Complete assignment of the1H and13C NMR spectra of the Coccinellidae-defensive alkaloids myrrhine, precoccinelline and hippodamine, theirN-oxides and the corresponding hydrochlorides

Abstract

The 1H and 13C NMR spectra of the 2-methylperhydro-9b-azaphenalene alkaloids characteristic of coccinellid beetles, myrrhine, precoccinelline, hippodamine, their N-oxides and the corresponding hydrochlorides were completely assigned for the first time by a one- and two-dimensional homo- and heteronuclear study (1H, 13C, 1H–1 H COSY, HMQC, HMBC) at 600 and 150.87 MHz. The influence of the ring junction stereochemistry and of the N-oxide function on the proton and carbon chemical shifts in this series of compounds is discussed. Protonation shifts are also considered © 1999 John Wiley & Sons, Ltd.