Synthetic Studies in Natural Product Chemistry

I. A stereospecific total synthesis of D-(-)-shikimic acid: The evidence which led to assignment of the structure and absolute stereochemistry of shikimic acid is reviewed. The role of shikimic acid in biosyntnesis is discussed, including its transformation into aromatic amino-acids, lignin and alkaloids, as is its formation from carbohydrates. A synthetic approach to shikimic acid via the dehydroacid corresponding to XXII was unsuccessful. The Diels-Alder adduct (XXXI) of trans-trans-1,4-diacetoxybutadiene and acrylic acid provided the starting point for a successful synthesis. Hydroxylation with osmium tetroxide, isoprepylation and elimination of acetic acid led to (+/-)-shikimic acid which was resolved via the quinine methohydroxy-salt of the corresponding triacetate. II. The catalytic hydrogenation of cyclic anhydrides: Catalytic hydrogenation of the adduct (XXIV) prepared in Part (I) led, in addition to the expected saturated anhydride (XXIX), to the lactol (XXXV), the lactone (XXXVIII) and the acid (XXXIX). A series of anhydrides, chosen to throw light on the influence of structure on the course of hydrogenation, were subjected to catalytic reduction. The three possible products were not obtained in all cases. An attempt is made to rationalise the observed products in terms of the structures of the initial adducts and postulated intermediates. III. Approaches to the total synthesis of diterpenoids:- Published diterpene synthesis are briefly reviewed. Two projected routes to dl-ambreinolide, which is capable of further transformation into the naturally occurring bicyclic diterpenes such as manool, sclareol, cativic acid, and labdanolic acid, are outlined. The first route, based on the condensation of 2-methyl-cyclopentane-1,3-dione with ethyl vinyl ketone, failed when elaboration of the bicyclic enone (CXVI) was attempted. A second approach envisaged the simultaneous formation of rings (A) and (B) by condensation of the vinyl ketone (CXLVI) with the cyclopentanedione. The preparation of this vinyl ketone is recorded

Slurry nebulization ICP-OES for the determination of Cu, Fe, Mg, Mn and Zn

A method that involves analysis of bovine liver by slurry nebulization and ICP-OES has been developed. This method permits rapid and accurate determination of Cu, Fe, Mg, Mn and Zn in bovine liver. Aliquots of freeze-dried and powdered bovine liver sample were dispersed in 2.0 M HNO3 and sonicated to homogenize the resulting slurries. Bovine liver samples were also microwave digested or subjected to aqueous extraction for comparison of analytical results. Concentrations of Cu, Fe, Mg, Mn and Zn in aqueous slurries, the digests, and aqueous extracts were determined by the ICP-OES using external calibration curves. A student’s t-test showed that the results obtained using the slurry method were in good agreement at 95 % confidence level (CL) with those of microwave digestion or aqueous extraction techniques, except for Fe. To check the accuracy and precision of the slurry method, a bovine liver CRM was analyzed and good agreement was achieved with the certified values at 95 % CL. The results demonstrate inefficiency of aqueous extraction technique for complete removal of Fe in bovine liver sample. KEY WORDS: Bovine liver, ICP-OES, Slurry nebulization, Cu, Fe, Mg, Mn, Zn   Bull. Chem. Soc. Ethiop. 2008, 22(3), 313-321.

Effect of farming activities on seasonal variation of water quality of Bonsma Dam, KwaZulu-Natal

Agriculture has both direct and indirect effects on the quality of surface water and groundwater and is among the leading causes of water quality degradation, mainly as a result of the excessive use of agrochemicals. Water samples were collected in a selected catchment area (Bonsma Dam) in KwaZulu-Natal and analysed for physicochemical variables. The concentrations of most of the elements and total dissolved solids, as well as the pH and electrical conductivity values, met the water quality requirements for domestic, agricultural, livestock and aquatic ecosystem uses. However, the inlet streams feeding the dam were found to be eutrophic during the wet season. Analysis of nitrate in the water body of the study area indicated that agricultural applications of manure and fertilisers may be a potential source of nitrate contamination. Most elements were more concentrated in the dam during the wet season. The overall ionic conductivity values were also higher in the wet season, while the pH was lower. The outcome of this work links the concentrations of physicochemical variables to land use, agricultural practice and local geomorphology. Seasonal patterns in the concentration of physicochemical variables occur, as land use, rainfall and farming activities change seasonally, and these concentrations should therefore be determined periodically.The National Research Foundation and the Inkaba yeAfrica projecthttp://www.sajs.co.za/am201

Assessment of levels of V, Cr, Mn, Sr, Cd, Pb and U in bovine meat

Pollution of the environment with heavy metals can be a serious problem. In SouthAfrica, particularly, there are many sources of heavy metals, often due to smelter and mining activities. This has led to toxic metals in the environment that directly affect air, water and food. The presence of heavy metal residues in foodstuffs is potentially hazardous to humans and animals. Heavy metals accumulate in certain organs, particularly in the liver and kidney. The objective of this study was to determine the levels of V, Cr, Mn,Sr, Cd, Pb and U in bovine organs and tissues obtained from polluted areas of North West Province, South Africa. Bovine liver, kidney, muscle, fat and bone samples were freeze-dried, homogenized and mineralized using a microwave-assisted digestion system. The levels were quantified using dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS). A bovine muscle (NIST-RM8414) and bovine liver, reference material (NIST-RM1577b), were also analyzed and results agreed with certified values. The study revealed accumulation of Sr in bone, Cd, Pb and U in kidney and bone, Mn in liver and, V and Cr in kidney tissues of cattle.Tshwane University of Technology (TUT) and National Research Fund (NRF).http://journals.sabinet.co.za/sajchem/nf201

