3-Alkyl-3-hydroxyglutaric acids: a new class of hypocholesterolemic HMG CoA reductase inhibitors. 1

Copper-catalyzed desymmetrization of prochiral 4,4-disubstituted cyclopentenes via a site-selective allylic oxidation: a concise total synthesis of untenone A

The desymmetrization of prochiral 4,4-disubstituted cyclopentenes via a site-selective copper-catalyzed allylic oxidation is described.

Enantioselective Total Synthesis of Avrainvillamide and the Stephacidins

In this article, full details regarding our total synthesis of avrainvillamide and the stephacidins are presented. After an introduction and summary of prior synthetic studies in this family of structurally complex anticancer natural products, the evolution of a final synthetic approach is described. Thus, a thorough description of three separate model studies is provided for construction of the characteristic bicyclo[2.2.2]diazaoctane ring system common to these alkaloids. The first and second approaches sought to build the core using formal Diels-Alder and vinyl radical pathways, respectively. Although these strategies failed in their primary objective, they fostered the development of a new and mechanistically intriguing method for the synthesis of indolic enamides such as those found in numerous bioactive natural products. The scope and generality of this simple method for the direct dehydrogenation of tryptophan derivatives is described. Finally, details of a third and successful route to the core of these alkaloids are described which features oxidative C-C bond formation. Specifically, the first heterocoupling of two different types of carbonyl species (ester and amide) is accomplished in good yield, on a preparative scale, and with complete stereocontrol. The information gained in these model studies enabled an enantioselective total synthesis of stephacidin A. The absolute configuration of these alkaloids was firmly established in collaboration with Professor William Fenical. A full account of our successful efforts to convert stephacidin A into stephacidin B via avrainvillamide is presented. Finally, the first analogues of these natural products have been prepared and evaluated for anticancer activity.

Substrate and inhibitor specificity of mevalonate kinase determined with substrate analogues

Substrate analogues of mevalonate kinase were prepared and their kinetic properties determined with the enzyme from pig liver. The analogues are derived from mevalonate by substitutions of hydroxyl and/or methyl at C3(group 1), by systematic prolongation of C6 to yield 3-alkyl-3,5-dihydroxyvalerates (group 2) and by methylation at C2, C6 and C4 (group 3). Compounds of group 1 were inhibitors of mevalonate kinase, their Ki values ranging over 140 mM to 2.5 mM and decreasing in the series CH2 > C(CH3)2 > CH(OH) > CH(CH3) > C(OH)-CO2H > C(OH)CH2OH. Three of these analogues, the competitive inhibitors 3,5-dihydroxyvalerate, 3-methyl-5-hydroxy-valerate and 3,3-dimethyl-5-hydroxyvalerate are alos (poor) substrates of the kinase. Substances of group 2 contain an additional hydrophobic group and are noncompetitive inhibitors with Ki values decreasing systematically from 7.7 mM to 0.7 mM in the sequence 3-n-propyl, 3-n-butyl, 3-n-pentyl and 3-n-hexyl derivative of 3,5-dihydroxyvalerate. The methylated mevalonates of group 3 are competitive inhibitors as well as good substrates of the kinase, their Ki = Km values ranging over 4.3-0.2 mM and their maximal velocities related to mevalonate varying between 7-65%. All of these analogues have in common the carbon chain and 5-hydroxy group of the substrate and could, therefore, fit to the active site of mevalonate kinase and be phosphorylated by ATP. The results, however, indicate a strong dependence of such interaction on the ligands at C3 of the substrate. Enzymic activity as well as affinity are lost if both of these ligands are replaced by hydrogen; partial restoration occurs at a low level if only one of the ligands is concerned. In the presence of the ligands even monomethylation at C2 and C4 yields enzymically active products. Oxidation of C6 of the substrate yields inhibitors but methylation yields a reasonably good substrate. Thus 3,5-dihydroxy-3-ethylvalerate fits into the active site whereas higher C6 homologues are only inhibitory and probably bind to a hydrophobic region of the enzyme. Some of these results are shown to have parallels in the enzymic behaviour of fluorinated mevalonates.

Mode of action of lipid-lowering drugs

Following the recent demonstration that both cholestyramine and nicotinic acid decrease mortality from coronary heart disease, there is a new enthusiasm for hypolipidaemic therapy. The agents in current use are, however, insufficiently active or are accompanied by unacceptable side effects. An understanding of the mode of action is necessary, both to optimize treatment guidelines (e.g. regarding combination therapy or use in specific subsets of patients) and to develop new agents with preferred actions on rate-limiting steps. A reduction in LDL cholesterol concentration remains the principal desired action, although an elevation in HDL may also be beneficial. The main categories of commercially available agent comprise the anion exchange resins (inhibitors of bile acid absorption); cholesterol absorption inhibitors; fibrates (probably acting by enhancing lipoprotein lipase); and probucol (affecting LDL clearance). The most interesting of the new agents in clinical trials are the beta-hydroxy-beta-methylglutaryl-CoA reductase inhibitors, but other types of agent are at an earlier stage of evaluation, e.g. acyl-CoA: cholesterol acyltransferase inhibitors and peptide cofactors. It is not yet certain whether all the approaches to cholesterol lowering have equal validity, although an effect on biological endpoints is obtained for a variety of agents. Future evaluation will be aided by the implementation of noninvasive methods to quantify atherosclerosis and by the use of simple, 'dry-chemistry', cholesterol assays to screen populations.