Complete proton and carbon-13 NMR assignment of the alkaloid gephyrotoxin through the use of homonuclear Hartmann-Hahn and two-dimensional spectroscopy

Abstract

Three different types of modem NMR techniques have been used to obtain a complete proton and carbon- 13 assignment of the alkaloid gephyrotoxin. In addition to the two-dimensional phase-sensitive homo- and heteronuclear shift correlation methods, use of the recently proposed one-dimensional homonuclear Hartmann-Hahn difference experiment was crucial for obtaining the required long-range connectivity. Guidelines are presented for optimal use of these techniques. Experiments were performed at 500-MHz 'H frequency, using 8 mg of sample. The introduction of two-dimensional (2D) NMR techniques has greatly simplified the NMR analysis of many natural products, permitting the study of problems hitherto considered intractable. As an example, we present here a study of the alkaloid gephy- rotoxin (GyTx), extracted from the skin of the frog Dendrobates histrionicus. Routine application of standard 2D NMR techniques is not sufficient in this case because of the complexity of the 'H