Pharmacophore Directed Retrosynthesis Toward the Anti-Inflammatory Agent Rameswaralide and Anti-Cancer Agent Ineleganolide

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Project Summary. The study of natural products has impacted drug discovery dramatically from the standpoint of identifying novel therapeutic targets and drug leads. Herein, we propose to apply our group’s ‘Pharmacophore- Directed Retrosynthesis (PDR) concept to the synthesis and biological studies of two structurally, and biologically intriguing natural products, rameswaralide and ineleganolide, having anti-inflammatory and anticancer activity, respectively. Due to the complex structure of many natural products, their use as therapeutics can be limited if an adequate supply is not available through, for example, fermentation or from a renewable source. With this in mind, we will pursue a total synthesis of these natural products guided by PDR to enable the identification of simplified equipotent lead molecules in route to the natural products. The pharmacophore of these natural products is hypothesized to be the common 5,5,7 tricyclic core. The core will be accessed in a concise manner through an organocatalyzed, Diels-Alder-Lactonization (DAL) cascade involving a kinetic resolution developed in our laboratory followed by a ring expansion. We propose that the disparate biological activity of these natural products is derived from the structural variations beyond the common 5,5,7-tricyclic core. Systematic annulation onto this tricyclic core of (i) a substituted cyclohexanone in the case of rameswaralide and (ii) both a substituted cyclohexanone and tetrahydrofuran through intramolecular oxa-Michael addition in the case of ineleganolide, will provide extensive SAR data. Over the course of our synthetic endeavors, Prof. Jun Liu’s group (Johns Hopkins) will assay synthetic intermediates leading up to rameswaralide and ineleganolide for anti-inflammatory and anti-cancer activity, respectively. These data will further refine the synthesis of proposed alkynylated cellular probes for subsequent cellular target identification in collaboration with Prof. Jun Liu’s Laboratory (Johns Hopkins University). The proposed research seeks to identify an equipotent, simplified derivative of these natural products as potential anti-inflammatory and anticancer drug leads while also potentially revealing novel cellular targets for therapeutic intervention of human disease. A caveat to our hypothesis is that the fully or almost fully functionalized natural product may be required for the observed bioactivity; however, application of a PDR approach has the potential to identify simpler derivatives prior to completion of a total synthesis. Hypothesis. We hypothesize that the common 5,5,7 core tricycle of rameswaralide and ineleganolide is the pharmacophore of these bioactive natural products. We further hypothesize that the selectivity and disparate bioactivity, namely anti-inflammatory and anticancer activity, observed for these structurally related natural products arises from a substituted cyclohexanone in the case of rameswaralide and both a substituted cyclohexanone and a tetrahydrofuran derived from intramolecular oxa-Michael addition in the case of ineleganolide.