Enantioselective Intramolecular Michael Addition of Nitronates onto Conjugated Esters: Access to Cyclic γ-Amino Acids with up to Three Stereocenters

A highly stereoselective synthesis of conformationally constrained cyclic γ-amino acids has been devised. The key step involves an intramolecular cyclization of a nitronate onto a conjugated ester, promoted by a bifunctional thiourea catalyst. This methodology has been successfully applied to generate a variety of γ-amino acids, including some containing three contiguous stereocenters, with very high diastereoselectivity and excellent enantioselectivity. It is postulated that an interaction that is key to the success of the process is the simultaneous coordination of the thiourea functionality to both the conjugated ester and the nitronate. Finally, the synthetic utility of these compounds is demonstrated in the synthesis of two dipeptides derived from the C- and N-termini.

Effect of addition of protein fractions extracted from flours of different baking quality on gluten rheology

The effect of change of the rheological properties of gluten with the addition of fractions with specific molecular weight was investigated. Fractions extracted from Hereward, Riband and Soissons flours were added to the dough prior to gluten extraction. Once extracted, the glutens were subjected to temperature sweeps and creep recovery rheological tests. In the temperature sweeps, Hereward fractions containing the larger polypeptides had a strengthening effect on the gluten, indicated by a decrease in tan delta and an increase in elastic creep recovery, while those fractions that comprised monomeric gliadins had a weakening effect. Adding total gluten also had a strengthening effect. For the biscuit-making flour Riband, the results were quite the reverse: all fractions appeared to strengthen the gluten network, while the addition of total gluten did not have a strengthening effect. For Soissons gluten, the addition of total gluten had a strengthening effect while adding any individual fraction weakened the gluten. The results were confirmed with creep-recovery tests.

Enhancing the oxidative stability of rice crackers by addition of the ethanolic extract of phytochemicals from Cratoxylum formosum Dyer

Craloxylum formosum Dyer is consumed throughout the year as food and medicine in Thailand. It contains large amounts of chlorogenic acid and quinic acid derivatives. The antioxidative activity of the extract was studied in refined soybean oil coating on rice crackers without any seasoning. They were stored in accelerated oxidation conditions at 40 degrees C, 80% relative humidity (RH) in the dark for 18 days. The oxidative state of each sample was monitored by analyzing of the peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) as well as by odor analysis by quantitative descriptive analysis (QDA). The C formosum extract was more effective than alpha-tocopherol due to metal ions present in the crackers, which resulted in alpha-tocopherol being less effective as an antioxidant. Sensory odor attributes of rice crackers were related more closely to TBARS than to PV values by linear regression analysis. The present study indicated that C. formosum extract was a promising source of a natural food antioxidant and was effective in inhibiting lipid oxidation in rice crackers.

A homo-proline tetrazole as an improved organocatalyst for the asymmetric Michael addition of carbonyl compounds to nitro-olefins

A new homo-proline tetrazole derivative 7 has been prepared and shown to have improved properties for achieving asymmetric Michael addition of carbonyl compounds to nitro-olefins.

Metal cluster expansion by addition of low valent group 14 reagents: III. Reaction of bis[bis(trimethylsilyl)methyl]tin with M3(CO)12 or its derivatives (M = Fe, Ru, or Os): the crystal and molecular structures of M3(μ-SnR2)2(CO)10(R = CH(SiMe3)2; M = Ru or Os)

The stannylene [SnR2] (R = CH(SiMe3)2) reacts in different ways with the three dodecacarbonyls of the iron triad: [Fe3(CO)12] gives [Fe2(CO)8(μ-SnR2)], [Ru3(CO)12] gives the planar pentametallic cluster [Ru3(CO)10(μ-SnR2)2], for which a full structural analysis is reported, while [Os3(CO)12] fails to react. Different products are also obtained from three nitrile derivatives: [Fe3-(CO)11(MeCN)] gives [Fe2(CO)6(μ-SnR2)2], which has a structure significantly different from that of known Fe2Sn2 clusters, [Ru3(CO)10(MeCN)2] gives the pentametallic cluster described above, while [Os3(CO)10(MeCN)2] gives the isostructural osmium analogue, which shows the unusual feature of a CO group bridging two osmium atoms.

Metal cluster expansion by addition of low-valent group 4B reagents: crystal and molecular structure of [Os3SnH2(CO)10{CH(SiMe3)2}2]; a compound with hydrogen bridging osmium and tin

Cluster expansion of [Os3H2(CO)10] with [SnR2][R = CH(SiMe3)2] take place in high yield to give [Os3SnH2(CO)10R2], the first closed triosmium–main-group metal cluster to be structurally characterized; a novel feature is the presence of a hydrogen atom bridging the tin atom and one of the osmium atoms.

