Studies on sensitivity to racemization of activated residues in couplings ofN‐benzyloxycarbonyldipeptides
作者:
N. LEO BENOITON,
YOUNG C. LEE,
RENE STEINAUR,
FRANCIS M.F. CHEN,
期刊:
International Journal of Peptide and Protein Research
(WILEY Available online 1992)
卷期:
Volume 40,
issue 6
页码: 559-566
ISSN:0367-8377
年代: 1992
DOI:10.1111/j.1399-3011.1992.tb00441.x
出版商: Blackwell Publishing Ltd
关键词: activation;BOP;carbodiimides;epimers;HBTU;high‐performance liquid chromatography;1‐hydroxybenzotriazole;mixed anhydride;PyBOP;racemization
数据来源: WILEY
摘要:
A series of 24 peptides Z‐Gly‐Xaa(R)‐OH where Xaa= 15 different residues and R= H, NH2, tBu, Bzl, Trt, Mtr, and StBu were coupled with valine benzyl ester in dimethylformamide or dichloromethane at +5°. The accompanying racemization was determined by analysis of the epimeric products by normal phase high‐performance liquid chromatography (HPLC) for Xaa(R) = Met, Cys(StBu) and Lys(Z) and by reversed‐phase HPLC after removal of benzyl‐based protecting groups for Xaa(R) = Ser(tBu), Thr(tBu) and Arg(Mtr). The coupling methods examined included mixed anhydride (MxAn) at ‐5°, andN,N′‐dicyclohexylcarbodiimide (DCC), benzotriazol‐1‐yl‐tris(dimethylamino)phosphonium hexafluorophosphate (BOP) andO‐benzotriazol‐1‐yl‐N,N,N′,N′‐tetramethyluroniumhexafluorophosphate (HBTU) in the presence of 1‐hydroxybenzotriazole (HOBt). Very few couplings gave stereochemically pure products. The order of sensitivity to racemization of residues depended on the method of coupling and the solvent. It varied most when comparing MxAn to HOBt‐assisted reactions; it varied moderately when comparing HOBt‐assisted reactions. There was less variation in comparing BOP and HBTU reactions that are initiated by the same mechanism. Leu, Nle, Phe, Asn, Lys(Z) and Asp(OBzl) are identified as the residues least sensitive to racemization. DCC‐HOBt generally l
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