Diisopropylethylamine Research Articles

Novel Poly( EThylene Amido Amine) (PETAA) dendrimers produced through a unique and highly efficient synthesis

Polyamidoamine (PAMAM) dendrimers have unique attributes that have led to their use in a wide variety of biomedical applications. However, the complex synthesis of this polymer leads to variations in the structure and consistency of the final product, and makes scale-up of manufacturing difficult. This has limited the clinical translation of PAMAM-based materials. Here we describe a rapid and highly efficient two-step method for the synthesis of novel Poly( EThylene Amido Amine) (PETAA) dendrimers that have many of the favorable characteristics of PAMAM dendrimers. Generation 0 (G0) to 5 (G5) PETAA dendrimers were synthesized using a 3-(bis(2-(2,2,2,-trifluoroacetamido)ethyl)amino)propanoic acid AB 2 (compound 1) building block via a divergent approach. An ethylenediamine core was coupled with the AB 2 building block via O-(7-Azabenzotriazol-1-yl) N,N,N’,N’-tetramethyluronium hexafluorophosphate (HATU) in the presence of diisopropylethyl amine to give a G0 trifluoroacetamide surface dendrimer. The G0 amine surface dendrimer was then obtained by treating the G0 trifluoroacetamide surface dendrimer with potassium carbonate. Repetitions of these two coupling/deprotection reactions were then used to build the dendrimer by coupling the surface amino groups to the carboxyl moiety of the AB 2 building block, followed by the deprotection step with potassium carbonate. The resulting PETAA dendrimers have the same number of surface primary amino groups, the same number of chemical bonds between the dendrimer core and the surface, and the same number of tertiary amino groups throughout the structures as similar generations of PAMAM dendrimers. In contrast, the structure of the PETAA dendrimers is more complete and more uniform than PAMAM dendrimers, especially at higher generations. This unique synthetic process for PETAA dendrimers also offers the potential for large-scale production, therefore providing inherently more uniform and complete structures for exacting biomedical applications.

Heteroaryl Hydroxycarbonylation: An Efficient, Robust, Practically Scalable Approach Using Formyl Acetate as the CO Source

A simple, efficient, regioselective, and scalable palladium-catalyzed hydroxycarbonylation of heteroaryl halides to corresponding carboxylic acids using acetic–formic anhydride in presence of Pd(OAc)2, dppf, and diisopropylethyl amine in dimethyl formamide at 80–90 °C in excellent yields.

Sulfonamide synthesis using N-hydroxybenzotriazole sulfonate: an alternative to pentafluorophenyl (PFP) and trichlorophenyl (TCP) esters of sulfonic acids

The N-hydroxybenzotriazole (HOBt) sulfonate esters undergo amidation under ambient conditions in the presence of di-isopropylethyl amine. This method can be applied to varieties of amines including sterically hindered amino acid esters in less time with reasonably good yields.HOBt ester of sulfonic acids can be a replacement for pentafluorophenyl and trichlorophenyl ester as well as chloride moiety of sulfonyl chloride for amidation.

An efficient 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU)-mediated synthesis of 5-(trifluoromethyl)-N-alkyl-1-(3-phenylisoquinoline-1-yl)-1H-pyrazole-4-carboxamides

A series of 5-(trifluoromethyl)-N-alkyl-1-(3-phenylisoquinoline-1-yl)-1H-pyrazole-4-carboxamides 4 has been effectively achieved in high yield and purity from the reaction of pyrazole carboxylic acid 2 with amines 3 in the presence of TBTU as a catalyst and diisopropyl ethylamine as a base in acetonitrile at room temperature.

Click to Join Peptides/Proteins Together

Copper(I) is able to catalyze Huisgen 1,3-dipolar cycloaddition in a "click" fashion. This copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction presents excellent chemoselectivity and occurs over a wide-range of reaction conditions. It shows tolerance to variation in both pH and solvent polarity, thereby facilitating the ligation of peptides and proteins to produce peptidomimetics and synthetic proteins. In addition, the only product formed is a 1,4-disubstituted-1,2,3-triazole moiety, in many aspects resembling the natural peptide bond, including hydrogen-bonding capability, planarity, distance between the 1 and 4 substituents, and conformational restriction of the peptide backbone; thus the triazole-backbone-modified peptide, in which a triazole replaces the amide bond, may be anticipated to present a secondary structure similar to that of its natural counterpart. This Focus Review describes the scope and applications of copper(I)-catalyzed alkyne–azide cycloaddition in synthetic peptide/protein chemistry.

