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, and an oxygen moiety at the 11‐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, cryptolepinone, with substantial changes in double bond isomerization relative to that which would be required if it were indeed the latter. The structure of the alkaloid was confirmed by, total assignment of the 1H, 13C, and 15N nmr spectra at natural abundance using 3 mm micro inverse nmr probe technology at 400 and 500 MHz.