Semisynthesis of Novel Dispiro-pyrrolizidino/thiopyrrolizidino-oxindolo/indanedione Natural Product Hybrids of Parthenin Followed by Their Cytotoxicity Evaluation

Abstract

Natural products possess unique and broader intricacies in the chemical space and have been essential for drug discovery. The crucial factor for drug discovery success is not the size of the library but rather its structural diversity. Although reports on the number of new structurally diverse natural products (NPs) have declined recently, researchers follow the next logical step: synthesizing natural product hybrids and their analogues using the most potent tool, diversity-oriented synthesis (DOS). Here, we use weed Parthenium hysterophorus as a source of parthenin for synthesis of novel dispiro-pyrrolizidino/thiopyrrolizidino-oxindolo/indanedione natural product hybrids of parthenin via chemo-, regio-, and stereoselective azomethine ylide cycloaddition. All synthesized compounds were characterized through a detailed analysis of one-dimensional (1D) and two-dimensional (2D) NMR and HRMS data, and the stereochemistries of the compounds were confirmed by X-ray diffraction analysis. All compounds were evaluated for their cytotoxicity against four cell lines (HCT-116, A549, Mia-Paca-2, and MCF-7), and compound 6 inhibited the HCT-116 cells with an IC 50 of 5.0 ± 0.08 μM.