Synthesis of Constrained Peptidomimetics Containing 2‐Oxo‐1,3‐oxazolidine‐4‐carboxylic Acids

AbstractSulfonyl peptides containing a serine or threonine residue undergo cyclization with bis(succinimidyl) carbonate (DSC) and diisopropylethylamine (DIPEA) to give peptides with a 2‐oxo‐1,3‐oxazolidine‐4‐carboxylate (Oxd) group, either in solution or in the solid phase. The position of the serine or threonine residue in the sequence is relatively unimportant. Under the same conditions, the corresponding Fmoc‐ or Boc‐peptides gave dehydration products, in agreement to previous studies. The protocol constitutes a valuable approach to the preparation of oxazolidinone‐containing peptides, which are a recently emerging class of constrained peptidomimetics. As a representative example, an Oxd analogue of the endogenous opioid peptide endomorphin‐1, characterized by an all‐trans conformation, was readily prepared.

The Role of Intermolecular Hydrogen Bonding and Proton Transfer in Proton-Coupled Electron Transfer

An example of proton-coupled electron transfer (PCET) comprised by the electrochemical oxidation of 1,4-hydroquinone (1,4-H2Q) in acetonitrile was studied in the presence of Bronsted bases in acetonitrile. Of the two types of bases studied, the negatively charged carboxylates, trifluoroacetate (TFAC–), benzoate (BZ–), and acetate (AC–), showed hydrogen bonding with 1,4-H2Q, whereas the neutral amines, pyridine (PY) and N,N′-diisopropylethylamine (DIPEA), did not. This difference allowed a unique investigation of the effect of proton transfer on PCET with and without the influence of hydrogen bonding using two bases (TFAC– and PY) with approximately the same pKa (∼12). The study revealed that hydrogen bonding of 1,4-H2Q with the base TFAC– made the half wave redox potential of 1,4-H2Q more negative (easier to oxidize) by 0.186 V with respect to the oxidation in the presence of the same concentration of added PY, which does not hydrogen bond with 1,4-H2Q. Both types of bases studied, carboxylates and amines...

Complexation of amino compounds by 18C6 improves selectivity by IMS-IMS-MS: application to petroleum characterization.

Complexation of a series of related amino compounds by 18-crown-6 ether (18C6) is studied as a means of improving the resolution of mixtures by combinations of ion mobility spectrometry (IMS) and mass spectrometry (MS) techniques. Mixtures of the isomeric amines n-octylamine (NOA), dibutylamine (DBA), and diisopropylethylamine (DIPEA) were electrosprayed to produce gaseous [M + H](+) ions. These species have overlapping mobilities and are not resolved by IMS. Addition of 18C6 yields [M + 18C6 + H](+) ion complexes that are resolved by IMS. In subsequent experiments, [M + 18C6 + H](+) ion complexes are separated according to their mobilities and specific species are selected and exposed to collisional activation. This analysis yields dissociation voltages that are inversely correlated with the number of separate substitutions on the nitrogen atom of the amino compounds; dissociation voltages of ~40, ~90, and ~150 V are obtained for the tri-, di-, and mono-substituted amino compounds DIPEA, DBA, and NOA, respectively. For these complexes, an inverse correlation is also observed with respect to the gas-phase basicities (GB) of the amino compounds (964, 935, and 895 kJ mol(-1), respectively). Studies of 18C6 complexes with a series of n-alkylamines (C( n )H(2n+3)N where n=3 to 18, respectively) show that dissociation voltages increase systematically (from ~140 to ~190 V) under the conditions employed. The sensitivity to collision energy provides an additional means of distinguishing between classes of compounds. The approach is extended as a means of separating nitrogen-containing compounds from petroleum.

Diffusion-Controlled Luminescence Quenching in Metal−Organic Frameworks

Diffusion-controlled luminescence quenching of a phosphorescent metal-organic framework built from the Ru(bpy)(3)(2+)-derived bridging ligand (MOF-1) was studied using a series of amines of different sizes as quenchers. The dynamics of amine diffusion into solvent-filled MOF-1 channels was probed by modeling time-dependent luminescence quenching data, which provide quantitative diffusion coefficients for the amine quenchers. Triethylamine, tripropylamine, and tributylamine were found to follow Fickian diffusion with a diffusivity of (1.1 ± 0.2) × 10(-13), (4.8 ± 1.2) × 10(-14), and (4.0 ± 0.4) × 10(-14) m(2)/s, respectively. Diisopropylethylamine (DIPEA), on the other hand, was found to be too large to enter the MOF channels. Despite its size, 4-MeOPhNPh(2) can enter the MOF channels via a slow, complicated framework/guest intercalation process to result in extensive framework distortion as revealed by powder X-ray diffraction. This work represents the first quantitative study of the dynamics of molecular diffusion into solvent-filled MOF channels. Such quantitative information on molecular diffusion in MOFs is of fundamental importance to many of their potential applications (e.g., heterogeneous catalysis).

