Acid Bromides Research Articles

Alkyl pectin: Hydrophobic matrices for controlled drug release

ABSTRACTAlkyl pectin with various fatty acid (C4–C16) bromides increased its hydrophobic characteristic and made important changes in its structural features. Unmodified pectin exhibited a low degree of order (DO) and a weak tablet‐crushing strength. Pectin alkylated with a short chain length (C4) possessed similar properties but exhibited significant swelling. Alkylation with longer side chains (C8–C16) resulted in a higher DO and crushing strength but a lower swelling. The best mechanical characteristics and drug‐release properties were found for octanoyl pectin (OP; degree of substitution = 7.06–15.41%) tablets with 20% bovine serum albumin as a tracer. The high stability of these monolithic tablets appeared to be due to hydrophobic interactions between side chains, as shown by a more organized structure. IR spectroscopy and differential scanning calorimetry analyses of OP were consistent with a hydrophobic self‐assembling model. The drug dissolution kinetics showed longer release times for higher degrees of functionalization, that is, 35 h (for 10.88% substitution) and 80 h (for 15.41% substitution); this suggested OP excipients as interesting candidates for oral and subdermal pharmaceutical applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41302.

ChemInform Abstract: A Novel Thiazolium Type Peptide Coupling Reagent for Hindered Amino Acids.

Abstract A highly efficient coupling reagent, 2-bromo-3-ethyl-4-methyl thiazolium tetrafluoroborate (BEMT), was designed, synthesized and successfully applied to the synthesis of oligopeptides containing N-alkyl or α-C-dialkyl amino acids. Its efficiency was evaluated by HPLC and 1H NMR methods, and demonstrated by synthesis of a number of N-methyl-rich peptide segments with good yields and negligible racemization. The mechanism of coupling was studied by HPLC, 1H NMR and IR monitoring; it is proposed that labile (acyloxy)thiazolium salts and N-protected amino acid bromides were the major active intermediates with concomitant formation of N-ethyl-4-methyl thiazolidones and a small amount of oxazolones and N-protected amino acid anhydrides.

Novel and Efficient Route for the Synthesis of 4-Aryl-Substituted 2(5H)-Furanones

4-Aryl-substituted 2(5H)-furanones were prepared by reaction of diethylphosphono acetic acid and phenacyl bromides, followed by an intramolecular Horner–Emmons-type cyclization. Both the reactions were carried out in situ to give the desired 4-aryl substituted 2(5H)-furanone derivatives.

Radical mediated-direct conversion of aldehydes into acid bromides

A method of preparing acid bromides directly from aldehydes with Br 3CCO 2Et under radical conditions was developed. Aromatic aldehydes with electron-donating group were found to be more reactive than aromatic aldehydes with electron-withdrawing group and aliphatic aldehydes under reaction conditions.

A Mild and Efficient Reaction for Conversion of Carboxylic Acids into Acid Bromides with Ethyl Tribromoacetate/Triphenylphosphine under Acid‐Free Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

A mild and efficient reaction for conversion of carboxylic acids into acid bromides with ethyl tribromoacetate/triphenylphosphine under acid-free conditions

Acid bromides were prepared efficiently from carboxylic acids with readily available ethyl tribromoacetate and triphenylphosphine at room temperature under neutral conditions. The present process is applicable to the preparation of various acid bromides from aromatic and aliphatic carboxylic acids. Aromatic carboxylic acids were found to be more reactive than aliphatic carboxylic acids under reaction conditions.

Amino acid bromides: their utilization for difficult couplings in solid-phase peptide synthesis

Use of N-protected-α-amino acid bromides for facile solid-phase synthesis of peptides (SPPS) containing extremely sterically hindered non-proteinogenic amino acids is presented. Amino acid bromides (Aaa-Br), generated in situ, were used for the synthesis of long chain homopeptides containing up to eight successive α-MeVal or Aib residues. SPPS of a heteropeptide containing a very bulky amino acid building block is also described. The choice of suitable N-protections is discussed.

