Chiral Brønsted Acid Catalyzed Cascade Alcohol Deprotection and Enantioselective Cyclization.

The protection-deprotection sequence is vital to organic synthesis. Here, we describe a novel catalytic cascade where a chiral Brønsted acid selectively removes ether protecting groups and catalyzes intramolecular cyclization in one pot. We tested three model substrates from our previous work and investigated the rate of deprotection through gas chromatography (GC) studies. This work builds on our stereoselective synthesis of lactones by streamlining our synthesis. It also opens the door for additional investigations into other catalytic cascade reactions using chiral Brønsted acid catalysts.

Stereoselective Desymmetrizations of Dinitriles to Synthesize Lactones.

Nitriles are important organic functional groups, allowing for installation of nitrogen in organic synthesis. The Pinner reaction transforms nitriles into esters via the imidate group, but in general has previously necessitated harsh acid conditions. This work builds on the utility of the Pinner reaction through a stereoselective desymmetrization of dinitriles to form γ- and δ-lactones in good yields and diastereoselectivites.

Chiral Brønsted Acid Catalyzed Kinetic Resolutions.

The synthesis of enantioenriched small molecules is an ongoing goal of organic chemists. This focus review explores the use of kinetic resolutions catalyzed by chiral Brønsted acids. Methods include classic kinetic resolutions and dynamic kinetic resolutions. The small molecules obtained are potentially valuable intermediates in the synthesis of biologically important compounds.

Solenopsin A and analogs exhibit ceramide-like biological activity.

BACKGROUND: (-)-Solenopsin A is a piperidine alkaloid that is a component of the venom of the fire ant Solenopsis invicta. Previously, we have demonstrated that solenopsin exhibit anti-angiogenic activity and downregulate phosphoinositol-3 kinase (PI3K) in the p53 deficient renal cell carcinoma cell line 786-O. Solenopsin has structural similarities to ceramide, a major endogenous regulator of cell signaling and cancer therapy induced apoptosis. METHODS: Different analogs of solenopsin were synthesized in order to explore structure-activity relationships. The anti-proliferative effect of solenopsin and analogs was tested on six different cell lines, including three tumor cell lines, two normal cutaneous cell lines, and one immortalized hyperproliferative cell line. FRET-based reporters were used to study the affect of solenopsin and analogs on Akt activity and PDK1 activation and sucrose density gradient fractionation was performed to examine recruitment of PTEN to membrane rafts. Western-blotting was used to evaluate the affect of solenopsin and analogs on the Akt and the MAPK 44/42 pathways in three different tumor cell lines. Measurement of cellular oxygen consumption rate together with autophagy staining was performed to study mitochondrial function. Finally, the affect of solenopsin and analogs on ROS production was investigated. RESULTS: In this paper we demonstrate that solenopsin analogs with potent anti-proliferative effects can be synthesized from inexpensive dimethylpyridines. To determine whether solenopsin and analogs act as ceramide analogs, we examined the effect of solenopsin and analogs on two stereotypic sites of ceramide activity, namely at lipid rafts and mitochondria. We found that native solenopsin, (-)-solenopsin A, inhibits functional Akt activity and PDK1 activation in lipid rafts in a similar fashion as ceramide. Both cis and trans analogs of solenopsin reduce mitochondrial oxygen consumption, increase reactive oxygen, and kill tumor cells with elevated levels of Akt phosphorylation. However, only solenopsin induces mitophagy, like ceramide. CONCLUSIONS: The requirements for ceramide induced mitophagy and inhibition of Akt activity and PDK1 activation in lipid rafts are under strict stereochemical control. The naturally occurring (-)-solenopsin A mimic some of the functions of ceramide and may be therapeutically useful in the treatment of hyperproliferative and malignant disorders of the skin, even in the presence of elevated levels of Akt.

Asymmetric Synthesis of Hydroxy Esters with Multiple Stereocenters via a Chiral Phosphoric Acid Catalyzed Kinetic Resolution.

The kinetic resolution of hydroxy tert-butyl esters through a Brønsted acid catalyzed lactonization is described. The resulting enantioenriched molecules have cyclic backbones and/or multiple stereocenters. DFT calculations explore how small changes in substrate structure can have a large impact on the selectivity of the process.

Nonenzymatic enantioselective synthesis of all-carbon quaternary centers through desymmetrization.

