Structure Elucidation of Two New Diterpenoids from Isodon phyllostachys : Phyllostacins A and B

Two new ent ‐kaurane‐derived diterpene derivatives, phyllostacins A ( 1 ) and B ( 2 ), were isolated from the aerial parts of Isodon phyllostachy s, together with two known compounds, irroratin A ( 3 ) and serrin B ( 4 ). Both 1 and 2 were found to be present as diastereoisomers. In the case of 1 , the corresponding diastereoisomeric diacetates 5 and 6 were prepared and separated. The structures of the new compounds were elucidated by extensive 1D‐ and 2D‐NMR spectroscopic methods, in combination with MS experiments. In (D 5 )pyridine solution, the two epimers of 1 are present in equal amounts, but in CDCl 3 or CD 3 OD, the ( S )‐epimer predominates in the mixture of hemiacetals.