Star polymers by ATRP of styrene and acrylates employing multifunctional initiators

AbstractMultifunctional initiators for atom transfer radical polymerization (ATRP) are prepared by converting ditrimethylolpropane with four hydroxyl groups, dipentaerythritol with six hydroxyl groups, and poly(3‐ethyl‐3‐hydroxymethyl‐oxetane) with ∼11 hydroxyl groups to the corresponding 2‐bromoisobutyrates or 2‐bromopropionates as obtained by reaction with acid bromides. Star polystyrene (PS) is produced by using these macroinitiators and neat styrene in a controlled manner by ATRP at 110 °C, employing the catalytic system CuBr and bipyridine. Mn up to 51,000 associated with narrow molecular weight distributions (PDI < 1.1) are obtained with conversions up to 32%. Hydrolysis of the star‐PS leads to linear chains having the expected Mn values. The star‐PS polymers based on dipentaerythritol degrade thermally in nitrogen in a two‐step process in which the first low‐temperature step involves scission of the ester linkages and the second step corresponds to the normal PS degradation. Star poly(methyl acrylates) with various cores are likewise prepared in a controlled manner by ATRP of methyl acrylate in bulk and in solution at 60–80 °C with the 1,1,4,7,7‐pentamethyldiethylene triamine ligand. Under these conditions, higher conversions were possible still maintaining low PDI signaling controlled star growth. Multiarm stars of poly(n‐butyl acrylate) and poly(n‐hexyl acrylate) with controlled characteristics have also been prepared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3748–3759, 2005

Triphenylphosphine‐2,4,4,6‐tetrabromo‐2,5‐cyclohexadienone Complex as a Reagent for Preparation of Carboxylic Acid Bromides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Triphenylphosphine-2,4,4,6-tetrabromo-2,5-cyclohexadienone complex as a reagent for preparation of carboxylic acid bromides

Triphenylphosphine-2,4,4,6-tetrabromo-2,5-cyclohexadienone complex was successfully used as a new reagent for the synthesis of carboxylic acid bromides which were isolated as individual substances or were identified by conversion into the corresponding anilides. The reaction is chemoselective, and it can be applied to polyfunctional compounds, e.g., hydroxy acids.

Amino Acid Bromides: Their N-Protection and Use in the Synthesis of Peptides with Extremely Difficult Sequences.

Amino Acid Bromides: Their N-Protection and Use in the Synthesis of Peptides with Extremely Difficult Sequences.

Amino acid bromides: their N-protection and use in the synthesis of peptides with extremely difficult sequences.

N(alpha)-Protected alpha-amino acid bromides were easily generated in situ with 1-bromo-N,N-2-trimethyl-1-propenylamine from the corresponding amino acids under very mild conditions. o-Nbs and the azido moieties proved to be compatible with these overactivated halides and were successfully applied in difficult peptide bond formations. N-Deprotection methods and the total step-by-step solution synthesis of a peptide containing up to seven consecutive L-(alphaMe)Valine residues are also reported. The assembly of this homopeptide was achieved in a short time and in very high yields by the azido/bromide system in a single repetitive operation.

ChemInform Abstract: N‐Protected Amino Acid Bromides: Efficient Reagents for the Incorporation into Peptides of Extremely Hindered α,α‐Dialkyl‐ and α‐Fluoroalkyl‐amino Acids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

N-Protected amino acid bromides: efficient reagents for the incorporation into peptides of extremely hindered α,α-dialkyl- and α-fluoroalkyl-amino acids

N-Protected amino acid bromides were found to be exceptionally well suited for the coupling of extremely hindered amino acids. Bromides were generated in situ under neutral conditions and used for coupling with a number of α,α-dialkyl- and N-Me-amino acids, affording configurationally pure peptides in very high yields. For the first time, peptide bond formation on the amino group of α-fluoroalkyl-amino acids is described with satisfactory yields.

N-n-alkyl N,N-dimethylammonioacetic acid bromides: the first complete series of crystal and molecular structure determinations of an amphiphilic compound with alkyl chain lengths n = 1,..., 16

The molecular and crystal structures of 16 N-n-alkyl N,N-dimethylammonioacetic acid bromides with chain lengths between n = 1 and n = 16 have been determined. All compounds from n = 5 to n = 16 form bilayers with interdigitated chains. The even-numbered chains display the chain packing type M2(II). The chain packing of the odd-numbered chain compounds is less regular. The head groups of all compounds are connected via electrostatic N+...Br- interactions, and by OH...Br- hydrogen bonds. The compounds with short chains are packed in different ways. Their molecular conformation depends on the crystal packing.

