Was adenine the first purine?
Oligomerization of HCN (1 molar) in the presence of added formaldehyde (0.5 molar) produced an order of magnitude more 8-hydroxymethyladenine than adenine or any other biologically significant purine.  This result suggests that on the prebiotic Earth, nucleoside analogs may have been synthesized directly in more complex mixtures of HCN with other aldehydes.
Schwartz
A W
AW
Laboratory of Exobiology, University of Nijmegen Toernooiveld, the Netherlands.
Bakker
C G
CG
D000225:Adenine / Q000031:analogs & derivatives* / Q000138:chemical synthesis*; D000447:Aldehydes / Q000737:chemistry; D005557:Formaldehyde / Q000737:chemistry; D006856:Hydrogen Cyanide / Q000737:chemistry; D006868:Hydrolysis; D009705:Nucleosides / Q000138:chemical synthesis; D011108:Polymers / Q000138:chemical synthesis; D011687:Purines / Q000032:analysis / Q000138:chemical synthesis*
D000447:Aldehydes; D009705:Nucleosides; D011108:Polymers; D011687:Purines; D005557:Formaldehyde; D006856:Hydrogen Cyanide; D000225:Adenine