Structure revision and assignment of absolute stereochemistry of a marine C-21 bisfuranoterpene

The C-21 bisfuranoterpene (-)-isotetradehydrofurospongin-1 (6), previously isolated from a Western Australian Spongia sp., has been reisolated from a specimen of Spirastrella papilosa collected during scientific trawling operations in the Great Australian Eight. A 2D NMR analysis of 6 has prompted reassignment of the published structure 5, while degradation and chiral HPLC analysis have allowed determination of the absolute stereochemistry.

On the structure, electrochemistry, and spectroscopy of the (N,N'-bis(2'-(dimethylamino)ethyl)-N,N'-dimethylpropane-1,3-diamine)copper(II) ion

The synthesis, spectroscopy, and electrochemistry of the acyclic tertiary tetraamine copper(II) complex [CuL(1)](ClO4)(2) (L(1) = N,N-bis(2'-(dimethylamino)ethyl)-N,N'-dimethylpropane-1,3-diamine) is reported. The X-ray crystal structure of [CuL(1)(OClO3)(2)] reveals a tetragonally elongated CuN4O2 coordination sphere, exhibiting relatively long Cu-N bond lengths for a Cu-II tetraamine, and a small tetrahedral distortion of the CuN4 plane. The [CuL(1)](2+) ion displays a single, reversible, one-electron reduction at -0.06 V vs Ag/AgCl. The results presented herein illustrate the inherent difficulties associated with the separation and characterization of Cu-II complexes of tertiary tetraamines, and some previously incorrect assertions and unexplained observations of other workers are discussed.

Noninvasive tests of vascular function and structure: Why and how to perform them

Background Early atherosclerosis involves the endothelium of many arteries. Information about peripheral arterial anatomy and function derived from vascular imaging studies such as brachial artery reactivity (BAR) and carotid intima media thickness (IMT) may be pertinent to the coronary circulation. The prevention and early treatment of atherosclerosis is gaining more attention, and these tests might be used as indications or perhaps guides to the effectiveness of therapy, but their application in clinical practice has been limited. This review seeks to define the anatomy and pathophysiology underlying these investigations, their methodology, the significance of their Findings, and the issues that must be resolved before their application. Methods The literature on BAR and IMT is extensively reviewed, especially in relation to clinical use. Results Abnormal flow-mediated dilation is present in atherosclerotic vessels, is associated with cardiovascular risk factors, and may be a marker of preclinical disease. Treatment of known atherosclerotic risk Factors has been shown to improve flow-mediated dilation, and some data suggest that vascular responsiveness is related to outcome. Carotid IMT is associated with cardiovascular risk factors, and increased levels can predict myocardial infarction and stroke. Aggressive risk factor management can decrease IMT. Conclusions BAR and IMT ate functional and structural markers of the atherosclerotic process. The clinical use of BAR has been limited by varying reproducibility and the influence by exogenous factors, but IMT exhibits less variability. A desirable next step in the development of BAR and IMT as useful clinical tools would be to show an association of improvement in response to treatment with improvement in prognosis.

A generalised dynamic model for char particle gasification with structure evolution and peripheral fragmentation

A generalised model for the prediction of single char particle gasification dynamics, accounting for multi-component mass transfer with chemical reaction, heat transfer, as well as structure evolution and peripheral fragmentation is developed in this paper. Maxwell-Stefan analysis is uniquely applied to both micro and macropores within the framework of the dusty-gas model to account for the bidisperse nature of the char, which differs significantly from the conventional models that are based on a single pore type. The peripheral fragmentation and random-pore correlation incorporated into the model enable prediction of structure/reactivity relationships. The occurrence of chemical reaction within the boundary layer reported by Biggs and Agarwal (Chem. Eng. Sci. 52 (1997) 941) has been confirmed through an analysis of CO/CO2 product ratio obtained from model simulations. However, it is also quantitatively observed that the significance of boundary layer reaction reduces notably with the reduction of oxygen concentration in the flue gas, operational pressure and film thickness. Computations have also shown that in the presence of diffusional gradients peripheral fragmentation occurs in the early stages on the surface, after which conversion quickens significantly due to small particle size. Results of the early commencement of peripheral fragmentation at relatively low overall conversion obtained from a large number of simulations agree well with experimental observations reported by Feng and Bhatia (Energy & Fuels 14 (2000) 297). Comprehensive analysis of simulation results is carried out based on well accepted physical principles to rationalise model prediction. (C) 2001 Elsevier Science Ltd. AH rights reserved.

Sub-structure syntheses and relative stereochemistry in the bistramide (bistratene) series of marine metabolites

The (6R*,9S*,11S*) and (22S*,23R*,27R*,31R*) stereochemistry, respectively, of the tetrahydropyranyl and spiroacetal moieties in bistramide A (1) have been established by stereoselective syntheses and high field NMR comparisons. Routes to the gamma-amino acid moiety are outlined. (C) 2002 Elsevier Science Ltd. All rights reserved.

A suite of novel allenes from Australian melolonthine scarab beetles. Structure, synthesis, and stereochemistry

A suite of allenic hydrocarbons, previously unknown as a molecular class from insects, has been characterized from several Australian melolonthine scarab beetles. The allenes are represented by the formula CH3(CH2)nCH=.=CH(CH2)(7)CH3 with n being 11-15, 17 and 19, and thus, all have Delta(9,10)-unsaturation. These structures have been confirmed by syntheses and comparisons of spectral and chromatographic properties with those of the natural components. The enantiomers of (+/-)-Delta(9,10)-tricosadiene and Delta(9,10)-pentacosadiene were separable on a modified beta-cyclodextrin column (gas chromatography), and the natural Delta(9,10)-tricosadiene (n = 11) and Delta(9,10)-pentacosadiene (n = 13) were shown to be of >85% ee. Syntheses of nonracemic allenes of known predominating chirality were acquired using both organotin chemistry and sulfonylhydrazine intermediates, and comparisons then demonstrated that the natural allenes were predominantly (R)-configured.

