2'-Deoxypseudoisocytidine is a modified base that can be used as an allele-specific blocker probe to discriminate sequence variation between different alleles and quantitate rare (e.g., mutant) allelic variants [1]. 2'-Deoxypseudoisocytidine and its analogues are also used as novel base-pairing agents in oligonucleotides to investigate DNA and RNA structures and functions [2].