The preparation, spectral properties and structure elucidations of the hitherto undocumented 3-oxo-, 3-thioxo-, 3-propylimino-, 3-imino-, and 3-propylamino- derivatives of 4-ethyl-2-propyl-2, 3-dihydro-pyrrolo[3, 4-b]quinoline-1, 9-dione are described. Mechanistic aspects relating particularly to the formation of the latter two unprecedented products are considered. Magnetic anisotropic effects (deshielding / line broadening of signals) are exhibited by the α-methylene protons of the 4-ethyl moiety in the 1H NMR spectra of the first four of the above, and in several 3, 3-dichloro-thieno[3, 4-b]quinoline-1, 9-diones and intramolecular H-bonded, 1, 2-dialkyl-4-oxo-3-quinolinecarboxylic acid precursor substrates.
Lead in emissions from motor vehicles using leaded petrol are usually monitored by analysing gas samples. In view of the many problems associated with gas sampling, this project focussed on the analysis of lead in kerbside samples. To this end, soil samples were collected from kerbsides and road islands within and outside the city of Durban. Thus urban, peri-urban and rural roads were included in the survey. In a preliminary study, kerb-side dust samples were collected from a vehicle-busy city street where many pavement food vendors ply their trade. The horizontal distribution of metals as a function of distance from the kerb was determined by analysing samples which were collected at various distances of 1-20 metres from the edge of a road. The determination of vertical distribution of lead was achieved by taking samples at depths of 0-2 cm, 10-15 cm and 20-25 cm at each of the sampling spots. Some sub-samples were leached at pHs found in soils using a Hazardous Waste Filtration System while parallel sub-samples from the same gross sample were acid-digested in a Microwave Digester. Analyses were done using ICP-AES, AAS and GF-AAS. The values for lead were found to be highest for urban sites and lowest for rural ones. Values of lead from leached samples were found to be lower than that for digested samples whilst the values for lead over all sites was in the range 0.02-923 ppm.
A novel labdane diterpenoid, leonurun, has been isolated from the leaves of Leonotis leonurus. This structure was determined from spectroscopic data and the relative stereochemistry from single-crystal X-ray diffraction analysis.
A few novel furanylalkyl hex- and pentenopyranones have been synthesized from the corresponding hexenopyranosides or hydroxymethylfurfural. In the hexose series, the reactions proceeded through monosilylation of the primary alcohol followed by oxidation of secondary alcohols. The pentenopyranones have been obtained by glycosidation of hydroxymethylfurfural oxidation product.
Although a great deal of success has been achieved in the synthesis of dibenzodioxaphosphepin derivatives during the last few decades with the introduction of hundreds of its six-, and seven-membered ring systems, the search for more practical agronomic pesticides that is readily available and of good activity, remains attractive and important to an agronomic chemist. During the course of the development of synthetic routes to a promising pesticide, a facile preparation for a nine-membered heterocyclic dibenzodioxaphosphonine compound was discovered. Previously reported compounds consist of six- and seven-membered ring systems. The pure product was fully characterized by spectroscopic [IR, NMR (1H, 13C, 31P) and Mass] analyses. The pure compound possesses a LC50 value of 19.3 µg cm-3 in a brine shrimp lethality assay (BST). The preliminary field study on the cowpea weevil bioassay shows 51% success. Details of the synthetic route as well as bioassay results are reported herein.
Tetrameric DABCO-bromine is a powerful brominating agent but shows reasonable selectivity with certain substrates. The selective bromination for activated aromatic compounds and alkenes is reported. Synthesis of α-bromo ketones and nitriles has also been achieved by using this reagent and the results are also reported. All products reported were obtained in good to excellent yields.
The structures, interaction energies and vibrational spectra of the van der Waals complexes formed between boron trifluoride, as Lewis acid, and water and hydrogen sulphide, as Lewis bases, have been determined by means of ab initio calculations at the second-order level of Moller-Plesset perturbation theory, using a number of basis sets, including double- and triple-zeta, with polarization and diffuse functions. Two conformers, an eclipsed and a staggered species, have been examined for each complex. In the case of the boron trifluoride-water complex, the spectra computed using the largest basis set have been compared with the spectra obtained experimentally in nitrogen, argon and neon matrices at cryogenic temperatures.
Polymeric conjugates of methotrexate (MTX) with macromolecular carriers, obtained from amine-functionalized polyaspartamides by coupling with one of the drug's carboxyl groups, are used in this preliminary screening project for in vitro cytotoxicity assessment. The water-soluble conjugates, crudely fractionated by aqueous dialysis, possess mass-average molecular masses in the range of 20000-30000. Screens are performed by standard procedures against cultured CEM/S human leukemic lymphoblast cells, a drug-sensitive line, and against CEM/E, its drug-resistant subline, for comparison also against unconjugated MTX. All compounds tested, including the unconjugated drug, display decreasing activity on going from CEM/S to CEM/E, resistance factors (IC50 [CEM/E]/IC50 [CEM/S]) being in the vicinity of 15-20 for MTX as well as for the majority of conjugates. On the other hand, comparisons of IC50 values for conjugates versus free drug, both against CEM/S and CEM/E, show vastly superior antiproliferative performance of the drug in the carrier-anchored state over the free form, with activity factors (IC50 [free MTX]/IC50 [conjugate]) typically in the 10-50 range and higher. On the basis of these promising in vitro findings, the polyaspartamide-MTX conjugates are considered to be excellent candidates for further cell culture and extended in vivo tests.