Noninvasive tests for arterial structure, function, and compliance: Do they identify risk or diagnose disease?

Background: Brachial artery reactivity (BAR), carotid intima-media thickness (IMT), and applanation tonometry for evaluation of total arterial compliance may provide information about preclinical vascular disease. We sought to determine whether these tests could be used to identify patients with coronary artery disease (CAD) without being influenced by their ability to identify those at risk ford CAD developing. Methods: We studied 100 patients and compared 3 groups: 35 patients with known CAD; 34 patients with symptoms and risk factors but no CAD identified by stress echocardiography (risk group); and 31 control subjects. BAR and IMT were measured using standard methods, and total arterial compliance was calculated by the pulse-pressure method from simultaneous radial applanation tonometry and pulsed wave Doppler of the left ventricular outflow. Ischemia was identified as a new or worsening wall-motion abnormality induced by stress. Results: In a comparison between the control subjects and patients either at risk for developing CAD or with CAD, the predictors of risk for CAD were: age (P = .01); smoking history (P = .002); hypercholesterolemia (P = .002); and hypertension (P = .004) (model R = 0.82; P = .0001). The independent predictors of CAD were: IMT (P = .001); BAR (P = .04); sex (P = .005); and hypertension (P = .005) (model R = 0.80; P = .0001). Conclusion: IMT, BAR, and traditional cardiovascular risk factors appear to identify patients at risk for CAD developing. However, only IMT was significantly different between patients at risk for developing CAD and those with overt CAD.

Marine isocyanides and related natural products structure, biosynthesis and ecology

This review highlights structural and biosynthetic work on a group of nitrogen-functionalised terpenes that are almost exclusively found in marine invertebrates and the animals that feed on them. The chemical functionality reviewed includes isocyanides, isothiocyanates, formamides, thiocyanates, isocyanates, and dichloroimines. The literature through mid 2003 is reviewed and there are 143 citations.

Semisolid structure formation and semisolid casting

Semisolid metal forming has now been accepted as a viable technology for production of components with complex shape and high integrity. The advantages of semisolid metal forming can only be achieved when the feedstock material has a non-dendritic semisolid structure. A controlled nucleation method has been developed to produce such structures for semisolid forming. By controlling grain nucleation and growth, fine-grained and non-dendritic microstructures that are suitable for semisolid casting can be generated. The method was applied to hypoeutectic and hypereutectic Al-Si casting alloys, Al wrought alloys and a Mg alloy. Parameters such as pouring temperature, cooling rate and grain refiner addition were controlled to achieve copious nucleation, nuclei survival and dendritic growth suppression during solidification. The influences of the controlling parameters on the formation of semisolid structure were different for each of these alloy groups. The as-cast structures were then partially remelted and isothermally held. Semisolid structures were developed and followed by semisolid casting into a stepped die.

NaSi-1 and Sat-1: structure, function and transcriptional regulation of two genes encoding renal proximal tubular sulfate transporters

Sulfate (SO42-) is an important anion regulating many metabolic and cellular processes. Maintenance Of SO42- homeostasis occurs in the renal proximal tubule via membrane transport proteins. Two SO42- transporters that have been characterized and implicated in regulating serum SO42- levels are: NaSi- 1, a Na+-SO4 (2-) cotransporter located at the brush border membrane and Sat-1, a SO4 (2-) -anion exchanger located on the basolateral membranes of proximal tubular cells. Unlike Sat-1, for which very few studies have looked at regulation of its expression, NaSi- 1 has been shown to be regulated by various hormones and dietary conditions in vivo. To study this further, NaSj- I (SLC13A1) and Sat- I (SLC26A1) gene structures were determined and recent studies have characterized their respective gene promoters. This review presents the current understanding of the transcriptional regulation of NaSj- I and Sat- 1, and describes possible pathogenetic implications which arise as a consequence of altered SO(4)(2-)homeostasis. (c) 2005 Elsevier Ltd. All rights reserved.

A novel suite of cyclotides from Viola odorata: sequence variation and the implications for structure, function and stability

Cyclotides are a fascinating family of plant-derived peptides characterized by their head-to-tail cyclized backbone and knotted arrangement of three disulfide bonds. This conserved structural architecture, termed the CCK (cyclic cystine knot), is responsible for their exceptional resistance to thermal, chemical and enzymatic degradation. Cyclotides have a variety of biological activities, but their insecticidal activities suggest that their primary function is in plant defence. In the present study, we determined the cyclotide content of the sweet violet Viola odorata, a member of the Violaceae family. We identified 30 cyclotides from the aerial parts and roots of this plant, 13 of which are novel sequences. The new sequences provide information about the natural diversity of cyclotides and the role of particular residues in defining structure and function. As many of the biological activities of cyclotides appear to be associated with membrane interactions, we used haemolytic activity as a marker of bioactivity for a selection of the new cyclotides. The new cyclotides were tested for their ability to resist proteolysis by a range of enzymes and, in common with other cyclotides, were completely resistant to trypsin, pepsin and thermolysin. The results show that while biological activity varies with the sequence, the proteolytic stability of the framework does not, and appears to be an inherent feature of the cyclotide framework. The structure of one of the new cyclotides, cycloviolacin O14, was determined and shown to contain the CCK motif. This study confirms that cyclotides may be regarded as a natural combinatorial template that displays a variety of peptide epitopes most likely targeted to a range of plant pests and pathogens.