preferred_name: a beta-D-galactosyl-(1->3)-N-acetyl-alpha-D-galactosaminyl derivative + CMP-N-acetyl-beta-neuraminate => a beta-D-galactosyl-(1->3)-[N-acetyl-alpha-neuraminyl-(2->6)]-N-acetyl-alpha-D-galactosaminyl derivative + CMP + H(+)