An efficient Pd-catalyzed cross-coupling/cycloisomerization of 3-(2-pyridyl) propargyl carbonates with organoboronic acids has been developed, which provides a straightforward route for the synthesis of 1,3-disubstituted indolizines with a wide variety of substituents. The mechanistic study indicates that the reaction proceeds via formation of an allenyl pyridine intermediate through palladium-catalyzed coupling reaction followed by cyclization.

There are many reports for andrographolide modification regarding antitumor effects. Transformation of the five-membered lactone ring to furan aromatic ring still results in compounds with good cytotoxicity. To determine further the importance of the five-membered lactone ring and to obtain better lead compounds, we transformed the five-membered lactone ring in andrographolide. New types of ent-labdane diterpene derivatives were made, whose cytotoxic activities were measured in vitro. Preliminary SAR was summarized and two compounds, 7 and 26, with good cytotoxic activity were obtained, which have the potential to be developed into new antitumor drugs.

A series of tetracyclic diterpenoids bearing the α-methylenelactone group have been synthesized and screened for their in vitro anti-tumor activities against six human cancer cell lines. The results showed that compounds 1c, 2a and 2b exhibited significant cytotoxicity superior to the positive control doxorubicin hydrochloride against MDA-MB-231, K562 and HepG2 cell lines. In particular, compound 2b was identified as the most promising anticancer agent against HepG2 cells with IC50 value of 0.09 μM.A series of tetracyclic diterpenoids bearing α-methylenelactone group were synthesized from stevioside. Some of them exhibited significant cytotoxicity against all the six tumor cell lines with the IC50 values ranging from 0.09 to 5.71 μM.

An efficient Pd-catalyzed cross-coupling/cycloisomerization of 3-(2-pyridyl) propargyl carbonates with organoboronic acids has been developed, which provides a straightforward route for the synthesis of 1,3-disubstituted indolizines with a wide variety of substituents. The mechanistic study indicates that the reaction proceeds via formation of an allenyl pyridine intermediate through palladium-catalyzed coupling reaction followed by cyclization.