Libraries of N-alkylaminoheterocycles from nucleophilic aromatic substitution with purification by solid supported liquid extraction

SLE Single-Step Purification and HPLC Isolation Method for Sterols and Triterpenic Dialcohols Analysis from Olive Oil

The unsaponifiable fraction of oils and fats constitutes a very small fraction but it is an essential part of the healthy properties of some specific oils. It is a complex fraction formed by a large number of minor compounds and it is a source of information to characterize and authenticate the oil sample. Specially, the composition of sterols of any oil or fat is a distinctive feature of itself and, therefore, it has become a useful tool for detecting contaminants and adulterants in oils. A new supported liquid extraction (SLE) technique for the analysis and characterization of the unsaponifiable fraction of fats and oils is proposed. The SLE system includes, as a stationary phase, a combination of adsorbent materials which allow a highly purified unsaponifiable matter ready to be isolated by high performance liquid chromatography (HPLC) and quantified by gas chromatography (GC). This method ensures the removal of fatty acids, avoiding possible interferences and making the analysis of sterols and triterpenic dialcohols easier. The procedure uses a small sample size (0.2 g), reduces the volume of solvents and reagents, and reduces the handling of samples subjected to analytical control. All this is achieved without losing either precision—a relative standard deviation of each compound lower than the reference value (≤16.4%)—or recovery, being for all compounds higher than 88.00%. Therefore, this new technique represents a significant economic and time saving in business control laboratories, a larger productivity and enhancement of working safety.

Synthesis, characterization, and antiproliferative and apoptosis inducing effects of novels-triazine derivatives

In an attempt to design and synthesize a new class of antitumor agents, a mild and eco-friendly protocol for nucleophilic substitution using ans-triazine scaffold,viaamine and Schiff base derivatives, has been developed.

Recent advances in the application of hydrophilic interaction chromatography for the analysis of biological matrices

Hydrophilic interaction chromatography (HILIC) is being increasingly used for the analysis of hydrophilic compounds in biological matrices. The complexity of biological samples demands adequate sample preparation procedures, specifically adjusted for HILIC analyses. Currently, most bioanalytical assays are performed on bare silica and ZIC-HILIC columns. Trends in HILIC for bioanalysis include smaller particle sizes and miniaturization of the analytical column. For complex biological samples, multidimensional techniques can separate and identify more compounds than 1D separations. The high volatility of the mobile phase, the added separation power and high sensitivity make MS the detection method of choice for bioanalysis using HILIC, although other detectors such as evaporative light scattering detection, charged aerosol detection and nuclear magnetic resonance have been reported.

Solid-phase parallel synthesis of drug-like artificial 2H-benzopyran libraries

This review covers the construction of drug-like 2H-benzopyrans and related libraries using solid-phase parallel synthesis. In this context, the preparation of substituted benzopyrans such as mono-, di- and trisubstituted benzopyran derivatives and additional ring-fused benzopyrans such as benzopyranoisoxazoles, benzopyranopyrazoles, six-membered ring-fused benzopyrans, and polycyclic benzopyrans are highlighted.

Efficient solid-phase synthesis of a library of imidazo[1,2-a]pyridine-8-carboxamides

A versatile method for the solid-phase synthesis of imidazo[1,2-a]pyridine-based derivatives, imidazo[1,2-a]pyridine-8-carboxamides, has been developed. They were obtained by treatment of the amino group of the polymer-bound 2-aminonicotinate with different alpha-haloketones, followed by halogenation at the 3-position of the polymer-bound imidazo[1,2-a]pyridine. The derived polymer-bound imidazo[1,2-a]pyridines 5, 6, and 7 were finally cleaved from the solid-support with an excess of primary or secondary amines. The final crude products were purified from excess amines by solid-supported liquid-liquid extraction (SLE).

Discovery of Chemical Reactions through Multidimensional Screening

Multidimensional reaction screening of ortho-alkynyl benzaldehydes with a variety of catalysts and reaction partners was conducted in an effort to identify new chemical reactions. Reactions affording unique products were selected for investigation of preliminary scope and limitations.

Enantioselective Synthesis of Linear Polypropionate Arrays Using Anthracene-Tagged Organosilanes

[reaction: see text] Preparation and use of anthracene-tagged organosilanes in an iterative, resin-capture-release protocol for the stereocontrolled synthesis of polypropionate arrays are described.

