Parallel Solid-phase Synthesis Research Articles

High-throughput manual parallel synthesis using SynPhase crowns and lanterns.

The high-throughput manual solid-phase parallel synthesis of libraries comprising thousands of discrete samples using pellicular supports (i.e. SynPhase crowns and lanterns) and a suite of novel tools and techniques is described. Key aspects of this approach include the combination of a split-split-split synthesis strategy with spatial encoding to differentiate thousands of crowns, the rapid washing and filtration of up to 48 reaction vessels in parallel, the application of an inexpensive and environmentally friendly technique to remove trifluoroacetic acid from sixteen 96-well plates in parallel, and a high-throughput method for removing cleaved crowns from reusable pin racks. Tens of thousands of discrete samples have been produced in-house using this conceptually and operationally straightforward strategy.

New Strategies for the Solid-Phase Synthesis of Highly Functionalized, Small Molecules: Sequential Nucleophilic Substitutions on Polymer-Bound Polyelectrophiles

Publisher Summary The screening of large and diverse arrays of compounds prepared on insoluble supports is one of the most efficient approaches for fast identification of lead compounds for novel, small molecule enzyme inhibitors, or other ligands for proteins. Parallel solid-phase synthesis is particularly well suited for the preparation of such arrays of diverse compounds, since multistep synthetic sequences on insoluble supports can be conducted on fully automated synthesizers. The advantages of using nucleophilic reagents for library production can be exploited by performing sequential nucleophilic substitutions on a polymer-bound polyelectrophile. A suitable polyelectrophile would be a polymer-bound compound with two or more leaving groups that could be orthogonally displaced by different nucleophiles. The sequential nucleophilic substitutions on support-bound polyelectrophiles gives quick access to highly functionalized, pharmacophore-rich small molecules. Because no protective groups are required, the scope of these syntheses is broad and a multitude of different pharmacophoric patterns can be generated by using exclusively simple, commercially available reagents. The use of 2,3-dichloropropionic acid and 4,5-difluoro-2-nitrobenzoic acid is discussed in the chapter to illustrate the scope and limitations of this strategy for the preparation of lead-like compound arrays.

Traceless solid phase synthesis of 2-substituted pyrimidines using an 'off-the-shelf' chlorogermane-functionalised resin.

The parallel solid phase synthesis of an 18-member library of 2-substituted pyrimidines is described using a chlorogermane-functionalised resin. The success of the key Pinner-type condensations between a resin-bound enaminone and an array of amidine hydrochlorides highlights the stability of arylgermane linkers (cf. arylsilanes) towards strongly basic/nucleophilic conditions.

Design and parallel solid-phase synthesis of ring-fused 2-pyridinones that target pilus biogenesis in pathogenic bacteria.

A new method for the solid-phase synthesis of enantiomerically enriched highly substituted ring-fused 2-pyridinones 13 has been developed. The synthesis mediates introduction of substituents at two positions in the 2-pyridinone ring in a diverse manner and is suitable for parallel synthesis. (19)F NMR spectroscopy was used as a tool to monitor each of the five steps in the reaction sequence. The optimized conditions thus obtained were then used to prepare a library of 20 2-pyridinones with high yields. The library members were chosen from a statistical multivariate design to ensure diversity and reliable data for structure-activity relationships. Screening of the library against the bacterial periplasmic chaperone PapD was performed using surface plasmon resonance. Three new 2-pyridinones with a higher affinity for the chaperone PapD than the previous best 13[10,1] were found, and important structural features could be deduced.

An efficient and practical method for solid-phase synthesis of tripeptide-bearing glycopeptide antibiotics: combinatorial parallel synthesis of carboxamide derivatives of chloroorienticin B

An efficient and practical method was established for solid-phase parallel synthesis of the peptide-bearing carboxamide derivatives of chloroorienticin B, and over 80 compounds were synthesized simultaneously. Among the derivatives prepared, compounds having both tryptophan and tyrosine residues ( 1– 3) were found to possess potent antibacterial activity against VRE.

