J. Mazaleyrat, K. Wright, M. Wakselman
May 1, 2001
Citations
0
Influential Citations
13
Citations
Journal
European Journal of Organic Chemistry
Abstract
Acylation of the anion of N-benzyl-4,5-diazafluorene-9-methyleneamine with methyl or benzyl chloroformate, followed by acidic hydrolysis, resulted in 9-amino-4,5-diazafluorene-9-carboxylic acid methyl ester (H-Daf-OMe) and benzyl ester (H-Daf-OBzl), respectively. Nα-protection with Boc2O at 60 °C gave Boc-Daf-OMe and Boc-Daf-OBzl, saponification or hydrogenolysis of which resulted in complete decarboxylation. However, hydrazinolysis of the ester function afforded Boc-Daf-NHNH2, which was efficiently coupled with H-Ala-OMe by the acylazide method. Coupling of Boc-Ala-OH at the N-terminus of Daf could also be performed by the mixed anhydride method. However, coupling of the crowded Aib residue required the use of Boc-Aib-NCA. Daf, a new Cα,α-disubstituted glycine, is the first α-amino acid containing a rigid bipyridine ligand in a totally controlled spatial disposition relative to the Cα atom.