Synthesis of a Library of Complex Macrodiolides Employing Cyclodimerization of Hydroxy Esters

The synthesis of complex macrodiolides involving microwave-accelerated transesterification of chiral, nonracemic, hydroxy esters is described. Methodology development studies indicate that both microwave power and reaction temperature play an important role in the efficiency of cyclodimerizations. Hydroxy ester monomer pairs were evaluated using an analytical rehearsal leading to the preparation of a 127-member library of highly diverse and stereochemically well-defined macrodiolides. Preliminary assays identified a novel macrodiolide antagonist of the kappa opioid receptor.

A facile and improved synthesis of sildenafil (Viagra) analogs through solid support microwave irradiation possessing tyrosinase inhibitory potential, their conformational analysis and molecular dynamics simulation studies

Herein, the synthesis of some analogs of sildenafil (Viagra) (21) is described, employing MW irradiations in key steps such as, SNAr reaction on important precursor bromopyrazole (7). Compound 7 was synthesized by the bromination followed by the amidation of readily available 1-methyl-3-propyl-1H-pyrazole-5-carboxylic acid (5). Compounds 9 and 10 were obtained as SNAr reaction products, apparently through the proposed dipolar high-energy transition states TS-1 and TS-2 under MW irradiation, respectively. In contrast, conventional heating failed to produce similar results, even after prolonged heating. Compound 10, upon chlorosulfonation followed by the coupling of various nucleophiles, yielded a series of compounds 12-20 as analogs of sildenafil (21). Compounds 12-21 were subjected to tyrosinase inhibition studies and SAR studies were carried out. This study reflected that the inhibition was enhanced with increase of carbon chain. In case of the compound 17, the -OH group was replaced with -CH2-CH2-OH with a resulting increase in inhibition against tyrosinase. Compound 17 was found to be more potent than the potent reference inhibitor LM and KA. The 2D and 3D hydrogen bonding descriptors that help to study QSPR were also calculated. Energetically most stable conformations of these compounds were analyzed. Their kinetic, potential and total energies were also calculated through MD simulation.

Solid-Phase Synthesis of 1,2,3,4-Tetrahydroisoquinoline Derivatives Employing Support-Bound Tyrosine Esters in the Pictet−Spengler Reaction

The solid-phase synthesis of 1,2,3,4-tetrahydroisoquinoline-3-carboxamides employing carboxyl-supported, o-alkylated tyrosine esters in a Pictet-Spengler reaction is described. Esterification of [4-(hydroxyphenyl)thiomethyl]polystyrene (Marshall resin) with ethers of N-BOC-L-tyrosine using diisopropylcarbodiimide (DIC) and 4-dimethylaminopyridine (4-DMAP) afforded the solid-supported ester derivatives. Removal of the BOC group with trifluoroacetic acid (TFA) afforded the carboxyl-supported tyrosine ester, which was then treated with paraformaldehyde and TFA to afford the desired solid-supported counterpart. Acylation of the secondary amine with arylsulfonyl chlorides followed by reaction with amines resulted in the formation of the desired 2-arylsulfonyl-7-alkoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxamides. Alternatively, the support-bound tetrahydroisoquinoline-3-carboxylate derivatives could be treated with an aldehyde and a reducing agent to give the corresponding support-bound tertiary amine. Exposure of these resin-bound products to amines afforded the corresponding 2-alkyl-7-alkoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxamides after cleavage from the resin. Alternative routes to the desired chemotypes, as well optimization of the conditions for the Pictet-Spengler reaction and the conditions for the acylation and reductive amination of the support-bound secondary amines, are also described.

