A Bayesian Approach to Kinetic Modeling of Accelerated Stability Studies and Shelf Life Determination.

Kinetic modeling of accelerated stability data serves an important purpose in the development of pharmaceutical products, providing support for shelf life claims and expediting the path to clinical implementation. In this context, a Bayesian kinetic modeling framework is considered, accommodating different types of nonlinear kinetics with temperature and humidity dependent rates of degradation and accounting for the humidity conditions within the packaging to predict the shelf life. In comparison to kinetic modeling based on nonlinear least-squares regression, the Bayesian approach allows for interpretable posterior inference, flexible error modeling and the opportunity to include prior information based on historical data or expert knowledge. While both frameworks perform comparably for high-quality data from well-designed studies, the Bayesian approach provides additional robustness when the data are sparse or of limited quality. This is illustrated by modeling accelerated stability data from two solid dosage forms and is further examined by means of artificial data subsets and simulated data.

Ruthenium-Catalyzed Reductive Arylation of N-(2-Pyridinyl)amides with Isopropanol and Arylboronate Esters.

A new three-component reductive arylation of amides with stable reactants (iPrOH and arylboronate esters), making use of a 2-pyridinyl (Py) directing group, is described. The N-Py-amide substrates are readily prepared from carboxylic acids and PyNH2 , and the resulting N-Py-1-arylalkanamine reaction products are easily transformed into the corresponding chlorides by substitution of the HN-Py group with HCl. The 1-aryl-1-chloroalkane products allow substitution and cross-coupling reactions. Therefore, a general protocol for the transformation of carboxylic acids into a variety of functionalities is obtained. The Py-NH2 by-product can be recycled.

The evolution of amidine-based brain penetrant BACE1 inhibitors.

Beta site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors hold great potential as disease modifying anti-Alzheimer's drugs. This digest provides an overview of the amidine containing class of BACE1 inhibitors, of which multiple examples are now progressing through clinical trials. The various structural modifications highlight the struggle to combine potency with the optimal properties for a brain penetrant BACE1 inhibitor, and illustrate the crowded competitive landscape. This overview concludes with a summary of potential issues including substrate and target selectivity and a synopsis of the status of the current and past clinical assets.

The role of the alcohol and carboxylic acid in directed ruthenium-catalyzed C(sp3)-H α-alkylation of cyclic amines.

A general directed Ru-catalyzed C(sp(3))-H α-alkylation protocol for piperidines (less-reactive substrates than the corresponding five-membered cyclic amines) has been developed. The use of a hindered alcohol (2,4-dimethyl-3-pentanol) as the solvent and catalyst activator, and a catalytic amount of trans-1,2-cyclohexanedicarboxylic acid is necessary to achieve a high conversion to product. This protocol was used to effectively synthesize a number of 2-hexyl- and 2,6-dihexyl piperidines, as well as the alkaloid (±)-solenopsin A. Kinetic studies have revealed that the carboxylic acid additive has a significant effect on catalyst initiation, catalyst longevity, and reverses the reaction selectivity compared with the acid-free reaction (promotes alkylation versus competing alkene reduction).

The Liebeskind-Srogl C-C cross-coupling reaction.

Although a plethora of highly selective and reliable methods for the construction of C-C bonds are known to organic chemists, there is growing interest in the development of new protocols that offer different or orthogonal reactivity to that of existing methods. In 2000, Liebeskind and Srogl described a mechanistically unprecedented transition-metal-catalyzed cross-coupling of thioesters with boronic acids to produce ketones under neutral conditions. This desulfitative cross-coupling process is catalytic in palladium(0), stoichiometric in copper(I), and applicable to a range of organosulfur derivatives and nucleophilic organometallic reagents. In this Minireview, we highlight recent applications of this intriguing cross-coupling reaction in modern organic synthesis, with an emphasis on cases in which traditional methods for C-C bond formation have failed.

Evaluation of a Series of ß-Secretase 1 Inhibitors Containing Novel Heteroaryl-Fused-Piperazine Amidine Warheads.

Despite several years of research, only a handful of ß-secretase (BACE) 1 inhibitors have entered clinical trials as potential therapeutics against Alzheimer's disease. The intrinsic basic nature of low molecular weight, amidine-containing BACE 1 inhibitors makes them far from optimal as central nervous system drugs. Herein we present a set of novel heteroaryl-fused piperazine amidine inhibitors designed to lower the basicity of the key, enzyme binding, amidine functionality. This study resulted in the identification of highly potent (IC50 ≤ 10 nM), permeable lead compounds with a reduced propensity to suffer from P-glycoprotein-mediated efflux.

Optimization of 1,4-Oxazine ß-Secretase 1 (BACE1) Inhibitors Toward a Clinical Candidate.

