Search results for "CONDENSATION"
showing 10 items of 468 documents
Synthesis of peptides with α,β‐dehydroamino acids, I. synthesis of N‐benzyloxycarbonyl and N‐trifluoroacetyl dipeptides of dehydroalanine and dehydro…
1984
Condensation of amides of N-(benzyloxycarbonyl)- and N-(trifluoroacetyl)amino acid with pyruvic and phenylpyruvic acid yields, in the presence of p-toluenesulfonic acid as a catalyst, N-(benzyloxycarbonyl)- and N-(trifluoroacetyl)dehydro dipeptides with C-terminal Δ Ala and ΔPhe, respectively (Table 2 and 3). Synthese von Peptiden mit α,β-Dehydroaminosauren, I. - Synthese von N-(Benzyloxycarbonyl)-und N-(Trifluoracetyl) dipeptiden von Dehydroalanin und Dehydrophenylalanin Die Kondensation von Nα-(Benzyloxycarbonyl)- und Nα-(Trifluoracetyl)aminosaureamiden mit Brenztrauben- und Phenylbrenztraubensaure in Gegenwart von p-Toluolsulfonsaure als Katalysator fuhrt zu N-(Benzyloxycarbonyl)- und N-…
A three-component Mannich-type condensation leading to phosphinic dipeptides—extended transition state analogue inhibitors of aminopeptidases
2011
Abstract N-Protected α-aminoalkylphosphinic acids bearing a P–H function were found to be novel practical building blocks in three-component condensations with formaldehyde and secondary amines (amino acids). Such Mannich-type N -phosphonomethylation is a common approach for phosphorus acid derived substrates and leads to multifunctional (phosphonic/amino/carboxylic) compounds of diverse relevance. The utility of this reaction was examined for construction, in a single synthetic step, of advanced phosphinic pseudodipeptides designed to act as extended transition state analogue inhibitors of selected aminopeptidases. Phosphinomethylation of primary amino acids was less efficient and yielded …
Selektive enzymatische Schutzgruppenabspaltungen: Der n-Heptylester als Carboxylschutzgruppe in der Peptidsynthese
1991
Selective Enzymatic Removal of Protecting Groups: n-Heptyl Esters as Carboxy Protecting Functions in Peptide Synthesis Amino acid heptyl (Hep) esters are accessible as generally crystalline hydro tosylates 3 from the amino acids by azeotropic esterification with 1-heptanol in high yields. They can be condensed with Z-, Boc-, and Aloc-protected amino acids to give the dipeptides 7–9 in the presence of 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). From the fully protected dipeptides the N-terminal protecting groups are cleaved by chemical methods without affecting the Hep esters. On the other hand, the heptyl esters can be hydrolyzed under mild conditions (pH = 7.0, 37°C) and with hi…
Synthesis of 1,3,5-Trisubstituted Hydantoins by Regiospecific Domino Condensation/Aza-Michael/O→N Acyl Migration of Carbodiimides with Activated α,β-…
2005
[reaction: see text] Carbodiimides and suitably activated alpha,beta-unsaturated carboxylic acids react effectively to afford a vast array of 1,3,5-trisubstituted hydantoins by means of a regiospecific domino condensation/aza-Michael/N--O acyl migration. The reaction works well in very mild conditions (20 degrees C, dichloromethane) with fumaric acid derivatives bearing an electron-withdrawing group in the beta position. Good results have been obtained also with less activated substrates bearing only one electron-withdrawing group in the beta position, using more polar solvents (acetonitrile, DMF), and in the presence of a base (2,4,6-trimethylpyridine). Reactions with asymmetric carbodiimi…
Calix[4]arenes with resorcinol units incorporated in 2,6-position
1990
Abstract Calix[4]arenes containing one or two resorcinol units incorporated via their 2,6-positions were prepared by fragment condensation. Due to the cyclic array of intramolecular hydrogen bonds these molecules assume the cone-conformation.
The Amazonian boundary layer and mesoscale circulations
2009
Numerous biogenic volatile organic compounds (VOC) species are released into the atmosphere from tropical forests. Measuring all those which are relevant for atmospheric chemistry or for the carbon budget is challenging. Large-Scale Biosphere-Atmosphere (LBA) Experiment field campaigns substantially increased the number of field studies of isoprene and monoterpene emissions, as well as of the exchange of several other VOC species. This chapter reports about the progress made within LBA from primary emission measurements at the plant species level up to discussions of the oxidative capacity of the atmosphere and formation of secondary organic aerosol particles and cloud condensation nuclei f…
Catalytic condensation of aromatic aldehydes with acetone on activated Mg-Al mixed oxides
2004
Abstract The factors affecting the aldol condensation of some model aromatic aldehydes (benzaldehyde, the three isomers of F-benzaldehyde and 2-naphthaldeyde) with acetone have been investigated using heterogeneous catalysts obtained by the calcination of hydrotalcite-type (HT) precursors at 773 K for 8 h, followed by rehydration at room temperature for 7 h under a flow of N 2 saturated with water vapour. At 273 K the main product was the β-hydroxy-ketone, while at 318 K it mainly dehydrated to the corresponding trans -arylideneacetone, with small amounts ( cis -arylideneacetone, 1,3-diarylideneacetone and 4-hydroxy-4-methyl-2-pentanone. High reaction times favoured the formation of trans -…
Competing salt effects on phase behavior of protein solutions: tailoring of protein interaction by the binding of multivalent ions and charge screeni…
2014
The phase behavior of protein solutions is affected by additives such as crowder molecules or salts. In particular, upon addition of multivalent counterions, a reentrant condensation can occur; i.e., protein solutions are stable for low and high multivalent ion concentrations but aggregating at intermediate salt concentrations. The addition of monovalent ions shifts the phase boundaries to higher multivalent ion concentrations. This effect is found to be reflected in the protein interactions, as accessed via small-angle X-ray scattering. Two simulation schemes (a Monte Carlo sampling of the counterion binding configurations using the detailed protein structure and an analytical coarse-grain…
New hexanuclear FeIII clusters with the gem-diol hydrated form of di(2-pyridyl)ketone and carboxylato ligands: Crystal structures and magnetic proper…
2019
Abstract The hexanuclear compounds [Fe6O2Cl2{(py)2CO2}2(pyOH)2(pyCOO)2(ButCOO)6] (1) and [Fe6O2{(py)2CO2}2(pyCOO)4(ButCOO)6] (2) were obtained by condensation of the trinuclear μ3-oxo-centered iron(III) pivalate [Fe3O(ButCOO)6(H2O)3]+ in the presence of di(2-pyridyl)ketone [(py)2CO] in MeCN at ambient temperature. Both complexes contain an analogous core which can be described as two {Fe3O}7+ units joined by gem-diolato (py)2CO22− bridges. Variable-temperature magnetic susceptibility measurements in polycrystalline samples of 1 and 2 reveal strong antiferromagnetic couplings between the iron(III) ions leading to S = 0 ground states.
Cyclocondensation reaction of 1,2-diamino-4-methylbenzene andp-substituted acetophenones
1993
1,2-Diamino-4-methylbenzene 1 reacts in the presence of sulphuric acid with 4-substituted acetophenones 2a-e yielding 2,4-diaryl-2,3-dihydro-2,8-dimethyl-1H-1,5-benzodiazepines 3a-e and as minor component 2,4-diaryl-2,3-dihydro-2,7-dimethyl-1H-1,5-benzodiazepines 4a-e. The ratio 3:4 is in the range of 7:3. The structure determination of the regioisomers was performed by NOE measurements.