Solid-Phase Synthesis of 1-Substituted Tetrahydroisoquinoline Derivatives Employing BOC-Protected Tetrahydroisoquinoline Carboxylic Acids

Compounds containing the tetrahydroisoquinoline ring system were prepared using solid-supported ester derivatives on a nucleophile-sensitive resin, starting from the corresponding BOC-protected amino acids. The key heterocyclic intermediates were obtained from the Pictet-Spengler reaction between ethyl glyoxylate or methyl 4-formylbenzoate and dopamine or 3-hydroxyphenethylamine. After the resulting amino esters were converted to the BOC derivatives, the phenolic hydroxyl groups were alkylated with a series of alkyl halides to afford the corresponding ethers. Ester hydrolysis afforded the BOC-protected tetrahydroisoquinoline carboxylic acid scaffolds, which were then attached to (4-hydroxyphenyl)sulfide resin (Marshall linker) as the corresponding ester. The BOC group was removed under acidic conditions, and the resulting support-bound amine hydrochlorides were converted to the corresponding amides using a set of carboxylic acids. The support-bound amides were liberated with amines to produce the desired tetrahydroisoquinoline carboxamides. Optimization of the resin loading conditions is described in addition to the identification of impurities observed during the development of the optimum conditions for solid-phase synthesis.

Safety-Catch Approach to Orthogonal Synthesis of a Triazine Library

A novel safety-catch method for orthogonal synthesis of highly pure trisubstituted triazines was developed. Since the polymer-support used in this method is not acid-labile, this strategy can be uniquely applied to the synthesis of acid-sensitive triazine library compounds. This method will dramatically increase the diversity of triazine and other related heterocyclic library compounds.

Amino acid-derived heterocycles as combinatorial library targets: spirocyclic ketal lactones

The spirocyclic ketal-lactone frameworks of 3 and 4 were designed as novel structures amenable to combinatorial synthesis. The synthesis of representative analogues was developed in solution and on solid support, the scope of effective input materials was determined, and the stability and stereochemistry of the products was evaluated. The spirocycles are obtained in modest overall yields (5-36%) and excellent purities (>72%) and offer a promising motif for combinatorial prospecting libraries.

Suzuki cross-coupling of solid-supported chloropyrimidines with arylboronic acids

The utility of the Suzuki cross-coupling to synthesize biaryl compounds is expanded herein to include reactions of resin-supported chloropyrimidines with boronic acids. In particular, an efficient method is described for the synthesis of a library of biaryl compounds from solid-supported chloropyrimidines. The Suzuki reaction was performed in an inert atmosphere using Pd(2)(dba)(3)/P(t-Bu)(3) as catalyst, spray-dried KF as base, and THF as solvent. The reaction was allowed to proceed overnight at 50 degrees C. Upon cleavage with acid, a library of 4-(substituted amino)-6-arylpyrimidines was obtained in moderate yield and high purity.

FluoMar, a fluorous version of the Marshall resin for solution-phase library synthesis

[structure: see text] The fluorous counterpart of the Marshall resin, 4-(1H,1H,2H,2H-perfluorodecylsulfanyl)phenol (FluoMar), is prepared by S-alkylation of 4-mercaptophenol with C(8)F(17)CH(2)CH(2)I and employed in the synthesis of amide and diamide analogues. The final products are purified by solid-phase extraction (SPE) over FluoroFlash silica cartridges.

High-throughput catch-and-release synthesis of oxazoline hydroxamates. Structure-activity relationships in novel inhibitors of Escherichia coli LpxC: in vitro enzyme inhibition and antibacterial properties

LpxC is a zinc amidase that catalyses the second step of lipid A biosynthesis in Gram-negative bacteria. Oxazolines incorporating a hydroxamic acid, which is believed to coordinate to the single essential zinc ion, at the 4-position are known inhibitors of this enzyme. Some of these enzyme inhibitors exhibit antibacterial activity through their inhibition of LpxC. We recently developed a method for the synthesis of oxazolines using resin capture and ring-forming release that eliminates traditional purification steps and can be used in high-throughput synthesis. Using our method, oxazoline hydroxamates with diverse 2-substituents were prepared in library form as candidate inhibitors for LpxC. Two conventional methods for oxazoline synthesis were also applied to generate more than 70 compounds. The groups at the 2-position included a wide variety of substituted aromatic rings and a limited selection of alkyl groups. These compounds were screened against wild-type and LpxC inhibitor-sensitive strains of Escherichia coli, as well as wild-type Pseudomonas aeruginosa. Inhibition of the E. coli LpxC enzyme was also investigated. A broad correlation between enzyme inhibitory and antibacterial activity was observed, and novel compounds were discovered that exhibit antibacterial activity but fall outside earlier-known structural classes.

