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The use of 15N-NMR spectroscopy for assigning the structures of isomeric N7- and N9-substituted purines
Affiliation:2. Australian Center for Sexual Health, Sydney, New South Wales, Australia;3. Department of Pharmacology, Utrecht Institute of Pharmaceutical Sciences, University of Utrecht, Utrecht, The Netherlands;4. Department of Psychiatry, Case Western Reserve University School of Medicine, West Palm Beach, FL, USA;5. Department of Urology, University of California at Davis, Davis, CA, USA;11. Division of Urology, University of Buenos Aires, Buenos Aires, Argentina;12. St. Peter''s Sexual Medicine Centre, The London Clinic, London, UK;8. Neuro‐Uro‐Andrology Unit, Physical Medicine and Rehabilitation Department, Raymond Poincaré Hospital, Paris, France;9. Department of Urology, Tulane University Health Sciences Center, New Orleans, LA, USA;112. Department of Urology, Instituto H. Ellis, Sao Paulo, Brazil;123. Erasmus MC–Daniel den Hoed Cancer Center, Rotterdam, The Netherlands;84. Endocrinology and Medical Sexology, Department of Experimental Medicine, University of L''Aquila, L''Aquila, Italy;95. School of Psychology, Deakin University, Melbourne, Victoria, Australia;1111. Graduate School, Valparaiso University, Valparaiso, IN, USA;1212. Department of Psychiatry, Case Western Reserve University School of Medicine, Cleveland, OH, USA;88. Department of Urology, University of California, San Francisco, CA, USA;99. Clinica de Urologia e Andrologia, Belo Horizonte, Minas Gerais, Brazil;2. Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, United States
Abstract:An 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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