CH3Li/TiCl4: A non-basic and highly selective grignard analogue

Synthesis of Allenes by Hydroalkylation of 1,3-Enynes with Ketones Enabled by Cooperative Catalysis

A method for the synthesis of allenes by the addition of ketones to 1,3-enynes by cooperative Pd(0)Senphos/B(C6F5)3/NR3 catalysis is described. A wide range of aryl- and aliphatic ketones undergo addition to various 1,3-enynes in high yields at room temperature. Mechanistic investigations revealed a rate-determining outer-sphere proton transfer mechanism, which was corroborated by DFT calculations.

Bioreductively activatable prodrug conjugates of phenstatin designed to target tumor hypoxia

A variety of solid tumor cancers contain significant regions of hypoxia, which provide unique challenges for targeting by potent anticancer agents. Bioreductively activatable prodrug conjugates (BAPCs) represent a promising strategy for therapeutic intervention. BAPCs are designed to be biologically inert until they come into contact with low oxygen tension, at which point reductase enzyme mediated cleavage releases the parent anticancer agent in a tumor-specific manner. Phenstatin is a potent inhibitor of tubulin polymerization, mimicking the chemical structure and biological activity of the natural product combretastatin A-4. Synthetic approaches have been established for nitrobenzyl, nitroimidazole, nitrofuranyl, and nitrothienyl prodrugs of phenstatin incorporating nor-methyl, mono-methyl, and gem-dimethyl variants of the attached nitro compounds. A series of BAPCs based on phenstatin have been prepared by chemical synthesis and evaluated against the tubulin-microtubule protein system. In a preliminary study using anaerobic conditions, the gem-dimethyl nitrothiophene and gem-dimethyl nitrofuran analogues were shown to undergo efficient enzymatic cleavage in the presence of NADPH cytochrome P450 oxidoreductase. Each of the eleven BAPCs evaluated in this study demonstrated significantly reduced inhibitory activity against tubulin in comparison to the parent anti-cancer agent phenstatin (IC50=1.0μM). In fact, the majority of the BAPCs (seven of the eleven analogues) were not inhibitors of tubulin polymerization (IC50>20μM), which represents an anticipated (and desirable) attribute for these prodrugs, since they are intended to be biologically inactive prior to enzyme-mediated cleavage to release phenstatin.

Complex N-heterocycle synthesis via iron-catalyzed, direct C-H bond amination

The manipulation of traditionally unreactive functional groups is of paramount importance in modern chemical synthesis. We have developed an iron-dipyrrinato catalyst that leverages the reactivity of iron-borne metal-ligand multiple bonds to promote the direct amination of aliphatic C-H bonds. Exposure of organic azides to the iron dipyrrinato catalyst furnishes saturated, cyclic amine products (N-heterocycles) bearing complex core-substitution patterns. This study highlights the development of C-H bond functionalization chemistry for the formation of saturated, cyclic amine products and should find broad application in the context of both pharmaceuticals and natural product synthesis.

6-Magnesiated Purines: Preparation and Reaction with Aldehydes

[reaction: see text] Halogen-metal exchange reaction of 9-benzyl-6-iodopurine with iPrMgCl in toluene at -80 degrees C proceeds almost quantitatively. Such a purine-derived Grignard reagent reacts selectively with aldehydes in toluene, giving the corresponding alcohols in 25-62% yield, while other functional groups such as ketones, esters, and nitriles do not react under these conditions. The reaction can be extended to protected 6-iodopurine ribonucleoside.

Increased Felkin-Anh selectivity using AlMe(3) in the addition of vinyllithiums to alpha-chiral aldehydes: do "ate" complexes play any role?

[reaction: see text] AlMe(3) dramatically increases the diastereoselectivity of addition of vinyllithiums to alpha-chiral aldehydes but decreases that of methyllithium. Our results are explained in terms of an addition of the free vinyllithium on the Me(3)Al-aldehyde complex.

Quinolones as gonadotropin releasing hormone (GnRH) antagonists: simultaneous optimization of the C(3)-aryl and C(6)-substituents

A series of 3-arylquinolones was prepared and evaluated for their ability to act as gonadotropin releasing hormone (GnRH) antagonists. A variety of substitution patterns of the 3-aryl substituent are described. The 3,4,5-trimethylphenyl substituent (23h) was found to be optimal.

Vasopeptidase inhibitors: incorporation of geminal and spirocyclic substituted azepinones in mercaptoacyl dipeptides

A series of 7-(di)alkyl and spirocyclic substituted azepinones were generated and incorporated as conformationally restricted dipeptide surrogates in mercaptoacyl dipeptides. Clear structure-activity relationships with respect to both angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) activity in vitro were observed. The best in this series, compound 1g, a geminally dimethylated C-7-substituted azepinone, demonstrated excellent blood pressure lowering in animal models. Compound 1g (BMS-189921) is characterized by a good duration of activity and excellent oral efficacy in models relevant to ACE or NEP inhibition, and its activity is comparable to that of the clinically efficacious agent omapatrilat. Consequently this inhibitor has been advanced clinically for the treatment of hypertension and congestive heart failure.

Synthesis of a series of aryl kainic acid analogs and evaluation in cells stably expressing the kainate receptor humGluR6

The synthesis and pharmacological characterization of a novel series of 4-aryl-substituted kainic acid analogs are described. Receptor affinities were determined on recombinantly expressed humGluR6 kainate receptors and on [3H]kainate binding to rat forebrain kainate receptors. Functional agonist potencies were assessed using whole cell voltage clamp recordings in cells expressing humGluR6 receptors. Substitution of phenyl for the methyl at the C-4 position of kainic acid produced 11 which has high affinity and agonist potency at the GluR6 receptor. Substitution on phenyl led to a series of compounds with varying affinity for this kainate receptor. Agonist potency correlated with receptor affinity and with no derivative could antagonist activity be identified. Affinities for the humGluR6 kainate receptor were approximately 10-50 less than the observed affinities at rat forebrain kainate receptors. Furthermore, within the series of 4-aryl-substituted kainic acid analogs, there was a high degree of correlation between binding affinities for humGluR6 receptors and competition with kainate binding to rat forebrain kainate receptors.