3'-(α-L-Aminoacylamido)deoxyadenosines are ribosomal A-site binders and mimic the nascent peptide accepting 3'-terminus of aminoacyl transfer RNA. Their α-amino groups exhibit intrinsic basicities in bulk water that differ by up to 1.8 pK(a) units. Only the neutral form of these nucleophiles can be active during ribosomal peptidyl transfer catalysis.