The use of 15N-NMR spectroscopy for assigning the structures of isomeric N7- and N9-substituted purines
1986; Elsevier BV; Volume: 42; Issue: 18 Linguagem: Inglês
10.1016/s0040-4020(01)88059-5
ISSN1464-5416
AutoresGérald S. Remaud, J. Kjellberg, Hervé Bazin, Nils Gunnar Johansson, Jyoti Chattopadhyaya,
Tópico(s)Muon and positron interactions and applications
ResumoAn 15N-NMR study has shown a considerable difference in electronic structures between the isomeric N7 and N9 substituted purines. A comparison of 15N chemical shifts amongst the seven pairs of N7 and N9 isomers has revealed that (1) the N3 resonances are shielded by 18–20 ppm in an N9 isomers; (2) the amino nitrogens at the C-2 or at C-6 positions are always shielded by 3–4 ppm in the N7 isomers; (3) the N7 chemical shifts in the N7 isomers are always more shielded by 6–7 ppm than the N9 resonances in the N9 isomers. It has a also been found by protonation studies that the N9 of the N7 isomer is much more basic than the N7 of the N9 isomer.
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