Total Syntheses and Cytotoxicity of (R)- and (S)-Boehmeriasin A

Both enantiomers of boehmeriasin A were synthesized in seven steps each using a chiral pool approach. Key steps in the syntheses are a one-flask, two-step protocol to generate the quinolizine core and a C−H functionalization reaction between tetrahydroquinolizinones and an aryltrifluoroborate. The natural product (R)-boehmeriasin A demonstrated potent cytotoxicity against several cancer cell lines, whereas the unnatural (+)-(S)-isomer was significantly less potent.