Karl-Heinz Pook

Cyclic guanidines. Part 2. Rearrangement of N-substituted 2-arylamino-4,5,6,7-tetrahydro-1H-1,3-diazepines. X-Ray molecular structure of 1-(2,6-dichlorophenyl)-2-(2-methylallylimino)hexahydro-1,3-diazepine

1,3-Aryl migrations of title compounds (2) are shown to be triggered by base catalysis under mild conditions. Alternative rearrangement conditions, limiting factors, as well as the occurrence of byproducts, and competing products are investigated. A crossover experiment reveals the purely intramolecular nature of the Chapman-type rearrangement. The structure of the rearrangement product 1-(2,6-dichlorophenyl)-2-(2-methylallylimino)hexahydro-1,3-diazepine (3a) is confirmed by X-ray analysis. An explanation for the directionality of the reaction is furnished by an MNDO calculation on the reaction enthalpy.

Modern Nuclear Magnetic Resonance Spectroscopy of Peptides

Publisher Summary This chapter presents the modern nuclear magnetic resonance spectroscopy (NMR) of peptides. The chapter describes the most useful modern 2D NMR techniques for peptides and highlights their application using as a practical example the cyclic decapeptide antamanide. It explores the conformational homogeneity and general strategy for nuclear magnetic resonance investigation of peptides. The chapter discusses the methods for assigning specific signals to molecular constitution, that is, the identification of NMR parameters for the various amino acids, the assignment of sequence, and in connection with this, the differentiation of amino acids that appear more than once in the molecule. The chapter also discusses recent developments in the NMR spectroscopy of peptides and highlights extraction and assignment of NMR parameters related to molecular structure. The state of the art in NMR spectroscopy generally allows an unequivocal assignment of the spectra.