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Amino acid tetrabutylammonium salt

A series of atropisomeric thioureas was prepared from optically pure isothiocyanates 397f and 398d with primary amines. Atropisomeric ureas were prepared by reacting 397e or 398c with various isocyanates. Tlie resulting ureas and thioureas were used as neutral enantioselective anion receptors for N-protected amino acid tetrabutylammonium salts (06CHI762). [Pg.105]

Calix[4]arene is a very popular building block for the design of molecules with well-defined mutual positions of substituents. The attachment of amidic residues to this molecule resulted in receptors 35 [65] and 36 [66]. Upon the H NMR titration of 35 by tetrabutylammonium salts of amino acids in acetone-d6y moderate chiral recognition was observed N-Ac-L-Ala K=4,900 M-1, AT-Ac-D-Ala K=5,700 M"1, AT-Ac-L-Phe iC=7,900 M-1, AT-Ac-D-Phe K= 10,500 M"1. The receptors 36a-c formed stable complexes with AT-tosyl-L-phenylalaninate in deuteriochloroform (36a K= 1,626 M"1, 36b 1C=4,836 M"1, 36c K=6y924 M-1). Unfortunately, the measurement using AT-tosyl-D-phenylalaninate has not been reported. [Pg.47]

The use of either tetrabutylammonium salts or DMF containing strong acids (TEA, HBF4, or TosOH) and an excess of tertiary base with pAT <6, preferably pyridine, has also been proposed as a method to dissolve amino acids in organic solvents for their acylation. Amino acids and peptides are acylated efficiently even in the zwitterionic form as a suspension in organic solvents such as whereby sonication of the suspension was... [Pg.193]

Protected peptides are cleaved from the resin with N-hydroxypiperidine (HOPip), followed by treatment with zinc in AcOH to afford the free acidJ Resin-bound peptides can be cleaved from the oxime resin using the tetrabutylammonium salts of side-chain protected amino acids to directly provide the a-amino-protected (Boc), side-chain-protected pep-tide.[ 3o- 32] Peptide esters can be obtained from peptidyl oxime resin by treating with amino acid estersJ Peptide hydrazides are derived from peptidyl oxime resins on treatment with anhydrous hydrazine.b Protected peptide amides can be also derived from peptidyl oxime resins on treatment with ammoniaJ l Cyclic peptide acids as carboxy components were successfully prepared by this procedure through the Pac ester. [Pg.616]

Boc-Asp(OtBu)-Ala-Glu(OBzl)-Phe-Arg(Mts)-His(Bom)-Asp(OCy)-Ser(Bzl)-oxime-resin was synthesized according to the modified standard procedure [Bop (5 equiv), amino acid (5 equiv), DIPEA (8.9 equiv) used for each coupling]. An acetylation step [AcjO (10 equiv), DIPEA (5 equiv)] was performed after each coupling. The peptide was cleaved with the tetrabutylammonium salt of glycine. The combined filtrate from the cleavage was concentrated to a solid residue and dissolved in DMF. The soln was purified by HPLC [semiprep H20/MeCN 37 63, 0.1% TEA, I v=1040mL (/ v=retention volume)] yield 45% [based on Ser(Bzl)-oxime-resin] MS-FAB (m/z) [M -f H]+ calcd, 1752.8 found, 1753.1. [Pg.617]

The complexation of biologically important amino acid derivatives has been the driving force behind Kilbum and coworkers research in this area. By combining thiourea and amide moieties in cryptand-like macrobi-cyclic stractures. e.g., 40, Kilburn and coworkers synthesized receptors for amino acid derivatives that show selectivity for particular side-chain residues. Extraction methods were used to calculate association constants with a number of N-protected tetrabutylammonium amino acid salts in chloroform. Receptor 40 is selective for A/ -Ac-L-lysine x 10" M ) over N-Ac-L-glycine... [Pg.38]

