‘One-pot’ four-step synthesis of cerpegin

Cerpegin (1) was synthesized through a ‘one-pot’ reaction in 71% overall yield. Lithiation of commercially available 2-methoxynicotinic acid (2) as its lithium salt using LTMP, followed by addition of acetone at low temperature and a specific acidic treatment of the intermediate 3 thus obtained, gave the 1,1-dimethyl-3,4-dioxo-1,3,4,5-tetrahydrofuro[3,4-c]pyridine (4). The latter was finally selectively alkylated using methyl iodide and caesium carbonate to afford cerpegin (1).     

High throughput synthesis of polyesters using entropically driven ring-opening polymerizations

Copolyesters were synthesized in a high throughput (HT) manner and in high yield on ca. a 90 mg scale using entropically driven ring-opening polymerizations (ED-ROPs). This synthetic approach is a valuable addition to the HT polymer synthesis arsenal in that it allows condensation-type polymers with relatively large repeat units, such as those in poly(ethylene terephthalate) and poly(butylene terephthalate), to be obtained easily. The synthetic procedure involved taking mixtures of the appropriate macrocyclic oligoesters and heating them together under neat conditions at 250-300 degrees C for 2 h in the presence of 0.1 mol % of di- n-butyltin oxide or tetra- n-butylammonium tetrafluoroborate. In most cases Mw values were >25,000 and, as expected for ED-ROPs, the polydispersity indices were close to 2.0. Higher molecular weights could be obtained by using longer reaction times, but this might lead to product decomposition. The method worked well for esters formally derived from aliphatic or aromatic acids and alcohols, but less well for esters derived from phenols. Attempts were also made to synthesize copolymers by mixing together the two homopolymers and heating with a catalyst. These reactions were successful in a few instances, but generally, they were not. This is probably because the homopolymers did not mix well. An aluminum reaction block with 36 wells lined with Teflon cups, that fitted snugly in a cylindrical Buchi oven, was the most successful method for carrying out syntheses in an HT manner.     

2D and 3D spatially addressed arrays for high-throughput automated synthesis of combinatorial libraries

One of the key elements in the drug discovery process is the use of automation to synthesize libraries of compounds for biological screening. The "split-and-mix" approaches in combinatorial chemistry have been recognized as extremely powerful techniques to access large numbers of compounds, while requiring only few reaction steps. However, the need for effective encoding/deconvolution strategies and demands for larger amounts of compounds have somewhat limited the use of these techniques in the pharmaceutical industry. In this paper, we describe a concept of directed sort and combine synthesis with spatially arranged arrays of macroscopic supports. Such a concept attempts to balance the number of reaction steps, the confidence in compound identity, and the quantity of synthesized compounds. Using three-dimensional arrays of frames each containing a two-dimensional array of macroscopic solid supports, we have conceptualized and developed a modular semiautomated system with a capacity of up to 100 000 compounds per batch. Modularity of this system enables flexibility either to produce large diverse combinatorial libraries or to synthesize more focused smaller libraries, both as single compounds in 12-15 micromol quantities. This method using sortable and spatially addressed arrays is exemplified by the synthesis of a 15 360 compound library.     

‘Click’ synthesis of triazole-based spirostan saponin analogs

Novel analogs of spirostan saponins in which the glycosidic bond has been replaced by a triazole linkage are described. For this, a direct oligosaccharide-steroid conjugation approach based on the Cu^I-catalyzed azide-alkyne 1,3-dipolar cycloaddition was implemented, leading to diverse combinations of saponin analogs with variations in the trisaccharide moiety, the artificial linkage, and the steroid-skeleton functionalization. This ‘click’ process proved great efficiency for the ligation of two bulky building blocks (e.g., chacotriose derivatives and spirostanes bearing axial azides), which enabled the rapid creation of a small library of triazole-based analogs for cytotoxicity evaluation. A molecular modeling study was performed to understand the conformational and electronic differences between a natural saponin and its triazole-based analogs.     

High throughput synthesis of ester library utilizing selective molecular reactivity and recognition technology

This paper reports a new solid support reagent that showed high degrees of selective molecular reactivity and molecular recognition in homo-functional reactions (reactions having similar reactive functionality in reactants and products).     