Effects of addition of phenolic compounds on the acid gelation of milk

Tannic acid (0.1–1%, w/w) and gallic acid (0.3–1%, w/w) were added to skim milk prior to acidification with GDL. The acid gelation of tannic and gallic acid fortified milk had a faster gelation time in comparison with the control gel without phenolic compounds. The addition of tannic acid and gallic acid (up to 0.8%) to the milk resulted in a higher storage modulus (G′), decrease in the water mobility (T2 time) and had no significant effect on the syneresis index (SI). However, the inclusion of 1% gallic acid resulted in a significant decrease in G′, a significant increase in the SI and a wider T2 distribution. Lowering the temperature of the gels from 30 to 5 °C caused the G′ for the gels with gallic and tannic acid to increase significantly in comparison with the control, possibly due to increased hydrogen bonding in the presence of phenolic compounds

Reversible addition of CO to coordinatively unsaturated high-spin iron(II) complexes

Several new coordinatively unsaturated iron(II) complexes of the types [Fe(EN-iPr)X2] (E = P, S, Se; X = Cl, Br) and [Fe(ON-iPr)2X]X containing bidentate EN ligands based on N-(2-pyridinyl)aminophosphines as well as oxo, thio, and seleno derivatives thereof were prepared and characterized by NMR spectroscopy and X-ray crystallography. Mössbauer spectroscopy and magnetization studies confirmed their high-spin nature with magnetic moments very close to 4.9 μB, reflecting the expected four unpaired d-electrons in all these compounds. Stable low-spin carbonyl complexes of the types [Fe(PN-iPr)2(CO)X]X (X = Cl, Br) and cis-CO,cis-Br-[Fe(PN-iPr)(CO)2X2] (X = Br) were obtained by reacting cis-Fe(CO)4X2 with the stronger PN donor ligands, but not with the weaker EN donor ligands (E = O, S, Se). Furthermore, the reactivity of [Fe(PN-iPr)X2] toward CO was investigated by IR spectroscopy. Whereas at room temperature no reaction took place, at −50 °C [Fe(PN-iPr)X2] added readily CO to form, depending on the nature of X, the mono- and dicarbonyl complexes [Fe(PN-iPr)(X)2(CO)] (X = Cl) and [Fe(PN-iPr)(CO)2X2] (X = Cl, Br), respectively. In the case of X = Br, two isomeric dicarbonyl complexes, namely, cis-CO,trans-Br-[Fe(PN-iPr)(CO)2Br2] (major species) and cis-CO,cis-Br-[Fe(PN-iPr)(CO)2Br2] (minor species), are formed. The addition of CO to [Fe(PN-iPr)X2] was investigated in detail by means of DFT/B3LYP calculations. This study strongly supports the experimental findings that at low temperature two isomeric low-spin dicarbonyl complexes are formed. For kinetic reasons cis,trans-[Fe(PN-iPr)(CO)2Br2] releases CO at elevated temperature, re-forming [Fe(PN-iPr)Br2], while the corresponding cis,cis isomer is stable under these conditions.

Addition of different fats to a carbohydrate food: impact on gastric emptying, glycaemic and satiety responses and comparison with in vitro digestion

In vitro, the addition of lipids to a carbohydrate food has been found to increase the digestibility of starch. In contrast, in vivo studies have shown that the addition of fat to a food can reduce the glycaemic response (GR). The aim of this study was to assess if delayed gastric emptying (GE) causes reduced GR with the addition of lipids to a carbohydrate food and if a relationship between GR and in vitro digestion of starch exists for high fat foods. Ten healthy volunteers were tested on five occasions after consuming pancakes containing 50 g of available carbohydrate and 202 kcal of sunflower oil, olive oil, butter, medium chain triglyceride (MCT) oil or a control containing no oil. GR was measured using fingerpick blood samples, satiety using visual analogue scales and GE using the 13C octanoic acid breath test. There was a significant difference in GR between the different pancake breakfasts (p = 0.05). The highest GR was observed following the control pancakes and the lowest following the olive oil pancakes. There were significant differences in GE half time, lag phase and ascension time (p < 0.05) between the different pancakes with the control pancakes having the shortest GE time and the MCT pancakes the longest. There was a significant difference in satiety parameters fullness (p = 0.003) and prospective consumption (p = 0.050), with satiety being lowest following the control pancakes. There was a significant inverse correlation between the GR and all satiety parameters. A significant inverse correlation (p = 0.009) was also observed between the digestibility of starch in vitro and GR in vivo. The paper indicates that the digestibility of starch in vitro does not predict the GR for high fat containing foods