Novel orthogonal strategy toward solid-phase synthesis of 1,3,5-substituted triazines

[reaction: see text] To improve upon the previous orthogonal method for synthesis of a triazine library, an alternative strategy has been developed via oxidation-activation of the thioether to the sulfone. Through a comparison between these two methods, the sulfone strategy was demonstrated as an enhanced method in the generation of highly pure triazine library compounds.

A novel microtubule destabilizing entity from orthogonal synthesis of triazine library and zebrafish embryo screening

The first orthogonal combinatorial synthesis of a high-purity triazine library was demonstrated. Novel triazine-based microtubule inhibitors were discovered by an efficient zebrafish embryo screening and in vitro microtubule polymerization assay.

Solution-phase parallel synthesis of substituted benzimidazoles

A solution-phase parallel synthesis of o-phenylenediamines is described. These intermediates were then subsequently converted to benzimidazole scaffolds (three-point diversity) in excellent purities and yields. High-throughput purification of this multistep synthetic sequence was accomplished using polymer-bound scavengers and reagents and liquid-liquid extraction protocols.

High-throughput mass-directed parallel purification incorporating a multiplexed single quadrupole mass spectrometer

We report on the development of a parallel HPLC/MS purification system incorporating an indexed (i.e., multiplexed) ion source. In the method described, each of the flow streams from a parallel array of HPLC columns is directed toward the multiplexed (MUX) ion source and sampled in a time-dependent, parallel manner. A visual basic application has been developed and monitors in real-time the extracted ion current from each sprayer channel. Mass-directed fraction collection is initiated into a parallel array of fraction collectors specific for each of the spray channels. In the first embodiment of this technique, we report on a four-column semipreparative parallel LC/MS system incorporating MUX detection. In this parallel LC/MS application (in which sample loads between 1 and 10 mg on-column are typically made), no cross talk was observed. Ion signals from each of the channels were found reproducible over 192 injections, with interchannel signal variations between 11 and 17%. The visual basic fraction collection application permits preset individual start collection and end collection thresholds for each channel, thereby compensating for the slight variation in signal between sprayers. By incorporating postfraction collector UV detection, we have been able to optimize the valve-triggering delay time with precut transfer tubing between the mass spectrometer and fraction collectors and achieve recoveries greater than 80%. Examples of the MUX-guided, mass-directed fraction purification of both standards and real library reaction mixtures are presented within.

Kinetics study of amine cleavage reactions of various resin-bound thiophenol esters from marshall linker

The kinetics of cleavage reactions of seven resin-bound thiophenol esters with three amines has been studied by single-bead FTIR. The reactivity of these seven thiophenol esters was dependent on their structures and could be summarized as follows: 5-benzimidazolecarboxylic thiophenol ester > alkyl thiophenol ester > aromatic thiophenol ester. The reactivity of three amines was summarized as follows: n-butylamine > 3,4-dimethoxyphenethylamine > 1-piperonylpiperazine. The rate of the cleavage reaction increased 2-fold per 10 degrees C rise in reaction temperature. Oxidation of the thiophenol linker increased the rate of the cleavage reaction by 580-fold.

Resin-capture and release strategy toward combinatorial libraries of 2,6,9-substituted purines

A resin-capture and release strategy for making combinatorial 2,6,9-trisubstituted purine libraries is demonstrated by capturing N9-derivatized purines at the C6 position with a thio-modified polymer. The C2 fluoro group is subsequently substituted with primary and secondary amines followed by thioether oxidation and release by C6 substitution with amines and anilines. This approach complements a previously reported strategy where a 6-phenylsulfenylpurine scaffold was captured at the C2 position with a resin-bound amine.(3)

Work-up strategies for high-throughput solution synthesis

The key bottleneck in parallel synthesis has, in truth, always been the isolation and purification of the reaction products, rather than carrying out the reactions themselves. Solution-phase chemistry for parallel synthesis has recently been re-emphasized and has stimulated the development of a wide-range of practical tools for efficient high-throughput work-up, which are gaining increasing acceptance in medicinal chemistry groups.

Solid-phase library synthesis of alkoxyprolines

The library synthesis of alkoxyprolines was achieved using an acid-stable, nucleophile-cleavable solid support. A hydroxythiophenol linker derived from Merrifield resin was esterified with the corresponding ethers of BOC-hydroxyproline. Removal of the BOC protecting group with trifluoroacetic acid followed by acylation gave solid-supported hydroxyproline derivatives. Cleavage from the solid support with excess primary amines or excess secondary amines followed by purification of the crude products from the excess amine by supported liquid-liquid extraction gave the alkoxyproline library in high purity.

