Unifying the Absolute Configuration of Dibenzopyrrocoline Alkaloids with Relative Configuration Revision of Cryptowolinol and Description of Isocryptaustoline from Cryptocarya oubatchensis.

Dibenzopyrrocoline alkaloids, found in lauraceous and hernandiaceous plants, have been studied since the 1950s. The absolute configuration of these alkaloids, including cryptaustoline, has been a topic of debate due to conflicting studies. Having in our laboratory some authentic samples of dibenzopyrrocoline-type Cryptocarya alkaloids, we decided to reinvestigate their absolute configuration using modern spectroscopic techniques along with TDDFT calculations. The NMR reinvestigation of the authentic sample of cryptowolinol led us to revise its relative configuration using ML-J-DP4 and DP4+ analyses. Moreover, the absolute configuration of all dibenzopyrrocoline alkaloids reported to date benefitted from a complete re-evaluation based on a comparison with TDDFT-SR and TDDFT-ECD predictions leading to a unified absolute configuration. At last, this patrimonial reinvestigation unveiled a historical sample corresponding to a heretofore unpublished dibenzopyrrocoline alkaloid, which we named isocryptaustoline. The reisolation of this molecule from the total alkaloid extract of Cryptocarya oubatchensis makes it a genuine natural product.