Effects of stabiliser addition and in-container sterilisation on selected properties of milk related to casein micelle stability

Different stabilising salts and calcium chloride were added to raw milk to evaluate changes in pH, ionic calcium, ethanol stability, casein micelle size and zeta potential. These milk samples were then sterilised at 121 °C for 15 min and stored for 6 months to determine how these properties changed. Addition of tri-sodium citrate (TSC) and di-sodium hydrogen phosphate (DSHP) to milk reduced ionic calcium, increased pH and increased ethanol stability in a concentration-dependent fashion. There was relatively little change in casein micelle size and a slight decrease in zeta potential. Sodium hexametaphosphate (SHMP) also reduced ionic calcium considerably, but its effect on pH was less noticeable. In contrast, sodium dihydrogen phosphate (SDHP) reduced pH but had little effect on ionic calcium. In-container sterilisation of these samples reduced pH, increased ethanol stability and increased casein micelle size, but had variable effects on ionic calcium; for DSHP and SDHP, ionic calcium decreased after sterilisation but, for SHMP, it remained little changed or increased. Milk containing 3.2 mM SHMP and more than 4.5 mM CaCl2 coagulated upon sterilisation. All other samples were stable but there were differences in browning, which increased in intensity as milk pH increased. Heat-induced sediment was not directly related to ionic calcium concentration, so reducing ionic calcium was not the only consideration in terms of improving heat stability. After 6 months of storage, the most acceptable product, in appearance, was that containing SDHP, as this minimised browning during sterilisation and further development of browning during storage.

In vitro evaluation of fibrolytic enzymes as additives for maize (Zea mays L.) silage - I. Effects of ensiling temperature, enzyme source and addition level

A series of experiments was completed to investigate the impact of addition of enzymes at ensiling on in vitro rumen degradation of maize silage. Two commercial products, Depot 40 (D, Biocatalysts Ltd., Pontypridd, UK) and Liquicell 2500 (L, Specialty Enzymes and Biochemicals, Fresno, CA, USA), were used. In experiment 1, the pH optima over a pH range 4.0-6.8 and the stability of D and L under changing pH (4.0, 5.6, 6.8) and temperature (15 and 39 degreesC) conditions were determined. In experiment 2, D and L were applied at three levels to whole crop maize at ensiling, using triplicate 0.5 kg capacity laboratory minisilos. A completely randomized design with a factorial arrangement of treatments was used. One set of treatments was stored at room temperature, whereas another set was stored at 40 degreesC during the first 3 weeks of fermentation, and then stored at room temperature. Silages were opened after 120 days. Results from experiment I indicated that the xylanase activity of both products showed an optimal pH of about 5.6, but the response differed according to the enzyme, whereas the endoglucanase activity was inversely related to pH. Both products retained at least 70% of their xylanase activity after 48 h incubation at 15 or 39 degreesC. In experiment 2, enzymes reduced (P < 0.05) silage pH, regardless of storage temperature and enzyme level. Depol 40 reduced (P < 0.05) the starch contents of the silages, due to its high alpha-amylase activity. This effect was more noticeable in the silages stored at room temperature. Addition of L reduced (P < 0.05) neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents. In vitro rumen degradation, assessed using the Reading Pressure Technique (RPT), showed that L increased (P < 0.05) the initial 6 h gas production (GP) and organic matter degradability (OMD), but did not affect (P > 0.05) the final extent of OMD, indicating that this preparation acted on the rumen degradable material. In contrast, silages treated with D had reduced (P < 0.05) rates of gas production and OMD. These enzymes, regardless of ensiling temperature, can be effective in improving the nutritive quality of maize silage when applied at ensiling. However, the biochemical properties of enzymes (i.e., enzymic activities, optimum pH) may have a crucial role in dictating the nature of the responses. (C) 2003 Elsevier B.V. All rights reserved.

