title: Extending long-range heteronuclear NMR connectivities by HSQMBC-COSY and HSQMBC-TOCSY experiments.
abstract: The detection of long-range heteronuclear correlations presenting J(CH) coupling values smaller than 1-2Hz is a challenge in the structural analysis of small molecules and natural products. HSQMBC-COSY and HSQMBC-TOCSY pulse schemes are evaluated as complementary NMR methods to standard HMBC/HSQMBC experiments. Incorporation of an additional J(HH) transfer step in the basic HSQMBC pulse scheme can favor the sensitive observation of traditionally missing or very weak correlations and, in addition, facilitates the detection of a significant number of still longer-range connectivities to both protonated and non-protonated carbons under optimum sensitivity conditions. A comparative (1)H-(13)C study is performed using strychnine as a model compound and several examples are also provided including (1)H-(15)N applications.
authors.affiliation: Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain; NMR Structure Elucidation, Process and Analytical Chemistry, Merck & Co. Inc., 126 E. Lincoln Avenue, Rahway, NJ 07065, USA.
authors.forename: Josep
authors.initials: J
authors.lastname: Saurí
authors.affiliation: Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain.
authors.forename: Núria
authors.initials: N
authors.lastname: Marcó
authors.affiliation: NMR Structure Elucidation, Process and Analytical Chemistry, Merck & Co. Inc., 126 E. Lincoln Avenue, Rahway, NJ 07065, USA.
authors.forename: R Thomas
authors.initials: RT
authors.lastname: Williamson
authors.affiliation: NMR Structure Elucidation, Process and Analytical Chemistry, Merck & Co. Inc., 126 E. Lincoln Avenue, Rahway, NJ 07065, USA.
authors.forename: Gary E
authors.initials: GE
authors.lastname: Martin
authors.affiliation: Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Spain. Electronic address: teodor.parella@uab.cat.
authors.forename: Teodor
authors.initials: T
authors.lastname: Parella
keywords: HSQC-TOCSY; HSQMBC; HSQMBC-COSY; HSQMBC-TOCSY; Heteronuclear coupling constants; LR-HSQMBC; Long-range correlations