Complete assignment of the H-1 and C-13 NMR spectra of the Coccinellidae-defensive alkaloids myrrhine, precoccinelline and hippodamine, their N-oxides and the corresponding hydrochlorides

The H-1 and C-13 NMR spectra of the 2-methylperhydro-9b-azaphenalene alkalo ids characteristic of coccinellid beetles, myrrhine, precoccinelline, hippo damine, their N-oxides and the corresponding hydrochlorides were completely assigned for the first time by a one- and two-dimensional homo- and hetero nuclear study (1H, 13C, H-1-H-1 COSY, HMQC, HMBC) at 600 and 150.87 MHz. Th e influence of the ring junction stereochemistry and of the N-oxide functio n on the proton and carbon chemical shifts in this series of compounds is d iscussed. Protonation shifts are also considered (C) 1999 John Wiley & Sons , Ltd.