A novel thiazolium type peptide coupling reagent for hindered amino acids

A highly efficient coupling reagent, 2-bromo-3-ethyl-4-methyl thiazolium tetrafluoroborate (BEMT), was designed, synthesized and successfully applied to the synthesis of oligopeptides containing N-alkyl or α- C-dialkyl amino acids. Its efficiency was evaluated by HPLC and 1H NMR methods, and demonstrated by synthesis of a number of N-methyl-rich peptide segments with good yields and negligible racemization. The mechanism of coupling was studied by HPLC, 1H NMR and IR monitoring; it is proposed that labile (acyloxy)thiazolium salts and N-protected amino acid bromides were the major active intermediates with concomitant formation of N-ethyl-4-methyl thiazolidones and a small amount of oxazolones and N-protected amino acid anhydrides.

Increased Coupling Size in J-Aggregates through N-n-Alkyl Betaine Surfactants

The spectroscopic properties of a J-aggregating cyanine dye in the presence of betainic N-n-alkyl-N,N-dimethylammonio acid bromides with alkyl chain lengths between 10 and 16 carbon atoms are examined. In contrast to the usually observed deaggregating influence of micelle-forming agents, an increase in absorptivity and a decrease in J-band width are established. Furthermore, the spectroscopic properties of the J-band depend on the N-n-alkyl chain length of the surfactant. The coupling size of the aggregates increases in surfactant solution as compared to that in aqueous solution. The effects are attributed to a new type of supramolecular structure based on J-aggregates with enclosed monomer molecules of the surfactant.

ChemInform Abstract: New General Synthesis of Mixed Phosphorus and Sulfonic Acid Anhydrides via Reaction of Phosphorus Acid Bromides and Iodides with Silver Salts of Sulfonic Acids: A Route to P‐Chiral Anhydrides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis and characterization of some amine complexes of bromocarboxyboranes and bromo(methoxycarbonyl)boranes

Amine-carboxyboranes [A.BH 2COOH; A = Me 3N, Et 3N, quinuclidine (Q)] are readily decarbonylated with bromine in dichloromethane to produce amine-dibromoboranes (A.BHBr 2). The formation of A.BHBr 2 is explained by fast loss of CO from the acid bromides A.BH(Br)COBr generated because of the action of HBr. In proton-acceptor solvents (such as H 2O), however, only substitution takes place giving a chiral boron atom containing A.BH(Br)COOH and/or A.BBr 2COOH. Also, bromocarboxyborane complexes can be prepared easily using bromination with N-bromosuccinimide (NBS). The products are rather stable in water under acidic conditions but bases induce fast decarbonylation followed by complete decomposition. Amine(methoxycarbonyl)boranes A.BH 2COOMe (A = Me 3N, Et 3N and Q) are conveniently synthesized, with good yields, in methanol by treatment with a cation exchange resin (H +) as a catalyst. The bromo derivatives A.BH 2- nBr n COOMe ( n = 1, 2) have been prepared by treatment of amine complexes of BH 2COOMe with bromine or NBS, or by esterification of the bromocarboxylic derivatives. In addition, these bromo compounds can be readily obtained in a one-pot reaction from A.BH 2COOH with bromine; when esterification proceeds unexpectedly fast in parallel with the bromination. The structures of the new derivatives were substantiated by elemental analyses and IR, UV, 1H NMR and 11B NMR spectroscopic methods.

Activated Basic Alumina Promotes a Mild, Clean and High-Yield Racemization-Free Synthesis of t-Butyl Esters from Chiral Acid Bromides and t-Butyl Alcohol

Abstract Esterification of a variety of acid bromides having even steric bulkiness with t-BuOH/activated basic alumina gave the corresponding t-butyl esters in good to excellent yields. In the case of chiral acid bromides, no racemization has been ascertained for the first time.