A deoxyadenosyl radical is a free radical that is structurally related to adenosine by removal of a 5â²-hydroxy group from adenosine. This radical occurs in nature as a reactive intermediate. It is generated by radical SAM enzymes and by some varieties of vitamin B<sub>12</sub>. The deoxyadenosyl radical abstracts hydrogen atoms from substrates, causing rearrangements and other post transcriptional modifications required for biosynthesis.