title: Synthesis of 3-aminoimidazo[4,5-c]pyrazole nucleoside via the N-N bond formation strategy as a [5:5] fused analog of adenosine.
abstract: 3-Amino-6-(beta-D-ribofuranosyl)imidazo[4,5-c]pyrazole (2) was synthesized via an N-N bond formation strategy by a mononuclear heterocyclic rearrangement (MHR). A series of 5-amino-1-(5-O-tert-butyldimethylsilysilyl-2,3-O-isopropylidene-beta-D-ribofuranosyl)-4-(1,2,4-oxadiazol-3-yl)imidazoles (6a-d), with different substituents at the 5-position of the 1,2,4-oxadiazole, were synthesized from 5-amino-1-(beta-D-ribofuranosyl)imidazole-4-carboxamide (AICA Ribose, 3). It was found that 5-amino-1-(5-O-tert-butyldimethylsilyl-2,3-O-isopropylidene-beta-D-ribofuranosyl)-4-(5-methyl-1,2,4-oxadiazol-3-yl)imidazole (6a) underwent the MHR with sodium hydride in DMF or DMSO to afford the corresponding 3-acetamidoimidazo[4,5-c]pyrazole nucleoside(s) (7b and/or 7a) in good yields. A direct removal of the acetyl group from 3-acetamidoimidazo[4,5-c]pyrazoles under numerous conditions was unsuccessful. Subsequent protecting group manipulations afforded the desired 3-amino-6-(beta-D-ribofuranosyl)imidazo[4,5-c]pyrazole (2) as a 5:5 fused analog of adenosine (1).
authors.affiliation: Department of Chemistry, College of Literature, Science and Arts, The University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
authors.forename: Tun-Cheng
authors.initials: TC
authors.lastname: Chien
authors.forename: David A
authors.initials: DA
authors.lastname: Berry
authors.forename: John C
authors.initials: JC
authors.lastname: Drach
authors.forename: Leroy B
authors.initials: LB
authors.lastname: Townsend
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D011720:Pyrazoles / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: C436945:3-aminopyrazole; D011720:Pyrazoles; D000241:Adenosine