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A series of 1,3,4-oxadiazole-2-thiol derivatives bearing various alkyl or aryl moieties were designed, synthesized, and characterized using modern spectroscopic methods to yield 17 compounds (6a-6q) that were screened for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes in the search for 'lead' compounds for Alzheimer's disease treatment (AD). The compounds 6q, 6p, 6k, 6o, and 6l showed inhibitory capability against AChE and BChE, with IC

Eine regio- und stereoselektive inverse Prenylierung von Indol- und Tryptophan-Derivaten wird prasentiert. Alle vier moglichen Stereoisomere sind durch diese Iridium-katalysierte Reaktion zuganglich. Die Stereoselektivitat wird durch eine Kombination aus chiralem Phosphoramidit-Liganden mit einem achiralen Boran-Additiv gesteuert und kann abhangig von der Art des Borans vollstandig umgekehrt werden. Es genugt somit nur ein Enantiomer des Liganden, um alle denkbaren Stereoisomere herzustellen. Das synthetische Potential der Methode wurde in einer kurzen Synthese von Amauromin und seinen zwei naturlichen Diastereomeren demonstriert.

This review focuses on the application of glycol cleavage reactions in the synthesis and derivatization of complex natural products. Reagent classics as well as recent developments are discussed. 1 Introduction 2 Mechanistic Aspects 3 Reagents and Examples 3.1 Periodate and Hypervalent Iodine 3.1.1 Periodic Acid and Periodates 3.1.2 Periodate on Wet Silica Gel 3.1.3 Phenyliodine Diacetate 3.1.4 Other Iodine Reagents 3.2 Lead Tetraacetate 3.3 Chromium Reagents 3.3.1 Pyridinium Chlorochromate 3.3.2 Other Chromium Reagents 3.4 Ruthenium Reagents 3.4.1 Tetra- n -propylammonium Perruthenate 3.4.2 Other Ruthenium Reagents 3.5 Manganese Reagents 3.5.1 Manganese(III) Acetate 3.5.2 Manganese Dioxide 3.5.3 Other Manganese Reagents 3.6 Miscellaneous 4 Conclusion

The synthesis of 2-nitro-4-oligoprenyl-substituted pyrrole derivatives relevant to the heronapyrroles and related natural products was investigated. Among numerous approaches, nitration of a 3-farnesyl-substituted unprotected pyrrole using AcONO2 gave the best results, albeit still with unsatisfactory yield and regioselectivity. Therefore, the synthesis of (-)-heronapyrrole C acid, an analogue of the naturally occurring antibiotic heronapyrrole C carrying a bioisosteric carboxylate in place of the nitro group, was examined. In lieu of the unsatisfactory nitration, a regioselective acylation with Cl3CCOCl was carried out (>8:1 regioselectivity, in contrast to the 1:1.3 ratio for the nitration). The trichloromethyl ketone was converted to the desired acid in a haloform reaction at the final stage of the synthesis. Further key steps of the analogue synthesis involved a position- and stereoselective Corey-Noe-Lin dihydroxylation and an organocatalytic double Shi epoxidation. A biomimetic polyepoxide cyclization cascade established the bis-THF backbone. Thus, (-)-heronapyrrole C acid was synthesized in eight steps (14.5% overall yield) from commercially available starting materials.

The reaction uses NMO as a sole oxidant and is applied to a wide range of diols leading to the carboxylic acids, bisacids and esters.

We present a simple, mild, and highly effective method for the direct conversion of primary alcohols to carboxylic acids. TPAP serves as the catalyst, and NMO·H2O plays a dual role, acting as the co-oxidant and as a reagent for aldehyde hydrate stabilization. This previously unknown stabilizing effect of geminal diols by N-oxides is the key for the efficiency of the overall transformation.

The de novo synthesis of a full set of hydroxymethyl C-glycosides from only two precursors is described. The seven-carbon target molecules contain five stereocentres and bridge the stereochemical gap between natural D-configured and non-natural L-configured series of hexoses. Key steps include hydroxylation, differential protection, stereoselective reduction and desymmetrization of 8-oxabicyclo[3.2.1]oct-6-enes. C-Terminus differentiation and C-terminus excision of the seven-carbon polyol backbone lead to hexoses, including those of the L-series. A stereochemical and genetic classification of C-glycosides is presented.