(1R,2R,5R,6S,9R,10S,13S,14S,18R)-1,6,7,8,9,14,15,16,17,17,18-Undeca­chloro­penta­cyclo­[12.2.1.16,9.02,13.05,10]octa­deca-7,15-diene

The title compound, C18H13Cl11, is an undecachlorinated commercial flame retardant. The asymmetric unit contains two independent half-mol­ecules. The complete mol­ecules are generated by crystallographic inversion symmetry, causing the terminal H atoms and one of the Cl atoms to be disordered equally over two sites in each mol­ecule. The central eight-membered rings are in chair-type conformations. In the crystal structure, there is a single weak inter­molecular C—H⋯Cl hydrogen bond

4,5,6,7-Tetra­bromo-1,1,3-trimethyl-3-(2,3,4,5-tetra­bromo­phen­yl)indane

The title compound (OctaInd), C18H12Br8, is a commercial brominated flame retardant (BFR). In the mol­ecule, the five-membered ring has a slight envelope conformation, with a deviation of 0.317 (9) Å for the flap C atom from four essentially planar C atoms. The dihedral angle between the two benzene rings is 74.00 (16) Å

Balloon angioplasty of native coarctation: clinical outcomes and predictors of success

AbstractOBJECTIVESWe sought to investigate the clinical impact of balloon angioplasty for native coarctation of the aorta (CoA) and determine predictors of outcome.BACKGROUNDBalloon dilation of native CoA remains controversial and more information on its long-term impact is required.METHODSHemodynamic, angiographic and follow-up data on 69 children who underwent balloon angioplasty of native CoA between 1988 and 1996 were reviewed. Stretch, recoil and gain of CoA circumference and area were calculated and related to outcomes.RESULTSInitial systolic gradients (mean ± SD, 31 ± 12 mm Hg) fell by −74 ± 27% (p < 0.001), with an increase in mean CoA diameters of 128 ± 128% in the left anterior oblique and 124 ± 87% in the lateral views (p < 0.001). Two deaths occurred, one at the time of the procedure and one 23 months later, both as a result of an associated cardiomyopathy. Seven patients had residual gradients of >20 mm Hg. One patient developed an aneurysm, stable in follow-up, and four patients had mild dilation at the site of the angioplasty. Freedom from reintervention was 90% at one year and 87% at five years with follow-up ranging to 8.5 years. Factors significantly associated with decreased time to reintervention included: a higher gradient before dilation, a smaller percentage change in gradient after dilation, a small transverse arch and a greater stretch and gain, but not recoil.CONCLUSIONBalloon dilation is a safe and efficient treatment of native CoA in children. Greater stretch and gain are factors significantly associated with reintervention, possibly related to altered elastic properties and vessel scarring

Heavy metal partitioning in sediments from rivers flowing through coal fields in Mpumalanga, South Africa

The association of elements Cd, Co, Cr, Fe, Mn, Pb, Ti and V with various geochemical phases in the sediments from the Olifants, Klein Olifants, Wilge rivers and a tributary of the Olifants River was studied using a four step sequential extraction scheme. By employing enrichment factors these elements were found to be contaminating the sediments. Sequential extraction enabled partitioning of the metals into exchangeable, reducible, oxidizable and residual fractions. Most of the elements were found to exist in the residual fraction, characterized by stable compounds. Application of risk assessment code (RAC) to the exchangeable fraction revealed that most of the elements posed a medium risk to aquatic life, with the exception of Co, Pb, and Mn which were classified into the high risk category. Non-residual/more bioavailable fractions were examined using statistics. Correlation analysis was employed to understand the interaction between the more bioavailable fractions of the metals with the reducible phase consisting of oxides of Fe-and Mn. These oxides contribute to the adsorption of trace metals onto sediments. Elements Co, V, Pb, Cr and Cd in the reducible fraction were found to be associated with Fe-oxides, while some V, Cr and Ti were associated with Mnoxides, as indicated by significantly high correlation coefficients. Through cluster and factor analysis three anthropogenic activities associated with mining and use of coal and iron and steel manufacturing were found to be contributing metals to the sediments.Tshwane University of Technology (TUT) and the National Research Fund (NRF).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1863-06692016-06-30hb201

(1R,2R,5R,6R,9S,10S,13S,14S)-1,6,7,8,9,14,15,16,17,17-Decachloro­penta­cyclo­[12.2.1.16,9.02,13.05,10]octa­deca-7,15-diene

The title compound, C18H14Cl10, is a decachlorinated commercial flame retardant. The structure determination confirms the relative stereochemistry. The central eight-membered ring is in a chair-type conformation. In the crystal structure, there are no significant inter­molecular inter­actions and mol­ecules are separated by normal van der Waals distances

Investigation of biological samples for monofluoroacetate and Dichapetalum cymosum poisoning in southern Africa

A need has existed for the accurate identification of monofluoroacetate (MFA) poisoning in southern Africa. The development of a new method for the determination of MFA has made the analysis of a variety of biological samples (n=50) feasible. The method has been used in the laboratory over 24 months. Monofluoroacetate was present in 66% of samples from cases of suspected poisoning, reflecting the extent of the problem. Stability of MFA in samples was also determined so as to have a time-bound baseline for the acceptance of samples submitted. It was found that there was a decrease in the level of MFA and, after 14 days at room temperature, only 50% of the spiked dose could be identified. It is suggested that samples be analyzed within 7 days of mortality if they not kept frozen.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat v.9 was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201