N-Acylureas in Peptide Synthesis: An X-Ray Diffraction and IR-Absorption Study

✍ Scribed by Claudio Toniolo; Giovanni Valle; Marco Crisma; Vittorio Moretto; Jan Izdebski; Jacek Pelka; Conrad H. Schneider

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: German
• Weight: 477 KB
• Volume: 73
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19900730311

✦ Synopsis

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 Hbonded 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)NH…OC(peptide) H‐bonds in CH~2~Cl~2~.