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N ‐Acylureas in Peptide Synthesis: An X‐Ray Diffraction and IR‐Absorption Study
Author(s) -
Toniolo Claudio,
Valle Giovanni,
Crisma Marco,
Moretto Vittorio,
Izdebski Jan,
Pelka Jacek,
Schneider Conrad H.
Publication year - 1990
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19900730311
Subject(s) - chemistry , peptide , carbodiimide , stereochemistry , intermolecular force , x ray , x ray crystallography , derivative (finance) , crystallography , absorption (acoustics) , diffraction , medicinal chemistry , molecule , organic chemistry , biochemistry , physics , quantum mechanics , financial economics , optics , economics , acoustics
Abstract An X‐ray diffraction analysts of two N ‐acyl derivatives of symmetrical dialkylureas, N ‐[ N α ‐(benzyloxycarbonyl)‐ L ‐valyl] ‐ N , N ′‐diisopropylurea ( 1 ) and N ‐{ N α( tert ‐butyloxy)carbonyl ‐ L ‐valyl}‐ N ‐ N′ ‐dicyclohexylurea ( 2 ), and one N ‐acyl derivative of an unsymmetrical N‐N′ ‐dialkylurea, N ‐[ N α ‐(benzyloxycarbonyl)‐ L ‐valyl] ‐ N′ ‐( tert ‐butyl)‐ N ‐ethylurea ( 3 ), has been performed. It was established that it is the least hindered O ‐acylisourca N‐atom that attacks intramolecularly the carbonyl group of the N α ‐protected amino acid activated by the unsymmetrical carbodiimide to form the major rearrangement product. The occurrence and nature of intra‐ and intermolecularly Hbonded forms of the N ‐acylureas in the crystal state were also assessed. It was also shown that soluble N ‐acylureas may compete with intermolecular (peptide)NH…OC(peptide) H‐bonds in CH 2 Cl 2 .