Selective acidolytic cleavage of aralkyl carbonyl amino protecting groups

The acidolytic cleavage of a series of new N-aralkyloxycarbonyl protecting groups has been found to proceed as a first-order reaction, the rate of cleavage being dependent on the stability of the corresponding aralkyl carbonium ions. Some of the groups are cleaved at much the same rate as the N-trityl residue and up to 60000 times faster than the t-butyloxycarbonyl (Boc) group. The rate is also strongly influenced by the acidity of the reaction media. The relative rates at which aralkyloxycarbonyl and Boc groups are split off can be largely controlled by appropriate selection of the reaction conditions. The implications of these findings for peptide syntheses are discussed and the use of the 2-(p-diphenyl)-isopropyloxycarbonyl residue as an especially suitable N-protecting group is proposed.     

Peptide synthesis under application of the 2-(p-diphenyl)-isopropyloxycarbonyn (Dpoc)-amino protection groups

The 2-(p-diphenyl)-isopropyloxycarbonyl (Dpoc) residue has been chosen for the selective protection of α-amino groups in the synthesis of peptides containing additional acid-labile protecting residues. It is easily introduced into amino-acids by reacting either the mixed carbonate I or the azide III with esters or salts of amino-acids. It is split by dilute acetic acid and other weakly acidic reagents at rates which permit a selective cleavage in the presence of other acid-labile protecting groups, especially those derived from t-butanol A number of peptide syntheses have been carried out with the new group either in the conventional manner or by the solid-phase method. No effects due to steric hindrance, as observed previously with the N-trityl residue, are encountered. The application of the Nα-Dpoc group to solid-phase peptide synthesis permits the use of a new combination of protecting groups in which the side chains of trifunctional amino-acids are blocked by acid-labile residues that can be easily split in the final step of the synthesis.     

Selektive Spaltung substituierter Phenylsulfenyl-Schutzgruppen bei Peptidsynthesen

The selective cleavage of the N-sulphenyl protecting group from amino-acids and peptides containing additional acid-labile protecting residues has been investigated. Among various nucleophilic reagents tested for their ability to effect rapid and specific removal of the N-sulphenyl groups, hydrogen cyanide, sulfurous acid and thioacetamide have been found to be particularly suitable. The application of this method to the solid phase synthesis of peptides is described and discussed.     

Über die Synthese von 2-(p-Biphenylyl)-isopropyloxycarbonyl-(Bpoc)-Aminosäuren und den Zerfall von Aralkyl-phenyl-carbonaten

The syntheses of a number of new Bpoc-amino acids and the preparation of some activated esters of Bpoc-amino acids are described. In recent work on the total synthesis of calcitonin hormones the Bpoc residue has been found to be very useful for the selective protection of α-amino groups of complicated intermediate peptide fragments. The reagent preferentially used for the introduction of the Bpoc group into amino acids, [2-(p-biphenylyl)-isopropyl]-phenyl-carbonate (I), is stable at 0°, but undergoes at higher temperatures a decomposition which is a accelerated by phenol. Based on the reaction products formed — [2-(p-biphenylyl)-isopropyl]-phenyl-ether (II), 2-(p-biphenylyl)-propene (III), and phenol — a scheme is proposed for this thermal decomposition, and the possibility of a correlation between the stability of carbonates R₃C—O—CO—OC₆H₅ and the rate of the acidolytic cleavage of urethanes R₃C—O—CO—NHR′ depending on the substituents R is discussed.     

Editorial for Focus Issue on Enabling Science and Technology for High-Speed Optical Communications

<正>Fiber optics underpins the communications infrastructure for the information society today. Cables consisting of hair-like fibers speed data around the globe in the form of rapid pulses of light. Modern telecom     

Mikrochemie

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