A multidetachable sulfamate linker successfully used in a solid-Phase strategy to generate libraries of sulfamate and phenol derivatives

The sulfamates and phenols constitute two families of compounds with numerous interesting biological properties. Using the ability of a new multidetachable sulfamate linker to generate these two families of compounds from the same resin, we designed and synthesized libraries of estradiol derivatives, sulfamoylated or not. A C-16β side chain was then judiciously diversified to target two key steroidogenic enzymes, the steroid sulfates and the type 1 17β-HSD. Four libraries of sulfamate and phenol derivatives were easily obtained by solid-phase parallel synthesis in good crude overall yields (13–62%) and HPLC purities (85–96%). Such strategy using the new two-in-line sulfamate linker could be also extended to other therapeutic targets than steroidogenic enzymes, thus adding to its potential.

Solid-phase synthesis of dual α4β1/α4β7 integrin antagonists: two scaffolds with overlapping pharmacophores

Two structural classes of dual α4β1/α4β7 integrin antagonists were investigated via solid-phase parallel synthesis. Using an acylated amino acid backbone, lead compounds containing biphenylalanine or tyrosine carbamate scaffolds were optimized for inhibition of α4β1/VCAM and α4β7/MAdCAM. A comparison of the structure–activity relationships in the inhibition of the α4β7/MAdCAM interaction for substituted amines employed in both scaffolds suggests a similar binding mode for the compounds.

A traceless approach for the parallel solid-phase synthesis of 2-(arylamino)quinazolinones.

A traceless approach for the parallel solid-phase synthesis of 2-arylamino-substituted quinazolinones is described. Acylation of MBHA resin with o-nitrobenzoic acid derivatives, followed by reduction of the nitro group with tin chloride, generated a resin-bound o-anilino derivative. Reaction of resin-bound o-anilino derivative with arylisothiocyanates yielded resin-bound thioureas, which reacted with amines in the present of Mukaiyama's reagent (2-chloro-1-methylpyridinium iodide) to afford resin-bound guanidines. Following intramolecular cyclization of the resin-bound guanidines during cleavage from the resin by HF/anisole (95/5) for 1.5 h at 0 degrees C, the desired products were obtained in good yield and purity.

Palladium(0)-catalyzed coupling-cyclization reaction of polymer-supported aryl iodides with 1,2-allenyl carboxylic acids. Solid-phase parallel synthesis of butenolides.

In this contribution, we constructed a library of butenolides with 77 members by parallel synthesis strategy on Merrifield resin. Sixteen 2,3-allenoic acids and 12 polymer-bound aryl iodides were combined to react with each other, and then the polymer-supported products were cleaved to release butenolide derivatives. The reactions with alkyl-substituted 2,3-allenoic acids in acetonitrile afforded the corresponding products in high yields and high purities, whereas those with aryl-substituted acids in acetonitrile failed. After some reaction conditions were screened, the solid-phase reactions with aryl-substituted 2,3-allenoic acids were realized in toluene, and the products are of good purities albeit in slightly low yields. In the benzyl ether linkage, a new cleavage model was found. By adding 6 equiv of acetyl bromide, we can get single (5-oxo-2,5-dihydrofuran-3-yl)benzyl bromide other than the corresponding benzyl acetate. To further increase the diversities, a dihydropyran (DHP) linker was introduced into our combinatorial synthesis of butenolides. By reversing the addition sequence of 2,3-allenoic acids and organic base, we realized the solid-phase cyclization reaction of polymer-bound aryl iodides with the THP linkage in moderate yields and good purities. Now the library of butenolides includes (5-oxo-2,5-dihydrofuran-3-yl)benzoic acids, -aryl acetates, -benzyl bromides, -benzyl alcohols, and -phenols, which are difficult to synthesize with conventional solution methods.

Application of parallel liquid chromatography/mass spectrometry for high throughput microsomal stability screening of compound libraries

