Ultra-high resolution band-selective HSQC for nanomole-scale identification of chlorine-substituted 13C in natural products drug discovery

Ultra-high resolution band-selective HSQC (bsHSQC) has been employed for detection of Cl-35-Cl-37 isotope shifted C-13 NMR signals for assignment of regioisomerism in bromo-chloro natural products. Optimum pulse sequence and instrumental parameters for maximization of detection of the isotope shifts were explored. The chlorine isotope shifts (Delta delta) were detected within crosspeaks and were shown to vary with hybridization of C-13, substitution of C-13, presence of beta-chloro substituents, and their relative configuration. Deconvolution of Cl-substituted CH bsHSQC crosspeaks may provide other useful information, including a potentially MS-independent method for quantitating Cl-37/C-35 isotopic fractionation during the biosynthesis of halogenated natural products. Copyright (C) 2016 John Wiley & Sons, Ltd.