Thr), leucine (Leu), phenylglycine (Phg), and phenylalanine (Phe), in form of tetrabutylammonium salts were used in this study. Addition of amino acid anions to solution of 21 or 22 caused chelation enhanced fluorescence quenching (CHEQ) for both anion receptors. The CHEQ effect for host 21 can be ascribed to photoinduced charge transfer (PCX), whereas for 22 quenching can be attributed to photoinduced electron transfer processes (PET). The DNB protected amino acids displayed larger... [Pg.478]

Tetrabutylammonium amino-acid salts have been coupled to amino-acid esters using bis(n-nitrophenyl)phenyl phosphonate and (5-nitropyridyl)diphenyl phosphinate. The heterocyclic phosphonate (219) is also an effective reagent for the activation of carboxylic acids which react with amino-acid esters in its presence to form peptides in good yield. ° ... [Pg.152]

I2/K2C03, tetrabutylammonium hydroxide, tungsten phosphoric acid, ionic liquids, reactions in water, solvent-free conditions, microwave promoted reactions, reactions promoted by phase-transfer catalysts, and finally, for some very reactive substrates, uncatalyzed reactions. " Unfortunately for the practicing chemist, few of these conditions are well worked out enough or understood well enough to have become common, and almost all examples of the Knoevenagel condensation in the literature employ an amine base, or a salt thereof (Cope conditions, or amino acid catalysis) or TiCl4/Base(Lehnert conditions). ... [Pg.485]

Jain and co-workers reported a concise total synthesis of cefuroxin (Ceftin) from readily accessible 7-amino-3-acetoxymethyl-3-cephem-4-carboxylic acid. Hydrolysis of 7-amino-3-acetoxymethyl-3-cephem-4-carboxylic acid in aqueous methanol followed by acidification with tetrabutylammonium hydroxide provided the corresponding alcohol in 88% yield. Condensation of this compound with the ammonium salt of 2-furanyl-(Z)-2-methoxyiminoacetyl chloride provided the core structure in 77% yield. Protection of the free alcohol as a carbamate with chlorosulfonyl isocyanate, followed by conversion to the sodium salt, gave the desired compound in 83% yield (56% overall yield). [Pg.155]

In a novel approach, an enantiomerically pure derivative of 2-amino-4,4,4- trifluorobutanoic acid was synthesized via nucleophilic trifluoromethylation (Figure 3) (5). In the key step. Gamer s aldehyde (2) (6), an oxazolidine derived from L-serine, reacted with the Ruppert-Prakash reagent, TMS-CF3 (a trifluoromethide equivalent) (7) and tetrabutylammonium fluoride. (S) - 5,5,5,5, 5, 5 - Hexafluoroleucine (3) (88% ee) was prepared in 18% overall yield from hexafluoroacetone and ethyl bromopyruvate in seven steps (8). The highly enantioselective reduction of the keto carbonyl group of 4 to the hydroxyester 5 either by baker s yeast and sucrose (91% ee) or by catecholborane and an oxazaborolidine catalyst (99% ee) was the pivotal reaction of the sequence. These workers (9) also prepared (-)-(R)- 4,4,4,4, 4, 4 -hexafluorovaline (6) (98% ee). The key step was the separation of the tosylate salts of the diastereomers formed by anti-Michael addition of (+)-(R)-... [Pg.4]


See other pages where Amino acid tetrabutylammonium salt is mentioned: [Pg.150]    [Pg.148]    [Pg.307]    [Pg.440]    [Pg.49]    [Pg.50]    [Pg.334]    [Pg.46]    [Pg.193]    [Pg.218]    [Pg.1006]    [Pg.274]    [Pg.479]    [Pg.956]    [Pg.203]    [Pg.1080]    [Pg.1155]    [Pg.192]    [Pg.18]    [Pg.1006]    [Pg.45]    [Pg.466]    [Pg.357]    [Pg.460]    [Pg.1119]   
See also in sourсe #XX -- [ Pg.53 ]




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