Cryptolepinone vs. hydroxycryptolepine: Resolution of a question of substituent functionality and double bond isomerization

An indolo[3,2-b]quinoline alkaloid bearing an N-methyl substituent at N5, a nd an oxygen moiety at the Ii-position has been variously described as both cryptolepinone and 11-hydroxycryptolepine by independent research groups. The structure of this alkaloid is unequivocally confirmed as the former, cr yptolepinone, with substantial changes in double bond isomerization relativ e to that which would be required if it were indeed the latter. The structu re of the alkaloid was confirmed by, total assignment of the H-1, C-13, and N-15 nmr spectra at natural abundance using 3 mm micro inverse nmr probe t echnology at 400 and 500 MHz.