Introduction of the (-)-berkelic acid side chain and assignment of the C-22 stereochemistry.
A Kiyooka aldol condensation of an aldehyde with a trimethylsilyl ketene acetal and the oxazaborolidinone prepared from N-Ts-(S)-valine gives two of the four possible aldol adducts, which were oxidized and deprotected to complete the synthesis of (-)-berkelic acid and (-)-22-epi-berkelic acid. This synthesis establishes the absolute stereochemistry and assigns the stereochemistry at C-22. A biosynthetic pathway is proposed that is consistent with the known absolute stereochemistry at the quaternary carbon of spiciferone A, spicifernin, and berkelic acid and provides a simple explanation for the differing stereochemistry at C-18 and C-19 of spicifernin and berkelic acid.
Wu
Xiaoxing
X
Department of Chemistry MS 015, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
Zhou
Jingye
J
Snider
Barry B
BB
D045744:Cell Line, Tumor; D006801:Humans; D020128:Inhibitory Concentration 50; D013141:Spiro Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D013237:Stereoisomerism
D013141:Spiro Compounds; C520589:berkelic acid