title: Long-range heteronuclear coupling constants in 2,6-disubstituted purine derivatives.
abstract: Four- and five-bond heteronuclear J-couplings between the hydrogen H-8 and carbons C-6 and C-2 in a series of 7- and 9-benzyl substituted purine derivaties with variuous substituents in positions 2 and 6 were studied by coupled (13)  C NMR and H,C-HMBC experiments and by DFT calculations. We have found that for some of the derivatives, the five-bond coupling H8-C2 is higher than the four-bond H8-C6 coupling, which is also evidenced by a stronger crosspeak in the HMBC. This finding contradicts the generally accepted opinion that only strong three-bond crosspeaks and one weak four-bond H8-C6 crosspeak can be observed in the HMBC spectra of purine derivatives. The misinterpretation of HMBC spectra may lead to an incorrect determination of the purine derivatives' structure.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo náměstí 2, 166 10, Prague, Czech Republic.
authors.forename: Eliška
authors.initials: E
authors.lastname: Procházková
authors.forename: Lucie
authors.initials: L
authors.lastname: Cechová
authors.forename: Petr
authors.initials: P
authors.lastname: Jansa
authors.forename: Martin
authors.initials: M
authors.lastname: Dračínský
mesh_terms: D001593:Benzyl Compounds / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D002247:Carbon Isotopes; D006859:Hydrogen / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D011687:Purines / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D001593:Benzyl Compounds; D002247:Carbon Isotopes; D011687:Purines; D002244:Carbon; D006859:Hydrogen