Synthesis of D-Ring Annulated Pyridosteroids from β-Formyl Enamides and Their Biological Evaluations

Herein, we report the synthesis of a novel class of substituted androst[17,16-b]pyridines (pyridosteroids) from the reaction of β-formyl enamides with alkynes in high yields. The optimized reaction protocol was extended to acyclic and cyclic β-formyl enamides to afford nonsteroidal pyridines. Cell survival assay of all compounds were carried against prostate cancer PC-3 cells wherein 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst[17,16-b]pyridine showed the highest cytotoxic activity. Phase contrast microscopy and flow cytometry studies exhibited marked morphological features characteristic of apoptosis in 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst[17,16-b]pyridine and abiraterone treated PC-3 cells. The treatment of 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst[17,16-b]pyridine induces G2/M phase cell cycle arrest in prostate cancer PC-3 cells. Enhancement of apoptotic inductions of PC-3 cells by 3-hydroxy-5-en-2′,3′-dicarbethoxy-androst[17,16-b]pyridine and abiraterone through the activation of caspases-6, -7, an...