Catalyzes the activation of 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN) to cytidine 5'-monophosphate 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (CMP-KDN), a substrate required for the addition of sialic acid. Also has weak activity towards N-acetylneuraminic acid (NeuNAc) and N-glycolylneuraminic acid (Neu5Gc). an N-acylneuraminate + CTP = a CMP-N-acyl-beta-neuraminate + diphosphate Amino-sugar metabolism; N-acetylneuraminate metabolism. Homotetramer. During early stages of development (9-18 hours post fertilization, hpf) has weak and ubiquitous expression. Expression is restricted to brain at 24 hpf. At the hatching stage (48 hpf), detected in heart but not in brain. Belongs to the CMP-NeuNAc synthase family.