Synthesis of Di-, Tri-, and Tetrasulfides through Multifold Carbon−Sulfur Cross-Coupling Reactions with Indium Tri(organothiolates) in a One-Pot Procedure

Pd-catalyzed multifold (2-, 3-, and 4-fold) carbon-sulfur cross-coupling reaction of indium tri(organothiolates) with polybromonated aromatic and heteroaromatic compounds was developed in a one-pot procedure. Both 2,5-dibromopyridine and 2,6-dibromopyridine reacted with indium tri(organothiolates) (0.68 equiv) in the presence of 4 mol % of Pd(OAc)(2), 4.2 mol % of Xantphos, and 1 equiv of diisopropylethylamine (DIPEA), producing disulfides in good to excellent yields. These results indicate that indium tri(organothiolates) transfer all three alkyl- or arylthio groups attached to indium metal to electrophilic coupling partners. Indium tri(organothiolates) derived from alkyl thiol having a low boiling point, such as n-propyl, isopropyl, and tert-butyl thiol, acted as good nucleophilic coupling partners. In addition, indium tri(arylthiolates) derived from aryl thiols possessing an electron-withdrawing or -donating group on the aromatic ring participated well in the Pd-catalyzed multifold carbon-sulfur cross-coupling reaction. 4,4'-Dibromo-1,1'-biphenyl, 9,10-dibromoanthracene, 2,4-dibromoanisole, 2,7-dibromo-9,9-dimethylfluorene, 3,4-dibromothiophene, 2,3-dibromothiophene, 2,2'-bithiophene, 1,3,5-tribromobenzene, and 1,2,4,5-tetrabromobenzene were converted smoothly to the corresponding di-, tri-, and tetrasulfides.

Automated radiochemical synthesis of [18F]FBEM: A thiol reactive synthon for radiofluorination of peptides and proteins

The automated radiochemical synthesis of N-[2-(4-[(18)F]fluorobenzamido)ethyl]maleimide ([(18)F]FBEM, IUPAC name: N-maleoylethyl-4-[(18)F]fluorobenzamide), a prosthetic group for radiolabeling the free sulfhydryl groups of peptides and proteins, is herein described. 4-[(18)F]fluorobenzoic acid was first prepared by nucleophilic displacement of a trimethylammonium moiety on a pentamethylbenzyl benzoate ester with [(18)F]fluoride. In the second step the ester was cleaved under acidic conditions. Finally, 4-[(18)F]fluorobenzoic acid was coupled to N-(2-aminoethyl)maleimide using diethylcyanophosphate and diisopropylethyl amine. Following high-performance liquid chromatography (HPLC) purification, [(18)F]FBEM was obtained in 17.3±7.1% yield (not decay corrected) in approximately 95 min. Isolation from the HPLC eluate and preparation for subsequent use, which was conducted manually, required an additional 10-15 min. The measured specific activity for three batches was 181.3, 251.6, and 351.5 GBq/μmol at the end of bombardment (EOB).

ChemInform Abstract: Angular Hydroxymethylation of Functionalized Decalin Systems.

Functionalized β-dicarbonyl bicyclic compounds were hydroxymethylated at the angular position as the (benzyloxy) methoxy derivatives with diisopropylethylamine (DIPEA) and benzyl chloromethyl ether in the presence of paraformaldehyde

ChemInform Abstract: A New Short Synthesis of (.+-.)-Eburnamonine.

A new short synthesis of the indole alkaloid eburnamonine (1), starting from the easily available enamine (3) (1,12b-didehydroindolo[2,3-a]quinolizidine) is described. Pentacyclic lactam (7) (18-nor-19- ethoxycarbonyl-21-epieburnamonine) (trans D/E ring juncture), the key intermediate in this synthesis, was prepared from enamine (3) by dialkylating with ethyl iodoacetate in the presence of diisopropylethylamine (DIPEA). LiAlH 4 -reduction of lactam (7) gave a 2:1 mixture of compounds (10a) (21-epi-18-hydroxyeburnamine) and (10b) (16-epi-21-epi-18-hydroxyeburnamine)

An Efficient and Economical Method for the Preparation of Fmoc‐Argω,ω′(Boc)2‐OH

AbstractThe arginine derivative Fmoc‐Argω,ω′(Boc)2‐OH has been prepared in perfect yield starting from Fmoc‐Orn·HCl and N,N′‐di‐Boc‐N′′‐triflyguanidine with the presence of diisopropylethylamine (DIEA). This work provides an efficient and economical method for the preparation of this compound.

