[A new method for synthesis of peptides: activation of the carboxyl group with dicyclohexylcarbodiimide using 1-hydroxybenzotriazoles as additives]

On the transport of tripeptide antibiotics in bacteria

The two tripeptide antibiotics L-2-amino-4-methylphosphinobutyryl-alanyl-alanyl-alanine (L-phosphinothricyl-alanyl-alanine) and L-(N5-phosphono)methionine-S-sulfoximinyl-alanyl-alanine, both inhibitors of the glutamine synthetase, are transported into the cell of Escherichia coli K 12 via the oligopeptide transport system. The uptake by this system is proved first of all by cross-resistance with tri-L-ornithine using oligopeptide-transport-deficient mutants, and secondly by antagonism tests demonstrating competitive reversal of the action of the antibiotic by several peptides which have been shown to be transported via the oligopeptide transport system, e.g. tri-L-alanine, tetra-L-alanine, tri-L-lysine, tri-L-serine, tri-glycine, glycyl-glycyl-L-alanine and the synthetic tripeptide L-azadenyl-aminohexanoyl-alanyl-alanine. On the other hand, there is no effect on the action of the antibiotic in antagonism tests with compounds which use different transport systems, such as L-alanyl-alanine, L-lysyl-lysine, glutathione and the synthetic amino acid azaadenylaminohexanoic acid, i.e. 2-amino-6-(7-amino-3H-v-triazolo-[4,5-d]-pyrimidin-3-yl)hexanoic acid. Another inhibitor of the glutamine synthetase, L-methionine-S-dioxide (methioninesulfone) could be converted into a tripeptide form by linkage to L-alanyl-alanine analogously to the tripeptide antibiotics described above. Whereas the free L-methionine-S-dioxide seems to be transported via the methionine transport system, the tripeptide form is transported via the oligopeptide transport system. Thus, this glutamine synthetase inhibitor can be taken up by the cell via two different transport mechanisms. Our results indicate that this could provide a synergistic effect. The syntheses of the new tripeptides L-azaadenylaminohexanoyl-alanyl-alanine and L-methionine-S-dioxidyl-alanyl-alanine were performed by dicyclohexylcarbodiimide couplings of the unusual N-protected L-alpha-amino acids azaadenylaminohexanoic acid and L-methionine-S-dioxide to L-alanyl-alanine-tert-butyl ester followed by common deprotection steps. Tri-L-ornithine was synthesized without carboxyl protection via two successive couplings of hydroxybenzotriazol esters of Nalpha-butoxycarbonyl-Ndelta-benzyloxycarbonyl-L-ornithine.

A new semisynthesis of human insulin

A new semisynthesis of human insulin starting from porcine insulin is described. NalphaA1, NalphaB1-di-Boc-desoctapeptide-(B23-30)-insulin bearing 6 free carboxyl groups is coupled with the suitably protected human insulin-(B23-30)-octapeptide. The preferred reaction site is the carboxyl group of ArgB22. Side products are eliminated by extensive chromatographic purification.

New useful reagents for peptide synthesis. Insoluble active esters of polystyrene-bound 1-hydroxybenzotriazole

Insoluble 1-hydroxbenzotriazole-bound polystyrene was prepared through a series of chemical modifications of commercially available polystyrene. Reaction of 3-nitro-4-chlorobenzyl alcohol or of 3-nitro-4-chlorobenzyl bromide with polystyrene in the presence of aluminium trichloride yielded (3-nitro-4-chloro)benzylated polystyrene. Upon reaction with hydrazine it was converted to (3-nitro-4-hydrazine) benzylated polystyrene which was cyclized, by acidolysis, to yield 1-hydroxybenzotriazole-bound polystyrene. This was coupled, using N, N' -dicyclohexylcarbodiimide as the coupling agent, to many N-blocked amino acid derivatives, yielding polymeric polystyrene-bound active esters. Such derivatives are highly reactive and their efficacy in the synthesis of several peptides, including that of the tetrapeptide Boc-L-Leu-L-leu-L-Val-0bzl-L-Tyr-0Bzl and of thyrotropin-releasing hormone was demonstrated.

A technique for the determination of enantiomeric amino acids in biological samples

Racemic amino acids can be separated into their enantiomers by means of gas-liquid chromatography. The most applied technique, today, is the conversion of chiral compunds into diastereoisomers with optically active reagents and subsequent chromatography on conventional optically inactive stationary phases. In previous studies it has been realized that this technique is associated with various problems. We studied the use of optically active stationary phases for separating enantiomers directly via a diastereoisomeric association complex. The optically acitve stationary phases employed are N- and C-terminal substituted dipeptides of the type N-trifluoroacetyl-dipeptide-cyclohexyl esters and have been synthesised by the I-hydroxibenztriazole dicyclohexylcarbodiimide method. The quality of these phases with respect to separation factors, resolution factors, and thermodynamical properties have been evaluated. All synthetic phases show excellent properties; however, when attempting separation of mixtures of naturally occurring amino acids extensive overlap in the elution diagram was detected. Only one phase - N-TFA-L-chi-amino-n-butyryl-L-chi-amino butyric acid cyclohexyl ester - gave complete resolution of the naturally occurring amino acids alanine, valine, glycine, threonine, leucine, isoleucine, serine and proline on a 400 ft x 0.02 in capillary column. Less volatile amino acids such as aspartic acid, phenylalanine, methionine, glutamic acid, tyrosine, arginine, and tryptophan can be resolved at a 100 ft x 0.02 in column.

The specificity of the S1' subsite of papain

The specificity of the S(1)' subsite of the proteolytic enzyme papain was investigated by studying the effect of l-alpha-amino acid amides on the enzyme-catalysed hydrolysis of N-benzyloxycarbonylglycine p-nitrophenyl ester and by determining the kinetic parameters for the enzyme-catalysed hydrolysis of some N-benzyloxycarbonylglycyl-l-amino acid amides. These studies showed that the S(1)' subsite has a predilection for hydrophobic residues, in particular l-leucine and l-tryptophan. The specificity for these residues is manifest in both the binding and acylation steps. N-Benzyloxycarbonylglycine amide is not hydrolysed under comparable conditions, indicating that the amide group adjacent to and on the C-terminal side of the peptide bond about to be cleaved makes an important contribution to the rate of the papain-catalysed hydrolysis of peptides.