NUCLEOSIDE ANTIBIOTICS .V. BIOSYNTHESIS AND INTERCONVERSION OF 3'-AMINO-3'-DEOXYADENOSINE AND 3'-ACETAMIDO'-3-DEOXYADENOSINE BY HELMINTHOSPORIUM SP.-215

Three nucleosides have been isolated from the culture filtrates of Helminthosporium sp. 215. They are adenosine, 3′-amino-3′-deoxyadenosine and 3′-acetamido-3′-deoxyadenosine. 3′-Acetamido-3′-deoxyadenosine appears in the culture filtrates first. At the end of nucleoside production, the molar ratio of 3′-amino-3′-deoxyadenosine: 3′-acetamido-3′-deoxyadenosine is 2:1, respectively. Uniformly 14C-labeled adenosine was incorporated into 3′-amino-3′-deoxyadenosine and 3′-acetamido-3′-deoxyadenosine without cleavage of the N-riboside bond. Uniformly 14C-labeled 3′-deoxyadenosine (cordycepin) is not a precursor for these nucleoside analogs. [1-14C]Acetate is incorporated exclusively into the acetyl group of 3′-acetamido-3′-deoxyadenosine. The interconversion of the two aminonucleoside analogs was determined by adding either uniformly 14C-labeled 3′-amino-3′-deoxyadenosine or 3′-acetamido-3′-deoxyadenosine to the culture filtrates of Helminthosporium at the time of nucleoside production. Both nucleosides are interconverted. The conversion of 3′-amino-3′-deoxyadenosine to the acetamidonucleoside is the most rapid. The distribution of 14C in the adenine and sugar moieties of the aminonucleosides is the same before and after interconversion. Therefore, no cleavage of the N-riboside bond took place. It is not known if this interconversion occurred in the culture filtrates or within the mycelium. © 1969.