Cysteine Racemization

JH Park, et al. reported in J Pept Sci. 2012 ;18(7):442-8 that in the synthesis of Protoxin II, they saw up to 50% racemization of Cys during coupling when they used N-methylmorpholine.  They could significantly reduce racemization if they used 2,4,6-collidine in place of N-methylmorpholine.