High throughput screening of gene functions in mammalian cells using reversely transfected cell arrays: review and protocol

Reversely transfected cell microarrays (RTCM) have been introduced as a method for parallel high throughput analysis of gene functions in mammalian cells. Hundreds to thousands of different recombinant DNA or RNA molecules can be transfected into different cell clusters at the same time on a single glass slide with this method. This allows either the simultaneous overexpression or--by using the recently developed RNA interference (RNAi) techniques--knockdown of a huge number of target genes. A growing number of sophisticated detection systems have been established to determine quantitatively the effects of the transfected molecules on the cell phenotype. Several different cell types have been successfully used for this procedure. This review summarizes the presently available knowledge on this technique and provides a laboratory protocol.     

High throughput screening arrays of rhodium and iridium complexes as catalysts for intramolecular hydroamination using parallel factor analysis

Parallel factor analysis (PARAFAC) was used to analyze data from the high throughput screening of an array of organometallic rhodium and iridium complexes as catalysts for the intramolecular hydroamination of 2-(2-phenylethynyl)aniline to give 2-phenylindole. The progress of the hydroamination reactions was monitored using UV-visible spectroscopy. The overlapped UV-visible spectra of the mixture of starting material, product and solvent in the samples taken at different times were deconvoluted using PARAFAC. Unique PARAFAC models led to close approximations of the actual UV-visible spectra of the compounds in the mixture. The performance of the catalysts was then compared by estimating the final concentration of the starting material and product using PARAFAC loadings. A library of 63 complexes generated in situ was examined in a single experiment using this methodology. The complexes were generated from combinations of seven ligands (bis(N-methyl2-imidazolyl)methane, bis(1-pyrazolyl)methane, 1,10-phenanthroline, N,N'-bis(p-tolyl)diazabutadiene, N,N'-bis(p-tolyl)1,2-dimethyldiazabutadiene, N,N'-bis(mesityl)1,2-dimethyldiazabutadiene and bis(2,4,6-trimethylphenylimino)acenapthene) and nine metal precursors ([Ir(COD)Cl](2) (COD = 1,5-cyclooctadiene), [Ir(CO)(2)Cl](n), [Ir(COE)(2)Cl](2), [IrCp*Cl(2)](2) (Cp* = 1,2,3,4,5-pentamethylcyclopentadiene), [Rh(COD)Cl](2), [Rh(CO)(2)Cl](2), [Rh(COE)(2)Cl](2), [RhCp*Cl(2)](2) and [RhCpCl(2)](2)) (Cp = cyclopentadiene)). The proposed method can be used for the fast screening of arrays of metal complexes for identifying effective catalysts, providing information that can augment traditional methods used for the analysis of catalyzed reactions.     

A new ‘one-pot’ synthesis of hydrazides by reduction of hydrazones

A new, high-yielding methodology for reducing hydrazones to hydrazines is described, which allows the synthesis of different mono-, di- and trisubstituted hydrazines. Moreover, the reduction step can be followed by an in situ reaction with a carboxylic acid making possible a ‘one-pot’ synthesis of trisubstituted hydrazides. The method is relatively general and, in principle, suitable for industrial applications.     

Zr-promoted ‘pair’-selective and regioselective synthesis of penta-substituted benzene derivatives

Tetra-substituted zirconacyclopentadiene derivatives, obtainable via in situ generation of zirconacyclopropenes and their cyclic carbozirconation with alkynes, can be treated with alkynyllithiums to induce 1,2-migration accompanied by aromatization and protonolysis, leading to the formation of penta-substituted benzene derivatives, in which all five substituted may be different.     

High throughput synthesis of diverse 2,5-disubstituted indoles using titanium carbenoids bearing boronate functionality

A titanium benzylidene complex bearing a boronate group converted resin-bound esters into enol ethers. Suzuki cross-coupling with aryl iodides followed by cleavage with acid completed the solid-phase synthesis of 2,5-disubstituted N-Boc-indoles. Also reported is the use of tert-butyllithium and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane to convert an aryl bromide into an arylboronate in the presence of a dithiane, with simultaneous reduction of an aryl azide to an amine.     

