Nucleic acid related compounds. 108. Biomimetic modeling of the abstraction of H3 ' by ribonucleotide reductases. 1,5-hydrogen atom transfer of H3 toaminyl and oxyl, but not thiyl, free radicals in homoribofuranose derivatives

Generation of 6-oxyl radicals from homoribofuranose (5-deoxy-D-ribo-hexofur anose) 6-O-nitro esters with Bu3SnD/AIBN/benzene/Delta resulted in abstract ion of H3 by a [1,5]-hydrogen atom shift. Transfer of H-2 from the stannane to . C3 effected incorporation of deuterium at C3. Analogous treatment of 6-azido-6-deoxy-D-ribo-hexofuranose derivatives gave C3-deuterated aminosug ars. In contrast, no deuterium incorporation was detected upon parallel tre atment of 6-thio-D-ribo-hexofuranose derivatives. Abstraction of H3' by a t hiyl radical (. SCys) is the postulated first step in reactions that are ut ilized by ribonucleotide reductases to convert ribonucleotides into 2'-deox ynucleotides. Results are discussed relative to the enzyme reaction cascade that couples abstraction of H3' with irreversible loss of water from C2'. (C) 1999 Elsevier Science Ltd. All rights reserved.