E. Blake Watkins

The Epothilones and Related Analogues-A Review of Their Syntheses and Anti-Cancer Activities

The macrocylic polyketide class of compounds known as the epothilones has generated substantial interest over the last few years in the areas of chemistry, biology, and medicine due to their interesting structure and, more importantly, their activity against numerous cancer cell lines, including drug-resistant, especially Taxol-resistant, cancer cell lines. To date, numerous total syntheses have been published, hundreds of epothilone analogues have been synthesized, and detailed structure activity relationship studies have been conducted. The purpose of this review is to give a brief summary of the latest advances made concerning the epothilones. Recent total or partial syntheses will be presented along with the syntheses of new epothilone analogues and their corresponding biological data. In addition, we will look at the current state of research into an economically viable method for the biosynthesis of the epothilones and related analogues.

Synthesis of 3-substituted and 3,4-disubstituted pyrazolin-5-ones

Abstract The synthesis of 3-substituted and 3,4-disubstituted pyrazolin-5-ones from acylated ethyl acetoacetates and diethyl malonates is described. The reaction of acylated ethyl acetoacetates and diethyl acetylmalonate with hydrazine (98%) gave 3-substituted pyrazolin-5-ones and malonyldihydrazide, respectively, following a deacetylation–condensation sequence. The reaction of ethyl 2-acetyl-3-hydroxy-2-butenoate and diethyl 2-(1-hydroxyethylidene)malonate with hydrazine monohydrochloride yielded ethyl 3,5-dimethyl-1 H -pyrazole-4-carboxylate and 4-ethoxycarbonyl-3-methylpyrazolin-5-one, respectively, following a dehydration–cyclocondensation sequence, in high yields.

Palladium-Catalyzed Direct Arylation of C(sp3)–H Bonds of α-Cyano Aliphatic Amides

Pd(OAc)2-catalyzed arylation of C(sp(3))-H bonds in α-cyano-α-methyl aliphatic amides is achieved in the presence of 8-aminoquinoline, as a removable directing group, using Mn(OAc)2 and Na2CO3. The current strategy enables the placement of an aryl/heteroaryl group at the β-position of α-cyano aliphatic acids for the first time. Wide functional group tolerance and easily accessible starting materials provide an efficient protocol for the synthesis of arylated α-cyano amides. Furthermore, the synthetic utility of the products has been demonstrated by their efficient conversions to medicinally important α,α-dialkylated acid and β-amino acid derivatives.

1,3-Diaxially substituted trans-decalins: potential nonsteroidal human progesterone receptor inhibitors.

On the basis of molecular modeling and QSAR analysis of the known human progesterone receptor (hPR) inhibitor Mifepristone (RU-486) and other hPR ligands, a new class of potential nonsteroidal hPR inhibitors was designed. The parent racemic compound 1 was synthesized through an efficient 13-step synthetic pathway. The key constructive steps are a stereoselective epoxide ring opening and the reductive Heck cyclization to form the main framework of (+/-)-1. The current established flexible synthetic route allows for further chemical diversification.

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.MethodsDifferent 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.ResultsIn 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.ConclusionsThe 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.

Design, Synthesis and Evaluation of Trisubstituted Thiazoles Targeting Plasmodium Falciparum Cysteine Proteases

The Plasmodium falciparum cysteine proteases, falcipains, have been established as novel targets for antimalarial drug design. Using the de novo design approach, several trisubstituted thiazole analogs were generated as potential inhibitors of these enzymes. A general and convenient synthetic approach for these novel trisubstituted thiazoles is reported here. Substituents at the 4th and 5th positions of the target thiazoles were introduced by a Hantzsch reaction, and the chain at the second position was extended through a Sandmeyer reaction, formylation, and Wittig olefination. In vitro enzyme inhibition studies have identified three inhibitors (14, 16, 23) of the falcipains with one (14) showing dual activity against both falcipain-2 and falcipain-3 and IC50 values of 6.6 and 29.4 μM, respectively.

EFFICIENT SYNTHESIS OF 4-ETHOXYCARBONYL PYRAZOLIN-5-ONE DERIVATIVES

ABSTRACT Concise and efficient methods for the preparation of 3-substituted 4-ethoxycarbonylpyrazolin-5-ones are described. The synthetic strategies involve carbon-acylation in the presence of base, followed by ring cyclization with hydrazine or hydrazine monohydrochloride.

Toward the total synthesis of pseudolaric acid B. Preparation of a key intermediate by degradation and its use in the reassembly of the natural product

Synthetic studies of pseudolaric acid B, 2, provided a relay synthesis of pseudolaric acid B (PLAB) via aldehyde 5. The aldehyde 5 can serve: to complete the total synthesis of PLAB; as a precursor for the synthesis of PLAB analogs; or as a substrate for the generation of radiolabeled PLAB for mechanistic studies.

Development and Validation of a UPLC Method for Rapid and Simultaneous Analysis of Proton Pump Inhibitors

Proton pump inhibitors (PPIs) are used extensively for the relief of gastroesophageal reflux, peptic ulcers, and other hypersecretory conditions. Some of the commonly used PPIs—omeprazole, esomeprazole, lansoprazole, pantoprazole, and rabeprazole—were used in this study with the aim of developing a rapid ultra performance liquid chromatography (UPLC) method for detecting each and allowing separation and quantification of a mixture of PPIs. An analysis of samples was performed on a UPLC system equipped with a quaternary solvent delivery system, a refrigerated sample manager, a column heater, a photo diode array detector scanning from 210 to 400 nm, and a C18 analytical column (50 mm × 3.0 mm, 1.7-μm particle size). The chromatographic analysis of the PPI samples and standards was performed using gradient elution with acetonitrile and water. The calibration curve range varied for each of the PPIs ranging from a lower limit of 0.75–1.78 μg/mL to a maximum concentration of 200 μg/mL with a regression coefficient (r2) of ≥0.98. The accuracy and precision were calculated, and the %RSD was determined to be ≤0.21% (intraday) and ≤5% (interday). The LOD was 0.23–0.59 μg/mL and the LOQ was 0.71–1.78 μg/mL for each of the drugs analyzed. The method was capable of detecting and quantifying each drug in a mixture with good resolution and a total run time of less than 5 min. Herein, we report an efficient and rapid analytical method for the simultaneous detection of multiple PPIs in a mixture.

Enzymatic synthesis of aza-l-tyrosines.

Tyrosine phenol-lyase from Citrobacter freundii synthesizes 2-aza-L-tyrosine and 3-aza-L-tyrosine from 3-hydroxypyridine and 2-hydroxypyridine, respectively, and ammonium pyruvate.