Expedient synthesis and structure-activity relationships of phenanthroindolizidine and phenanthroquinolizidine alkaloids

The total synthesis of alkaloids phenanthroindolizidine 1a, tylophorine 1b, and phenanthroquinolizidine 1c, has been achieved in 46%, 49%, and 42% overall yield, respectively, starting from the corresponding phenanthrene-9-carboxaldehyde. Compound 1c exhibited potent inhibition activity in three human cancer cell lines, with IC50 values ranging from 104 to 130 nM. The structure-activity relations of these alkaloids and some of their synthetic intermediates against the three cell lines were also described.