High-throughput purification of compound libraries

Synthesis of combinatorial libraries by parallel synthesis, followed by high- throughput biological screening, is the new paradigm for drug discovery. Purity of these libraries is an important consideration to obtain high-quality assay data. Liquid-liquid extraction and solid-phase capture reagents are useful in special cases for small numbers of compounds. However, for libraries of a few thousand compounds, HPLC is a viable alternative. Beyond these numbers, factors such as solvent requirements, the number of fractions and tracking become prohibitive. Supercritical fluid chromatography has been successfully employed in automated purification instrumentation and is expected to be capable of purifying libraries of tens-of-thousands of compounds.

A novel approach to high-throughput quality control of parallel synthesis libraries

Combinatorial chemistry is a powerful tool to enhance drug discovery efforts in the pharmaceutical industry. One type of combinatorial chemistry, parallel synthesis, is now widely used to prepare numerous compounds of structural diversity. A novel high-throughput method for quality control of parallel synthesis libraries has been developed. The method uses flow injection MS, for proof of structure and estimation of purity, and a novel direct injection CLND technique for quantitation of amount. Following the synthesis of a small molecule library, compounds analyzed using this technique were characterized by mass spectrometry, and an accurate concentration of the compound was assessed by CLND. Characterization of one compound is completed in 60 s, allowing for up to 1000 compounds to be analyzed in a single day. The data is summarized using pass/fail criteria using internally developed software.

Combinatorial chemistry as a tool for drug discovery

The question 'will combinatorial chemistry deliver real medicines' has been posed [96]. First it is important to realise that the chemical part of the drug discovery process cannot stand alone; the integration of synthesis and biological assays is fundamental to the combinatorial approach. The results presented in Tables 3.1 to 3.8 suggest that so far smaller directed combinatorial libraries have obtained equivalent results to those obtained previously from traditional medicinal chemistry analogue programs. Unfortunately, because of the long time it takes to develop pharmaceutical drugs there are no examples yet of marketed drugs discovered by combinatorial methods. There are interesting examples where active leads have been discovered from the screening of the same library against multiple targets (e.g. libraries 13, 39, 43, 66, 71 and 76). It is now possible to handle much larger libraries of non-oligomeric structures and the chemistry required for such applications is becoming available. Whether combinatorial approaches can also be adapted to deal with all the other requirements of a successful pharmaceutical (lack of toxicity, bioavailability etc.) is open to question but there are already examples such as cassette dosing [235-237]. However we can still be optimistic about the possibility of larger libraries producing avenues of investigation for the medicinal chemist to develop into real drugs. Combinatorial chemistry is an important tool for the medicinal chemist.

Automated high-throughput liquid-liquid extraction for initial purification of combinatorial libraries

An automated high-throughput liquid-liquid extraction (LLE) methodology has been developed and utilized for the initial purification of the combinatorial library samples containing unreacted amines and other water-soluble byproducts or impurities. Various extraction solvents were evaluated along with different extraction devices. The LLE method was automated using 96-well-format plates and a robotic liquid-handling workstation. In the optimized LLE method, crude combinatorial library samples were dissolved in a water-immiscible organic solvent, butyl acetate, and added to each well in a 96-well-format plate packed with an inert support material coated with hydrochloric acid. Separation occurs based on the partitioning of the compounds between two liquid phases. Product recovery, purity, and amine removal efficiency were determined by HPLC with and without precolumn derivatization. The automated method was successfully applied to the cleanup of some representative combinatorial library samples with greater than 98% amine removal and an average product purity of 90%. The application of the automated high-throughput LLE method should greatly reduce the labor, time, and cost associated with the purification of combinatorial libraries.

Enantioselective parallel synthesis using polymer-supported chiral Co(salen) complexes

[formula: see text] The kinetic resolution of epoxides with phenols catalyzed by a polymer-supported Co(salen) complex is applied to the first enantioselective catalytic synthesis of parallel libraries. The corresponding 1-aryloxy-2-alcohols are obtained in high yield, purity, and enantiomeric excess. Further elaboration with diversity elements provides highly efficient access to important classes of pharmacologically active compounds.