The standard methods of stepwise solid phase synthesis according to Merrifield could not previously be applied to the synthesis of the important naturally occurring peptaibols because of difficulties arising from the pronounced steric hindrance caused by a, a- dialkylated amino acids (incomplete coupling, especially to adjacent similarly constituted units, racemization due to slow coupling to hindered amino acids, etc.), chain degradation ...
[Di Gioia, Maria Luisa; Leggio, Antonella; Le Pera, Adolfo; Liguori, Angelo; Siciliano, Carlo European Journal of Organic Chemistry, 2004 , # 3 p. 463 - 467]