Synthesis of Carbazole Alkaloids by Ring‐Closing Metathesis and Ring Rearrangement–Aromatization

Total Synthesis of Racemic Benzomalvin E, a Quinazolinone Isolated from Pencilium sp. FN070315 and Exploration to the Direct Synthesis of (E)-Benzomalvin B

We present the first total synthesis of (±) benzomalvin E, featuring a quinazolino moiety with a 6-6-6-7-fused tetracyclic skeleton containing three nitrogen atoms. The key transformation involves Cu-catalyzed intramolecular C-N arylation of quinazolinone, leading to a sclerotigenin analogue that undergoes nucleophilic addition with benzaldehyde, enabling the synthesis of (±) benzomalvin E in six linear steps with a 33% overall yield. The (±) benzomalvin E's structure was validated by 2-D NMR and single crystal XRD analysis and was further transformed into (E)-benzomalvin B.

Stereoselective Total Synthesis of Eburnane-Type Alkaloids Enabled by Conformation-Directed Cyclization and Rearrangement

Controlling the cis C20/C21 relative stereochemistry remains an unsolved issue in the synthesis of eburnane-type indole alkaloids. Provided herein is a simple solution to this problem by developing a unified and diastereoselective synthesis of four representative members of this class of natural products, namely, eburnamonine, larutensine, terengganensine B, and melokhanine E. The synthesis features the following key steps: a) an α-iminol rearrangement transforming the 3-hydroxyindolenine into spiroindolin-3-one, b) a highly diastereoselective conformation-directed cyclization leading to the melokhanine skeleton with the desired C20/C21 cis stereochemistry, and c) either an aza-pinacol or an unprecedented α-aminoketone rearrangement converting spiroindolinone back into the indole skeleton.

Facile synthesis of simple 2-oxindole-based compounds with promising antiproliferative activity

AIM

Discovery of novel potent anticancer agents with lower side effects is a challenge to overcome cancer, the second leading cause of death.

METHODOLOGY

2-oxindole-based hydrazides (6a-g) and benzenesulfonyl hydrazides (9a-d) were synthesized by simple condensation reactions of the appropriate hydrazides (2a-g) or (8a-d) with 1-ethyl-2,3-oxindolinedione (4). They were screened for their cytotoxicity against HepG2 (liver), MCF-7 (breast), HCT116 (colon) and A549 (lung) cancer cell lines.

RESULTS

The substituted benzohydrazides (6b-g) revealed higher activity and selectivity toward the tested cell lines than doxorubicin and 9a-d. Compound 6c exhibited the highest activity against MCF-7 cell line with IC₅₀ = 0.0058 μM and it induced apoptosis by caspase-3 activation, Bax upregulation and Bcl-2 downregulation in a dose-dependent manner.

CONCLUSION

This compound can be considered as a potent cytotoxic agent with apoptotic induction property.