The difficult coupling of alpha-aminoisobutyric acid (Aib) was carried out using PyBOP(R) and PyBroP in a comparative study with BOP and BroP. These reagents gave good results under simple conditions (one pot, r.t., 1 h). Coded amino acids could be coupled with Aib using PyBOP under standard conditions of peptide synthesis without racemization whereas the coupling of two Aib residues required PyBroP/DMAP. A fragment containing an Aib C-terminal could be coupled without epimerization of the penultimate residue.
FREROT, ERIC;COSTE, JACQUES;PANTALONI, ANTOINE;DUFOUR, MARIE-NOELLE;JOUIN+, TETRAHEDRON, 47,(1991) N, C. 259-270