The oxidation of 2',3'-isopropylideneadenosine (I) with potassium permanganate gives 2',3'-isopropylideneadenosine-5'-carboxylic acid (II) which with SOCl2 affords 2',3'-isopropylideneadenosine-5'-carbonyl chloride (III), which is treated first with dry liquid ethylamine and then hydrolyzed with aqueous hydrochloric acid.