Solution-phase and solid-phase parallel synthesis and high throughput screening have enabled biologically active and selective compounds to be identified at an unprecedented rate. The challenge has been to convert these hits into viable development candidates. To accelerate the conversion of these hits into lead development candidates, early assessment of the physicochemical and pharmacological properties of these compounds is being made. In particular, in vitro absorption, distribution, metabolism, and elimination (ADME) assays are being conducted at earlier and earlier stages of discovery with the goal of reducing the attrition rate of these potential drug candidates as they progress through development. In this report, we present an eight-channel parallel liquid chromatography/mass spectrometry (LC/MS) system in combination with custom Visual Basic and Applescript automated data processing applications for high throughput early ADME. The parallel LC/MS system was configured with one set of gradient LC pumps and an eight-channel multiple probe autosampler. The flow was split equivalently into eight streams before the multiple probe autosampler and recombined after the eight columns and just prior to the mass spectrometer ion source. The system was tested for column-to-column variation and for reproducibility over a 17 h period (approximately 500 injections per column). The variations in retention time and peak area were determined to be less than 2 and 10%, respectively, in both tests. The parallel LC/MS system described permits time-course microsomal incubations (t o, t 5, t 15, t 30) to be measured in triplicate and enables estimations of t 1/2 microsomal stability. The parallel LC/MS system is capable of analyzing up to 240 samples per hour and permits the complete profiling up to two microtiter plates of compounds per day (i.e., 176 test substrate compounds + sixteen controls).

Rapid parallel synthesis of polymer-bound enones utilizing microwave-assisted solid-phase chemistry.

A microwave-assisted parallel solid-phase synthesis of a collection of 21 polymer-bound enones has been developed. The two-step protocol involves initial high-speed acetoacetylation of polystyrene Wang resin with a selection of seven common beta-ketoesters. When microwave flash heating at 170 degreesC was employed, complete conversions were achieved within 1-10 min, a significant improvement over the conventional thermal method, which takes several hours for completion. Significant rate enhancements were also observed for the subsequent microwave-heated Knoevenagel condensations with a second set of 13 different aldehydes. Reaction times were reduced to 30-60 min at 125 degreesC in the microwave protocol compared to 1-2 days using conventional thermal conditions. Kinetic comparison studies indicate that the observed rate enhancements can be attributed to the rapid direct heating of the solvent (1,2-dichlorobenzene) by microwaves rather than to any specific microwave effect. All reactions have been carried out in commercially available parallel reactors with on-line temperature measurement, designed specifically for use in multimode microwave cavities.

Parallel Solid-Phase Synthesis of Partially Modified Retro and Retro-Inverso ψ[NHCH(CF3)]-Gly Peptides

The parallel solid-phase synthesis of small libraries of molecules belonging to a novel class of retro and retro-inverso peptides having a ψ[NHCH(CF3)] surrogate of the conventional retro-peptide bond (NH-CO) has been accomplished. Key step for the synthesis of the -NHCH(CF3)- unit is a Michael-type N-addition of resin bound α-amino acid esters H-AA1-OWang (1), dipeptide H-Val-Gly-OWang (8), and tripeptide H-Val-Val-Ala-OWang (12) to (S)-3-(E-enoyl)-1,3-oxazolidin-2-one (3), which took place very effectively under mild condition. Chemoselective exocyclic oxazolidinone cleavage, followed by parallel couplings of the resulting polymer-bound pseudopeptides WangO-AA1-ψ[NHCH(CF3)]-Gly-OH (5), WangO-Gly-Val-ψ[NHCH(CF3)]-Gly-OH (10), and WangO-Ala-Val-Val-ψ[NHCH(CF3)]-Gly-OH (14) with different α-amino acid esters afforded, after release from the resin, a representative set of ψ[NHCH(CF3)] retro and retro-inverso tripeptides HO-AA1-ψ[NHCH(CF3)]-Gly-AA2-OX1 (7), tetrapeptides HO-Gly-Val-ψ[NHCH(CF3)]-Gly-AA3-OX2 (11), and pentapeptides HO-Ala-Val-Val-ψ[NHCH(CF3)]-Gly-AA4-OX3 (15), respectively, with good to excellent purity in all cases.

Identification of potent and selective mechanism-based inhibitors of the cysteine protease cruzain using solid-phase parallel synthesis.

Targeted libraries of ketone-based cysteine protease inhibitors were synthesized and screened against cruzain, a cysteine protease implicated in Chagas' disease. A number of single digit nanomolar, low molecular weight inhibitors were identified and optimized for solubility and potency. Specifically, the best inhibitors identified have K(i) values of 0.9-10 nM and molecular weights between 499 and 609 Da. The most effective inhibitor was also found to be greater than 1000-fold selective for cruzain relative to cathepsin B and 100-fold selective for cruzain relative to cathepsin L.

