Biosynthetic Production of [N2,1,3,7,9‐15N]Guanosine and [1,3,7,9‐15N]inosine and conversion into [N6,1,3,7,9‐15N]adenosine for structure elucidation of RNA by heteronuclear NMR

A procedure was developed for the biosynthetic preparation of 15N‐labelled guanosine and inosine through the action of a mutant Bacillus subtilis strain. Crude [N2,1,3,7,9‐15N]guanosine and [1,3,7,9‐15N]inosine were isolated from the culture filtrate by precipitation and anion‐exchange chromatography (Scheme 1). No cell lysis and no enzymatic degradation was necessary. The per‐isobutyrylated derivatives 1 and 2 were isolated from a complex mixture, purified by virtue of their different lipophilicity, and separated in three steps involving normal‐and reversed‐phase silica‐gel chromatography. One litre of complex nutrient medium yielded 8.44 mmol of guanosine derivative and 2.84 mmol of inosine derivative with high average 15N enrichment (83.5 and 91.9 atom‐%, resp.). [N6,1,3,7,9‐15N]Adenosine (4) was obtained from 2′,3′,5′‐tri‐O‐isobutyryl[1,3,7,9‐15N]inosine (1) through the ammonolysis of its 1,2,4‐triazolyl derivative with aqueous 15NH3 (Scheme 2).