Synthesis of 4-epi-Parviflorons A, C, and E: Structure–Activity Relationship Study of Antiproliferative Abietane Derivatives

The first syntheses of 4- epi-parviflorons A, C, and E (4- epi-1-3) were achieved in 12-13 steps from commercially available (-)-abietic acid (5). All synthesized compounds, including intermediates and derivatives, were evaluated for antiproliferative activity against five human tumor cell lines. A structure-activity relationship study revealed no significant difference between Pf E and 4- epi-Pf E, the importance of two oxygen functional groups at C-11 and C-12 for antiproliferative activity, as well as a combination of carbomethoxy at C-4 and a benzoyl ester with electron-drawing group at C-12 or hydroxymethyl at C-4 and an appropriate oxidation state of ring-B/C for triple-negative breast cancer cell selectivity.