Stereochemistry of atropisomeric 9,10-dihydrophenanthrene dimers from Pholidota chinensis

Nine bis-9,10-dihydrophenanthrene and 9,10-dihydrophenanthrene/(dihydro)stilbene derivatives, including the new phochinenins G-L 1–6, were isolated from the whole plant of Pholidota chinensis. Their structures were elucidated on the basis of extensive spectroscopic investigations (1D, 2D NMR, and HR-EIMS). Owing to the sterically hindered rotation around the biaryl axis, some of these biaryl compounds can exist as a pair of enantiomers, but were isolated as racemates. Computed inversion barriers of selected atropisomeric derivatives suggested that phochinenins K 5, gymconpin C 7, and flavanthrin 9 have stable atropisomers. Their racemates were separated by HPLC on an optically active stationary phase, and were stereochemically characterized on-line by circular dichroism (CD) spectroscopy (LC-CD coupling), in conjunction with quantum-mechanics CD calculations.

Figure optionsDownload as PowerPoint slide

(aS)-8-(2-(3-Hydroxyphenethyl)-4-hydroxy-6-methoxyphenyl)-7-methoxy-9,10-dihydrophenanthrene-2,5-diolC30H28O6(−)-CD [310 nm]Absolute configuration: (aS)

C30H26O6(aS)-1-(2,7-Dihydroxy-4-methoxy-9,10-dihydrophenanthren-1-yl)-4-methoxy-9,10-dihydrophenanthrene-2,7-diol(+)-CD [310 nm]Absolute configuration: (aS)