Antitumor Agents. 274. A New Synthetic Strategy for E-Ring SAR Study of Antofine and Cryptopleurine Analogues

A new versatile synthetic methodology for the synthesis of enantiomerically pure natural phenanthroindolizidines and phenanthroquinolizidines has been established and described. Natural products R-antofine and R-cryptopleurine, as well as a novel E-ring expanded analogue 13c (E7), 12-oxo-S-antofine (17), and 12N-methyl-12-aza-S-antofine (18) were synthesized with the new method. This strategy will greatly facilitate future SAR studies on the natural alkaloids with E-ring variations.