Natural occurrence of 2′,5′-linked heteronucleotides in marine spongesLopp, Annika; Reintamm, Tõnu; Kuusksalu, Anne; Tammiste, Indrek; Pihlak, Arno; Kelve, MerikeMarine drugs2010 / 2, p. 235-254 https://pubmed.ncbi.nlm.nih.gov/20390103/