In previous studies, the introduction of electron withdrawing groups to 1,4-oxazine BACE1 inhibitors reduced the p Ka of the amidine group, resulting in compound 2 that showed excellent in vivo efficacy, lowering Aß levels in brain and CSF. However, a suboptimal cardiovascular safety margin, based on QTc prolongation, prevented further progression. Further optimization resulted in the replacement of the 2-fluoro substituent by a CF3-group, which reduced hERG inhibition. This has led to compound 3, with an improved cardiovascular safety margin and sufficiently safe in GLP toxicity studies to progress into clinical trials.

1,4-Oxazine ß-Secretase 1 (BACE1) Inhibitors: From Hit Generation to Orally Bioavailable Brain Penetrant Leads.

1,4-Oxazines are presented, which show good in vitro inhibition in enzymatic and cellular BACE1 assays. We describe lead optimization focused on reducing the amidine pKa while optimizing interactions in the BACE1 active site. Our strategy permitted modulation of properties such as permeation and especially P-glycoprotein efflux. This led to compounds which were orally bioavailable, centrally active, and which demonstrated robust lowering of brain and CSF Aß levels, respectively, in mouse and dog models. The amyloid lowering potential of these molecules makes them valuable leads in the search for new BACE1 inhibitors for the treatment of Alzheimer's disease.

Structure-activity relationships and molecular docking of novel dihydropyrimidine-based mitotic Eg5 inhibitors.

Dihydropyrimidine-based compounds belong to the first discovered inhibitors of the human mitotic kinesin Eg5. Although they are used by many research groups as model compounds for chemical genetics, considerably less emphasis has been placed on the improvement of this type of inhibitor, with the exception of two recent studies. Dihydropyrimidines can be divided into class I (analogues that bind in the S configuration) and class II type inhibitors, which bind in the R configuration. Herein we report the synthesis and optimization of novel class II type dihydropyrimidines using a combination of in vitro and docking techniques.

Structural basis for inhibition of Eg5 by dihydropyrimidines: stereoselectivity of antimitotic inhibitors enastron, dimethylenastron and fluorastrol.

Human kinesin Eg5, which plays an essential role in mitosis by establishing the bipolar spindle, has proven to be an interesting drug target for the development of cancer chemotherapeutics. Here, we report the crystal structures of the Eg5 motor domain complexed with enastron, dimethylenastron, and fluorastrol. By comparing these structures to that of monastrol and mon-97, we identified the main reasons for increased potency of these new inhibitors, namely the better fit of the ligand to the allosteric binding site and the addition of fluorine atoms. We also noticed preferential binding of the S-enantiomer of enastron and dimethylenastron to Eg5, while the R-enantiomer of fluorastrol binds preferentially to Eg5. In addition, we performed a multidrug resistance (MDR) study in cell lines overexpressing P-glycoprotein (Pgp). We showed that one of these inhibitors may have the potential to overcome susceptibility to this efflux pump and hence overcome common resistance associated with tubulin-targeting drugs.

Palladium(0)-catalyzed, copper(I)-mediated coupling of boronic acids with cyclic thioamides. selective carbon-carbon bond formation for the functionalization of heterocycles.

The palladium-catalyzed cross-coupling of cyclic thioamides with arylboronic acids in the presence of stoichiometric amounts of a copper(I) cofactor is described. The desulfitative carbon-carbon cross-coupling protocol is performed under neutral conditions and can be applied to a range of heterocyclic structures with embedded thioamide fragments. Successful carbon-carbon cross-coupling is independent of the ring size, aromaticity/nonaromaticity, the presence of additional heteroatoms, or other functional groups in the starting thioamide structure. Employing controlled microwave irradiation at 100 degrees C, most cross-couplings can be completed within 2 h and proceed in high yields. An advantage of using thioamides as starting materials is the fact that the system can be tuned to an alternative carbon-sulfur cross-coupling pathway by changing to stoichiometric copper(II) under oxidative conditions. Both types of thioamide cross-couplings are orthogonal to the traditional base-catalyzed Suzuki-Miyaura cross-coupling of aryl halides with boronic acids.

5-aroyl-3,4-dihydropyrimidin-2-one library generation via automated sequential and parallel microwave-assisted synthesis techniques.

An efficient two-step synthetic pathway toward the preparation of diversely substituted 5-aroyl-3,4-dihydropyrimidin-2-ones is realized. The protocol involves an initial trimethylsilyl chloride-mediated Biginelli multicomponent reaction involving S-ethyl acetothioacetate, aromatic aldehydes, and ureas as building blocks to generate a set of 3,4-dihydropyrimidine-5-carboxylic acid thiol esters. These thiol esters serve as starting materials for a subsequent Pd-catalyzed Cu-mediated Liebeskind-Srogl cross-coupling reaction with boronic acids to provide the desired 5-aroyl-3,4-dihydropyrimidin-2-one derivatives. Both steps were performed using microwave heating in sealed vessels, either in an automated sequential or parallel format using dedicated microwave reactor instrumentation. A diverse library of 30 5-aroyl-3,4-dihydropyrimidin-2-ones was prepared with commercially available aldehyde, urea, and boronic acid building blocks as starting materials.