in metabolism and protein expression were analysed during cryopreservation of the ancient apple variety Annurca. Our experiments concerned transglutaminase activity, polyamine levels and protein expression associated with shoot tip dehydration. Cryopreserved shoot tips displayed 72% regrowth after treatment in liquid medium with 0.75 M sucrose for 1 day followed by dehydration to 19% moisture content (fresh weight basis). After dehydration, the concentration of polyamines putrescine and spermidine decreased compared with untreated controls, while spermine concentration remained unaffected. Transglutaminase activity was slightly reduced in treated samples, while post-thaw regrowth enzyme activity approached control values. We also detected significant changes in protein expression profiles and identified six proteins related with stress response or involved in the slowing down of the cell cycle. The relationship between biochemical parameters, protein synthesis and cryotolerance is discussed.     

A new reaction in organosilicon chemistry: the oxidative fragmentation of γ-hydroxy silanes

The Ce⁺⁴ fragmentation of γ-hydroxy silanes leads to keto-olefins of predictable structure and stereochemistry.     

The reaction of 3-hydroxypyridine N-oxide with active hydrogen compounds and the synthesis of 3-substituted 2-aminofuro[3,2-b] pyridines

3-Hydroxypyridine N-oxide reacts readily in acetic anhydride with ethyl cyanoacetate, cyanoacetone and malononitrile. The three reaction products (2-substituted-3-acetoxypyridines) show different equilibria between tautomeric structures; in strong acids they undergo cyclization to 3-substituted 2-aminofuro[3,2-b]pyridines.     

Stereolabile and configurationally stable atropisomers of hindered aryl carbinols

Carbinols of the Ar-C(OH)R(2) type, Ar being o-isopropylphenyl, exist as stereolabile syn-clinal (sc) and anti-periplanar (ap) atropisomers when R = Me, Et, i-Pr. In the latter compound, the major atropisomer also comprises two enantiomeric forms that interchange with a barrier of 6.4 kcal mol(-1). X-ray diffraction, NOE experiments, and ab initio calculations indicate that the sc-atropisomer is the more stable form when R = Me, i-Pr, t-Bu but is the less stable one when R = Et. NMR spectra at variable temperature allowed the determination of the barriers for the interconversion of the sc- into the ap-atropisomers (DeltaG++ = 7.6, 8.8, and 13.5 kcal mol(-1) for Me, Et, i-Pr, respectively). When R is a tert-butyl group, the two atropisomers are configurationally stable: the ap-atropisomer is obtained as the kinetic controlled compound, which can be transformed into the thermodynamically more stable sc-atropisomer with a free energy of activation of 29.3 kcal mol(-1). Both atropisomers exhibit restricted rotation of the tert-butyl moiety, the corresponding DeltaG++ values being 9.4 and 8.8 kcal mol(-1) for the sc- and ap-atropisomer, respectively.     

Synthesis and Solid-State Conformation of a Calix[8]arene 1,5-Diquinone Derivative

The first example of a calix[8]quinone derivative, hexamethoxy-p-tert-butylcalix[8]-1,5-diquinone 5, has been synthesized from p-tert-butylcalix[8]arene 1by exploiting a protection-deprotection procedure. The structure of the 5·toluene inclusion compound has been determined by a single crystal X-ray diffraction study. The calix[8]arene molecule possesses a crystallographic inversion centre and assumes a ‘pseudo-chair-like’ conformation, with two opposite 3/4-cone moieties, which resembles the previously reported chair-like conformation of p-tert-butylcalix[8]arene. The 4 toluene molecules per unit cell occupy interstitial voids and are released in the temperature range of 30–160 °C.This revised version was published online in July 2005 with a corrected issue number.     

Minor cacospongionolide derivatives from the sponge Fasciospongia cavernosa

Together with the known cacospongionolide, three new related sesterterpenes have been isolated from the sponge Fasciospongia cavernosa, collected from the Northern Adriatic Sea. The structures of the new compounds were proposed on the basis of spectroscopic data.     

Low complexity secant quasi-Newton minimization algorithms for nonconvex functions

In this work some interesting relations between results on basic optimization and algorithms for nonconvex functions (such as BFGS and secant methods) are pointed out. In particular, some innovative tools for improving our recent secant BFGS-type and algorithms are described in detail.     

On the formulation of the planar ANCF triangular finite elements

In this paper, new planar isoparametric triangular finite elements (FE) based on the absolute nodal coordinate formulation (ANCF) are developed. The proposed ANCF elements have six coordinates per node: two position coordinates that define the absolute position vector of the node and four gradient coordinates that define vectors tangent to coordinate lines (parameters) at the same node. To shed light on the importance of the element geometry and to facilitate the development of some of the new elements presented in this paper, two different parametric definitions of the gradient vectors are used. The first parametrization, called area parameterization, is based on coordinate lines along the sides of the element in the reference configuration, while the second parameterization, called Cartesian parameterization, employs coordinate lines defined along the axes of the structure (body) coordinate system. The fundamental differences between the ANCF parameterizations used in this investigation and the parametrizations used for conventional finite elements are highlighted. The Cartesian parameterization serves as a unique standard for the triangular FE assembly. To this end, a transformation matrix that defines the relationship between the area and the Cartesian parameterizations is introduced for each element in order to allow for the use of standard FE assembly procedure and define the structure (body) inertia and elastic forces. Using Bezier geometry and a linear mapping, cubic displacement fields of the new ANCF triangular elements are systematically developed. Specifically, two new ANCF triangular finite elements are developed in this investigation, namely four-node mixed-coordinate and three-node ANCF triangles. The performance of the proposed new ANCF elements is evaluated by comparison with the conventional linear and quadratic triangular elements as well as previously developed ANCF rectangular and triangular elements. The results obtained in this investigation show that in the case of small and large deformations as well as finite rotations, all the elements considered can produce correct results, which are in a good agreement if appropriate mesh sizes are used.     

Whole 3D shape reconstruction of vascular segments under pressure via fringe projection techniques

Understanding and modelling vascular wall mechanics is a primary issue in the study of circulatory diseases. Although theoretical and numerical studies on arteries compliance are continuously increasing, relatively little work has been documented on the use of non-invasive imaging techniques for monitoring 3D vascular wall deformations. Usually, 2D video dimension analyzer (VDA) systems recover diameter and length variations during inflation/extension tests by tracking position changes of few markers put on the blood vessel surface. Then, strain determination relies on the assumption of axisymmetric deformations. However, more rigorous evaluations of whole wall deformation map are required for properly modelling the highly anisotropic and inhomogeneous vascular tissue mechanical response.

This paper describes the development and application of a fringe projection (FP)-based procedure for the 360° 3D shape reconstruction of tubular samples subjected to internal pressure. A specially designed fixture for mounting and inflating the tubular segment allows specimen rotation about its axis. Movement is controlled by a high-precision rotational stage. This yields accurate positioning of the surface to be investigated with respect to the viewing direction. Data point clouds obtained from multiple recorded images are then processed and merged in a CAD environment, thus providing the whole shape of the sample with very high spatial resolution.

The entire procedure has successfully been applied to latex specimens and porcine vascular segments. Further improvements will make the present procedure suitable for in vitro tests under more closely reproduced physiological conditions.