Multitrophic effects of nutrient addition in upland grassland

Although the effects of nutrient enhancement on aquatic systems are well documented, the consequences of nutritional supplements on soil food webs are poorly understood, and results of past research examining bottom-up effects are often conflicting. In addition, many studies have failed to separate the effects of nutrient enrichment and the physical effects of adding organic matter. In this field study, we hypothesised that the addition of nitrogen to soil would result in a trophic cascade, through detritivores (Collembola) to predators (spiders), increasing invertebrate numbers and diversity. Nitrogen and lime were added to plots in an upland grassland in a randomised block design. Populations of Collembola and spiders were sampled by means of pitfall traps and identified to species. Seventeen species of Collembola were identified from the nitrogen plus lime (N + L) and control plots. Species assemblage, diversity, richness, evenness and total number were not affected by nutrient additions. However, there was an increase in the number of Isotomidae juveniles and Parisotoma anglicana trapped in the N + L plots. Of the 44 spider species identified, over 80% were Linyphiidae. An effect on species assemblage from the addition of N + L to the plots was observed on two of the four sampling dates (July 2002 and June 2003). The linyphiid, Oedothorax retusus, was the only species significantly affected by the treatments and was more likely to be trapped in the control plots. The increased number of juvenile Collembola, and change in community composition of spiders, were consequences of the bottom-up effect caused by nutrient inputs. However, despite efforts to eliminate the indirect effects of nutrient inputs, a reduction in soil moisture in the N + L plots cannot be eliminated as a cause of the invertebrate population changes observed. Even so, this experiment was not confounded by the physical effects of habitat structure reported in most previous studies. It provides evidence of moderate bottom-up influences of epigeic soil invertebrate food webs and distinguishes between nutrient addition and plant physical structure effects. It also emphasises the importance Of understanding the effects of soil management practices on soil biodiversity, which is under increasing pressure from land development and food production.

Relative importance of fertiliser addition to plants and exclusion of predators for aphid growth in the field

Herbivore dynamics and community structure are influenced both by plant quality and the actions of natural enemies. A factorial experiment manipulating both higher and lower trophic levels was designed to explore the determinants of colony growth of the aphid Aphis jacobaeae, a specialist herbivore on ragwort Senecio jacobaea. Potential plant quality was manipulated by regular addition of NPK-fertiliser and predator pressure was reduced by interception traps; the experiment was carried out at two sites. The size and persistence of aphid colonies were measured. Fertiliser addition affected plant growth in only one site, but never had a measurable effect on aphid colony growth. In both habitats the action of insect predators dominated, imposing strong and negative effects on aphid colony performance. Ants were left unmanipulated in both sites and their performance on the aphid colonies did not significantly differ between sites or between treatments. Our results suggest that, at least for aphid herbivores on S. jacobaea, the action of generalist insect predators appears to be the dominant factor affecting colony performance and can under certain conditions even improve plant productivity.

Effects of hydrocolloid addition and high pressure processing on the rheological properties and microstructure of a commercial ostrich meat product "Yor" (Thai sausage)

"Yor" is a traditional sausage like product widely consumed in Thailand. Its textures are usually set by steaming, in this experiment ultra-high pressure was used to modify the product. Three types of hydrocolloid; carboxymethylcellulose (CMC), locust bean gum (LBG) and xanthan gum, were added to minced ostrich meat batter at concentration of 0-1% and subjected to high pressure 600 Mpa, 50 degrees C, 40 min. The treated samples were analysed for storage (G) and loss (G '') moduli by dynamic oscillatory testing as well as creep compliance for control stress measurement. Their microstructures using confocal microscopy were also examined. Hydrocolloid addition caused a significant (P < 0.05) decrease in both the G' and G '' moduli. However the loss tangent of all samples remained unchanged. Addition of hydrocolloids led to decreases in the gel network formation but appears to function as surfactant materials during the initial mixing stage as shown by the microstructure. Confocal microscopy suggested that the size of the fat droplets decreased with gum addition. The fat droplets were smallest on the addition of xanthan gum and increased in the order CMC, LBG and no added gum, respectively. Creep parameters of ostrich yors with four levels of xanthan gum addition (0.50%, 0.75%, 1.00% and 1.25%) showed an increase in the instantaneous compliance (J(0)), the retarded compliance (J(1)) and retardation time (lambda(1)) but a decrease in the viscosity (eta(0)) with increasing levels of addition. The results also suggested that the larger deformations used during creep testing might be more helpful in assessing the mechanical properties of the product than the small deformations used in oscillatory rheology. (c) 2007 Elsevier Ltd. All rights reserved.

Asymmetric synthesis of cyclic β-amino acids and cyclic amines via sequential diastereoselective conjugate addition and ring closing metathesis

Diastereoselective conjugate addition of lithium (S)-N-allyl-N-alpha-methylbenzylamide to a range of alpha,beta-unsaturated esters followed by ring closing metathesis is used to afford efficiently a range of substituted cyclic beta-amino esters in high d.e. Alternatively, conjugate addition to alpha,beta-unsaturated Weinreb amides, functional group conversion and ring closing metathesis affords cyclic amines in high d.e. The further application of this methodology to the synthesis of a range of carbocyclic beta-amino esters via conjugate addition, enolate alkylation and ring closing metathesis is also described. Application of this methodology affords, after deprotection, (S)-homoproline, (S)-homopipecolic acid, (S)-coniine and (1S,2S)-trans-pentacin.