Synthesis of Isocryptolepine-Triazole Adducts and Evaluation of Their Cytotoxic Activity

Eighteen hybrid compounds between 8-bromo-2-fluoro-isocryptolepine (4) and 1,2,3-triazole were synthesized via azide rearrangement-annulation reaction. Compound 4 underwent regioselective N-propargylation and click reaction to form 8-bromo-2-fluoro-isocryptolepine-triazole hybrids 11 which were evaluated for cytotoxic activity. Compound 11 c containing 1-anisyltriazole was the most effective in inhibiting HepG2, HuCCA-1 and A549 cell lines (IC₅₀ values of 1.65-3.07 μM) while compounds 11 a (1-phenyltriazole), 11 j (1-para-CF₃ -benzyltriazole) and 11 l (1-meta-Cl-benzyltriazole) were potent inhibitors of HuCCA-1, HepG2 and A549 cell lines, respectively. Moreover, 11 l showed the lowest cytotoxicity to normal human kidney cell line. Compounds 11 c and 11 l provided improvement of cytotoxic activity over 4. Compounds 4, 11 c and 11 l were selected to investigate their mechanisms of action. The results showed that 4 could induce G2/M cell cycle arrest and was involved in the upregulation of p53 and p21 proteins. However, the mechanisms of growth inhibition by 11 c and 11 l were associated with G0/G1 cell cycle arrest and mediated by induction of oxidative stress.

Synthesis of isocryptolepine analogues and their structure-activity relationship studies as antiplasmodial and antiproliferative agents

Novel isocryptolepine analogues have been conveniently synthesized and evaluated for antimalarial and antiproliferative activities. We have found 3-fluoro-8-bromo-isocryptolepine (1n) to have the highest activities against chloroquine-resistant K1, chloroquine-sensitive 3D7, and chloroquine- and mefloquine-resistant SKF58 and SRIV35 strains. Several fluorine-substituted analogues (1b, 1n, and 1q) also showed excellent selectivities while maintaining good to excellent activities against all four Plasmodium falciparum strains. Additionally, antiproliferative properties of isocryptolepine derivatives against HepG2, HuCCA-1, MOLT-3 and A549 cancer cell lines are reported for the first time in this study. 2-Chloroisocryptolepine (1c) and benzo-fused-2-chloroisocryptolepine (1i) showed significant bioactivities whereas several novel fluorinated compounds and 2-chloro-8-bromoisocryptolepine (1f) displayed excellent selectivities.