High throughput determination of gains and losses of genetic material using high resolution BAC arrays and comparative genomic hybridization

Chromosome analysis has been a cornerstone both for the identification of genetic defects that predispose to a variety of genetic syndromes as well as for the analysis of cancer progression. The relatively low resolution of metaphase chromosomes, however, only allows characterization of major genetic events which are defined at the megabase level. The development of the human genome-wide bacterial artificial chromosome (BACs) libraries which were used as templates for the human genome project made it possible to design microarrays containing these BACs which can theoretically span the genome uninterrupted. Comparative genomic hybridization to these arrays using test and reference DNA samples reveals numerical chromosome abnormalities (deletions, gains and amplifications) which can be accurately defined with a resolution depending on the density of the arrays. Analysis of test DNA samples using these arrays reveals low level deletions and amplifications that cannot be detected by chromosome analysis and provides a global view of these genetic changes in a single overnight hybridization using a high throughput approach. The extent of the genetic changes can then be determined precisely and the gene content of the affected regions established. These BAC arrays have widespread application to the analysis of constitutional genetic abnormalities associated with human diseases as well as cancer patients and their tumors. The development of similar BAC arrays for the mouse genome means that it is now possible to extend the CGHa approach to the study of genetic disorders and cancer models in mice.     

New synthetic strategies for the stereocontrolled synthesis of substituted ‘skipped’ diepoxides

This report describes a number of new synthetic approaches toward methyl-substituted mono- and diepoxy alcohols that serve as substrates for endo-selective epoxide-opening cascades. The key transformations involve the manipulation of alkynes. Highlighted are the directed methylmetalation of bishomopropargylic alcohols, the bromoallylation of alkynes, and Pd-catalyzed cross-coupling between an alkenyl boronate ester and allylic bromides.     

A practical synthesis of carbamates using an ‘in-situ’ generated polymer-supported chloroformate

A versatile method for the synthesis of carbamates from an ‘in-situ’ generated polymer-supported chloroformate resin is presented. BTC (bis-trichloromethyl carbonate) is used as phosgene equivalent to afford a supported chloroformate, which, by sequential ‘one-pot’ reaction with a variety of alcohols and amines, furnishes the corresponding carbamates in high yields and purities.     

Design and synthesis of novel pinacolylboronate containing combretastatin ‘antimitotic agent’ analogues

We developed a procedure to synthesize pinacolyl boronate containing stilbene derivatives and used this procedure to synthesize boron-containing combretastatin analogues. The key step involves the Wittig reaction of the ylide 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboratophenyl)-methyl triphenylphosphonium bromide 11 with 3,4,5-trimethoxy benzaldehyde in the presence of ^tBuONa in DMF, providing 88% yield. We are now in a position to evaluate the biological activity of these derivatives as modulators of TGF-beta signaling pathways.     

Preparation of ‘cage molecule’ based polyazido core units for dendrimer synthesis

Core molecules based on benzene-, cubane-, and adamantane-polycarboxylates with peripheral polyazido substitution are reported. The first synthesis of 1,3-diazidoacetone and its conversion to the corresponding oxime, DNPH, and 2,2-dinitro derivatives is also reported.     

‘Click’ synthesis of ferrocenyl-, biferrocenyl-, and cobalticenyl-triazolyl-β-cyclodextrins

Cu^I-catalyzed Huisgen-type dipolar ‘click’ reactions between azidomethyl-β-cyclodextrin and ethynylferrocene, ethylnylcobaltocenium hexafluorophosphate, and bis(ethynyl)-biferrocene yield the corresponding metallocenyl-1,2,3-triazolyl-β-cyclodextrins. The monometallocenyl 1,2,3-triazolyl-β-cyclodextrins are soluble in water, unlike the biferrocene derivative.     

‘O-Acyl isopeptide method’ for the efficient synthesis of difficult sequence-containing peptides: use of ‘O-acyl isodipeptide unit’

A novel ‘O-acyl isodipeptide unit’, Boc-Thr(Fmoc-Val)-OH 5 has been successfully used for the efficient synthesis of a difficult sequence-containing pentapeptide based on the ‘O-acyl isopeptide method’, in which racemization-inducible esterification could be omitted, suggesting that the use of O-acyl isodipeptide units allows the application of this method to fully automated protocols for the synthesis of long peptides or proteins.     

A facile and practical one-pot ‘catch and release’ synthesis of substituted guanidines

A ‘catch and release’ two-step one-pot protocol has been developed for the facile and practical synthesis of substituted guanidines from thioureas and various amines utilizing readily available brominated polystyrene resin.