Naslov
DBU induced formation of 8-bromoguanosine dimer with three hydrogen bonds between the GG- pairs

Autori
Saftić, Dijana ; Žinić, Biserka ; Višnjevac, Aleksandar

Izvornik
Tetrahedron (0040-4020) 68 (2012), 4; 1062-1070

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
8-bromoguanosine ; hemideprotonation ; DBU ; X-ray analysis ; hydrogen bonding

Sažetak
Upon hemideprotonation of 8-bromoguanosine (8-BrG) at the N1 position, induced by DBU, the adduct (8-BrG)(8-BrG)–(DBU-H)+ was formed. Slow evaporation of the 8-BrG methanol solution, in the presence of 0.5 equivalents of DBU, yielded two polymorphic structures (1 and 2), where a neutral (8-BrG) (A) and N1 deprotonated, anionic 8-bromoguanosine (8-BrG)– (B) were joined together through three intermolecular hydrogen bonds involving O6, N1 and C2-NH2 sites. Such pairing gave planar GG– dimers as the basic motif of crystal packing in both polymorphs. Both neutral and deprotonated guanosine molecules in the structure of 1 had the ribose units in a syn conformation. In the structure of polymorph 2, the N1 deprotonated guanosine molecule (B) retained the syn glycosidic conformation, while the non-deprotonated guanosine molecule (A) adopted the natural anti conformation of the ribose unit with respect to the nucleobase. Ribose rings revealed different puckering ; only those of deprotonated molecules 1B and 2B possessed the usual C2'-endo envelope conformation. Crystal packing in both structures was guided by the highly complex H-bonded pattern. The CSD was searched for related structures, which are discussed with reference to polymorphs 1 and 2. 1H and 13C NMR spectroscopic evidence is provided showing that the three H-bonded adduct (8-BrG)(8-BrG)–(DBU-H)+ was also formed in the highly H-bond competitive DMSO solution.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

POVEZANOST RADA