In the late 1980s 2D heteronuclear correlation spectroscopic
methods became available; however, with direct detection of the
insensitive 13C nucleus these measurements took quite a long time
to acquire. Nevertheless, due to the additional information provided
by these techniques 2D NMR soon became widespread in the
NMR literature. In the bisindole class VCR and its derivatives were
the first where 13C 1H heteronuclear shift correlation experiments
were used to achieve a complete 13C assignment in 1989 [64]. It is
interesting to note here that VCR and its derivatives are much less
studied than VLB type bisindoles