One-Step Conversion of Azine N-Oxides to α-1,2,4-Triazolo-, 1,2,3-Triazolo, Imidazolo-, and Pyrazoloheteroarenes

Pyridine, quinoline, isoquinoline, azaindole, and pyrimidine N-oxides were converted to their alpha-triazole and alpha-diazole derivatives by treatment with the corresponding p-toluenesulfonylazoles and Hunig's base at elevated temperatures.

2,2-bis(4-Chlorophenyl)Acetic Acid (DDA), a Water-Soluble Urine Biomarker of DDT Metabolism in Humans

DDT metabolism in humans yields DDA as the principal urinary metabolite and potential exposure biomarker. A method for DDA analysis in human urine was developed using pentafluorobenzyl bromide and diisopropylethyl amine. Dried hexane extracts were reacted for 1 hour at room temperature. The stable DDA-pentafluorobenzyl-ester derivative was analyzed by gas chromatography-electron capture detector (GC-ECD) and confirmed by gas chromatography-mass spectrometry (GC-MS) in selective ion monitoring mode. The limit of detection for DDA was 0.1 microg/L urine by GC-ECD and 2 microg/L urine by GC-MS, with a relative standard deviation of 12%. Urine specimens from DDT applicators in Swaziland and South Africa were analyzed to evaluate the method. The mean DDA levels during the spray season and post season were 59 and 11 microg/L, respectively. These results must be interpreted cautiously because different groups of workers provided urine specimens in each case. The DDA urinalysis may be a feasible monitoring strategy for low-level occupational and residential DDT exposure assessment in antimalaria campaigns.

Conventional Tetrakis(triphenylphosphine)palladium‐Copper(I) Iodide‐Catalyzed Sonogashira Coupling of Free and BOC‐ Protected Propargylic Amines “On Water”

AbstractAlkynylation of aryl iodides with propargylic amines has been achieved by means of a Sonogashira coupling using “on water” methods. The use of less than 0.2 mol% of tetrakis(triphenylphosphine)palladium [Pd(PPh3)4] and 1.5 mol% copper(I) iodide [CuI] in the presence of diisopropylethylamine (DIPEA) allows the coupling to proceed at 95 °C yielding moderate to good yields of mono‐, bis‐, and tris‐aminoalkynylbenzene derivatives.

Six- and seven-membered ring carbenes: Rational synthesis of amidinium salts, generation of carbenes, synthesis of Ag(I) and Cu(I) complexes

Abstract Reactions of neat 1,3- and 1,4-dibromides with N,N′-diarylformamidines in the presence of diisopropylethylamine (DIPEA) afford corresponding amidinium salts in high yields (>80%). Six- and seven-membered ring amidinium salts bearing bulky Mes (2,4,6-Me3C6H2) and Dipp (2,6-iPr2C6H3) aryl groups were prepared using this method. Free six-membered ring carbene 6-Dipp was generated from amidinium salt using LiHMDS as a base. NHC–Ag(I) complexes were obtained by the reactions of amidinium salts with Ag2O. NHC complexes of Pd and Rh are not accessible by deprotonation of amidinium salts, nor by transmetallation of Ag(I) complexes. However NHC–Cu(I) complexes were obtained by transmetallation of NHC–Ag(I). Thus, transmetallation of six- and seven-membered NHC–Ag(I) complexes was documented for the first time.

The use of phosphonium anhydrides for the synthesis of 2-oxazolines, 2-thiazolines and 2-dihydrooxazine under mild conditions

Beta-hydroxy amides 6 and 7 were treated with triphenylphosphonium anhydride trifluoromethane sulfonate (3), or the cyclic analogue 4, to generate 2-oxazolines 5 and 8 under mild conditions. The reaction was optimised by examining the number of equivalents of reagents 3 or 4, or diisopropylethyl amine required to best effect cyclisation. The effects of altering the reaction temperature, reaction time, concentration, solvent, and addition rate also were investigated. However, it was found that use of a trityl group to block reaction at the hydroxyl or thiol group of the starting amides, and subsequent in situ detritylation, in the absence of base, led to greatly improved yields. Reagent 4 offered significant advantages in the purification of products and was used to dehydrate a range of trityl derivatives to form simple oxazolines, thiazolines, and a dihydro-1,3-oxazine, in high yield (85-99%), as well as a tetrahydro-1,3-oxazepine (31%).

Trans-Stereoselectivity in the Reaction between Homophthalic Anhydride and Imines

The reaction between homophthalic anhydride and imines in the presence of TiCl4 and diisopropyl ethyl amine is trans-selective. Under these conditions, the reaction using homochiral imines can be highly diastereoselective, thus allowing the synthesis of enantiopure 1,2,3,4-tetrahydro-1-oxoquinoline-4-carboxylic acids.