Two previously undescribed chimonanthine-type [sinodamines A and B] and five related known dimeric tryptamine-derived alkaloids were isolated and characterized from the leaves of the endangered ornamental plant Sinocalycanthus chinensis under the guidance of LC-MS detection and dereplication analyses, along with conventional isolation procedures. Their structures were established on the basis of spectroscopic methods and chemical transformations. Sinodamine A can be regarded as the naturally occurring N-oxide derivative of its pseudo-mesomer sinodamine B. An acid-catalyzed Meisenheimer rearrangement from sinodamine A to its oxazine-form with a final equilibrium of 1:2 was observed by monitoring their NMR spectra. (-)-Folicanthine showed significant cytotoxicity against human lung carcinoma A549 and colorectal carcinoma HT29鈥痗ells, with IC(50) values of 7.76 and 6.16鈥痬uM, respectively. CI - Copyright (c) 2018 Elsevier Ltd. All rights reserved.