title: HSQC-1,n-ADEQUATE: a new approach to long-range 13C-13C correlation by covariance processing.
abstract: Long-range, two-dimensional heteronuclear shift correlation NMR methods play a pivotal role in the assembly of novel molecular structures. The well-established GHMBC method is a high-sensitivity mainstay technique, affording connectivity information via (n)J(CH) coupling pathways. Unfortunately, there is no simple way of determining the value of n and hence no way of differentiating two-bond from three- and occasionally four-bond correlations. Three-bond correlations, however, generally predominate. Recent work has shown that the unsymmetrical indirect covariance or generalized indirect covariance processing of multiplicity edited GHSQC and 1,1-ADEQUATE spectra provides high-sensitivity access to a (13)C-(13) C connectivity map in the form of an HSQC-1,1-ADEQUATE spectrum. Covariance processing of these data allows the 1,1-ADEQUATE connectivity information to be exploited with the inherent sensitivity of the GHSQC spectrum rather than the intrinsically lower sensitivity of the 1,1-ADEQUATE spectrum itself. Data acquisition times and/or sample size can be substantially reduced when covariance processing is to be employed. In an extension of that work, 1,n-ADEQUATE spectra can likewise be subjected to covariance processing to afford high-sensitivity access to the equivalent of (4)J(CH) GHMBC connectivity information. The method is illustrated using strychnine as a model compound.
authors.affiliation: Merck Research Laboratories, Discovery and Preclinical Sciences, Global Chemistry, Structure Elucidation Group, Summit, NJ 07901, USA. gary.martin2@merck.com
authors.forename: Gary E
authors.initials: GE
authors.lastname: Martin
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Hilton
authors.forename: M Robert
authors.initials: MR
authors.lastname: Willcott
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Blinov
mesh_terms: D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards; D012015:Reference Standards; D013331:Strychnine / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D013331:Strychnine