Parallel solid-phase synthesis of 3β-peptido-3α-hydroxy-5α-androstan-17-one derivatives for inhibition of type 3 17β-hydroxysteroid dehydrogenase

Type 3 17β-hydroxysteroid dehydrogenase (17β-HSD), a key steroidogenic enzyme, transforms 4-androstene-3,17-dione (Δ 4-dione) into testosterone. In order to produce potential inhibitors, we performed solid-phase synthesis of model libraries of 3β-peptido-3α-hydroxy-5α-androstan-17-ones with 1, 2, or 3 levels of molecular diversity, obtaining good overall yields (23–58%) and a high average purity (86%, without any purification steps) using the Leznoff's acetal linker. The libraries were rapidly synthesized in a parallel format and the generated compounds were tested as inhibitors of type 3 17β-HSD. Potent inhibitors were identified from these model libraries, especially six members of the level 3 library having at least one phenyl group. One of them, the 3β-( N-heptanoyl- l-phenylalanine- l-leucine-aminomethyl)-3α-hydroxy-5α-androstan-17-one ( 42) inhibited the enzyme with an IC 50 value of 227 nM, which is twice as potent as the natural substrate Δ 4-dione when used itself as an inhibitor. Using the proliferation of androgen-sensitive (AR +) Shionogi cells as model of androgenicity, the compound 42 induced only a slight proliferation at 1 μM (less than previously reported type 3 17β-HSD inhibitors) and, interestingly, no proliferation at 0.1 μM.

Identification of a series of PPARγ/δ dual agonists via solid-Phase parallel synthesis

We have developed a general solid-phase synthesis for identification of PPAR ligands. Synthesis of a 480-member library led to the identification of a potent PPARγ/δ dual agonist 23. Compound 23 showed good plasma exposure in rats and demonstrated antihyperglycemic and antihyperlipidemic efficacy in diabetic fatty Zucker rats.

Parallel solid-Phase synthesis of zatebradine analogues as potential I f channel blockers

The first solid-phase synthesis of zatebradine 1 and its analogues is reported. This has resulted in the preparation of compounds with increased ability to reduce the spontaneous beating of isolated guinea-pig atria in a concentration-dependent manner. One example, 8g, showed a maximum reduction of beating of 80% at 3 μM compared to a reduction of 40% at 3 μM with zatebradine 1.

Parallel solid-phase synthesis of nucleoside phosphoramidate libraries

Combinatorial chemistry is playing an increasingly prominent role in the process of drug discovery. A nucleic acid-based (NAB TM) scaffold can be engineered to create functional group and topological diversity in a library. Described herein is the parallel solid-phase synthesis of combinatorial libraries of nucleoside phosphoramidates, and the first evaluation of antiviral activity against hepatitis B virus (HBV).

Parallel synthesis of 4,5-dihydro-1 H-1,4-benzodiazepine-2,3-diones

An efficient strategy for the parallel solid-phase synthesis of 4,5-dihydro-1 H-1,4-benzodiazepine-2,3-diones is described. The reductive alkylation of resin-bound primary amine with different substituted o-nitrobenzaldehydes generated a secondary amine, which was treated further with methyl chlorooxoacetate. The nitro group was reduced with tin(II) chloride. During the overnight reduction, an in situ intramolecular cyclization occurred to provide, following HF cleavage, the desired 4,5-dihydro-1 H-1,4-benzodiazepine-2,3-dione.

Inhibition of BCRP-mediated drug efflux by fumitremorgin-type indolyl diketopiperazines

A library of 42 diastereoisomeric mixtures of fumitremorgin-type indolyl diketopiperazines, prepared by parallel solid-phase synthesis, was screened for Breast Cancer Resistance Protein inhibitory activity and compared with GF120918. Demethoxy-fumitremorgin C was synthesized by solid-phase techniques and tested as well. Structure–activity relationship studies have identified several potent analogues, both in assays using the T6400 mouse and the T8 human cell line, whereas low cytotoxicity was seen at effective concentrations.

Asymmetric Acylation Reactions Catalyzed by Conformationally Biased Octapeptides

Octapeptides capable of adopting β-hairpin conformations have been found to function as efficient catalysts for the kinetic resolution of certain racemic secondary alcohols. Parallel solid phase synthesis of a series of peptides with the common feature of the d-Pro-Gly sequence at the turn region ( i+3 to i+4) was carried out to yield a family of octapeptide catalysts. The peptides were then screened for their efficiency in a number of enantioselective acylation reactions.