A highly efficient oxidative cleavage reaction of THF and THP alcohols to γ- and δ-lactones using catalytic PCC (1 mol%) and periodic acid as terminal oxidant is presented.

An α-deprotonation of carbonyl compounds with phosphazene bases in the presence of the internal quenching reagent, nonafluorobutane-1-sulfonyl fluoride furnishes the corresponding alkenyl nonaflates. The new general method provides high yields of alkenyl nonaflates from aldehydes and cyclic ketones. However, it is not applicable to acyclic ketones whose nonaflate derivatives undergo fast E2 elimination to give alkynes. Successful synthesis of nonaflates from aldehydes requires carefully controlled reaction conditions to avoid the subsequent elimination to alkynes. A kinetic control enables high regioselectivities in favor of least substituted nonaflate regioisomers derived from cyclic ketones and modest Z-selectivities of alkenyl nonaflates derived from aldehydes. A new efficient protocol for highly selective removal of perfluorosulfolane admixture from technical nonafluorobutane-1 -sulfonyl fluoride by basic hydrolysis is described.

A mechanistic study on the ligand-free room-temperature Heck reaction of alkenyl nonafluorobutanesulfonates (nonaflates) is described. Kinetic data obtained from poisoning experiments, centrifugation and variation of catalyst loading consistently provide evidence for a homogeneous palladium catalysis unprecedented in Heck chemistry. The Heck reaction of alkenyl perfluorobutanesulfonates represents a remarkably robust, active and efficient catalytic system generally applicable to the coupling with a broad range of terminal olefins including non-activated ones under ambient conditions. It features insensitivity towards atmospheric oxygen and moisture, furnishing uniformly high yields of the anticipated coupling products without the necessity to purify commercial reagents and solvents.

Addition of sewage sludge to grassland may be reflected in ingestion of lead by animals with implications for the human food chain. The research reported here was part of a series of experiments conducted to investigate the possible risk to the health of livestock and humans associated with the use of sewage sludge in agriculture. The transfer of several elements to the body tissues of lambs was examined, including that of cadmium, copper, zinc and lead. The results for lead are reported in this paper.Weaned Kent lambs (6/treatment, 20 to 45 kg liveweight) were given dried grass ad libitum (Trial 1, indoor feeding) either as the sole feed (C) or with 100 g/kg DM of one of two soils (CM, sandy -pH 6.18; or RM, a calcareous loam - pH 7.55) which had been amended historically with sewage sludge and which contained 102 (CM) and 130 (RM) mg Pb/kg DM.

SummaryIonophoric polyethers are produced by the exquisitely stereoselective oxidative cyclization of a linear polyketide, probably via a triepoxide intermediate. We report here that deletion of either or both of the monBI and monBII genes from the monensin biosynthetic gene cluster gave strains that produced, in place of monensins A and B, a mixture of C-3-demethylmonensins and a number of minor components, including C-9-epi-monensin A. All the minor components were efficiently converted into monensins by subsequent acid treatment. These data strongly suggest that epoxide ring opening and concomitant polyether ring formation are catalyzed by the MonB enzymes, rather than by the enzyme MonCII as previously thought. Consistent with this, homology modeling shows that the structure of MonB-type enzymes closely resembles the recently determined structure of limonene-1,2-epoxide hydrolase from Rhodococcus erythropolis.

Sewage sludge contains a range of essential and non-essential elements for livestock nutrition, many of which are toxic at elevated levels. Where sludge is applied to the surface of pasture regularly, contaminants principally heavy metals will accumulate in the surface layer (Davis et al 1988), and may represent a potential health hazard for grazing animals through the direct ingestion of contaminated soil much greater than that from plant uptake. Whilst it is known that soil ingestion can supplement mineral intake with benefits to grazing animals in some situations, the potentially toxic effects of ingesting soil from heavily sludged pastures are of principal concern (Stark 1988). Bearing in mind the strategic importance of grassland for sludge disposal, it must be demonstrated whether existing soil metals limits (DoE 1988) will adequately protect grazing animals. The principal objective of the trial was to study animal growth performance as well as mineral balance from a diet with elevated copper levels derived from a sludge treated soil. Lambs were used for their greater sensitivity to copper than cattle, and the length of the trial simulated the normal finishing period of five months for lambs on pasture.