Structural studies of chelirubine and chelilutine free bases

The structures of chelirubine and chelilutine free bases have been examined by 2D NMR spectroscopy and mass spectrometry. Chelirubine chloride (la) upon treatment with Na,CO, yielded free base which possessed the constitution of bis(5,6-dihydrochelirubin-6-yl) ether (2a). The free base of chelilutine (Ib) was determined to be bis(5,6-dihydrochelilutin-6-yl) ether (2b). The aqueous NH3 treatment of chelilutine (Ib) produced bis(5,6-dihydrochelilutin-6-yl)amine (3b). 6-Hydroxy-5,6-dihydrochelirubine (4a) and 6-hydroxy-5,6-dihydrochelilutine (4b) were detected only in CDCl3 solution by NMR spectroscopy. In CDCl3, the compound 2b underwent hydrolysis to 4b that was immediately followed by the reverse condensation to a diastereomer of 2b. Pseudokinetics of this reaction was followed by NMR spectroscopy and quantum chemical calculations were carried out to support the suggested type of molecular symmetry alteration. The known alkaloid dihydrochelirubine (5) was isolated for the first time from Sanguinaria canadensis.