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A new conversional synthesis of the ABC ring system of taxoids from the C19-diterpenoid alkaloid lycoctonine was developed in 6 steps with 2% overall yield. The distinctive features of the conversion include pinacol rearrangement, enlargement of ring B, and opening of a four-membered ring.

Five new C18-diterpenoid alkaloids, anthriscifolcines A (1), B (2), C (3), D (4), and E (5), together with a known C19-diterpenoid alkaloid delcorine (6), were isolated from the whole herb of Delphinium anthriscifolium var. savatieri. The structures of these new alkaloids were established on the basis of spectral data (1D- and 2D-NMR, HR-ESI-MS).

The regioselective demethylations of two C19-diterpenoid alkaloids, 2 and 3, have been achieved with HBr-HOAc, trimethylsilyl iodide, or BBr3. It was observed that HBr-HOAc is an optimal demethylating agent for these two C19-diterpenoid alkaloids because it could provide different O-demethylation products by using different reaction temperature and reaction time. Especially, 1-O-methyl group in 2 and 3, one of the most difficult ones to be demethylated, could be removed by the treatment with HBr-HOAc at an elevated temperature and a prolonged reaction time. [ABSTRACT FROM AUTHOR]