Amino acids and peptides. XXIII. Synthesis of N.ALPHA.-protected amino acid 6-chloro-2-pyridyl esters and their evaluation for peptide synthesis.
作者:Satoshi TSUBOI、Yoshio OKADA
DOI:10.1248/cpb.37.46
日期:——
and tert-butyloxycarbonylamino acids were synthesized by the N,N'-dicyclohexylcarbodiimide (DCC) method from the acids and 6-chloro-2-hydroxypyridine in dimethylformamide (DMF). The reactivity of the 6-chloro-2-pyridylester with amino group is much higher than that of the corresponding 2-pyridyl ester (OPy) and p-nitrophenyl esters (ONp) in dioxane and DMF, and a peptide bond is formed without acylation
N-Benzyloxycarbonylendothiodipeptide esters, 3, are synthesized without racemization from the corresponding N-benzyloxycarbonyldipeptide esters, 2, using 2,4-bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide, 1, as thionation reagent. The benzyloxycarbonyl amino-protecting group (Z) is removed from 3 by using HBr-AcOH.
N-Hydroxy-5-norbornene-2, 3-dicarboximide (HONB) was found to be an excellent reagent to be used in couple with N, N'-dicyclohexylcarbodiimide (DCC) for the peptide synthesis. Various racemization tests by the use of this reagent were conducted to see the degree of racemization during the peptide synthesis. The newly employed reagent (HONB) decreases racemization, prohibits formation of N-acylurea and affords peptides in excellent yields and a high state of purity. To evaluate this new reagent, luteinizing hormone releasing hormone (LH-RH) was prepared by the new active ester method.