The asymmetric desymmetrization of meso or prochiral compounds containing an all-carbon quaternary center is an attractive alternative to classical synthetic approaches aimed at the asymmetric formation of a new C-C bond. This review focuses on nonenzymatic desymmetrizations that utilize transition metal catalysts or organocatalysts to distinguish between enantiotopic groups to generate enantioenriched compounds containing all-carbon quaternary stereocenters.

Enantioselective desymmetrization of diesters.

The desymmetrization of prochiral diesters with a chiral phosphoric acid catalyst to produce highly enantioenriched lactones in excellent yield is reported. The process is easily scaled and accommodates a variety of substitution patterns, many of which result in the generation of an enantioenriched all-carbon quaternary center. Manipulation of lactone product to useful small building blocks is also described.

Facile synthesis of versatile enantioenriched α-substituted hydroxy esters through a Brønsted acid catalyzed kinetic resolution.

An efficient synthesis of enantioenriched α-substituted γ-hydroxy esters via a kinetic resolution event is described. Bulky racemic esters in the presence of a chiral Brønsted acid selectively lactonize to yield a recoverable enantioenriched hydroxy ester and lactone. These esters are highly versatile building blocks that can readily be converted to synthetically useful materials.

Asymmetric, organocatalytic, three-step synthesis of gamma-hydroxy-(E)-alpha,beta-unsaturated sulfones and esters.

Efficient and enantiocontrolled synthesis of gamma-hydroxy-alpha,beta-unsaturated sulfones and esters are reported through the reaction of enantioenriched alpha-selenyl aldehydes with EWG-stabilized carbanions and then a one-pot selenide oxidation, in situ epoxide formation, and final in situ epoxide opening.

Malaria-infected mice are cured by oral administration of new artemisinin derivatives.

In four or five chemical steps from the 1,2,4-trioxane artemisinin, a new series of 23 trioxane dimers has been prepared. Eleven of these new trioxane dimers cure malaria-infected mice via oral dosing at 3 x 30 mg/kg. The clinically used trioxane drug sodium artesunate prolonged mouse average survival to 7.2 days with this oral dose regimen. In comparison, animals receiving no drug die typically on day 6-7 postinfection. At only 3 x 10 mg/kg oral dosing, seven dimers prolong the lifetime of malaria-infected mice to days 14-17, more than double the chemotherapeutic effect of sodium artesunate. Ten new trioxane dimers at only a single oral dose of 30 mg/kg prolong mouse average survival to days 8.7-13.7, and this effect is comparable to that of the fully synthetic trioxolane drug development candidate OZ277, which is in phase II clinical trials.

Low-calcemic, highly antiproliferative, 23-oxa ether analogs of the natural hormone 1 alpha,25-dihydroxyvitamin D3: design, synthesis, and preliminary biological evaluation.

Eight new side-chain allylic, benzylic, and propargylic ether analogs of the natural hormone calcitriol have been rationally designed and easily synthesized. Three of these 23-oxa ether analogs lacking the typical side-chain OH group are more antiproliferative in vitro and desirably less calcemic in vivo than the natural hormone. One of these three 23-oxa analogs has transcriptional potency almost as high as that of calcitriol, even though it binds to the human vitamin D receptor only about 1% as well as calcitriol.

Difluoromethyl analogs of the natural hormone 1alpha,25-dihydroxyvitamin D3: Design, synthesis, and preliminary biological evaluation.

Three new Vitamin D analogs 3-5 incorporating a -CHF(2) group as an -OH surrogate have been prepared. Two of these new analogs (3 and 5) are strongly antiproliferative toward murine keratinocytes and are approximately 50 times less calciuric in vivo than the natural hormone calcitriol. The transcriptional activity of the 25-CHF(2) analog 3 is higher than that of the 1-CHF(2) analog 4.

Low-calcemic, highly antiproliferative, 1-difluoromethyl hybrid analogs of the natural hormone 1alpha,25-dihydroxyvitamin D3: design, synthesis, and preliminary biological evaluation.

Replacing the 1alpha-OH group of the natural hormone 1alpha,25-dihydroxyvitamin D(3) (calcitriol) by a 1alpha-CHF(2) group and incorporating a potentiating side chain produced two new hybrid analogs 6 and 7. Both of these two hybrid analogs are as transcriptionally active as calcitriol and are strongly antiproliferative in vitro but are low-calcemic in vivo.