Acylated amino acids characterization

Reaction between amines and the reactive HPMA copolymers forms the basis for attachment of oligopeptide sequences, targeting residues or therapeutic agents to the polymer precursor (Fig. 3). Reaction of aliphatic amines (tertiary butylamine and diisopropylamine) in dimethylsulphoxide at 25 C with reactive copolymers containing different side-chains has been used to characterize copolymer reactivity.It has been shown that copolymers of HPMA with p-nitrophenyl esters of a-(acylamino) acids react faster with amines than copolymers with p-nitrophenyl esters of g-(acyl-amino) acids or, e-(acylamino) acids.21... 

A number of low-molecular-weight A-acyl amino acid lipids of biological significance were identified based on values of t and miz values provided by IMS-MS. Both data acquisition and visnalization of the separated isomeric lipids is rapidly achieved. For example, A-arachidonoyl isoleucine, and A-arachidonoyl leucine exhibit t fingerprints that are sufficiently distinct to delineate isomeric composition. It is often difficult to obtain meaningful MS/MS fragment ions from these low abundant lipids for structural characterization. The mass window for parent ion selection for most MS instruments is insufficient to cleanly select isobaric compounds, and the fragmentation pattern of isomers is commonly very similar. 

Cobalt. The rate law for carbonylation of Schiff bases, catalysed by Co2(CO)8, has been reported. Dicobalt octacarbonyl also catalyses reaction between aldehydes, for instance formaldehyde or acetaldehyde, amides, for example acetamide or benzamide, and carbon monoxide. The products are iV-acyl-amino-acids. The main product from the reaction of acetylene with carbon monoxide in the presence of CoH(CO)4 is ethyl acrylate. Characterization of the intermediates permits suggestions to be made as to the mechanism of this reaction. Initial reactions between the acetylene and two molecules of catalyst may give (106), in equilibrium with its isomer (107) the carbon monoxide inserts into the cobalt-carbon bonds of the latter. Further information about Coa(CO)8-catalysed hydro-formylation of acrylonitrile and of 3-methyl[3- H]hex-l-ene has led... 

The synthesis and characterization of optically active amino acidate alkynyl complexes of formula CpRh(aa)(C=CR) (aa = L-prolinate (Pro), R = CMcs) were reported. A series of dirhodium cr-alkynyl complexes were also studied. The sterically demanding phosphine 2-(di-o-tolylphosphino)phenol was prepared and used to create a series of esters with A -acylated amino acids. The phosphine-containing esters reacted with [Rh(/t-Cl)(cyclooctene)2]2 to give products of oxidative addition of the ester carbonyl-oxygen bond to the Rh center, 231 and 232. The ligand 2- (diphenylphosphino)methyl)quinolin-8-acetate reacted with [Rh( -Cl)(cyclooctene)2]2 affording only one of the three possible diastereomers, 233. ... 

Yu, H., and Langer, R., Pseudopoly(amino acids) A study of the synthesis and characterization of poly(acyl-hydroxy-proline esters). Macromolecules. 22, 3250-3255, 1989. 

As demonstrated in Section I, numerous representatives of this type of compounds occur naturally. Such natural substances are commonly characterized by two special features, (a) The C-5 carbon atom of the pyrrolone ring is a stereo center that can be provided by natural derivatives of amino acids. (b) The acyl substituent at C-3 often includes a complex... 

As mentioned above, thiazolidine-4-carboxylic acid is characterized by an anomalously low basicity and thus difficult acylation in peptide synthesis. 189 Therefore, the incorporation of this amino acid residue into a growing peptide chain is preferentially preformed via dipeptide derivatives. 139 Suitably N-protected amino acids are coupled directly to the thiazolidine-4-carboxylic acid by the acid fluoride 139 or iV-carboxyan hydride 1392111 methods. The resulting dipeptides are used as building blocks without risk of racemization 139 and standard coupling procedures are applied as pentachlorophenyl esters prepared by the mixed anhydride procedure 121 or PyBOP. 171 ... 

Phosphopantetheine coenzymes are the biochemically active forms of the vitamin pantothenic acid. In figure 10.11, 4 -phosphopantetheine is shown as covalently linked to an adenylyl group in coenzyme A or it can also be linked to a protein such as a serine hydroxyl group in acyl carrier protein (ACP). It is also found bonded to proteins that catalyze the activation and polymerization of amino acids to polypeptide antibiotics. Coenzyme A was discovered, purified, and structurally characterized by Fritz Lipmann and colleagues in work for which Lipmann was awarded the Nobel Prize in 1953. 

The trypsin family of serine proteases includes over 80 well-characterized enzymes having a minimum sequence homology of >21%. Two amino acid residues are absolutely conserved (Cysl82, Glyl96) within their active sites [26,27]. These proteases have similar catalytic mechanisms that lead to hydrolysis of ester and amide bonds. This occurs via an acyl transfer mechanism that utilizes proton donation by histidine to the newly formed alcohol or amine group, dissociation and formation of a covalent acyl-enzyme complex. 

Growth of Fusariutn sp. at low iron concentration causes the accumulation of a variety of hydroxamic acids of which one has been characterized and named fusarinine, or NS-( s-5-hydroxy-3-methylpent-2-enoyl)-NS-hydroxy-L-ornithine (38). The cis configuration in the unsaturated acyl substituent accounts for the extreme acid lability of the hydroxamic acid bond. Fusarinine is the amino acid unit, bearing the hydroxamic acid linkage, present in ferrirhodin. The characterization of fusarinine has important implications for the biosynthesis of the ferrichrome group for it indicates that the hydroxamic acid bond is inserted at the free amino, acid, rather than at the peptide level. 

The animal fatty acid synthase (FAS EC 2.3.1.85) is one of the most complex multifunctional enzymes that have been characterized, as this single polypeptide contains all the catalytic components required for a series of 37 sequential transactions (Smith, 1994). The animal FAS consists of two identical polypeptides of approximately 2500 amino acid residues (MW, ca. 270 kDa), each containing seven catalytic subunits (1) ketoacylsynthase, (2) malonyl/acetyl transferase, (3) dehydrase, (4) enoyl reductase, (5) (3-kcto reductase, (6) acyl carrier protein (ACP), and (7) thioesterase. Although some components of the complex are able to carry out their respective catalytic steps in the monomeric form, only in the FAS dimer do the subunits attain conformations that facilitate coupling of the individual reactions of fatty acid synthesis to occur (Smith et al., 2003). 

Characterization or N-protection of amino acids by the f-butyloxycarbonyl group can be carried out either by acyl transfer from the triazole (335) prepared as in Scheme 144 or with t-butyl phenylcarbonate in the presence of triazole (73TL469) in lower yields. Although 1,2,4-triazole acts as a catalyst in the second of these reactions, it has to be present in an equimolar amount. 

---