15N NMR study of isoquinoline alkaloids

15N NMR chemical shifts of 40 tertiary and quaternary isoquinoline alkaloids of six constitutional types are reported. The selected compounds belong to the classes of benzo[c]phenanthridine, protoberberine, benzylisoquinoline, aporphine, pavinane, and β-carboline-proaporphine alkaloids. The 15N chemical shifts were measured by gradient-enhanced inverse-detected single-quantum (GSQMBC) and multiple-quantum (GHMBC) multiple-bond correlation experiments. The 1H–15N long-range coupling constants determined from the phase-sensitive GSQMBC spectra are also reported in order to facilitate optimization of multiple-bond correlation experiments.